Temperature-regulating additives for dual-color erasable thermal paper, their preparation methods and applications

Abstract

This invention relates to temperature-regulating additives for two-color erasable thermal paper, their preparation methods, and applications, and pertains to the field of printing consumables technology. The temperature-regulating additives include at least one of naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds. By using naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds as temperature-regulating additives, the problem of color overlap in two-color thermal paper is solved; by adding the above-mentioned temperature-regulating additives to the thermal coating, its color retention performance is improved.

Description

Technical Field

[0001] This invention relates to the field of printing consumables technology, specifically to a temperature-regulating additive for two-color erasable thermal paper, its preparation method, and its application. Background Technology

[0002] Currently, erasable information storage for identification cards utilizes thermal erasable technology, but its limited color options make it unsuitable for office use. Furthermore, two-color irreversible thermal paper, which can only be used once, leads to severe environmental pollution and resource waste. Therefore, developing erasable two-color thermal paper is of great significance.

[0003] There is relatively little research and development on two-color erasable thermal paper. The key to its process lies in designing temperature-regulating additives to achieve the layering of the two-color thermal layers. Therefore, this invention provides a temperature-regulating additive for two-color erasable thermal paper, its preparation method, and its application. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a temperature-regulating additive for two-color erasable thermal paper, its preparation method, and its application. The aim is to develop a temperature-regulating additive with naphthyl and biphenyl functions, achieving overlay of two thermal colors and contributing to the development of two-color thermal erasable paper.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] Firstly, based on a temperature-regulating additive for two-color erasable thermal paper, the temperature-regulating additive includes at least one of naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds.

[0007] The beneficial effects of this invention are: by using naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds as temperature-regulating agents, the problem of color overlap in thermosensitive dual-color coatings is solved; by adding the above-mentioned temperature-regulating agents to the thermosensitive coating, its color retention performance is improved.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the general structural formula of the naphthylurea compounds is shown in Formula I: In Equation I, the value of n ranges from 12 to 32;

[0010] The general structural formula of the naphthylamide compounds is shown in Formula II: In formula II, the value of n ranges from 12 to 32;

[0011] The general structural formula of the naphthyl ester compounds is shown in formula III-1 or III-2:

[0012] In equation Ⅲ-1, n takes values ​​from 12 to 32, or In Equation Ⅲ-2, the value of n ranges from 12 to 32;

[0013] The general structural formula of the naphthyl amino acid ester compounds is shown in Formula IV: In formula IV, n1 takes values ​​from 2 to 12; n2 takes values ​​from 12 to 32.

[0014] Furthermore, the temperature-regulating agent comprises at least one of the following specific structures:

[0015]

[0016] Secondly, regarding the preparation method of temperature-regulating additives for two-color erasable thermal paper,

[0017] (1) Synthesis methods of naphthylurea compounds:

[0018] Toluene and isocyanate (e.g., octadecyl isocyanate) are added at a certain temperature, and 2-naphthylamine is added after stirring to carry out the reaction. After the reaction is completed, the solvent is removed by evaporation, and then the mixture is washed, filtered and dried in sequence to obtain a white powder of naphthylurea compound.

[0019] (2) The synthetic methods for naphthylamide compounds are (2-1) or (2-2):

[0020] (2-1) Synthetic methods of naphthylamide compounds:

[0021] Toluene, stearic acid (e.g., octadecanoic acid), a relative equivalent of condensing agent, and a relative equivalent of catalyst are added at a certain temperature. After stirring, 2-naphthylamine is added and stirred to carry out the reaction. After the reaction is completed, the solvent is removed by evaporation, and then the mixture is washed, filtered, and dried in sequence to obtain a white powder of naphthylamide compound.

[0022] Or (2-2) Synthetic methods for naphthylamide compounds:

[0023] DCM (dichloromethane) was added under an ice-water bath, followed by the addition of 2-naphthylamine and stirring. Stearyl chloride was then added dropwise to initiate the reaction. After the reaction was complete, the solvent was removed by evaporation, and the mixture was washed, filtered, and dried sequentially to obtain a white powder of naphthylamide compounds.

