CN112227109B

CN112227109B - A novel multi-layer DASAs rewritable printing paper and preparation method thereof

Info

Publication number: CN112227109B
Application number: CN202010972266.8A
Authority: CN
Inventors: 王东升; 毛礼俊; 段永丽; 熊超越; 王真; 郑永豪
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2020-09-16
Filing date: 2020-09-16
Publication date: 2021-06-22
Anticipated expiration: 2040-09-16
Also published as: CN112227109A

Abstract

The invention discloses a multi-layer DASAs rewritable printing paper and a preparation method thereof. The preparation method comprises the following steps: (1) preparation of DASAs molecular intermediates; (2) preparation of DASA-1 molecules; (3) DASA -2 Preparation of molecules; (4) Preparation of paper. The invention uses a new type of organic photochromic molecule DASAs as a raw material, and uses polymers such as polyethylene glycol or polyethylene oxide for layered isolation to prepare a writing paper that can perform color conversion under a specific temperature range. The writing speed of the electric heating pen can complete the writing of different colors.

Description

Novel multi-layer DASAs rewritable printing paper and preparation method thereof

Technical Field

The invention relates to the technical field of paper preparation, in particular to novel multi-layer DASAs rewritable printing paper and a preparation method thereof.

Background

With the continuous development of science and technology, electronic communication and digital media technologies have the capabilities of fast transmission and super-strong information storage, and are widely applied in daily life. However, paper still plays an extremely important role in information transmission and knowledge inheritance due to its long history. In today's society, paper remains the most important medium for reading, writing and information transfer. However, in most cases, the paper carrying the information is disposed of after being read once, which causes both a serious waste of natural resources and a pollution destruction of the environment. Statistically, the worldwide paper demand in 2013 is 4.15 billion tons, and this figure still increases by 2% per year. This means that about 20 million trees are cut down for paper making every year worldwide, which has a great ecological impact on the earth. In fact, since 2008, china has replaced the united states as the world's largest paper producing country, and the demand for printing writing paper has increased dramatically. This has generated a great pressure on the environment of our country.

At present, the commonly used technology of rewritable printing paper mainly comprises the following methods: (1) photostimulation, i.e. photochromic. From the classification of the rewritable technology, the photochromism belongs to the sub-classification of the rewritable technology, and the basic writing principle of the photochromism method is that some organic or inorganic molecules can generate structural change under the irradiation of ultraviolet light or light with specific wavelength, so as to achieve the change of the absorption and reflection of light; and a color change occurs. The writing purpose is achieved by utilizing the property. Because the specific wavelength of the light source, such as ultraviolet light, is biologically destructive, the use of the ultraviolet light can cause irreversible damage to users, and the market utilization rate is low; (2) the chemical stimulation color-changing method is characterized by that it utilizes the properties of acid and alkali to stimulate some specific molecules to change their configuration and produce color change so as to meet the requirements for writing. However, such methods tend to be of a chemical nature or are not easily handled. Therefore, cannot be applied to large-scale markets; (3) the electrochromic method is that molecules are coated on the surface of common paper, and the molecules are stimulated by current to change the molecular structure, so that the color of the paper is changed, and the purpose of writing can be achieved.

However, the above rewritable writing and printing schemes can only achieve single-color writing on the surface of the same piece of rewritable paper. This still does not meet most of the demands. Thus, it is the problem to be solved to realize writing of multiple colors on the same surface of a piece of rewritable paper.

Disclosure of Invention

The invention aims to provide a multi-layer DASAs rewritable printing paper and a preparation method thereof, which can solve the problems of paper resource shortage, paper waste and incapability of repeated writing on the same paper at present.

To achieve the above object, the present invention provides a method for preparing a multi-layered DASAs rewritable printing sheet, comprising the steps of:

(1) preparation of DASAs molecular intermediates

Respectively carrying out heating and stirring reactions on 1, 3-dimethyl barbituric acid and furfural, and 1, 3-indandione and furfural to respectively obtain an intermediate of DASA-1 and an intermediate of DASA-2, wherein the reaction temperatures are both 30-40 ℃, and the stirring times are both 4-5 h;

(2) preparation of DASA-1 molecules

Dissolving the intermediate of DASA-1 obtained in the step (1) in an organic solvent, adding dipropylamine, stirring at 30-35 ℃ for 1.5-2h or stirring at normal temperature for 2-3h to prepare a DASA-1 molecule, adding the DASA-1 molecule into deionized water, and heating to form a ring DASA-1 aqueous solution;

