Oil-in-water type formaldehyde-free memory microcapsule pigment, hot-erasable formaldehyde-free water-based ink and preparation method of hot-erasable formaldehyde-free water-based ink

Abstract

The invention provides an oil-in-water type formaldehyde-free memory microcapsule pigment, hot erasable formaldehyde-free water-based ink and a preparation method thereof, the oil-in-water type formaldehyde-free memory microcapsule pigment comprises the following components in percentage by mass: 5%-20% of polyvinyl alcohol, 1.25%-10% of styrene-maleic anhydride, 5%-10% of chitosan, 7.5%-17.5% of a thermochromic pigment, 5%-10% of bisphenol AF, 5%-10% of a polyurethane prepolymer, 12%-20% of an oil phase solvent, 0.25%-2% of an accelerant and the balance of water. The hot erasable formaldehyde-free water-based ink prepared on the basis of the oil-in-water type formaldehyde-free memory microcapsule pigment has the advantages of being formaldehyde-free, green, environment-friendly, smooth in writing and the like.

Description

Technical Field

[0001] The invention belongs to the field of writing ink, and in particular relates to a microcapsule for heat-erasable formaldehyde-free water-based ink, a preparation method and an application thereof. Background Art

[0002] Heat-erasable ink has a memory function: it displays color at room temperature, fades due to frictional heat, and then recolors after cooling. Traditional heat-erasable inks use microcapsule color-changing pigments that contain formaldehyde during the preparation process, which affects the health of production line workers. Currently, melamine resins, urea-formaldehyde resins, etc. are mostly used. These resins will release some formaldehyde slightly and slowly during use, so the safety of using heat-sensitive reversible color-changing neutral inks is controversial. In addition, in the current production process of microcapsule pigments, formaldehyde is often added in excess to complete polymerization. Even if the post-processing process is perfect, there will still be residual free formaldehyde in the ink. This is not only harmful to the health of the user, but also causes the continued polymerization of formaldehyde during the storage process of the ink, resulting in excessive ink viscosity, broken and choppy writing, and a reduced writing feel. On the other hand, it will also cause a decrease in ink stability.

[0003] Currently, existing technologies have begun to adopt polyurethane wall materials to replace traditional melamine resins and urea-formaldehyde resins. A published patent application describes using a modified isocyanate prepolymer and a water-soluble fatty amine to prepare a formaldehyde-free polyurethane microcapsule wall material. A temperature-sensitive fluorescent dye is added to the thermochromic system, and the polyurethane is used to coat the core material containing the thermochromic fluorescent dye. The resulting water-based microcapsule color paste is formaldehyde-free, safe, environmentally friendly, and has bright colors and fluorescent properties. However, research has found that the ink prepared with this formula does not completely decolorize when erased. Summary of the Invention

[0004] The present invention addresses the defect of excessive formaldehyde in the prior art and makes process improvements. The invented ink does not contain formaldehyde, solves the problem of adverse effects on human health, and has the advantage of being environmentally friendly. In addition, the provided ink is significantly superior to the prior art in terms of writing feel and storage stability.

[0005] To achieve the purpose of the present invention, the present invention adopts the following technical solutions: As a first aspect of the present invention, a water-in-oil type formaldehyde-free memory microcapsule pigment is provided, which comprises the following components by mass fraction: 5% to 20% polyvinyl alcohol, 1.25% to 10% styrene-maleic anhydride, 5% to 10% chitosan, 7.5% to 17.5% thermochromic pigment, 5% to 10% bisphenol AF, 5% to 10% polyurethane prepolymer, 12% to 20% oil phase solvent, 0.25% to 2% accelerator, and the balance is water.

[0006] The oil phase solvent is an alkane solvent or a liquid unsaturated fatty acid; the alkane solvent is selected from one or more of n-hexane, n-dodecane or isododecane; the liquid unsaturated fatty acid is selected from one or more of octyl decanoate (ODO), benzyl alcohol, phenylethyl alcohol, coconut oil, and olive oil.

[0007] The accelerator is a fatty amine accelerator, a tin accelerator, ferric chloride or p-chlorobenzoic acid. The fatty amine accelerator is selected from DMP-30 and triethanolamine. The tin accelerator is selected from dibutyltin dilaurate or stannous octoate.

[0008] As a second aspect of the present invention, there is provided a method for preparing the oil-in-water type formaldehyde-free memory microcapsule pigment, comprising the following steps: a. dissolving polyvinyl alcohol in water to prepare an aqueous solution of polyvinyl alcohol; b The styrene - maleic anhydride (SMA) copolymer resin was dissolved in water to prepare an aqueous solution of styrene - maleic anhydride (SMA) copolymer resin; c. The two solutions were mixed, the mixed solution of polyvinyl alcohol and styrene - maleic anhydride (SMA) copolymer resin mass ratio of 4: 1 to 2: 1, stirred and heated to 65 ℃ ~ 75 ℃, to construct an aqueous phase; d. The chitosan, thermochromic pigment, bisphenol AF are mixed in order and melted for later use; e. Add the polyurethane prepolymer to the oil phase solvent and heat it to 65°C to 75°C for end-capping; f. Mix d and e to construct the oil phase; g. Inject the oil phase into the water phase at 50-70°C and stir and emulsify for 60-70 minutes; h. After emulsification is completed, add accelerator to complete the cross-linking and curing of the wall material to form water-in-oil type formaldehyde-free memory microcapsule pigment.

