A heat-sensitive sensitizer, a method for preparing the same and use thereof in a heat-sensitive recording material

Abstract

The application discloses a kind of heat-sensitive sensitizer and its preparation method and application in heat-sensitive recording material, belong to heat-sensitive sensitizer technical field.The preparation method of the heat-sensitive sensitizer is that terephthalic acid derivative, alcohol is mixed and stirred uniformly, obtain mixture, condensing agent is added to mixture, reaction is carried out at 48-52 ℃, alcohol is removed, water is added, post-processing is obtained heat-sensitive sensitizer.The application includes: preparation colorless dye dispersion, preparation developer dispersion, preparation heat-sensitive sensitizer dispersion, mixing, coating.The heat-sensitive sensitizer of the application, when using different developers, all greatly improve the chromogenic performance, after being applied to heat-sensitive recording material, it will not cause the waterproofness of heat-sensitive recording material to decline.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat-sensitive sensitizers, in particular to a heat-sensitive sensitizer, a preparation method thereof and application thereof in heat-sensitive recording materials. BACKGROUND

[0002] The basic elements of heat-sensitive recording are heat pen head and transmission roller, without complex processes such as fixing and transferring, and have the advantages of small size, light weight and low price. As a recording consumable material, the heat-sensitive recording material is different from the previous sublimation-type thermochromic material, and the image forming layer thereof is composed of color former (leuco dye) and color developer, etc. After heating, the leuco dye reacts with the color developer to develop color. For the leuco dye, monochromatic xanthene black leuco dye is the development direction, among which, the monochromatic xanthene black leuco dye with a larger usage amount includes 2-anilino-3-methyl-6-dibutylaminofluorane (ODB-2), and the heat-sensitive recording material prepared from ODB-2 has high sensitivity and good definition. For the color developer, the color developers with a larger usage amount include bisphenol A color developer (BPA), 4,4'-dihydroxydiphenyl sulfone (BPS), 2,4-diphenyl sulfone phenol (DBSP), 4-hydroxy-4'-isopropoxydiphenyl sulfone (D-8), 4,4'-sulfonyl bis[2-(2-propenyl)] phenol (TGSH), 3-(3-tolylureido) phenyl 4-methylbenzenesulfonate (PF-201), etc. With the rise of electronic commerce and the rapid development of the logistics industry, the demand for heat-sensitive recording materials in the label and packaging fields is gradually increasing, and the requirements for the sensitivity and definition of heat-sensitive recording materials are also increasing. The heat-sensitive sensitizer itself has a lower melting point, no sublimation, good compatibility with color former and color developer, and is generally a neutral compound with a lower viscosity in the melting point range. The addition of the heat-sensitive sensitizer can reduce the melting point of the color developing system and improve the sensitivity and definition of the heat-sensitive recording material. The currently used heat-sensitive sensitizers mainly include stearic amide, 2-benzyloxy naphthalene and 1,2-diphenoxy ethane, but all have the problems of low sensitivity, poor sensitization effect and high cost. Therefore, it is of great significance to develop a cheap and efficient heat-sensitive sensitizer.

[0003] Synthesis and properties of sensitizers for thermal recording materials. Shen Meiqin, Ding Yuemei. Transactions of Tianjin University. December 1995 discloses four sensitizers, including an ester-containing sensitizer, which generates free acid by hydrolysis, and the free acid can release protons, thereby accelerating the color development process. Application and development of sensitizers for thermal recording paper. Shen Meiqin. Dye Industry. May 1993 discloses that when an ester sensitizer is added to a thermal recording material, a hydrolysis reaction of the ester occurs at the same time as the color development reaction of the dye, generating a carboxylic acid compound that is more acidic than the color developer, thereby promoting the color development reaction of the dye, increasing the color development speed of the thermal recording material, and increasing the color development sensitivity and color development concentration. It is also disclosed that the sensitizer has a low melting point and melting heat, so it is a melting point depressant for a mixture of thermal dyes and color developers, and the sensitizer forms a low-melting eutectic mixture with the thermal dyes and color developers, thereby reducing the color development temperature of the thermal recording material and increasing the color development sensitivity of the thermal recording material when the color is developed by heating. Recent developments in thermal paper and recent process points. Cao Liyun. Shanghai Papermaking. May 2001 discloses that benzoic acid esters or terephthalic acid esters can be used as sensitizers.