[0024] (3) The synthetic methods for naphthyl ester compounds are (3-1), (3-2), (3-3), or (3-4):

[0025] (3-1) Synthesis methods of naphthyl ester compounds:

[0026] An alcohol (e.g., octadecyl alcohol) is added to toluene, stirred, and then 2-naphthic acid is added to carry out the reaction. After the reaction is complete, the solvent is removed by evaporation, and the product is washed, filtered, and dried to obtain a white powder of naphthyl ester compound.

[0027] Or (3-2) Synthesis method of naphthyl ester compounds:

[0028] DCM was added under an ice-water bath, followed by 2-naphthyl chloride. After stirring, an alcohol (e.g., octadecyl alcohol) was added dropwise to carry out the reaction. After the reaction was completed, the solvent was removed by evaporation, and the product was washed, filtered, and dried to obtain a white powder of naphthyl ester compound.

[0029] Or (3-3) Synthesis methods for naphthyl ester compounds:

[0030] Toluene and stearic acid were added at a certain temperature and stirred. Then, a relative equivalent of condensing agent and catalyst were added and stirred. 1-Naphthol was added and the reaction was carried out. After the reaction was completed, the solvent was removed by evaporation. The mixture was then washed, filtered and dried to obtain a white powder of naphthyl ester compound.

[0031] Or (3-4) Synthetic methods for naphthyl ester compounds:

[0032] DCM was added under an ice-water bath, followed by 2-naphthol and stirring. Stearyl chloride was then added dropwise to initiate the reaction. After the reaction was complete, the solvent was removed by evaporation, and the mixture was washed, filtered, and dried to obtain a white powder of naphthyl ester compound.

[0033] (4) Synthesis methods of naphthyl amino acid ester compounds:

[0034] Glycine, a relative equivalent of condensing agent and catalyst, were added to toluene, and alcohols were added after stirring. The reaction was carried out, and the solvent was removed by evaporation. The mixture was then washed, filtered and dried to obtain a white powder compound. The white powder compound was dissolved in toluene, and naphthalene isocyanate was added. The reaction was carried out, and the solvent was removed by evaporation. The mixture was then washed, filtered and dried to obtain a naphthyl amino acid ester compound.

[0035] The advantages of using the above scheme are: short reaction time, few by-products, and a yield of up to 98%.

[0036] Furthermore, in the synthesis method of naphthylurea compounds (1), the reaction temperature is 40-80℃, the reaction time is 2-3, and the washing with ethanol is performed 3-5 times; the molar ratio of the isocyanate to the 2-naphthylamine is 1-1.6;

[0037] In the (2-1) method for synthesizing naphthylamide compounds, the reaction temperature is 40–80 °C, the reaction time is 2–3 h, and the mixture is washed with ethanol 3–5 times; the condensing agent is at least one of DIC (N,N-diisopropylcarbodiimide), DCC (N,N-dicyclohexylcarbodiimide), and EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide); the catalyst is at least one of HOBt (1-hydroxybenzotriazole) and HATU (N,N,N′,N′-tetramethyl-O-(7-azabenzotriazole-1-yl)hexafluorophosphate urea); the molar ratio of stearic acid to 2-naphthylamine is 1.0–1.5.

[0038] In the (2-2) method for synthesizing naphthylamide compounds, the reaction time is 30-60 minutes; the washing with ethanol is performed 3-5 times; and the molar ratio of the stearyl chloride to the 2-naphthylamine is 1.0-1.5.

[0039] Furthermore, in the (3-1) method for synthesizing naphthyl ester compounds, the reaction temperature is 40–80°C, the reaction time is 2–4 hours, and the mixture is washed with ethanol 3–5 times; the mass ratio of the alcohol to the 2-naphthoic acid is 3–5:1–3.

[0040] In the (3-2) method for synthesizing naphthyl ester compounds, the reaction time is 2-4 hours, and the mixture is washed with ethanol 3-5 times; the mass ratio of the alcohol to the 2-naphthyl chloride is 3-5:1-3.

[0041] In the (3-3) method for synthesizing naphthyl ester compounds, the reaction temperature is 40–80 °C, the reaction time is 2–4 hours, and the washing with ethanol is performed 3–5 times; the condensing agent is at least one of DIC (N,N-diisopropylcarbodiimide), DCC (N,N-dicyclohexylcarbodiimide), and EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide); the catalyst is at least one of HOBt (1-hydroxybenzotriazole) and HATU (N,N,N′,N′-tetramethyl-O-(7-azabenzotriazole-1-yl)hexafluorophosphate urea); the molar ratio of stearic acid to 1-naphthol is 1–1.5.