(3) preparation of DASA-2 molecules

Dissolving the intermediate of DASA-2 obtained in the step (1) in an organic solvent, adding indoline, stirring for 2-3h at 30-35 ℃ to prepare a DASA-2 molecule, adding the DASA-2 molecule into deionized water, and heating to form a ring DASA-2 aqueous solution;

(4) preparation of paper

Taking common A4 paper as a substrate, dissolving polyethylene glycol or polyethylene oxide with deionized water, uniformly coating the dissolved polyethylene glycol or polyethylene oxide on the surface of the paper, placing the paper in a vacuum oven to be dried at 40-50 ℃, uniformly coating the DASA-1 aqueous solution obtained in the step (2) on the surface of polyethylene glycol or polyethylene oxide, naturally airing, uniformly coating a layer of polyethylene glycol or polyethylene oxide, naturally airing, uniformly coating the DASA-2 aqueous solution obtained in the step (3) on the surface of polyethylene glycol or polyethylene oxide, and airing to obtain the multilayer rewritable paper.

The beneficial effect who adopts above-mentioned scheme is: firstly, reacting 1, 3-dimethyl barbituric acid with furfural to prepare an intermediate of a DASA-1 molecule, reacting 1, 3-indandione with furfural to prepare an intermediate of a DASA-2 molecule, wherein the prepared intermediate can be used as a reactant in the preparation of DASA molecules; dissolving the intermediate of DASAs molecule as acceptor part and dipropylamine or indoline as donor part in organic solvent such as anhydrous dichloromethane or anhydrous tetrahydrofuran, stirring in oil bath at constant temperature to accelerate reaction speed and obtain primary DASAs molecule, and using anhydrous dichloromethane or anhydrous tetrahydrofuran as solvent with strong dissolving capacity and no influence on DASAs molecule production caused by chemical reaction with reactant; and finally, coating polyethylene glycol (PEG) or polyethylene oxide (PEO) deionized water solution on common A4 paper serving as a substrate, drying the paper serving as a first layer of the rewritable printing paper, sequentially coating purified DASA-1 molecules, polyethylene glycol (PEG) or polyethylene oxide (PEO) and purified DASA-2 molecules on the surface of the paper, and drying the paper to obtain the rewritable printing paper, wherein the PEG or PEO isolates-OH and DASAs on the surface of the paper to ensure that the color development process of the paper is not influenced by the paper as much as possible, and the PEG or PEO is also used as a heat insulation layer to ensure that the color development of DASA-2 does not influence DASA-1.

Further, the step (1) further comprises the steps of washing and filtering the intermediate product, extracting the intermediate product by using saturated sodium bisulfite and sodium chloride aqueous solution in sequence, removing moisture in the intermediate by using anhydrous magnesium sulfate, removing the anhydrous magnesium sulfate by using a suction filtration mode, purifying by using a chromatographic column technology, and removing the solvent by using a rotary evaporation mode to prepare the purified intermediate, wherein an eluent used by the chromatographic column technology is dichloromethane.

The beneficial effect who adopts above-mentioned scheme is: the initial product of the DASAs intermediate is a mixture with impurity ions, and some impurity particles are simply removed by water washing and suction filtration; impurities are left in saturated sodium bisulfite and sodium chloride aqueous solution through extraction, wherein the sodium bisulfite has strong reducibility, can remove substances with oxidation in yellow products, is extracted together with the sodium chloride aqueous solution, and can effectively separate intermediate products and other impurities; anhydrous magnesium sulfate is used for removing water in the intermediate, the anhydrous magnesium sulfate absorbs water quickly and is a neutral compound, the anhydrous magnesium sulfate does not react with a product during water absorption, and the whole water absorption process is green and clean; removing a block formed after the anhydrous magnesium sulfate absorbs water through suction filtration, and leaving an anhydrous intermediate with greatly improved purity; finally, purifying the primary product by column chromatography, and respectively collecting different components by the difference of the adsorption capacities of different compounds, so that the required primary product can be efficiently separated without reaction caused by adding new substances and compounds; and finally, recovering and evaporating the organic solvent by rotary evaporation, and removing the anhydrous dichloromethane or anhydrous tetrahydrofuran in the initial product and the organic solvent carried out by column chromatography to obtain the purified DASAs molecules.

Further, the temperature of the intermediate of DASA-1 and the intermediate of DASA-2 generated in the step (1) are 35 ℃ respectively, and the stirring time is 4.5h respectively.