[0009] In the preparation method provided by the present invention, water and oil are fully mixed and stirred to form a stable oil-in-water emulsion. After emulsification, chitosan is added, a thermochromic material is used as an electron donor, bisphenol AF is used as an electron acceptor, an oily solvent is selected, the thermochromic pigment and bisphenol AF are fully fused, and a accelerator is added to complete cross-linking and curing to form a stable three-dimensional network structure.

[0010] According to the comparison between the examples of the present invention and the comparative examples, it is found that the addition of chitosan can achieve almost no background color or a very light background color after wiping, further improving the decolorizing effect.

[0011] The water-in-oil type formaldehyde-free memory microcapsule pigment prepared by the method is water-resistant, oil-resistant, acid-resistant and alkali-resistant and has good stability.

[0012] Furthermore, in the step a of preparing the oil-in-water type formaldehyde-free memory microcapsule pigment, the polyvinyl alcohol (hereinafter abbreviated as PVA) preferably has a polymerization degree of 1700≤≤2400 and an alcoholysis degree ≥88, such as PVA1788, PVA1799, PVA2488, PVA2499, etc.

[0013] PVA is an emulsion polymerization stabilizer that can enhance the stability of the microcapsule emulsion system. When synthesizing microcapsules, excessive PVA dosage results in excessive aqueous phase viscosity and incomplete emulsification. Excessive PVA dosage leads to unstable emulsions and easy demulsification of the microcapsules. Furthermore, polyvinyl alcohol (PVA) has a low degree of polymerization (DP) and low molecular weight, resulting in unstable emulsions and easy demulsification of the microcapsules. Excessive DP also leads to excessive aqueous phase viscosity and incomplete emulsification, which also results in unstable emulsions. Low alcoholysis degree results in poor solubility in water. Therefore, the PVA of the present invention preferably has a DP of 1700 ≤ ≤ 2400 and an alcoholysis degree of 88 or higher, such as PVA1788, PVA1799, PVA2488, and PVA2499.

[0014] Furthermore, if the oil-phase solvent required for oil-in-water microcapsule pigments is used in excessive amounts, it can easily cause demulsification, oil-water separation, unstable emulsion system, and shortened shelf life. If the amount is too low, the dissolution of bisphenol AF and the thermochromic material is incomplete, and the thermochromic material (core material) is insufficiently coated, resulting in poor water resistance, light resistance, and stability. Therefore, the oil-phase solvent of the present invention is preferably 12% to 20%. The oil-phase solvent of the present invention can be selected from n-hexane, n-dodecane, or isododecane; the liquid unsaturated fatty acid is preferably glyceryl caprylate (ODO), benzyl alcohol, phenylethyl alcohol, coconut oil, olive oil, or one or more thereof.

[0015] Furthermore, if the accelerator used in the production of oil-in-water microcapsule pigments is too high, the reaction will be too fast. First, it will cause rapid polymerization, shorten the curing time, and the resulting wall material will be unstable and poorly resistant to water, oil, acid and alkali. Second, it will release a large amount of heat in a short period of time, causing the thermochromic material to fade. If the amount is too low, first, the reaction will be slow and time-consuming. Second, the molecular weight of the cured wall material will be too high, resulting in high viscosity, which will affect the writing effect. Therefore, the accelerator of the present invention is preferably 0.25% to 2%.

[0016] As a third aspect of the present invention, there is provided a heat-erasable formaldehyde-free water-based ink, which comprises: 10-30% microcapsule pigment, 0.5-3% dispersant, 10-40% water-soluble organic solvent, 5-20% specific gravity regulator, 0.1-2% flocculant, 0.1-2% surfactant, and the rest is water.

[0017] Furthermore, the microcapsule pigment is the oil-in-water type formaldehyde-free memory microcapsule pigment described in the present invention.

[0018] Furthermore, the dispersant of the heat-erasable formaldehyde-free water-based ink is mainly used to improve the dispersibility and stability of the formaldehyde-free memory microcapsules. If the dosage is too much, it will destroy the emulsification system of the microcapsule pigment itself, making the ink unstable, oil-water separation, and shortening the storage period; if the dosage is too little, the dispersion is insufficient and the ink is uneven. The dispersant can be selected from polyacrylic acid, naphthalenesulfonate formaldehyde polymer, styrene-maleic anhydride copolymer dispersant, styrene-acrylate dispersant, organosiloxane-acrylate dispersant, styrene-maleic anhydride-acrylate, sodium methylenenaphthalenesulfonate-sodium styrenesulfonate-sodium maleate copolymer, preferably sodium methylenenaphthalenesulfonate-sodium styrenesulfonate-sodium maleate copolymer. It contains a long-chain alkyl lipophilic group and two hydrophilic groups, sulfonic acid group and carboxyl group, which can fully connect with the oil phase and water phase of the microcapsule pigment without destroying the emulsification system, so that the capsules are stably dispersed in water.