[0042] In the (3-4) method for synthesizing naphthyl ester compounds, the reaction time is 20-30 minutes, and the washing with ethanol is performed 3-5 times; the molar ratio of the stearyl chloride to the 2-naphthol is 1.0-1.5.

[0043] Furthermore, the synthesis method of naphthyl amino acid ester compounds (4) includes the following specific steps:

[0044] Toluene, glycine, and a relative equivalent of condensing agent DIC and catalyst HOBt (0.2 g DIC, 0.1 g HOBt) are added at 40–60 °C. After stirring, an alcohol (e.g., octadecyl alcohol) is added, with a mass ratio of glycine to alcohol of 3–5:4–6. The reaction is carried out for 4–6 hours. After the reaction is complete, the solvent is removed by evaporation, the mixture is washed three times with ethanol, filtered, and dried to obtain a white powder compound. The white powder compound is dissolved in toluene at 60–90 °C, and naphthalene isocyanate is added, with a molar ratio of the white powder compound to naphthalene isocyanate of 1–1.5. The reaction is carried out for 2–6 hours. After the reaction is complete, the solvent is removed by evaporation, and the mixture is washed, filtered, and dried sequentially to obtain a naphthyl amino acid ester compound.

[0045] Thirdly, based on the application of temperature-regulating additives for two-color erasable thermal paper, the aforementioned temperature-regulating additives for two-color erasable thermal paper are used in the thermal coating of two-color erasable thermal paper.

[0046] The beneficial effects of adopting the above-mentioned further solution are: using temperature-regulating additives such as naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds in the thermal coating of two-color erasable thermal paper solves the problem of color overlap in thermal two-color paper and improves its color retention performance.

[0047] Fourthly, a two-color erasable thermal paper includes a protective layer, a thermal coating layer, a base coating layer, and a substrate arranged from top to bottom. The thermal coating layer includes a red thermal coating layer and a black thermal coating layer arranged sequentially. The red thermal coating layer is disposed between the black thermal coating layer and the protective layer. The red thermal coating layer contains the temperature-regulating additive for two-color erasable thermal paper.

[0048] Furthermore, the components of the protective layer, by weight, include: 5-15 parts of filler A, 70-90 parts of resin, 3-5 parts of lubricant, and 30-80 parts of adhesive resin A;

[0049] The red thermosensitive coating comprises, by weight, 5-10 parts of filler B, 20-40 parts of red color developer, 20-40 parts of adhesive resin B, 10-20 parts of red dye, and 20-40 parts of temperature-regulating agent.

[0050] The components of the black heat-sensitive coating, by weight, include: 5-10 parts of filler B, 20-40 parts of black color developer, 20-40 parts of adhesive resin B, and 10-20 parts of black dye.

[0051] The components of the base coating, by weight, include: 5-20 parts of thermal insulation filler, 70-90 parts of adhesive resin C, and 5-20 parts of filler C.

[0052] Preferably, in the protective layer, the filler A is one or two of benzotriazole, ZnO, MgO, and Al2O3; the resin is one or two of PVA, polyacrylate, and polyurethane; the lubricant is one or two of zinc stearate, calcium stearate, and organosilicon; and the adhesive resin A is one or two of PVA, polyurethane, and polyacrylate. More preferably, benzotriazole and ZnO are used in a mass ratio of 1:3.

[0053] In the red thermosensitive coating, filler B is one or two of calcium carbonate, montmorillonite, and talc; the red dye is at least one of scarlet, peach, and orange-red; the structural formula is as follows:

[0054] ;

[0055] The adhesive resin B is one or two of PVA, polyacrylate and polyurethane; the temperature regulating agent is at least one of naphthylurea, naphthylamide and naphthyl ester; the red color developer is one of PU, and the structural formula is as follows;

[0056] In the formula, p ranges from 12 to 32.