[0004] However, the applicants found the following problems when preparing thermal recording materials by using dimethyl terephthalate and diethyl terephthalate as thermal sensitizers, respectively: first, the hydrolysis of the ester group is affected not only by temperature and humidity but also by the pH environment, and different color developers have different pH values, so the effect of the thermal sensitizer on the color development performance is different after using different color developers, which limits the use range of the thermal sensitizer; second, the hydrolysis of the ester group generates free acid and hydroxyl groups, and the hydrophilicity of the hydroxyl groups is strong, which can cause the waterproofness of the thermal coating to decrease, and further cause the waterproofness of the thermal recording material to decrease; third, dimethyl terephthalate and diethyl terephthalate have poor dispersibility and are prone to agglomeration, which further causes the color development performance of the thermal recording material to decrease. SUMMARY

[0005] In view of the deficiencies in the prior art, the present application provides a thermal sensitizer, a preparation method thereof and application thereof in thermal recording materials. The thermal sensitizer of the present application can greatly improve the color development performance when different color developers are used, and will not cause the waterproofness of the thermal recording material to decrease when applied to the thermal recording material.

[0006] To solve the above technical problems, the technical solutions adopted by the present application are as follows:

[0007] A thermal sensitizer has the following structural formula:

[0008] ;

[0009] In the structural formula, R1, R2, R3, R4 are independently one of hydrogen atom, bromine atom, methyl, chlorine atom, and R1, R2, R3, R4 cannot be hydrogen atom at the same time;

[0010] X is an oxygen atom;

[0011] Y is one of ethyl, n-propyl, isopropyl;

[0012] Further, the structural formula of the heat-sensitive sensitizer is one of the following:

[0013] .

[0014] The preparation method of the aforementioned heat-sensitive sensitizer, terephthalic acid derivative and alcohol are mixed and stirred uniformly to obtain a mixture, a condensing agent is added to the mixture, and the mixture is reacted at 48-52℃, alcohol is removed, water is added, and post-treatment is performed to obtain the heat-sensitive sensitizer.

[0015] The terephthalic acid derivative is one of tetrabromoterephthalic acid, 2,3,5,6-tetramethyl terephthalic acid, 2,5-dimethyl terephthalic acid, 2,6-dimethyl terephthalic acid, 2,5-dichloroterephthalic acid, and 2,6-dichloroterephthalic acid;

[0016] The alcohol is one of ethanol, n-propanol, and isopropanol;

[0017] The condensing agent is dichlorosulfoxide or oxalyl chloride;

[0018] The ratio of the amount of use of terephthalic acid derivative to alcohol is 0.2 mol:150-200 mL;

[0019] The molar ratio of terephthalic acid derivative to condensing agent is 0.2:0.4-0.42;

[0020] When the condensing agent is added, the temperature of the mixture is 18-22℃;

[0021] When the condensing agent is added, a dropwise adding method is used, and the dropwise adding time is 1-1.2 hours;

[0022] When the reaction is carried out at 48-52℃, the reaction time is 5-5.5h;

[0023] When the alcohol is removed, a concentration method is used;

[0024] When the water is added, a stirring and dropwise adding method is used, and the dropwise adding time is 25-35 minutes;

[0025] The post-treatment is that the pH is adjusted to neutral, filtration is performed, the filter residue is washed with water, and drying is performed.

[0026] The application of the aforementioned heat-sensitive sensitizer in the heat-sensitive recording material comprises: preparing a leuco dye dispersion, preparing a color developer dispersion, preparing a heat-sensitive sensitizer dispersion, mixing, coating;

[0027] In the preparation of the leuco dye dispersion, the water, polyvinyl alcohol and leuco dye are mixed, and then stirred at 83-87℃ until completely dissolved. The leuco dye dispersion is obtained by adding the leuco dye and stirring at room temperature and sanding.

[0028] In the preparation of the leuco dye dispersion, the mass ratio of water, polyvinyl alcohol and leuco dye is 65-67:3.8-4.2:29-31.

[0029] The average particle size of the leuco dye dispersion is 0.7-0.9μm.

[0030] In the preparation of the color developer dispersion, the water, polyvinyl alcohol and color developer are mixed, and then stirred at 83-87℃ until completely dissolved. The color developer dispersion is obtained by adding the color developer and stirring at room temperature and sanding.

[0031] In the preparation of the color developer dispersion, the mass ratio of water, polyvinyl alcohol and color developer is 65-67:1.8-2.2:31-33.

[0032] The average particle size of the color developer dispersion is 0.7-0.9μm.

[0033] In the preparation of the heat-sensitive sensitizer dispersion, the water and polyvinyl alcohol are mixed, and then stirred at 83-87℃ until completely dissolved. The heat-sensitive sensitizer dispersion is obtained by adding the heat-sensitive sensitizer and cetyltrimethylammonium bromide and stirring at room temperature and sanding.

