Black-red dual independent heat-sensitive color developing material and preparation method thereof

Abstract

The application relates to a black-red double-independent heat-sensitive color developing material and a preparation method thereof, and belongs to the technical field of multicolor heat-sensitive color developing materials. A crystal violet lactone and 4,4'-dihydroxy diphenyl sulfone obtain a black color developing dispersion system, and rhodamine B lactone and gallic acid obtain a red color developing dispersion system. The black color developing dispersion system, the red color developing dispersion system, a polyvinyl alcohol aqueous solution and stearic acid amide are mixed, the content of the crystal violet lactone is 5-8%, the content of the 4,4'-dihydroxy diphenyl sulfone is 10-12%, the content of the rhodamine B lactone is 4-6%, the content of the gallic acid is 8-10%, the content of the polyvinyl alcohol is 59-70%, and the content of the stearic acid amide is 3-5%. The composite slurry is coated on the surface of a base material and dried and solidified at 80-90 DEG C to obtain the black-red double-independent heat-sensitive color developing material. The material prepared in the application realizes single coating and precise double-color developing, and has no color cross.

Description

Technical Field

[0001] This application relates to the field of multicolor thermosensitive colorimetric materials technology, and in particular to a black-red dual independent thermosensitive colorimetric material and its preparation method. Background Technology

[0002] Currently, most thermal label color-developing materials on the market are single-color black color-developing systems. These systems consist of colorless dyes, color developers, carrier resins, and additives. The color development reaction is triggered by heating in a thermal printer, achieving only a single black color for carrying basic labeling information. For dual-color labeling, traditional solutions mainly employ a two-stage printing process (printing one color first, then another), multi-layer coating (different coatings corresponding to different colors), or pre-printing a base color before thermal color development. Essentially, these are still extensions of a single-color color-developing system. Furthermore, multi-layer coating solutions suffer from weak adhesion, easy peeling, and require specialized coating equipment, resulting in poor compatibility. Some solutions attempt to mix multiple dyes within a single color-developing system, but this easily leads to color bleeding, poor color stability, and insufficient color accuracy, failing to meet the high precision requirements of dual-color labeling scenarios such as tobacco retail price labels. Summary of the Invention

[0003] The purpose of this application is to address the shortcomings of existing technologies, such as the tendency for color mixing and weak adhesion of multilayer coatings in traditional thermal dual-color labels, and to propose a black-red dual independent thermal color-developing material and its preparation method.

[0004] Firstly, the preparation method of a black-red dual independent thermosensitive colorimetric material provided in this application adopts the following technical solution: the preparation method includes the following steps: S1. Crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone were added to anhydrous ethanol and ultrasonically dispersed to obtain a black color-developing dispersion system. Rhodamine B lactone and gallic acid were added to anhydrous ethanol and ultrasonically dispersed to obtain a red color-developing dispersion system. S2. The black color-developing dispersion system, the red color-developing dispersion system, the polyvinyl alcohol aqueous solution, and stearamide are mixed to obtain a composite slurry, wherein, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol, and stearamide as 100%, the content of crystal violet lactone is 5-8%, the content of 4,4'-dihydroxydiphenyl sulfone is 10-12%, the content of rhodamine B lactone is 4-6%, the content of gallic acid is 8-10%, the content of polyvinyl alcohol is 59-70%, and the content of stearamide is 3-5%. S3. The composite slurry is coated on the surface of the pretreated substrate and then dried and cured at 80~90 ℃ to form a dual-color coating on the surface of the substrate, thus obtaining a black-red dual independent thermosensitive color material.

[0005] Through the above technical solution, under the formulation conditions of this application, crystal violet lactone 5-8% and 4,4'-dihydroxydiphenyl sulfone 10-12% exhibit a stable black color after color development at 110-130 ℃, while rhodamine B lactone 4-6% and gallic acid 8-10% exhibit a stable red color after color development at 80-100 ℃. The role of 3-5% stearamide is to moderately reduce the color development temperature threshold of the two color development systems to improve color development sensitivity. The color development temperature reduction range is 5-8 ℃ for the black color development system and 10-15 ℃ for the red color development system. A safe temperature difference window of ≥20 ℃ is always maintained between the two color development systems to avoid color bleeding, thereby improving color development sensitivity. At the same time, it enhances the flexibility and adhesion of the coating and prevents the coating from falling off. The role of 59-70% polyvinyl alcohol is to uniformly disperse and fix the two color development systems to form a stable continuous phase of the coating and improve the adhesion between the coating and the substrate. The composite slurry, prepared by combining an independent red coloring system with an independent black coloring system, is pre-cured by drying at 80~90℃ to form a stable structure in advance. The corresponding coloring reaction can only be triggered under specific high-temperature conditions, while completely locking in the colored substances and preventing reversible color change.

[0006] Optionally, the preferred contents of each component are as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 63%, and stearamide 4%.

[0007] Optionally, in step S1, the maximum particle size D100 in the black colorimetric dispersion system and the red colorimetric dispersion system is ≤1 μm.

[0008] With the above technical solution, the smaller the particle size, the more uniform and independent the color development micro-area. During high-temperature printing, the black / red system will not penetrate each other, which can completely avoid color bleeding. At the same time, the larger the contact area with the polyvinyl alcohol carrier, the denser the coating film, the stronger the adhesion, and the less likely it is to fall off. If the particle size is too large, the boundary of the micro-area will be blurred, and edge smudging and color mixing will easily occur. At the same time, if the particle size is too large, the coating will be loose and easy to shed powder.