[0057] In the black heat-sensitive coating, filler B is one or two of calcium carbonate, montmorillonite, and talc; the black color developer is the same as the red color developer; the adhesive resin B is one or two of PVA, polyacrylate, and polyurethane; the black layer dye includes at least one of ODB2, S205, and B15; the structural formula is as follows:

[0058]

[0059] In the base coating, the heat insulation filler is one or two of glass microspheres and silica aerogel; the adhesive resin C is one or two of PVA, polyacrylate and polyurethane; and the filler C is one or two of calcium carbonate, montmorillonite and talc.

[0060] The preferred substrate is a paper made of copper plate or polyvinyl chloride.

[0061] The beneficial effects of adopting the above scheme are: the heat insulation filler used in the base coating of the present invention is a high-hollow material, which can enhance the heat insulation and improve the heat resistance and sensitivity of the red and black heat-sensitive coating two-color reversible erasable paper; the color developer is combined with a certain proportion of the above-mentioned temperature-regulating agent, and no sensitizer is required. Attached Figure Description

[0062] Figure 1 This is a two-color photograph of the present invention;

[0063] Figure 2 This is a schematic diagram of the two-color erasable thermal paper of the present invention. Figure I ;

[0064] Figure 3 This is a schematic diagram of the two-color erasable thermal paper of the present invention. Figure II . Detailed Implementation

[0065] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0066] The raw materials used in the embodiments of this invention, except for the color developer and temperature-regulating agent, are all commercially available raw materials; the temperature-regulating agent is designed in-house.

[0067] Example 1:

[0068] (1) Synthesis of temperature-regulating agent IV-1: 300 ml toluene, 20 g glycine, 0.2 g DIC, and 0.1 g HOBt were added at 60 °C and stirred for 20 min. Then 26 g octadecyl alcohol was added and the mixture was stirred for 6 h. After the reaction was completed, the solvent was removed by evaporation, the mixture was washed three times with ethanol, filtered, and dried to obtain a white powder compound. The white powder was dissolved in 300 ml toluene at 80 °C, 33 ml naphthalene isocyanate was added, and the mixture was reacted for 4 h. After the reaction was completed, the solvent was removed by evaporation, the mixture was washed three times with ethanol, filtered, and dried to obtain a white powder, temperature-regulating agent IV-1.

[0069] (2) Two-color erasable thermal paper

[0070] The dual-color erasable thermal paper of this embodiment includes a protective layer, a thermal coating layer, a base coating layer and a substrate arranged from top to bottom. The thermal coating layer includes a red thermal coating layer and a black thermal coating layer arranged in sequence. The red thermal coating layer is disposed between the black thermal coating layer and the protective layer.

[0071] The protective layer comprises, by weight, 20 parts calcium carbonate, 50 parts PVA adhesive resin, and 8 parts polyethylene wax emulsion.

[0072] The components of the red thermosensitive coating, by weight, include: 10 parts calcium carbonate, 20 parts red color developer, 25 parts PVA adhesive resin B, 25 parts red dye, and 20 parts temperature-regulating agent IV-1.

[0073] The components of the black heat-sensitive coating, by weight, include: 10 parts calcium carbonate, 20 parts black color developer, 25 parts PVA adhesive resin, and 25 parts black dye.

[0074] The preparation method of the two-color erasable thermal paper involved in this embodiment includes the following steps:

[0075] S1: Prepare the components of the base coating into a coating liquid, apply the coating liquid to the substrate, and dry it to obtain the base coating on the substrate;

[0076] S2: Prepare a coating liquid for red thermosensitive coating by taking the components of red thermosensitive coating; prepare a coating liquid for black thermosensitive coating by taking the components of black thermosensitive coating; coat the coating liquid for red thermosensitive coating and the coating liquid for black thermosensitive coating onto the base coating in sequence, and dry to obtain thermosensitive coating.

[0077] S3: Prepare the coating liquid of the protective layer by the components of the protective layer, coat it on the heat-sensitive coating, and dry it to obtain the protective layer;

[0078] S4: The substrate, base coating, thermal coating and protective layer are composited by hot pressing process to obtain two-color erasable thermal paper.

[0079] Example 2:

[0080] (1) Synthesis of temperature-regulating agent I-1:

[0081] Add 300 ml of toluene and 20 g of octadecyl isocyanate at 60 °C, stir for 4 min, then add 11 g of 2-naphthylamine and stir for 3 h. After the reaction is complete, remove the solvent by rotary evaporation, wash three times with ethanol, filter, and dry to obtain temperature-regulating agent I-1, whose structural formula is [insert structural formula here].