[0034] In the preparation of the heat-sensitive sensitizer dispersion, the mass ratio of water, polyvinyl alcohol, heat-sensitive sensitizer and cetyltrimethylammonium bromide is 65-67:2.4-2.6:31-32:0.4-0.6.

[0035] The average particle size of the heat-sensitive sensitizer dispersion is 0.7-0.9μm.

[0036] In the mixing, the leuco dye dispersion, color developer dispersion, heat-sensitive sensitizer dispersion, calcium carbonate, polyvinyl alcohol and water are mixed and stirred. The heat-sensitive coating is obtained by adding the auxiliary agent and stirring.

[0037] In the mixing, the mass ratio of leuco dye dispersion, color developer dispersion, heat-sensitive sensitizer dispersion, calcium carbonate, polyvinyl alcohol and water is 29-31:58-62:58-62:17-19:4.8-5.2:19-21.

[0038] The mass ratio of heat-sensitive sensitizer dispersion and auxiliary agent is 58-62:48-52.

[0039] The type of polyvinyl alcohol used in the preparation of the colorless dye dispersion liquid, the preparation of the color developer dispersion liquid, the preparation of the heat-sensitive sensitizer dispersion liquid and the mixing is polyvinyl alcohol 1799;

[0040] The preparation method of the auxiliary agent is mixing the cetyltrimethylammonium bromide aqueous solution and the polyvinyl alcohol aqueous solution, stirring, and standing to obtain the auxiliary agent;

[0041] In the preparation of the auxiliary agent, the concentration of cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide aqueous solution is 1.9-2.1 g / 500 mL;

[0042] The concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 6.4-6.6 g / 500 mL;

[0043] The type of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is polyvinyl alcohol 2488;

[0044] The mass ratio of cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide aqueous solution to polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1.9-2.1:6.4-6.6;

[0045] The stirring time is 1-1.5 h;

[0046] The standing time is 24-25 h;

[0047] The coating, coating the heat-sensitive coating on the surface of the base paper, and then drying to obtain the heat-sensitive recording material;

[0048] In the coating, when the heat-sensitive coating is coated on the surface of the base paper, the coating amount is 4.5-5.5 g / m 2 .

[0049] Compared with the prior art, the beneficial effects of the present application are:

[0050] (1) The heat-sensitive sensitizer of the present application, on the basis of the commonly used terephthalate heat-sensitive sensitizer, uses bromine atoms, chlorine atoms or methyl groups for substitution on the benzene ring, thereby improving the sensitizing performance and hydrophobicity of the terephthalate heat-sensitive sensitizer; in the application of the heat-sensitive sensitizer of the present application, cetyltrimethylammonium bromide is added in the dispersion of the heat-sensitive sensitizer of the present application using polyvinyl alcohol, the cetyltrimethylammonium bromide can form micelles, and plays a role of assisting the dispersion, bonding and colloidal protection of the polyvinyl alcohol with high alcoholysis degree, in the application, an auxiliary obtained by mixing cetyltrimethylammonium bromide and polyvinyl alcohol with low alcoholysis degree is also added, according to the NMR analysis of the interaction between the cationic surfactant CTAB and polyvinyl alcohol published in July 2011 in the journal of Polymer Materials Science and Engineering by Ge Heng, Zhao Xin and Sun Wanfu, there is interaction between the cationic surfactant CTAB and polyvinyl alcohol, mainly the interaction between the hydrophobic carbon hydrogen chains. And according to the preparation and performance of surfactant-polyvinyl alcohol composite hydrogel published in June 2020 in the master's degree thesis of Tianjin University by Yu Jingbin, the surfactant will form micelles in the solution through the interaction of hydrophilic and hydrophobic groups, and will have adsorption with the long molecular chain of polyvinyl alcohol to form a string of pearl structure. Therefore, the cetyltrimethylammonium bromide in the auxiliary and the polyvinyl alcohol form a string of pearl structure in water, the hydrophobic group of the cetyltrimethylammonium bromide combines with the hydrophobic segment of the polyvinyl alcohol, and the outer layer is the hydrophilic group of the cetyltrimethylammonium bromide combined with the hydrophilic segment of the polyvinyl alcohol, after the addition of the heat-sensitive coating, it can promote the dispersion of the heat-sensitive sensitizer, and in printing, the high temperature destroys the interaction between the cetyltrimethylammonium bromide and the polyvinyl alcohol, the hydrophobic segment of the cetyltrimethylammonium bromide is exposed and forms a hydrophobic region on the surface of the heat-sensitive coating, thereby further improving the water resistance of the heat-sensitive coating, at the same time, the auxiliary can also improve the stability of the micelles formed by the cetyltrimethylammonium bromide, and the micelles formed by the cetyltrimethylammonium bromide on the surface of the heat-sensitive sensitizer can avoid the influence of the external environment on the hydrolysis of the heat-sensitive sensitizer, thereby avoiding the influence of the color developer on the sensitizing performance of the heat-sensitive sensitizer;