Further, the step (2) also comprises purifying the DASA-1 molecule by a chromatographic column method, and removing the solvent by a rotary evaporation mode to prepare a purified DASA-1 molecule; adding the purified DASA-1 molecule into deionized water, and heating at 40-45 deg.C for 20-24h to form annular DASA-1 water solution; wherein, the eluent used in the chromatographic column technology is DCM and EA according to the volume ratio of 1: 3, and mixing to obtain a mixed solution.

The beneficial effect who adopts above-mentioned scheme is: the purified anhydrous linear DASA-1 molecule is red, deionized water is added, no impurity is introduced, colorless annular DASA-1 molecule can be prepared by heating after dissolving, water molecule is lost to become red linear DASA-1 molecule after heating at high temperature, and a process of color development and color loss is completed.

Further, in the step (2), dissolving the intermediate of DASA-1 in an organic solvent, adding dipropylamine, and stirring at 30 ℃ for 1.5h or at normal temperature for 2h to prepare a DASA-1 molecule; DASA-1 molecule is added into deionized water and heated at 40 deg.C for 24h to obtain annular DASA-1 aqueous solution.

Further, the step (3) also comprises purifying the DASA-2 molecule by a chromatographic column method, and removing the solvent by a rotary evaporation mode to prepare a purified DASA-2 molecule; adding the purified DASA-2 molecule into deionized water, and heating at 40-50 deg.C for 20-24h to form annular DASA-2 water solution; wherein, the eluent used in the chromatographic column technology is DCM and EA according to the volume ratio of 10: 1, and mixing the components.

The beneficial effect who adopts above-mentioned scheme is: the purified anhydrous linear DASA-2 molecule is blue, deionized water is added, no impurity is introduced, colorless annular DASA-2 molecule can be prepared by heating after dissolving, the water molecule is lost to be blue linear DASA-2 molecule after heating at high temperature, and a process of color development and color loss is completed.

Further, in the step (3), dissolving the intermediate of DASA-2 in an organic solvent, adding indoline, and stirring at 30 ℃ for 2h to obtain a DASA-2 molecule; DASA-2 molecule is added into deionized water and heated at 45 deg.c for 24 hr to obtain annular DASA-2 aqua.

Furthermore, the dehydration temperature of DASA-1 molecule is 180-200 ℃, and the dehydration temperature of DASA-2 molecule is 140-160 ℃.

The beneficial effect who adopts above-mentioned scheme is: the dehydration temperature of DASA-1 molecules is higher than that of DASA-2 molecules, so DASA-1 molecules are firstly smeared and then DASA-2 molecules are smeared, when the temperature is low, the blue characters are firstly displayed, and if the blue characters are covered, the temperature can be raised, and the red characters are displayed.

A method for writing on a multi-layer DASAs rewritable printing paper is characterized in that color conversion is completed by controlling the writing speed of an electric heating pen, when the writing speed is 1.5-2cm/s, DASA-2 on the upper layer is colored, and when the writing speed is 0.5-0.8cm/s, DASA-1 and DASA-2 are colored together.

In summary, the invention has the following advantages:

1. the repeatable allochroic writing effect is achieved by combining allochroic DASA molecules and polymer layers;

2. the common electric heating pen can be used for writing;

3. has the characteristics of easy preparation, low cost, easy operation, easy use and the like.

Drawings

FIG. 1 is a synthetic scheme for DASA-1;

FIG. 2 is a synthetic route to DASA-2;

FIG. 3 is a schematic illustration of the preparation of the present invention;

FIG. 4 shows the writing effect of the Cyclic DASA-1 of the present invention at a writing speed of 0.5-0.8 cm/s;

FIG. 5 shows the writing effect of Cyclic DASA-2 of the present invention at a writing speed of 1.5-2.0 cm/s;

FIG. 6 shows the writing effect of the paper made by the present application at a writing speed of 0.8-1.5 cm/s.

Detailed Description

The invention provides a multi-layer DASAs rewritable printing paper and a preparation method thereof, wherein the preparation method comprises the following steps: (1) preparation of DASAs molecular intermediates

(2) preparation of DASA-1 molecules

(3) preparation of DASA-2 molecules

(4) preparation of paper

By adopting the steps, the multilayer rewritable paper is obtained.