[0009] In this paper, the particle size of the black and red colorimetric dispersion systems was measured using a laser particle size analyzer. The test standard was GB / T 19627-2005. The slurry to be tested was diluted with anhydrous ethanol to a light-blocking rate of 10%~20%, and the test was conducted at a constant temperature of 25 ℃. The test was performed in parallel for 3 times, and the maximum particle size D100≤1 μm was used as the acceptance criterion.

[0010] Optionally, the mass ratio of 4,4'-dihydroxydiphenyl sulfone to crystal violet lactone is 1.5~2.0:1, and the mass ratio of gallic acid to rhodamine B lactone is 1.7~2.5:1.

[0011] Through the above technical solutions, a moderate excess of 4,4'-dihydroxydiphenyl sulfone can ensure that the lactone ring of crystal violet lactone is fully opened and the color development is improved, thus increasing the density of black color development. A moderate excess of gallic acid can ensure that rhodamine B lactone is fully developed.

[0012] Optionally, the degree of polymerization of polyvinyl alcohol is 1600~1800, and the degree of alcoholysis is 85~92%. Specifically, it is polyvinyl alcohol 1788.

[0013] The reason for selecting polyvinyl alcohol with a degree of polymerization of 1600~1800 through the above technical solution is that it provides sufficient molecular chain length, giving the coating good film-forming properties and mechanical strength; the degree of hydrolysis of 85~92% means that a certain amount of acetate groups are retained on the molecular chain. These hydrophobic groups can improve the compatibility between polyvinyl alcohol and organic color-developing components, making the two color-developing systems more uniformly dispersed in the carrier. At the same time, the appropriate degree of hydrolysis gives the polyvinyl alcohol aqueous solution a suitable viscosity, which is convenient for coating operations.

[0014] In a specific embodiment of step S2, the polyvinyl alcohol aqueous solution is prepared by adding polyvinyl alcohol to hot water at 90 °C while stirring, and continuing to stir for about 30 minutes until the polyvinyl alcohol is completely dissolved.

[0015] Optionally, in step S1, crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone are dissolved in anhydrous ethanol, wherein the amount of anhydrous ethanol used is 6 to 8 times the total mass of crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone; and rhodamine B lactone and gallic acid are dissolved in anhydrous ethanol, wherein the amount of anhydrous ethanol used is 6 to 8 times the total mass of rhodamine B lactone and gallic acid.

[0016] The above technical solution uses 6-8 times the mass of anhydrous ethanol as a solvent, which ensures that crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone and gallic acid are fully dissolved and dispersed to form a stable dispersion system. If the amount of ethanol is too small, the solutes will not dissolve completely and the dispersion will be uneven, resulting in uneven distribution of the colored micro-regions in the subsequent coating and affecting the uniformity of color development. If the amount of ethanol is too large, the concentration of the dispersion system will be too low, and the solid content will be insufficient when mixed with the polyvinyl alcohol aqueous solution, affecting the coating thickness and color density.

[0017] In a specific embodiment of step S2, the mass concentration of the polyvinyl alcohol aqueous solution is 8-12%. If the mass concentration of the polyvinyl alcohol aqueous solution is controlled at 8-12%, the coating solid content will be insufficient, the film-forming properties will be poor, and the coating will be thin and uneven. If the concentration is too high, the slurry viscosity will be too high, the leveling properties will be poor, the coating will be difficult to apply, and the coating thickness will be uneven.

[0018] Optionally, the thickness of the dual-color coating is 10~15 μm.

[0019] With the above technical solutions, if the thickness is too thin, the content of coloring components will be insufficient, the color density will be low, and the colors will not be vivid; if the thickness is too thick, the heat conduction efficiency will be reduced, affecting the color sensitivity and printing speed.

[0020] Optionally, the preparation method further includes coating the surface of the dual-color coating with an aqueous UV-curable resin with a thickness of 1~2 μm, and then performing UV curing to form a protective layer.

[0021] Through the above technical solution, the molecular chain of the water-based UV-curable resin has carbon-carbon double bond functional groups that can be cross-linked by UV, and cross-linking and curing can be achieved by UV irradiation. It is suitable for the protection requirements of 1~2 μm ultra-thin protective layer, improves the coating's abrasion resistance, weather resistance and water resistance, prevents the coating from being scratched and oxidized, and extends the label's service life. The thickness of the protective layer is controlled at 1~2 μm, which can provide sufficient protection without significantly affecting the heat conduction efficiency and color development sensitivity.

[0022] Optionally, in step S3, the pretreated substrate is obtained by corona treatment of synthetic paper.

[0023] In a specific embodiment, the substrate can also be a PET film with a thickness of 50~75 μm and a corona treatment intensity of ≥38 dyn / cm.

[0024] Through the above technical solution, the corona treatment of the dual-color thermosensitive coating can improve the surface energy of the substrate, enhance the adhesion between the coating and the substrate, and prevent the coating from falling off.

[0025] Secondly, this application provides a black-red dual independent thermosensitive color-developing material obtained by the preparation method described above. The coating thickness of the black-red dual independent thermosensitive color-developing material is 10~15μm, the maximum particle size D100≤1μm, and the black color development reaction is triggered separately under thermosensitive printing at 110~130 ℃, and the red color development reaction is triggered separately under thermosensitive printing at 80~100 ℃.