[0051] (2) The heat-sensitive sensitizer of the present application greatly improves the color development performance when using different color developers, and does not cause the water resistance of the heat-sensitive recording material to decrease after being applied to the heat-sensitive recording material; when the heat-sensitive sensitizer of the present application is used and BPA, BPS, PF-201, DBSP, D-8 and TGSH are used as color developers respectively, the color development concentration of the prepared heat-sensitive recording material after saturated color development is 1.22-1.39, and after the prepared heat-sensitive recording material is placed in an experimental box with a temperature of 40℃ and a relative humidity of 90% for 24 hours, the color development concentration is 1.21-1.40. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The nuclear magnetic resonance hydrogen spectrum of M8 prepared in Example 8 is shown. DETAILED DESCRIPTION

[0053] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the specific embodiments of the present application are described.

[0054] In Examples 1-8, when calculating the yield of M1-M8, since the purity of M1-M8 obtained by removing impurities through concentration and water washing can reach more than 99%, the purity of M1-M8 is assumed to be 100% when calculating the yield.

[0055] Example 1 Preparation of thermal sensitizing agent M1

[0056] Tetrabromoterephthalic acid (96 g, 0.2 mol) was added to ethanol (200 mL), stirred uniformly, and then the temperature was maintained at 20°C. Dichlorosulfoxide (47.2 g, 0.4 mol) was added dropwise in 1 hour while continuously stirring, and then the reaction was carried out at 50°C for 5 hours. After the reaction was completed, the recovered ethanol was removed by concentration, 500 mL of water was slowly added in 30 minutes while stirring, the pH was adjusted to neutral, and then it was filtered. The filter residue was washed with water, and then dried to obtain 102 g of white solid M1, with a yield of 95%.

[0057] The characterization results of the nuclear magnetic resonance of M1 are as follows:

[0058] 1 H NMR (500 MHz, DMSO- d 6) δ =4.25 (dd, 4H), 1.27 (t, 6H) ppm.

[0059] ESI-MS: (m / z, %) = 538 [M+H] + .

[0060] The structural formula of M1 is as follows:

[0061] .

[0062] Example 2 Preparation of thermal sensitizing agent M2

[0063] Tetrabromoterephthalic acid (96 g, 0.2 mol) was added to n-propanol (200 mL), stirred uniformly, and then the temperature was maintained at 20°C. Oxalyl chloride (50.8 g, 0.4 mol) was added dropwise in 1 hour while continuously stirring, and then the reaction was carried out at 50°C for 5 hours. After the reaction was completed, the recovered n-propanol was removed by concentration, 500 mL of water was slowly added in 30 minutes while stirring, the pH was adjusted to neutral, and then it was filtered. The filter residue was washed with water, and then dried to obtain 105 g of white solid M2, with a yield of 93%.

[0064] The characterization results of the nuclear magnetic resonance of M2 are as follows:

[0065] 1 H NMR (500 MHz, DMSO- d 6) δ =4.26 (t, 4H), 1.89 (m, 4H), 1.03 (t, 6H) ppm.

[0066] ESI-MS: (m / z, %) = 566 [M+H] + .

[0067] The structural formula of M2 is:

[0068] .

[0069] Preparation of heat-sensitive sensitizer M3 in Example 3

[0070] 2,3,5,6-tetramethyl-p-xylylenedi-carboxylic acid (44.4 g, 0.2 mol) was added into n-propanol (150 mL), after stirring uniformly, the temperature was kept at 20°C, while continuing to stir, oxalyl chloride (50.8 g, 0.4 mol) was added dropwise within 1 hour, after the dropwise addition was completed, the reaction was carried out at 50°C for 5 hours, after the reaction was completed, the recovered n-propanol was removed by concentration, while stirring, 400 mL of water was slowly added within 30 minutes and stirred, the pH was adjusted to neutral, filtered, the filter residue was washed with water, and dried to obtain 58.8 g of white solid M3, with a yield of 96%.