Example 1

A method of making a multi-layer DASAs rewritable printing sheet, comprising the steps of:

(1) preparation of DASAs molecular intermediates: firstly, heating and stirring 1mol of 1, 3-dimethyl barbituric acid and 1mol of furfural for reaction to prepare an intermediate of DASA-1, heating and stirring 1mol of 1, 3-indandione and 1mol of furfural for reaction to prepare an intermediate of DASA-2, wherein the reaction temperature is 30 ℃, the stirring time is 4 hours, washing and suction-filtering the obtained yellow intermediate, sequentially extracting the intermediate product by using saturated sodium bisulfite and saturated sodium chloride aqueous solution, further removing water in the intermediate by using anhydrous magnesium sulfate, removing the anhydrous magnesium sulfate by means of suction-filtering, finally purifying the intermediate by using a chromatographic column technology, and removing the solvent from the purified intermediate by means of rotary evaporation to obtain a yellow solid;

(2) preparation of DASA-1 molecule: dissolving 5mmol of the yellow solid obtained in the step (1), namely the intermediate of DASA-1, in 10ml of anhydrous Dichloromethane (DCM) solvent, adding 5mmol of dipropylamine, stirring and reacting in an oil bath kettle at constant temperature of 35 ℃ for 1.5h, purifying the product by a chromatographic method after the reaction is finished, removing the solvent by rotary evaporation to obtain purified linear DASA-1 molecules, adding 5ml of deionized water into 5mg of the purified linear DASA-1 molecules, and heating at 40 ℃ for 20h to obtain colorless Cyclic DASA-1 molecules; wherein, eluent used in chromatographic purification of the chromatographic column is DCM and EA according to the volume ratio of 1: 3 mixing the mixture;

(3) preparation of DASA-2 molecule: dissolving 5mmol of the yellow solid obtained in the step (1), namely the intermediate of DASA-2, in 10ml of anhydrous Dichloromethane (DCM), adding 5mmol of reactant indoline, stirring and reacting for 2h in an oil bath kettle at constant temperature of 35 ℃, purifying the product by a chromatographic method after the reaction is finished, removing the solvent by rotary evaporation to obtain a purified linear DASA-2 molecule, adding 5ml of deionized water into 5mg of the purified linear DASA-2 molecule, and heating for 20h at 45 ℃ to obtain a colorless Cyclic DASA-2 molecule; wherein, eluent used in chromatographic purification of the chromatographic column is DCM and EA according to the volume ratio of 10: 1, mixing the mixture;

(4) preparation of paper: firstly, using common A4 paper as a substrate, dissolving 0.5mg of polyethylene glycol (PEG) with 1ml of deionized water, uniformly coating the PEG solution on the surface of the paper, placing the paper in a vacuum oven, heating to 40 ℃ for drying, uniformly coating the surface of the PEG with the aqueous solution of Cyclic DASA-1, naturally drying, uniformly coating a layer of PEG, naturally drying, uniformly coating the surface of the PEG with the aqueous solution of Cyclic DASA-2, and drying to obtain the multilayer rewritable paper.

Example 2

(1) preparation of DASAs molecular intermediates: firstly, heating and stirring 2mol of 1, 3-dimethyl barbituric acid and 2mol of furfural for reaction to prepare an intermediate of DASA-1, heating and stirring 2mol of 1, 3-indandione and 2mol of furfural for reaction to prepare an intermediate of DASA-2, wherein the reaction time is 35 ℃, the stirring time is 4 hours, then washing and filtering the obtained yellow intermediate, sequentially extracting the intermediate product by using saturated sodium bisulfite and saturated sodium chloride aqueous solution, further removing water in the intermediate by using anhydrous sodium sulfate, removing the anhydrous sodium sulfate by using a suction filtration mode, finally purifying the intermediate by using a chromatographic column technology, and removing a solvent from the purified intermediate by using a rotary evaporation mode to obtain a yellow solid for later use;

(2) preparation of DASA-1 molecule: dissolving 6mmol of the yellow solid obtained in the step (1), namely the intermediate of DASA-1, in 10ml of anhydrous Tetrahydrofuran (THF) solvent, adding 6mmol of dipropylamine, stirring at normal temperature for reaction for 2h, purifying the product by a chromatographic column method after the reaction is finished, removing the solvent by rotary evaporation to obtain a purified DASA-1 molecule, adding 6ml of deionized water into 6mg of the purified DASA-1 molecule, and heating at 40 ℃ for 22h to obtain a colorless cyclic DASA-1 molecule; wherein, eluent used in chromatographic purification of the chromatographic column is DCM and EA according to the volume ratio of 1: 3 mixing the mixture;