[0082] (2) Two-color erasable thermal paper

[0083] Except for the temperature regulating agent, everything else is the same as in Example 1.

[0084] Example 3:

[0085] (1) Synthesis of temperature regulating agent II-1:

[0086] Add 300 ml of toluene, 20 g of octadecanoic acid, 0.2 g of DIC, and 0.1 g of HOBt at 60 °C and stir for 20 min. Then add 11 g of 2-naphthylamine and stir for 3 h. After the reaction is complete, remove the solvent by evaporation, wash three times with ethanol, filter, and dry to obtain temperature-regulating agent II-1, whose structural formula is:

[0087] (2) Two-color erasable thermal paper

[0088] Except for the temperature regulating agent, everything else is the same as in Example 1.

[0089] Example 4:

[0090] (1) Synthesis of temperature-regulating agent III-2:

[0091] Add 300 ml of toluene, 20 g of octadecanoic acid, 0.2 g of DIC, and 0.1 g of HOBt at 60 °C and stir for 20 min. Then add 11 g of 2-naphthol and stir for 3 h. After the reaction is complete, remove the solvent by evaporation, wash three times with ethanol, filter, and dry to obtain a white powder, which is a temperature-regulating agent III-2 with the following structural formula:

[0092] (2) Two-color erasable thermal paper

[0093] Except for the temperature regulating agent, everything else is the same as in Example 1.

[0094] Comparison example: 1

[0095] Compared with Example 1, no temperature-regulating agent was added to the red layer thermosensitive coating, while the remaining components and steps were the same as in Example 1. The results are as follows. Figure 1 As shown, it displays mixed colors.

[0096] Experimental example:

[0097] (1) Method for detecting static saturated color density:

[0098] Calibrate the reflectance densitometer according to the instrument manufacturer's instructions, then heat the static colorimeter, gradually increasing the temperature from low to high. Use 70°C as the starting temperature, with each 10°C increment. Once the desired temperature is reached and stabilized, place the sample flat on the heating plate of the static colorimeter, with the colored side facing the heating plate. Cover with the upper pressure plate and start timing. After heating for 10 seconds, remove the sample. At least three samples of each type should be colored at each temperature. After the statically colored samples have been placed for 120 minutes, measure the optical density using the reflectance densitometer. Measure three samples of each type, taking measurements at three points on each sample. The average of the nine measurements is used to represent the optical density of that sample. When the optical density reaches its maximum, the sample is considered to have saturated color, and the corresponding color temperature is the static saturation color temperature for that sample.

[0099] (2) Static saturated color density after 3 hours of ethanol protection test: First, place the sample on a flat glass plate with the colored side facing up. Then, place the liquid collector on each saturated colored sample and add 1.0 mL of ethanol to the liquid collector. After placing the sample at room temperature for 3 hours, remove the liquid collector from the sample and gently absorb the ethanol remaining on the sample surface with filter paper. After drying the sample with a hairdryer in cold air, measure its optical density value.

[0100] (3) Detection method of image retention rate; by using 80℃ and 1kgf / cm 2 Under pressure, using a heat gun, heat the image for 1 second, (erased image color density value / original color density) * 100%.

[0101] (4) Testing of reversible erasure and rewrite performance

[0102] Zebra printer with a density of 30 write, tested at 140℃ and 1kgf / cm². 2 Under pressure, using a heat gun, the image is heated and erased in 1 second. If the retention rate is less than 10%, it indicates that the reversibility was successful once.

[0103] Note: Except for (4), which is a self-defined standard, (1), (2), and (3) are based on GB / T 28210—201.

[0104] Table 1 Comparison of image retention performance between Examples 1-3 and Comparative Example 1

[0105]

[0106] Table 2 Comparison of erasure rate performance between Examples 1-3 and Comparative Example 1 Table 2 Comparison of erasure rate performance between Examples 1-3 and Comparative Example 1

[0107]

[0108]

[0109] In summary, this invention utilizes naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds as temperature-regulating agents to solve the color overlap problem in thermosensitive dual-color coatings; by adding the above-mentioned temperature-regulating agents to the thermosensitive coating, its color retention performance is improved.