[0071] The characterization results of the nuclear magnetic resonance of M3 are as follows:

[0072] 1 H NMR (500 MHz, DMSO- d 6) δ =4.28 (t, 4H), 2.21 (s, 12H), 1.88 (m, 4H),1.01 (t, 6H) ppm.

[0073] ESI-MS: (m / z, %) = 307 [M+H] + .

[0074] The structural formula of M3 is:

[0075] .

[0076] Preparation of heat-sensitive sensitizer M4 in Example 4

[0077] 2,3,5,6-tetramethyl-p-xylylenedicarboxylic acid (44.4 g, 0.2 mol) was added into isopropanol (150 mL), after stirring evenly, keep the temperature to 20 °C, continue to stir while droping oxalyl chloride (50.8 g, 0.4 mol) in 1 hour, after droping, react at 50 °C for 5 hours, after the reaction is completed, remove the recovered isopropanol by concentration, while stirring, slowly add 400 mL water in 30 minutes, stir, adjust the pH to neutral, filter, water wash the residue, dry to get 58.1 g white solid M4, yield 95%.

[0078] The characterization results of the nuclear magnetic resonance of product M4 are as follows:

[0079] 1 H NMR (500 MHz, DMSO- d 6) δ =5.21 (m, 2H), 2.22 (s, 12H), 1.38 (d, 12H)ppm.

[0080] ESI-MS: (m / z, %) = 307 [M+H] + .

[0081] The structural formula of M4 is:

[0082] .

[0083] Example 5 preparation of heat-sensitive sensitizer M5

[0084] 2,5-dimethyl-p-xylylenedicarboxylic acid (38.8 g, 0.2 mol) was added into isopropanol (150 mL), after stirring evenly, keep the temperature to 20 °C, continue to stir while droping thionyl chloride (47.6 g, 0.4 mol) in 1 hour, after droping, react at 50 °C for 5 hours, after the reaction is completed, remove the recovered isopropanol by concentration, while stirring, slowly add 400 mL water in 30 minutes, stir, adjust the pH to neutral, filter, water wash the residue, dry to get 53.9 g white solid M5, yield 97%.

[0085] The characterization results of the nuclear magnetic resonance of product M5 are as follows:

[0086] 1 H NMR (500 MHz, DMSO- d 6) δ =7.89(s, 2H), 5.23 (m, 2H), 2.46 (s, 6H), 1.36 (d, 12H)ppm.

[0087] ESI-MS: (m / z, %) = 279 [M+H] + .

[0088] The structural formula of M5 is:

[0089] .

[0090] Example 6 Preparation of thermal sensitizing agent M6

[0091] 2,6-dimethylterephthalic acid (38.8 g, 0.2 mol) was added into isopropyl alcohol (150 mL), after stirring evenly, the temperature was kept at 20°C, while continuing to stir, dichlorosulfoxide (47.6 g, 0.4 mol) was added dropwise within 1 hour, after the dropwise addition was completed, the reaction was carried out at 50°C for 5 hours, after the reaction was completed, the recovered isopropyl alcohol was removed by concentration, while stirring, 400 mL of water was slowly added within 30 minutes, stirring, the pH was adjusted to neutral, filtration, the filter residue was washed with water, and dried to obtain 52.2 g of white solid M6, with a yield of 94%.

[0092] The characterization results of M6 are as follows:

[0093] 1 H NMR (500 MHz, DMSO- d 6) δ =7.85(s,2H), 5.23 (m,2H), 2.47 (s,6H), 1.39(d,12H)ppm.

[0094] ESI-MS: (m / z, %) = 279 [M+H] + .

[0095] The structural formula of M6 is:

[0096] .

[0097] Example 7 Preparation of thermal sensitizing agent M7

[0098] 2,5-dichloroterephthalic acid (47 g, 0.2 mol) was added into isopropyl alcohol (150 mL), after stirring evenly, the temperature was kept at 20°C, while continuing to stir, dichlorosulfoxide (47.6 g, 0.4 mol) was added dropwise within 1 hour, after the dropwise addition was completed, the reaction was carried out at 50°C for 5 hours, after the reaction was completed, the recovered isopropyl alcohol was removed by concentration, while stirring, 400 mL of water was slowly added within 30 minutes, stirring, the pH was adjusted to neutral, filtration, the filter residue was washed with water, and dried to obtain 53.9 g of white solid M7, with a yield of 84%.

[0099] The characterization results of M7 are as follows:

[0100] 1 H NMR (500 MHz, DMSO- d 6) δ =8.02(s,2H), 5.24 (m,2H), 1.38 (d,12H)ppm.