(3) preparation of DASA-2 molecule: dissolving 6mmol of the yellow solid obtained in the step (1), namely the intermediate of DASA-2, in 10ml of anhydrous Tetrahydrofuran (THF), adding 6mmol of reactant indoline, stirring and reacting in an oil bath kettle at constant temperature of 32 ℃ for 1.5h, purifying the resultant by a chromatographic method after the reaction is finished, removing the solvent by rotary evaporation to obtain purified DASA-2 molecules, adding 6ml of deionized water into 6mg of the purified DASA-2 molecules, and heating at 45 ℃ for 20h to obtain colorless Cyclic DASA-2 molecules; wherein, eluent used in chromatographic purification of the chromatographic column is DCM and EA according to the volume ratio of 10: 1, mixing the mixture;

(4) preparation of paper: firstly, using common A4 paper as a substrate, dissolving 0.5mg of polyethylene oxide (PEO) with 1ml of deionized water, uniformly coating a PEO solution on the surface of the paper, placing the paper in a vacuum oven, heating to 45 ℃ for drying for later use, uniformly coating a Cyclic DASA-1 aqueous solution on the surface of the PEO, naturally airing, uniformly coating a layer of PEO, naturally airing, uniformly coating a Cyclic DASA-2 aqueous solution on the surface of the PEO, and airing to obtain the multilayer rewritable paper.

Example 3

(1) preparation of DASAs molecular intermediates: firstly, heating and stirring 5mol of 1, 3-dimethyl barbituric acid and 5mol of furfural for reaction to prepare an intermediate of DASA-1, heating and stirring 5mol of 1, 3-indandione and 5mol of furfural for reaction to prepare an intermediate of DASA-2, the reaction temperatures are respectively 40 ℃, the stirring time is 5 hours, then the obtained yellow intermediate is washed and filtered, then saturated sodium bisulfite and saturated sodium chloride aqueous solution are sequentially used for extracting the intermediate product, then anhydrous magnesium sulfate and anhydrous sodium sulfate are used for further removing the moisture in the intermediate, the anhydrous magnesium sulfate and the anhydrous sodium sulfate are removed by means of filtering, finally the intermediate is finally purified by adopting a chromatographic column technology, and the solvent is removed by means of rotary evaporation to obtain a yellow solid for later use;

(2) preparation of DASA-1 molecule: dissolving 8mmol of the yellow solid obtained in the step (1), namely the intermediate of DASA-1, in 10ml of anhydrous Tetrahydrofuran (THF) solvent, adding 8mmol of dipropylamine, stirring and reacting for 2h at constant temperature of 35 ℃ in an oil bath pot, purifying the product by a chromatographic method after the reaction is finished, removing the solvent by rotary evaporation to obtain a purified DASA-1 molecule, adding 8ml of deionized water into 8mg of the purified DASA-1 molecule, and heating for 24h at 45 ℃ to obtain a colorless cyclic DASA-1 molecule; wherein, eluent used in chromatographic purification of the chromatographic column is DCM and EA according to the volume ratio of 1: 3 mixing the mixture;

(3) preparation of DASA-2 molecule: dissolving 8mmol of the yellow solid obtained in the step (1), namely the intermediate of DASA-2, in 10ml of anhydrous Tetrahydrofuran (THF), adding 8mmol of reactant indoline, stirring and reacting in an oil bath kettle at constant temperature of 35 ℃ for 1.8h, purifying the resultant by a chromatographic method after the reaction is finished, removing the solvent by rotary evaporation to obtain a purified DASA-2 molecule, adding 8ml of deionized water into 8mg of the purified DASA-2 molecule, and heating at 50 ℃ for 22h to obtain a colorless Cyclic DASA-2 molecule; wherein, eluent used in chromatographic purification of the chromatographic column is DCM and EA according to the volume ratio of 10: 1, mixing the mixture;

(4) preparation of paper: firstly, using common A4 paper as a substrate, dissolving 0.8mg of polyethylene glycol (PEG) with 4ml of deionized water, uniformly coating a PEG solution on the surface of the paper, placing the paper in a vacuum oven, heating to 50 ℃ for drying for later use, uniformly coating a Cyclic DASA-1 aqueous solution on the surface of the PEG, naturally drying, uniformly coating a layer of PEG, naturally drying, uniformly coating a Cyclic DASA-2 aqueous solution on the surface of the PEG, and drying to obtain the multilayer rewritable paper.