[0026] Thermal printing utilizes extremely short heating pulse times (on the order of 1-3 ms). When printing red in low-temperature mode (80-100 ℃), the printhead temperature does not reach the color development threshold of the black system (above 110 ℃), therefore the black system is not triggered. When printing black in high-temperature mode (110-130 ℃), although the printhead heating process passes through the color development temperature range of the red system (80-100 ℃), due to the thermally reversible nature of the red system's color development reaction, the color product formed by rhodamine B lactone and gallic acid will undergo thermal fading and return to a colorless state after the temperature continues to rise above 110 ℃. Meanwhile, the color product of the black system (crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone) has higher thermal stability at this temperature and can maintain stable color development. Therefore, precise selective color development of black (110-130 ℃) and red (80-100 ℃) can be achieved, ensuring stable color development without color bleeding.

[0027] In summary, this application includes at least one of the following beneficial technical effects: 1. This application prepares a dual-color thermosensitive coating composed of an independent black color-developing system and a red color-developing system, and selects polyvinyl alcohol as the carrier resin and stearamide as the sensitizer to improve the color development performance, achieving precise selective color development of black (110~130 ℃) and red (80~100 ℃), with stable color development and no color bleeding; at the same time, the color retention rate is also high during long-term storage. When the color-developing material prepared in this application is sealed and stored for 12 months in an environment of 25 ℃ and relative humidity of 50~60%, the color retention rate of the black area is more than 85% and the color retention rate of the red area is more than 83%. 2. The color-developing material described in this application is a compound of an independent black color-developing system and a red color-developing system, integrated into the same coating, achieving single coating and precise dual-color development without secondary processing. It is compatible with existing production lines and thermal printers, reducing costs, improving efficiency, and meeting the dual-color differentiation and marking needs of multiple scenarios. Attached Figure Description

[0028] Figure 1 This is a thermal printing effect image of the black-red dual independent thermal colorimetric material prepared in Example 1 of this application. Detailed Implementation

[0029] The following combination Figure 1 The present application will be further described in detail with reference to specific embodiments.

[0030] The following examples further illustrate the black-red dual independent thermosensitive colorimetric material and its preparation method described in this application. The examples are implemented based on the technical solution of this application, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this application is not limited to the following examples.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0032] Crystal violet lactone: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number C804867, purity ≥98%; Rhodamine B lactone: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number R817623, purity ≥98%; Polyvinyl alcohol 1788: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number P815724, degree of polymerization 1700, degree of alcoholysis 88%; Polyvinyl alcohol 1799: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number P815725, degree of polymerization 1700, degree of alcoholysis 98~99%; Sodium carboxymethyl cellulose: Purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number V30066; Waterborne UV-curable resin: Purchased from Wanhua Chemical Group Co., Ltd., product number 4616.

[0033] Test case Color contrast: The color-developing material prepared in this application was thermally printed at 120 ℃ (triggered black color development) and 90 ℃ (triggered red color development) using a thermal printer. Color contrast was tested in the black and red color-developing areas according to the ISO 13655 standard for testing the optical density of printed matter. The specific testing method was as follows: Test environment: constant temperature and humidity environment of 25 ℃ and 55% relative humidity, with the sample placed for 24 hours to reach equilibrium before testing; Equipment calibration: a 45° / 0° spectral reflectance densitometer conforming to ISO 13655 standard was used, calibrated using a standard black and white plate before testing, and equipped with a thermal printer with a temperature control accuracy of ±2 ℃; Sample preparation: black and red pure color test blocks were printed on the sample at 120 ℃ and 90 ℃ respectively, preparing 3 sets of parallel samples, which were then left to stand for 24 hours after printing. h. Wait for the color to stabilize; Testing and calculation: First, measure the blank density OD0 of the undeveloped area of ​​the sample, then measure the color density OD of the black and red developed areas respectively, and calculate the color contrast (%) according to the formula = [(OD color - OD0) / OD color] × 100%. The result is the average value of parallel samples. Color bleeding control: The colorimetric material prepared in this application was printed in black at 120 °C and in red at 90 °C using a thermal printer, and the colorimetric area was observed under a 400x microscope. Accuracy of color development temperature range: The initial temperature was 25 ℃, and the temperature was increased at a gradient of 5 ℃ / min. The onset and termination temperatures of color development for black and red were recorded respectively. Color retention rate: The color-developing material prepared in this application was thermally printed at 120 ℃ (black) and 90 ℃ (red) using a thermal printer. Then, it was sealed and stored for 12 months in a high-humidity environment of 25 ℃ and 55% relative humidity. The color retention rate was measured and calculated. The formula for calculating the color retention rate is: Color retention rate (%) = [(OD1-OD0) / (OD2-OD0)]×100%, where OD0 is the optical density of the undeveloped substrate (blank), OD1 is the remaining color-developing optical density after 12 months of high-humidity storage, and OD2 is the color-developing optical density immediately after printing. Abrasion resistance: The colorimetric material prepared in this application was thermally printed at 120 ℃ (black) and 90 ℃ (red) using a thermal printer, and the abrasion resistance of printed matter was tested according to GB / T 7706, with 200 g weight and 500 cycles of reciprocating friction. High and low temperature cycling stability: The colorimetric material prepared in this application was thermally printed at 120 ℃ (black) and 90 ℃ (red) using a thermal printer. Then it was stored at high and low temperatures of -20 ℃ and 60 ℃ respectively. Each cycle consisted of 6 h at -20 ℃ and 6 h at 60 ℃. A total of 20 cycles were performed, and the color development was observed after each cycle.