[0101] ESI-MS: (m / z, %) = 320 [M+H] + .

[0102] The structural formula of M7 is:

[0103] .

[0104] Example 8 Preparation of thermal sensitizing agent M8

[0105] 2,6-dichloro-p-xylylenic acid (47 g, 0.2 mol) was added into isopropyl alcohol (150 mL), after stirring evenly, the temperature was kept at 20°C, while continuing to stir, dichlorosulfoxide (47.6 g, 0.4 mol) was added dropwise within 1 hour, after the dropwise addition was completed, the reaction was continued at 50°C for 5 hours, after the reaction was completed, the recovered isopropyl alcohol was removed by concentration, while stirring, 400 mL of water was slowly added within 30 minutes and stirred, the pH was adjusted to neutral, filtered, the filter residue was washed with water, and dried to obtain 51.6 g of white solid M8, with a yield of 81%.

[0106] The nuclear magnetic resonance hydrogen spectrum of M8 is shown in Figure 1 , Figure 1 The impurity peaks in the spectrum are water peak and tritium solvent peak, respectively.

[0107] The characterization results of M8 are as follows:

[0108] 1 H NMR (500 MHz, DMSO- d 6) δ=7.97(s, 2H), 5.25 (m, 2H), 1.40 (d, 12H)ppm.

[0109] ESI-MS: (m / z, %) = 320 [M+H] + .

[0110] The structural formula of M8 is:

[0111] .

[0112] Example 9 Preparation of auxiliary agent

[0113] 1. Preparation of aqueous solution of cetyltrimethylammonium bromide: 2 g of cetyltrimethylammonium bromide was added into 500 mL of water, stirred at room temperature until completely dissolved, to obtain an aqueous solution of cetyltrimethylammonium bromide;

[0114] 2. Preparation of aqueous solution of polyvinyl alcohol: 6.5 g of polyvinyl alcohol was added into 500 mL of water, stirred at 85°C until completely dissolved, to obtain an aqueous solution of polyvinyl alcohol;

[0115] The polyvinyl alcohol is polyvinyl alcohol 2488;

[0116] 3. Mixing: mixing all the aqueous cetyltrimethylammonium bromide solution obtained in step 1, all the aqueous polyvinyl alcohol solution obtained in step 2, stirring at room temperature for 1 h, then standing at room temperature for 24 h, to obtain the auxiliary agent.

[0117] Performance test

[0118] ODB-2 was used as the leuco dye, BPA, BPS, PF-201, DBSP, D-8, and TGSH were used as the color developer, M1-M8 prepared in Examples 1-8, dimethyl terephthalate (M9), and diethyl terephthalate (M10) were used as the heat-sensitive sensitizer, and the auxiliary agent prepared in Example 9 was used, and a heat-sensitive recording material was prepared according to the following method:

[0119] 1. Preparation of leuco dye dispersion liquid: mixing water and polyvinyl alcohol, stirring at 85°C until completely dissolved, adding leuco dye, stirring at room temperature for 30 minutes, adding to a sand mill, sand milling to an average particle size of 0.8 μm, to obtain a leuco dye dispersion liquid;

[0120] The mass ratio of water, polyvinyl alcohol, and leuco dye was 66:4:30;

[0121] 2. Preparation of color developer dispersion liquid: mixing water and polyvinyl alcohol, stirring at 85°C until completely dissolved, adding color developer, stirring at room temperature for 30 minutes, adding to a sand mill, sand milling to an average particle size of 0.8 μm, to obtain a color developer dispersion liquid;

[0122] The mass ratio of water, polyvinyl alcohol, and color developer was 66:2:32;

[0123] 3. Preparation of heat-sensitive sensitizer dispersion liquid: mixing water and polyvinyl alcohol, stirring at 85°C until completely dissolved, adding heat-sensitive sensitizer, cetyltrimethylammonium bromide, stirring at room temperature for 30 minutes, adding to a sand mill, sand milling to an average particle size of 0.8 μm, to obtain a heat-sensitive sensitizer dispersion liquid;

[0124] The mass ratio of water, polyvinyl alcohol, heat-sensitive sensitizer, and cetyltrimethylammonium bromide was 66:2.5:31.5:0.5;

[0125] 4. Mixing: mixing the leuco dye dispersion liquid, the color developer dispersion liquid, the heat-sensitive sensitizer dispersion liquid, calcium carbonate, polyvinyl alcohol, and water according to a mass ratio of 30:60:60:18:5:20, stirring uniformly at room temperature, then adding the auxiliary agent, controlling the mass ratio of the heat-sensitive sensitizer dispersion liquid to the auxiliary agent to be 60:50, stirring uniformly at room temperature, to obtain a heat-sensitive coating;

[0126] The type of polyvinyl alcohol used in steps 1-4 is polyvinyl alcohol 1799;

[0127] 5. Coating: The heat-sensitive coating is coated on the surface of the base paper, and the coating amount is controlled to be 5 g / m 2 Then drying is performed to obtain the heat-sensitive recording material.