[0110] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0111] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A two-color erasable thermal paper, characterized in that, The material comprises, from top to bottom, a protective layer, a thermosensitive coating, a base coating, and a substrate. The thermosensitive coating includes a red thermosensitive coating and a black thermosensitive coating arranged sequentially. The red thermosensitive coating is disposed between the black thermosensitive coating and the protective layer. The red thermosensitive coating contains a temperature-regulating agent but does not contain a sensitizer. The temperature-regulating agent includes at least one of naphthylurea compounds, naphthylamide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds; The general structural formula of the naphthylurea compounds is shown in Formula I: In Equation I, the value of n ranges from 12 to 32; The general structural formula of the naphthylamide compounds is shown in Formula II: In formula II, the value of n ranges from 12 to 32; The general structural formula of the naphthyl ester compounds is shown in formula III-1 or III-2: In equation Ⅲ-1, n takes values ​​from 12 to 32, or In Equation Ⅲ-2, the value of n ranges from 12 to 32; The general structural formula of the naphthyl amino acid ester compounds is shown in Formula IV: In formula IV, n1 takes values ​​from 2 to 12; n2 takes values ​​from 12 to 32.

2. The two-color erasable thermal paper according to claim 1, characterized in that, The temperature-regulating agent includes at least one of the following specific structures:

3. The two-color erasable thermal paper according to claim 1, characterized in that, (1) Synthesis methods of naphthylurea compounds: Toluene and isocyanate were added at a certain temperature, and 2-naphthylamine was added after stirring to carry out the reaction. After the reaction was completed, the solvent was removed by evaporation, and then the mixture was washed, filtered and dried to obtain a white powder of naphthylurea compound. (2) The synthetic methods for naphthylamide compounds are (2-1) or (2-2): (2-1) Synthetic methods of naphthylamide compounds: Toluene, stearic acid, a relative equivalent of condensing agent, and a relative equivalent of catalyst were added at a certain temperature and stirred. Then, 2-naphthylamine was added and stirred to carry out the reaction. After the reaction was completed, the solvent was removed by evaporation, and then the mixture was washed, filtered, and dried to obtain a white powder of naphthylamide compound. Or (2-2) Synthetic methods for naphthylamide compounds: DCM was added under an ice-water bath, followed by the addition of 2-naphthylamine and stirring. Stearyl chloride was then added dropwise to initiate the reaction. After the reaction was complete, the solvent was removed by evaporation, and the mixture was washed, filtered, and dried sequentially to obtain a white powder of naphthylamide compound. (3) The synthetic methods for naphthyl ester compounds are (3-1), (3-2), (3-3), or (3-4): (3-1) Synthetic methods of naphthyl ester compounds: An alcohol was added to toluene, and after stirring, 2-naphthic acid was added to carry out the reaction. After the reaction was completed, the solvent was removed by evaporation, and the mixture was washed, filtered, and dried to obtain a white powder of naphthyl ester compound. Or (3-2) Synthesis method of naphthyl ester compounds: DCM was added under an ice-water bath, followed by 2-naphthyl chloride. After stirring, alcohols were added dropwise to carry out the reaction. After the reaction was complete, the solvent was removed by evaporation, and the mixture was washed, filtered, and dried to obtain a white powder of naphthyl ester compounds. Or (3-3) Synthesis methods for naphthyl ester compounds: Toluene and stearic acid were added at a certain temperature and stirred. Then, a relative equivalent of condensing agent and catalyst were added and stirred. 1-Naphthol was added and the reaction was carried out. After the reaction was completed, the solvent was removed by evaporation. The mixture was then washed, filtered and dried to obtain a white powder of naphthyl ester compound. Or (3-4) Synthetic methods for naphthyl ester compounds: DCM was added under an ice-water bath, followed by 2-naphthol and stirring. Stearyl chloride was then added dropwise to initiate the reaction. After the reaction was complete, the solvent was removed by evaporation, and the mixture was washed, filtered, and dried to obtain a white powder of naphthyl ester compound. (4) Synthesis methods of naphthyl amino acid ester compounds: Glycine, a relative equivalent of condensing agent and catalyst, were added to toluene, and alcohols were added after stirring. The reaction was carried out, and the solvent was removed by evaporation. The mixture was then washed, filtered and dried to obtain a white powder compound. The white powder compound was dissolved in toluene, and naphthalene isocyanate was added. The reaction was carried out, and the solvent was removed by evaporation. The mixture was then washed, filtered and dried to obtain a naphthyl amino acid ester compound.