[0034] Examples 1-6 describe black-red dual independent thermosensitive colorimetric materials and their preparation methods. Example 1

[0035] A method for preparing a black-red dual independent thermosensitive colorimetric material, the method comprising the following steps: S1. Weigh 6 g of crystal violet lactone and 12 g of 4,4'-dihydroxydiphenyl sulfone, and add them to 108 g of anhydrous ethanol (6 times the total mass of crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone). Then place the mixture in an ultrasonic dispersion device and ultrasonically disperse it for 30 min at a power of 300 W and a frequency of 25 kHz to obtain a black colored dispersion system. The particle D100 is 0.8 μm. Weigh 5 g of rhodamine B lactone and 10 g of gallic acid, and add them to 90 g of anhydrous ethanol (6 times the total mass of rhodamine B lactone and gallic acid). Then place them in an ultrasonic dispersion device and ultrasonically disperse them for 30 min at a power of 300 W and a frequency of 25 kHz to obtain a red colorimetric dispersion system. The particle D100 was 0.9 μm. S2. Add 63 g of polyvinyl alcohol 1788 to hot water at 90 ℃ while stirring, and continue stirring for 30 min until completely dissolved to obtain a polyvinyl alcohol aqueous solution with a mass concentration of 10%. The above-mentioned black colorimetric dispersion system, red colorimetric dispersion system, polyvinyl alcohol aqueous solution and stearamide 4 g were mixed and placed in a high-speed stirring device and stirred at 800 r / min for 1 h to obtain a composite slurry. Based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol, and stearamide as 100%, the content of each component is as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 63%, and stearamide 4%; S3. The synthetic paper is subjected to corona treatment at a strength of 38 dyn / cm to obtain a pretreated substrate. The composite slurry is uniformly coated on the surface of the pretreated substrate using a micro-gravure coating process at a coating speed of 18 m / min. The coating is then dried and cured at 85 ℃ for 8 min to form a 12 μm thick dual-color coating on the substrate surface, resulting in a black-red dual independent thermosensitive color material.

[0036] The black-red dual independent thermosensitive color-developing material prepared in Example 1 was tested for color cross-contamination control. The results showed that there was no cross-contamination or edge bleed-through in the black and red color-developing areas. The color-developing material was tested for accuracy of the color-developing temperature range. The results showed that the red color developed only in the range of 82~98 ℃, and the black color developed only in the range of 112~128 ℃, with a temperature window spacing of ≥14℃ and no overlap. The color-developing material was tested for abrasion resistance. The results showed that after abrasion, there was no ink loss or significant fading in the black and red color-developing areas, and the text and barcodes were clearly legible. The color-developing material was tested for high and low temperature cycling stability. The results showed that after cycling, the labels did not curl up or peel off, the color-developing areas did not fade or cross-contamination, and the color retention rate of both the black and red areas was ≥90%. Example 2

[0037] A method for preparing a black-red dual independent thermosensitive colorimetric material, the method comprising the following steps: S1. Weigh 5 g of crystal violet lactone and 10 g of 4,4'-dihydroxydiphenyl sulfone, and add them to 120 g of anhydrous ethanol (8 times the total mass of crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone). Then place them in an ultrasonic dispersion device and ultrasonically disperse them for 25 min at a power of 300 W and a frequency of 30 kHz to obtain a black colored dispersion system. The particle D100 was 0.6 μm. Weigh 4 g of rhodamine B lactone and 8 g of gallic acid, and add them to 96 g of anhydrous ethanol (8 times the total mass of rhodamine B lactone and gallic acid). Then place them in an ultrasonic dispersion device and ultrasonically disperse them for 25 min at a power of 300 W and a frequency of 30 kHz to obtain a red colorimetric dispersion system. The particle D100 was 0.7 μm. S2. Add 65 g of polyvinyl alcohol 1788 to hot water at 90 ℃ while stirring, and continue stirring for 30 min until completely dissolved to obtain a polyvinyl alcohol aqueous solution with a mass concentration of 8%. The above-mentioned black colorimetric dispersion system, red colorimetric dispersion system, polyvinyl alcohol aqueous solution and stearamide 3 g were mixed and placed in a high-speed stirring device and stirred at 800 r / min for 1 h to obtain a composite slurry; Based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol, and stearamide as 100%, the contents of each component are as follows: crystal violet lactone 5.3%, 4,4'-dihydroxydiphenyl sulfone 10.5%, rhodamine B lactone 4.2%, gallic acid 8.4%, polyvinyl alcohol 68.4%, and stearamide 3.2%; S3. The synthetic paper is subjected to corona treatment at a strength of 38 dyn / cm to obtain a pretreated substrate. The composite slurry is uniformly coated on the surface of the pretreated substrate using a microgravure coating process at a coating speed of 18 m / min. The coating is then dried and cured at 80 ℃ for 10 min to form a 10 μm thick dual-color coating on the substrate surface, resulting in a black-red dual independent thermosensitive color material.

[0038] The black-red dual independent thermosensitive color-developing material prepared in Example 2 was tested for color cross-contamination control. The results showed that there was no cross-contamination or edge bleed-through in the black and red color-developing areas. The color-developing material was tested for accuracy of the color-developing temperature range. The results showed that the red color developed only in the range of 83~99 ℃, and the black color developed only in the range of 114~130 ℃, with a temperature window spacing of ≥15℃ and no overlap. The color-developing material was tested for abrasion resistance. The results showed that after abrasion, there was no ink loss or significant fading in the black and red color-developing areas, and the text and barcodes were clearly legible. The color-developing material was tested for high and low temperature cycling stability. The results showed that after cycling, the labels did not curl up or peel off, the color-developing areas did not fade or cross-contamination, and the color retention rate of both the black and red areas was ≥89%. Example 3