[0128] At the same time, when preparing heat-sensitive recording materials by using BPA, BPS, PF-201, DBSP, D-8, and TGSH as color developers, and M1 as a heat-sensitive sensitizer, a control test is set, and the control test is not using an additive, that is, the mixing step in step 4 is changed to:

[0129] The colorless dye dispersion liquid, the color developer dispersion liquid, the heat-sensitive sensitizer dispersion liquid, calcium carbonate, polyvinyl alcohol, and water are mixed in a mass ratio of 30:60:60:18:5:20, and then stirred uniformly to obtain a heat-sensitive coating. The remaining operation methods are unchanged.

[0130] The obtained each heat-sensitive recording material is saturatedly colored, and then the optical density (coloring concentration) after coloring is tested by using an optical density meter as the coloring concentration before wet aging treatment. Then, the wet aging test is performed, and specifically, the heat-sensitive recording material after saturated coloring is placed in an experimental box with a temperature of 40°C and a relative humidity of 90% for 24 hours for wet aging treatment. The coloring concentration is tested as the coloring concentration after wet aging treatment. The test results are shown in Tables 1-6:

[0131] Table 1 Test results when BPA is used as a color developer

[0132]

[0133] Table 2 Test results when BPS is used as a color developer

[0134]

[0135] Table 3 Test results when PF-201 is used as a color developer

[0136]

[0137] Table 4 Test results when DBSP is used as a color developer

[0138]

[0139] Table 5 Test results when D-8 is used as a color developer

[0140]

[0141] Table 6 Test results when TGSH is used as a color developer

[0142]

[0143] As can be seen from Tables 1-6, compared with M1-M8 heat-sensitive sensitizers, M9 heat-sensitive sensitizers and M10 heat-sensitive sensitizers have the problems that the color development concentration is greatly affected by the type of color developing agent after being applied to heat-sensitive recording materials, the waterproof property of the obtained heat-sensitive recording materials is poor, and the heat-sensitive recording materials without using the auxiliary agent also have the problem that the waterproof property of the obtained heat-sensitive recording materials is poor.

[0144] For the data in Tables 1-6, the color development concentration after the wet aging treatment is higher than that before the wet aging treatment. After repeated testing and analysis, the reason is that there is a testing error when testing the color development concentration. In addition, BPA and TGSH are used as color developing agents in Table 1 and Table 6, respectively, and the structural formulas of the color developing agents are quite different, but both BPA and TGSH contain phenolic hydroxyl groups and mainly play a color developing role through the phenolic hydroxyl groups. Therefore, the color development concentrations before the wet aging treatment are similar.

Claims

1. The application of a thermal sensitizer in thermal recording materials, characterized in that, include: Prepare colorless dye dispersion, prepare color developer dispersion, prepare thermosensitive sensitizer dispersion, mix, and coat; To prepare the colorless dye dispersion, water and polyvinyl alcohol are mixed and stirred at 83-87°C until completely dissolved. Then, the colorless dye is added, stirred, and milled to obtain the colorless dye dispersion. To prepare the color developer dispersion, water and polyvinyl alcohol are mixed and stirred at 83-87°C until completely dissolved. The color developer is then added, stirred, and milled to obtain the color developer dispersion. To prepare the thermosensitive sensitizer dispersion, water and polyvinyl alcohol are mixed and stirred at 83-87°C until completely dissolved. The thermosensitive sensitizer and hexadecyltrimethylammonium bromide are then added, stirred, and milled to obtain the thermosensitive sensitizer dispersion. The mixing process involves mixing a colorless dye dispersion, a color developer dispersion, a thermosensitive sensitizer dispersion, calcium carbonate, polyvinyl alcohol, and water, stirring the mixture, adding additives, and stirring again to obtain a thermosensitive coating. The auxiliary agent is prepared by mixing an aqueous solution of hexadecyltrimethylammonium bromide with an aqueous solution of polyvinyl alcohol, stirring, and allowing it to stand to obtain the auxiliary agent. In the preparation of the colorless dye dispersion, the preparation of the color developer dispersion, and the preparation of the thermosensitive sensitizer dispersion, the polyvinyl alcohol used in the mixture is of type 1799. In the preparation of the additive, the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is polyvinyl alcohol 2488; In the preparation of the thermosensitive sensitizer dispersion, the structural formula of the thermosensitive sensitizer is as follows: ； In the structural formula, R1, R2, R3, and R4 are each independently one of hydrogen atom, bromine atom, methyl atom, and chlorine atom, and R1, R2, R3, and R4 cannot all be hydrogen atoms at the same time. X is an oxygen atom; Y is one of ethyl, n-propyl, or isopropyl.