4. The two-color erasable thermal paper according to claim 3, characterized in that, In the synthesis method of naphthylurea compounds (1), the reaction temperature is 40-80℃, the reaction time is 2-3h, and the washing with ethanol is performed 3-5 times; the molar ratio of isocyanate to 2-naphthylamine is 1-1.

6. In the (2-1) method for synthesizing naphthylamide compounds, the reaction temperature is 40–80 °C, the reaction time is 2–3 h, and the mixture is washed with ethanol 3–5 times; the condensing agent is at least one of DIC, DCC, and EDC; the catalyst is at least one of HOBt and HATU; and the molar ratio of stearic acid to 2-naphthylamine is 1.0–1.

5. In the (2-2) method for synthesizing naphthylamide compounds, the reaction time is 30-60 minutes; the washing with ethanol is performed 3-5 times; and the molar ratio of stearyl chloride to 2-naphthylamine is 1.0-1.

5.

5. The two-color erasable thermal paper according to claim 3, characterized in that, In the (3-1) method for synthesizing naphthyl ester compounds, the reaction temperature is 40–80℃, the reaction time is 2–3 hours, and the mixture is washed with ethanol 3–5 times; the mass ratio of alcohol to 2-naphthoic acid is 3–5:1–3. In the (3-2) method for synthesizing naphthyl esters, the reaction time is 2-4 hours, and the mixture is washed with ethanol 3-5 times; the mass ratio of alcohol to 2-naphthyl chloride is 3-5:1-3. In the (3-3) method for synthesizing naphthyl ester compounds, the reaction temperature is 40-80℃, the reaction time is 2-4 hours, and the washing with ethanol is performed 3-5 times; the condensing agent is at least one of DIC, DCC, and EDC; the catalyst is at least one of HOBt and HATU; and the molar ratio of stearic acid to 1-naphthol is 1-1.

5. In the (3-4) method for synthesizing naphthyl ester compounds, the reaction time is 20-30 minutes, and the washing with ethanol is performed 3-5 times; the molar ratio of the stearyl chloride to the 2-naphthol is 1.0-1.

5.

6. The two-color erasable thermal paper according to claim 3, characterized in that, The synthesis method of naphthyl amino acid ester compounds in (4) includes the following specific steps: Toluene, glycine, and a relative equivalent of condensing agent DIC and catalyst HOBt are added at 40-60℃. After stirring, alcohols are added, with a mass ratio of glycine to alcohol of 3-5:4-6. The reaction is carried out for 4-6 hours. After the reaction is complete, the solvent is removed by rotary evaporation, and the mixture is washed three times with ethanol, filtered, and dried to obtain a white powder compound. The white powder compound is dissolved in toluene at 60-90℃, and naphthalene isocyanate is added, with a molar ratio of the white powder compound to naphthalene isocyanate of 1-1.

5. The reaction is carried out for 2-6 hours. After the reaction is complete, the solvent is removed by rotary evaporation, and the mixture is washed, filtered, and dried sequentially to obtain a naphthyl amino acid ester compound.

7. The two-color erasable thermal paper according to claim 1, characterized in that, The components of the protective layer, by weight, include: 5-20 parts of filler A, 70-90 parts of resin, 3-5 parts of lubricant, and 30-80 parts of adhesive resin A; The red thermosensitive coating comprises, by weight, 5-10 parts of filler B, 20-40 parts of red color developer, 20-50 parts of adhesive resin B, 5-10 parts of red dye, and 20-40 parts of temperature-regulating agent. The components of the black heat-sensitive coating, by weight, include: 5-10 parts of filler B, 20-40 parts of black color developer, 20-50 parts of adhesive resin B, and 5-10 parts of black dye. The components of the base coating, by weight, include: 10-20 parts of thermal insulation filler, 70-90 parts of adhesive resin C, and 5-20 parts of filler C.

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