[0039] A method for preparing a black-red dual independent thermosensitive colorimetric material, the method comprising the following steps: S1. Weigh 8 g of crystal violet lactone and 12 g of 4,4'-dihydroxydiphenyl sulfone, and add them to 140 g of anhydrous ethanol (7 times the total mass of crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone). Then place the mixture in an ultrasonic dispersion device and ultrasonically disperse it for 20 min at a power of 300 W and a frequency of 35 kHz to obtain a black colored dispersion system. The particle D100 is 0.5 μm. Weigh 6 g of rhodamine B lactone and 10 g of gallic acid, and add them to 112 g of anhydrous ethanol (7 times the total mass of rhodamine B lactone and gallic acid). Then place them in an ultrasonic dispersion device and ultrasonically disperse them for 20 min at a power of 300 W and a frequency of 35 kHz to obtain a red colorimetric dispersion system. The particle D100 was 0.5 μm. S2. Add 60 g of polyvinyl alcohol 1788 to hot water at 90 ℃ while stirring, and continue stirring for 30 min until completely dissolved to obtain a polyvinyl alcohol aqueous solution with a mass concentration of 12%. The above-mentioned black colorimetric dispersion system, red colorimetric dispersion system, polyvinyl alcohol aqueous solution and stearamide 5 g were mixed and placed in a high-speed stirring device and stirred at 800 r / min for 1 h to obtain a composite slurry. Based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol, and stearamide as 100%, the contents of each component are as follows: crystal violet lactone 7.9%, 4,4'-dihydroxydiphenyl sulfone 11.9%, rhodamine B lactone 5.9%, gallic acid 9.9%, polyvinyl alcohol 59.4%, and stearamide 5.0%; S3. The synthetic paper is subjected to corona treatment at a strength of 38 dyn / cm to obtain a pretreated substrate. The composite slurry is uniformly coated on the surface of the pretreated substrate using a microgravure coating process at a coating speed of 18 m / min. The coating is then dried and cured at 90 ℃ for 5 min to form a 15 μm thick dual-color coating on the substrate surface, resulting in a black-red dual independent thermosensitive color material.

[0040] The black-red dual independent thermosensitive color-developing material prepared in Example 3 was tested for color cross-contamination control. The results showed that there was no cross-contamination or edge bleed-through in the black and red color-developing areas. The color-developing material was tested for accuracy in the color-developing temperature range. The results showed that red only developed color in the range of 80~96 ℃, and black only developed color in the range of 110~126 ℃, with a temperature window spacing of ≥14℃ and no overlap. The color-developing material was tested for abrasion resistance. The results showed that after abrasion, there was no ink loss or significant fading in the black and red color-developing areas, and the text and barcodes were clearly legible. The color-developing material was tested for high and low temperature cycling stability. The results showed that after cycling, the labels did not curl up or peel off, the color-developing areas did not fade or cross-contamination, and the color retention rate of both the black and red areas was ≥89%. Example 4

[0041] The process was carried out in accordance with Example 1, except that in step S3, a water-based UV-curable resin with a thickness of 2 μm was finally coated onto the surface of the dried and cured dual-color coating using a spraying process, and then sent to a UV curing device to cure for 2 min using ultraviolet light at 365 nm to obtain a black-red dual independent thermosensitive color-developing material.

[0042] The black-red dual independent thermosensitive color-developing material prepared in Example 4 was tested for color cross-contamination control. The results showed that there was no cross-contamination or edge bleed-through in the black and red color-developing areas. The color-developing material was tested for accuracy of the color-developing temperature range. The results showed that red only developed color in the range of 81~97 ℃, and black only developed color in the range of 113~129 ℃. The temperature window spacing was ≥16℃, and there was no overlap. The color-developing material was tested for abrasion resistance. The results showed that after abrasion, there was no ink loss or obvious fading in the black and red color-developing areas, and the text and barcodes were clearly legible. The color-developing material was tested for high and low temperature cycling stability. The results showed that after cycling, the labels did not curl up or peel off, the color-developing areas did not fade or cross-contamination, and the color retention rate of both the black and red areas was ≥93%. Example 5

[0043] The method was implemented as in Example 3, except that in step S1, ultrasonic dispersion was not performed when preparing the two colorimetric dispersion systems; only stirring and mixing were performed to control the particle D100 of the two colorimetric systems to be 3~5 μm.

[0044] The black-red dual independent thermosensitive color-developing material prepared in Example 5 was tested for cross-color control. The results showed that slight smudging was observed at the edges of the black and red color-developing areas under a 400x microscope, and slight color mixing occurred in some areas. The color-developing material was tested for accuracy of the color-developing temperature range. The results showed that red developed color in the range of 76~102 ℃, and black developed color in the range of 106~134 ℃. The temperature window boundaries were slightly blurred, and the gap was reduced to 4 ℃. The color-developing material was tested for abrasion resistance. The results showed that slight powdering occurred in the black and red color-developing areas after abrasion. The text was still legible, but the clarity decreased. The color-developing material was tested for high and low temperature cycling stability. The results showed that after cycling, the label edges slightly curled up, the color-developing areas showed slight fading, the color retention rate of the black area was 86%, and the color retention rate of the red area was 84%. Example 6

[0045] The method was implemented as in Example 3, except that all of the polyvinyl alcohol 1788 (degree of polymerization 1700, degree of hydrolysis 88%) was replaced with polyvinyl alcohol 1799 (degree of polymerization 1700, degree of hydrolysis 99%).