2. The application of the thermosensitive sensitizer according to claim 1 in thermosensitive recording materials, characterized in that, The method for preparing the thermosensitive sensitizer is as follows: terephthalic acid derivative and alcohol are mixed and stirred to obtain a mixture; a condensing agent is added to the mixture; the mixture is reacted at 48-52°C; the alcohol is removed; water is added; and the mixture is post-treated to obtain the thermosensitive sensitizer.

3. The application of the thermosensitive sensitizer according to claim 2 in thermosensitive recording materials, characterized in that, In the preparation of the heat-sensitive sensitizer, the terephthalic acid derivative is one of tetrabromoterephthalic acid, 2,3,5,6-tetramethylterephthalic acid, 2,5-dimethylterephthalic acid, 2,6-dimethylterephthalic acid, 2,5-dichloroterephthalic acid, and 2,6-dichloroterephthalic acid. The alcohol is one of ethanol, n-propanol, and isopropanol; The condensing agent is thionyl chloride or oxaloyl chloride; The ratio of terephthalic acid derivative to alcohol is 0.2 mol: 150-200 mL; The molar ratio of terephthalic acid derivative to condensing agent is 0.2:0.4-0.

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4. The application of the thermosensitive sensitizer according to claim 2 in thermosensitive recording materials, characterized in that, In the preparation of the heat-sensitive sensitizer, the temperature of the mixture is 18-22℃ when the condensing agent is added; When adding the condensing agent, it should be added dropwise over a period of 1-1.2 hours. When the reaction is carried out at 48-52℃, the reaction time is 5-5.5 hours. When removing alcohol, a concentration method is used; When adding water, use a method of adding it dropwise while stirring, and the dripping time should be 25-35 minutes; The post-treatment involves adjusting the pH to neutral, filtering, washing the filter residue with water, and drying.

5. The application of the thermosensitive sensitizer according to claim 1 in thermosensitive recording materials, characterized in that, In the preparation of the colorless dye dispersion, the mass ratio of water, polyvinyl alcohol, and colorless dye is 65-67:3.8-4.2:29-31. In the preparation of the colorimetric reagent dispersion, the mass ratio of water, polyvinyl alcohol, and colorimetric reagent is 65-67:1.8-2.2:31-33; In the preparation of the thermosensitive sensitizer dispersion, the mass ratio of water, polyvinyl alcohol, thermosensitive sensitizer, and hexadecyltrimethylammonium bromide is 65-67:2.4-2.6:31-32:0.4-0.

6. In the mixture, the mass ratio of colorless dye dispersion, color developer dispersion, thermosensitive sensitizer dispersion, calcium carbonate, polyvinyl alcohol, and water is 29-31:58-62:58-62:17-19:4.8-5.2:19-21.

6. The application of the thermosensitive sensitizer according to claim 1 in thermosensitive recording materials, characterized in that, In the mixture, the mass ratio of the thermosensitive sensitizer dispersion to the additive is 58-62:48-52.

7. The application of the thermosensitive sensitizer according to claim 1 in thermosensitive recording materials, characterized in that, In the preparation of the auxiliary agent, the concentration of hexadecyltrimethylammonium bromide in the aqueous solution is 1.9-2.1 g / 500 mL; The concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 6.4-6.6 g / 500 mL; The polyvinyl alcohol in the aqueous solution is polyvinyl alcohol 2488. The mass ratio of hexadecyltrimethylammonium bromide in the aqueous solution to polyvinyl alcohol in the aqueous solution is 1.9-2.1:6.4-6.

6. The stirring time is 1-1.5 hours; The settling time is 24-25 hours.

8. The application of the thermosensitive sensitizer according to claim 1 in thermosensitive recording materials, characterized in that, The coating process involves applying a thermal coating onto the surface of the base paper and then drying it to obtain a thermal recording material. In the coating process, when the heat-sensitive coating is applied to the surface of the base paper, the coating amount is 4.5-5.5 g / m². 2 .

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