Comparative example 1

Unlike example 3, step (4) of comparative example 1, which is step (4), comprises the following specific steps: firstly, using common A4 paper as a substrate, dissolving 0.8mg of polyethylene glycol (PEG) with 4ml of deionized water, uniformly coating the PEG solution on the surface of the paper, placing the paper in a vacuum oven, heating to 50 ℃ for drying for later use, uniformly coating the surface of the PEG with a Cyclic DASA-1 aqueous solution, and naturally drying to obtain the Cyclic DASA-1 paper.

Comparative example 2

Unlike example 3, step (4) of comparative example 1, which is step (4), comprises the following specific steps: firstly, using common A4 paper as a substrate, dissolving 0.8mg of polyethylene glycol (PEG) with 4ml of deionized water, uniformly coating the PEG solution on the surface of the paper, placing the paper in a vacuum oven, heating to 50 ℃ for drying for later use, then uniformly coating the surface of the PEG with the aqueous solution of Cyclic DASA-2, and naturally drying to obtain the Cyclic DASA-2 paper.

The specific writing effect is as follows:

the papers prepared in examples 1-3 and comparative examples 1-2 were written with the same electric heating pen, and the fonts of comparative example 2 and examples 1-3 were blue (see fig. 5) and the font of comparative example 1 was not colored at a writing speed of 1.5-2 cm/s; at a writing speed of 0.5-0.8cm/s, the font of comparative example 1 appears red, the fonts of examples 1-3 appear red (see fig. 4), and the font of comparative example 2 appears blue; when the writing speed is 0.8-1.5cm/s, the font of the comparative example 1 is red, the font of the comparative example 2 is blue, and the color of the fonts of the examples 1-3 is gradually changed from blue to red (see figure 6).

Claims

1. A method of making a multi-layer DASAs rewritable printing sheet, comprising the steps of:

(1) preparation of DASAs molecular intermediates

(2) preparation of DASA-1 molecules

(3) preparation of DASA-2 molecules

(4) preparation of paper

2. The method of claim 1, wherein step (1) further comprises washing the intermediate product with water, filtering with suction, extracting the intermediate product with saturated aqueous solutions of sodium bisulfite and sodium chloride, removing water from the intermediate product with anhydrous magnesium sulfate, filtering with suction, purifying with chromatography, and removing the solvent with rotary evaporation to obtain a purified intermediate, wherein the eluent used in the chromatography is dichloromethane.

3. The method of claim 1, wherein the reaction of step (1) to produce DASA-1 and DASA-2 intermediates is carried out at 35 ℃ for 4.5 hours.

4. The method of claim 1, wherein step (2) further comprises purifying DASA-1 molecules by chromatography, and removing the solvent by rotary evaporation to produce purified DASA-1 molecules; adding the purified DASA-1 molecule into deionized water, and heating at 40-45 deg.C for 20-24h to form annular DASA-1 water solution; wherein, the eluent used in the chromatographic column technology is DCM and EA according to the volume ratio of 1: 3, and mixing to obtain a mixed solution.

5. The method according to claim 4, wherein in step (2), the DASA-1 intermediate is dissolved in an organic solvent, dipropylamine is added, and the mixture is stirred at 30 ℃ for 1.5h or at room temperature for 2h to obtain DASA-1 molecules; DASA-1 molecule is added into deionized water and heated at 40 deg.C for 24h to obtain annular DASA-1 aqueous solution.

6. The method of claim 1, wherein step (3) further comprises purifying DASA-2 molecules by chromatography, and removing the solvent by rotary evaporation to produce purified DASA-2 molecules; adding the purified DASA-2 molecule into deionized water, and heating at 40-50 deg.C for 20-24h to form annular DASA-2 water solution; wherein, the eluent used in the chromatographic column technology is DCM and EA according to the volume ratio of 10: 1, and mixing the components.

7. The method of claim 6, wherein in step (3), the DASA-2 intermediate is dissolved in an organic solvent, indoline is added, and the mixture is stirred at 30 ℃ for 2 hours to obtain DASA-2 molecules; DASA-2 molecule is added into deionized water and heated at 45 deg.c for 24 hr to obtain annular DASA-2 aqua.

8. A multi-layer DASAs rewritable printing sheet produced by the production method according to any one of claims 1 to 7.

9. The method of claim 8, wherein the color conversion is accomplished by controlling the writing speed of the electrical heating pen, wherein the DASA-2 layer on the top layer develops color at a writing speed of 1.5-2cm/s, and the DASA-1 layer and DASA-2 layer develop color together at a writing speed of 0.5-0.8 cm/s.