[0046] The black-red dual independent thermosensitive color-developing material prepared in Example 6 was tested for cross-color control. The results showed that there was no obvious cross-color development between the black and red color-developing areas, but the edge uniformity was slightly worse than that in Example 3. The color-developing material was tested for accuracy of the color-developing temperature range. The results showed that the red color developed only in the range of 81~97 ℃, and the black color developed only in the range of 111~127 ℃, with no overlap in the temperature windows. The color-developing material was tested for abrasion resistance. The results showed that there was no ink loss in the black and red color-developing areas after abrasion, but the coating flexibility was slightly poor, and micro-cracks appeared at the edges. The color-developing material was tested for high and low temperature cycling stability. The results showed that after cycling, the label did not curl up or peel off, but fine cracks appeared on the coating surface. The color retention rate of the black area was 87%, and the color retention rate of the red area was 85%.

[0047] Comparative Examples 1-10 are colorimetric materials and their preparation methods. Comparative Example 1 The procedure was carried out as described in Example 1, except that all stearamide was replaced with ethylene bis-stearamide.

[0048] The colorimetric material prepared in Comparative Example 1 was tested for color cross-contamination control. The results showed that, under a 400x microscope, a light purple halo appeared at the edge of the red colorimetric area, indicating slight color cross-contamination. The accuracy of the colorimetric temperature range was tested, showing that red developed color in the range of 75–98 °C, and black in the range of 105–130 °C. The temperature window gap between the two systems narrowed to 7 °C, increasing the risk of color cross-contamination. The abrasion resistance of the colorimetric material was tested, showing that slight powdering occurred in the colorimetric area after abrasion, and the red area showed significant fading. High and low temperature cycling stability tests were conducted, showing that the red area showed significant fading after cycling, while the black area retained 85% of its color, and the red area retained 80%.

[0049] Comparative Example 2 The procedure was carried out as described in Example 1, except that all of the polyvinyl alcohol 1788 was replaced with sodium carboxymethyl cellulose.

[0050] The colorimetric material prepared in Comparative Example 2 was tested for color cross-contamination control. The results showed that under a 400x microscope, the boundaries between the black and red colorimetric areas were blurred, indicating significant color cross-contamination. The accuracy of the colorimetric temperature range was tested, revealing that red developed color in the range of 72–105 °C, and black in the range of 102–138 °C, with overlapping temperature windows and severe color cross-contamination. The abrasion resistance was tested, showing that the coating peeled off over a large area after abrasion, making the writing illegible. High and low temperature cycling stability tests were conducted, showing severe coating cracking and peeling after cycling, significant fading in the colorimetric areas, with a color retention rate of 72% in the black area and 68% in the red area.

[0051] Comparative Example 3 The method of Example 1 was followed, except that, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol and stearamide as 100%, the content of each component was as follows: crystal violet lactone 3%, 4,4'-dihydroxydiphenyl sulfone 15%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 63%, stearamide 4%.

[0052] The colorimetric material prepared in Comparative Example 3 was tested for cross-contamination control. The results showed that the black color density was significantly insufficient, appearing gray rather than black, while the red area was normal. The colorimetric material was tested for accuracy in the colorimetric temperature range. The results showed that the red color only appeared in the range of 82~98 ℃, while the black color appeared in the range of 115~132 ℃ but the color was grayish. The colorimetric material was tested for abrasion resistance. The results showed that the black area faded significantly after abrasion, while the red area showed no significant change. The colorimetric material was tested for high and low temperature cycling stability. The results showed that the black area faded severely after cycling, with a color retention rate of only 78%, while the red area had a color retention rate of 89%.

[0053] Comparative Example 4 The method of Example 1 was followed, except that, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol and stearamide as 100%, the content of each component was as follows: crystal violet lactone 10%, 4,4'-dihydroxydiphenyl sulfone 8%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 63%, stearamide 4%.

[0054] The colorimetric material prepared in Comparative Example 4 was tested for color cross-contamination control. The results showed that under a 400x microscope, the black color area was uneven, with some areas appearing bluish-purple instead of pure black, while the red area was normal. The colorimetric material was tested for accuracy in the colorimetric temperature range. The results showed that the red color only appeared in the range of 82~98 ℃, while the black color appeared in the range of 108~134 ℃ but with a bluish-purple hue. The colorimetric material was tested for abrasion resistance. The results showed that the black area showed powder shedding after abrasion, while the red area showed no significant change. The colorimetric material was tested for high and low temperature cycling stability. The results showed that the black area faded significantly after cycling, with a color retention rate of 76%, while the red area had a color retention rate of 88%.

[0055] Comparative Example 5 The method of Example 1 was followed, except that, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol and stearamide as 100%, the content of each component was as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 3%, gallic acid 12%, polyvinyl alcohol 63%, stearamide 4%.

[0056] The colorimetric material prepared in Comparative Example 5 was tested for color cross-contamination control. The results showed that the red color density was significantly insufficient, appearing as a light pink rather than a bright red, while the black area was normal. The accuracy of the colorimetric temperature range was tested, showing that the red color developed in the 80-100 ℃ range but was a light pink, while the black color only developed in the 112-128 ℃ range. The abrasion resistance was tested, showing that the black area showed no significant change after abrasion, while the red area faded significantly. High and low temperature cycling stability was tested, showing that the black area retained 90% of its color after cycling, while the red area faded severely, with a color retention rate of 76%.

[0057] Comparative Example 6 The method was implemented in accordance with Example 1, except that, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol and stearamide as 100%, the content of each component was as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 8%, gallic acid 7%, polyvinyl alcohol 63%, stearamide 4%.

[0058] The colorimetric material prepared in Comparative Example 6 was tested for color cross-contamination control. The results showed that under a 400x microscope, the red color area was uneven, with some areas appearing orange-red, and a weak pink fluorescence was detected at the edge of the black color area. The accuracy of the colorimetric temperature range was tested, and the results showed that the red color was visible in the range of 78~102 ℃ but the hue was impure, while the black color was visible only in the range of 112~128 ℃. The abrasion resistance of the colorimetric material was tested, and the results showed that the black area did not change significantly after abrasion, while the red area showed slight powdering. The high and low temperature cycling stability of the colorimetric material was tested, and the results showed that the color retention rate of the black area was 89% and the color retention rate of the red area was 79% after cycling.

[0059] Comparative Example 7 The method was implemented in accordance with Example 1, except that, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol and stearamide as 100%, the content of each component was as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 65%, stearamide 2%.

[0060] The color development material prepared in Comparative Example 7 was tested for cross-color control. The results showed that there was no cross-color development in the black and red color development areas, but the color density was low in both cases. The accuracy of the color development temperature range was tested, and the results showed that red developed color in the range of 88~108 ℃ (high initial temperature), and black developed color in the range of 118~135 ℃ (high initial temperature), indicating insufficient sensitization effect. The abrasion resistance of the color development material was tested, and the results showed that there was no ink loss in the color development areas after abrasion, but the coating lacked flexibility and micro-cracks appeared at the edges. The high and low temperature cycling stability of the color development material was tested, and the results showed that the coating developed fine cracks after cycling, with a color retention rate of 88% in the black area and 86% in the red area.

[0061] Comparative Example 8 The method was implemented in accordance with Example 1, except that, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol and stearamide as 100%, the content of each component was as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 61%, stearamide 6%.

[0062] The colorimetric material prepared in Comparative Example 8 was tested for cross-color control. The results showed that under a 400x microscope, a slight pre-coloring was observed in the black colorimetric area at the low temperature end (approximately 100 °C), and the temperature window distance between the black and red systems decreased, indicating a risk of cross-coloring. The accuracy of the colorimetric temperature range was tested, showing that red colorimetrically developed in the 72–95 °C range and black in the 100–125 °C range, with the temperature window distance between the two systems decreasing to 5 °C. The abrasion resistance of the colorimetric material was tested, showing that no ink loss occurred in the colorimetric areas after abrasion, and the coating surface felt slightly sticky (due to excessive stearamide precipitation). The high and low temperature cycling stability of the colorimetric material was tested, showing that white precipitates appeared on the coating surface after cycling (stearamide migration), with a color retention rate of 85% in the black area and 82% in the red area.

[0063] Comparative Example 9 The procedure was carried out as described in Example 1, except that in step S3, the product was dried and cured at 75 °C for 20 min.

[0064] The colorimetric material prepared in Comparative Example 9 was tested for color bleeding control. The results showed that there was no obvious color bleeding in the black and red colorimetric areas, but residual solvent bubbles were present on the coating surface. The colorimetric material was tested for accuracy of the colorimetric temperature range. The results showed that red colorimetrically developed in the range of 81~97 ℃, and black colorimetrically developed in the range of 110~129 ℃, with no overlap in the temperature windows. The colorimetric material was tested for abrasion resistance. The results showed that the coating peeled off locally after abrasion, and the clarity of the writing decreased. The colorimetric material was tested for high and low temperature cycling stability. The results showed that the coating blistered and peeled off locally after cycling. The color retention rate in the black area was 80%, and the color retention rate in the red area was 77%.

[0065] Comparative Example 10 The procedure was carried out as described in Example 1, except that in step S3, the product was dried and cured at 95 °C for 2 min.

[0066] The color development material prepared in Comparative Example 10 was tested for color cross-contamination control. The results showed that under a 400x microscope, slight pre-development (light pink background) was observed in the red color development area. The excessively high drying temperature (95 ℃, close to the color development initiation temperature of the red system) caused premature triggering of some parts of the red system. The color development temperature range accuracy test of the color development material showed that the red color developed in the range of 76~97 ℃ (the initiation temperature decreased due to partial pre-development), while the black color developed only in the range of 112~128 ℃. The abrasion resistance test of the color development material showed that there was no significant ink loss in the color development area after abrasion, but the background color in the black area was uneven. The high and low temperature cycling stability test of the color development material showed that after cycling, the unevenness of the background color in the red area intensified, with a color retention rate of 83% and a color retention rate of 88% in the black area.

[0067] The color contrast and color retention rate of the black-red dual independent thermosensitive colorimetric materials prepared in Examples 1-6 and the colorimetric materials prepared in Comparative Examples 1-10 were measured respectively, and the test results are shown in Table 1. In Table 1, the black color contrast was measured under thermal printing conditions at 120 ℃, and the red color contrast was measured under thermal printing conditions at 90 ℃.

[0068] As shown in Table 1, Examples 1-3, using the proportioning range and process conditions defined in this application, all exhibited black color contrast ratios above 86% and red color contrast ratios above 84%. The temperature window spacing between the two color development systems was ≥23℃, with no color bleeding, and color retention rates all above 90%, demonstrating excellent overall performance. In Example 4, after adding a UV protective layer to the surface of the dual-color coating, the color retention rate was further improved to over 94%, and the abrasion resistance and high / low temperature cycling stability were also significantly enhanced.

[0069] Example 5: Without ultrasonic dispersion, the particle size increased to 3-5 μm, the color contrast decreased to below 81%, slight edge bleeding and color bleeding occurred, and the coating adhesion decreased, indicating that particle size control is crucial for color uniformity and color bleeding control. Example 6: Replacing polyvinyl alcohol 1788 with polyvinyl alcohol 1799, which has a higher degree of alcoholysis, resulted in a decrease in both color contrast and coating flexibility, and the appearance of microcracks in the coating, indicating that a moderate degree of alcoholysis (88%) plays an important role in improving the dispersibility of organic coloring components and the coating flexibility.

[0070] In Comparative Example 1, replacing stearamide with ethylene bis-stearamide reduced the temperature window gap between the two color development systems to 15°C, resulting in slight color bleeding. This indicates that stearamide has a better differential sensitizing effect on the two color development systems than ethylene bis-stearamide. In Comparative Example 2, replacing polyvinyl alcohol with sodium carboxymethyl cellulose caused a sharp decline in coating film-forming properties and adhesion, severe color bleeding, and a significant reduction in color retention. This demonstrates that polyvinyl alcohol plays an irreplaceable role as a carrier resin in coating performance.

[0071] Comparative Examples 3 to 6 varied the ratio of dye to developer in the black and red color development systems, respectively. When the dye was insufficient, the color density decreased significantly. When the dye was excessive, the color development was uneven and the hue shifted. This shows that the ratio range defined in this application is the key to achieving high-quality two-color development.

[0072] Comparative Example 7 had insufficient stearamide (2%), resulting in insufficient sensitization effect. The color development onset temperature of both systems was too high, and the color development sensitivity decreased. Comparative Example 8 had excessive stearamide (6%), which reduced the temperature window gap between the two systems to 15℃, posing a risk of color cross-contamination. Furthermore, the excessive stearamide migrated and precipitated after high and low temperature cycling, indicating that the amount of stearamide should be controlled between 3 and 5%.

[0073] Comparative Example 9 had an excessively low drying temperature (75℃), resulting in insufficient curing of the coating. Residual solvents caused instability in the coating structure, leading to a decrease in both abrasion resistance and color retention. Comparative Example 10 had an excessively high drying temperature (95℃), which was close to the color development initiation temperature of the black system. This resulted in partial pre-color development of the black system, with a gray background color appearing, affecting the accuracy of color development. This indicates that the drying and curing temperature needs to be controlled between 80 and 90℃.

[0074] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application.

Claims

1. A method for preparing a black-red dual independent thermosensitive colorimetric material, characterized in that, The preparation method includes the following steps: S1. Crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone were added to anhydrous ethanol and ultrasonically dispersed to obtain a black color-developing dispersion system. Rhodamine B lactone and gallic acid were added to anhydrous ethanol and ultrasonically dispersed to obtain a red color-developing dispersion system. S2. The black color-developing dispersion system, the red color-developing dispersion system, the polyvinyl alcohol aqueous solution, and stearamide are mixed to obtain a composite slurry, wherein, based on the total mass of crystal violet lactone, 4,4'-dihydroxydiphenyl sulfone, rhodamine B lactone, gallic acid, polyvinyl alcohol, and stearamide as 100%, the content of crystal violet lactone is 5-8%, the content of 4,4'-dihydroxydiphenyl sulfone is 10-12%, the content of rhodamine B lactone is 4-6%, the content of gallic acid is 8-10%, the content of polyvinyl alcohol is 59-70%, and the content of stearamide is 3-5%. S3. The composite slurry is coated on the surface of the pretreated substrate and then dried and cured at 80~90 ℃ to form a dual-color coating on the surface of the substrate, thus obtaining a black-red dual independent thermosensitive color material.

2. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, The preferred contents of each component are as follows: crystal violet lactone 6%, 4,4'-dihydroxydiphenyl sulfone 12%, rhodamine B lactone 5%, gallic acid 10%, polyvinyl alcohol 63%, and stearamide 4%.

3. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, In step S1, the maximum particle size D100 in both the black and red colorimetric dispersion systems is ≤1 μm.

4. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, The mass ratio of 4,4'-dihydroxydiphenyl sulfone to crystal violet lactone is 1.5~2.0:1, and the mass ratio of gallic acid to rhodamine B lactone is 1.7~2.5:

1.

5. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, The degree of polymerization of polyvinyl alcohol is 1600~1800, and the degree of alcoholysis is 85~92%.

6. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, In step S1, crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone are dissolved in anhydrous ethanol, wherein the amount of anhydrous ethanol used is 6 to 8 times the total mass of crystal violet lactone and 4,4'-dihydroxydiphenyl sulfone; Rhodamine B lactone and gallic acid were dissolved in anhydrous ethanol, wherein the amount of anhydrous ethanol was 6 to 8 times the total mass of rhodamine B lactone and gallic acid.

7. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, The thickness of the dual-color coating is 10~15 μm.

8. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 7, characterized in that, The preparation method further includes coating the surface of the dual-color coating with a water-based UV-curable resin with a thickness of 1~2 μm, and then performing UV curing to form a protective layer.

9. The preparation method of the black-red dual independent thermosensitive colorimetric material according to claim 1, characterized in that, In step S3, the pretreated substrate is obtained by corona treatment of synthetic paper.

10. A black-red dual independent thermosensitive colorimetric material obtained by the preparation method according to any one of claims 1 to 9, characterized in that, The coating thickness of the black-red dual independent thermosensitive color-developing material is 10~15μm, and the maximum particle size D100≤1μm. It triggers the black color development reaction independently under thermosensitive printing at 110~130 ℃ and triggers the red color development reaction independently under thermosensitive printing at 80~100 ℃.

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