[0019] Furthermore, the water-soluble organic solvent in heat-erasable formaldehyde-free water-based inks not only enhances the ink's adhesion to the writing medium but also helps keep the pen tip moist for extended periods. If added in too high an amount, the viscosity and adhesion increase, leading to poor erasability. If added in too low an amount, the pen tip dries easily and loses ink. The water-soluble organic solvent is an alcoholic solvent, preferably ethylene glycol, diethylene glycol, propylene glycol, or glycerol, which can be one or more.

[0020] The specific gravity adjuster for heat-erasable, formaldehyde-free water-based inks is a solid compound with a density ≥ 3.5 at 25°C. The specific gravity adjuster is primarily used to adjust the specific gravity of the carrier (the ink components other than the microcapsule pigment). If the specific gravity adjuster is too high, the carrier will have a high specific gravity, causing the microcapsule pigment to float while the carrier sinks. If the specific gravity adjuster is too low, the microcapsule pigment will sink while the carrier floats. Both of these situations can cause the pigment and carrier to separate when the ink is inverted or upright, resulting in a darker or lighter color during writing, affecting the writing experience. Extensive experiments have found that adding a specific gravity adjuster to a ratio of microcapsule pigment to carrier of 0.95-1.1, preferably 0.98-1.05, ensures good ink stability, preventing the color from darkening or lightening over time. The specific gravity adjuster can be selected from one or more of the following: tungstates, molybdates, heteropolyacid salts, and isopolyacid salts.

[0021] Furthermore, flocculants for heat-erasable, formaldehyde-free water-based inks prevent microcapsule pigments from aggregating through electrostatic repulsion and steric hindrance, thereby improving stability. If the dosage is too high, the ink viscosity increases, impairing both writing and erasability properties. If the dosage is too low, the anti-settling effect is poor. Optional agents include polyacrylamide, polyacrylic acid, sodium polyacrylate, styrene sulfonate, lignin sulfonate, and acrylic acid-methacrylic acid copolymer.

[0022] Furthermore, the surfactant of heat-erasable formaldehyde-free water-based ink is mainly used to adjust the surface tension of the ink. If the dosage is too high, the surface tension is small, the ink permeability is strong, and the handwriting is easy to smudge when writing, or the residual color is heavy when decolorizing. If the dosage is too low, the surface tension is large, causing the ink to clump together and form ink droplets when writing.

[0023] One or more of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, quaternary ammonium surfactant, fatty acid glyceride, fatty acid sorbitan, polysorbate, etc. can be selected.

[0024] As a fourth aspect of the present invention, there is provided a method for preparing the heat-erasable formaldehyde-free water-based ink, comprising the following steps: First, water is added to a pre-dispersion pot, and a specific gravity regulator is added under stirring. After the specific gravity regulator is completely dissolved, a dispersant, a water-soluble organic solvent, a flocculant, and a surfactant are added in sequence. After uniform dispersion, the microcapsule pigment is finally added. The mixture is stirred for 20 to 30 minutes and filtered to obtain the heat-erasable formaldehyde-free water-based ink of the present invention.

[0025] As a fifth aspect of the present invention, there is provided the use of the oil-in-water type formaldehyde-free memory microcapsule pigment in the preparation of inks for the following products: a, water-based ballpoint pen; b, watercolor pen; c, pen; d, marker pen.

[0026] Formaldehyde-free black, formaldehyde-free crystal blue, and formaldehyde-free dark blue prepared by changing the pigment can also be used in fountain pens and direct-liquid water-based ballpoint pens.

[0027] As a sixth aspect of the present invention, a replacement refill is provided, which contains the heat-erasable formaldehyde-free water-based ink described in the present invention.

[0028] As a seventh aspect of the present invention, there is also provided a water-based ballpoint pen containing the heat-erasable formaldehyde-free water-based ink of the present invention.

[0029] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: 1. The present invention provides an oil-in-water, formaldehyde-free memory microcapsule pigment. Using polyvinyl alcohol as an emulsion polymerization stabilizer, the stability of the microcapsule emulsification system is improved. Furthermore, the type and amount of the oil phase solvent and accelerator used in combination are selected to shorten the reaction time, further enhance the stability of the emulsification system, improve water resistance, acid and alkali resistance, and light resistance, and extend the shelf life. 2. The present invention also provides a heat-erasable formaldehyde-free water-based ink based on the oil-in-water formaldehyde-free memory microcapsule pigment. The ink has the advantages of being formaldehyde-free, environmentally friendly, and smooth to write, and improves the performance of the ink in terms of writing feel and storage stability.

[0030] 3. The heat-erasable formaldehyde-free water-based ink based on the oil-in-water formaldehyde-free memory microcapsule pigment provided by the present invention has a very light base color after wiping, and its decolorization effect is better than that of the product without chitosan. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0032] Figure 1 The manual marking results of each embodiment and comparative example are compared; Figure 2 This is a comparison chart of the decolorization effects of Comparative Example 1-7 and Example 2-1. DETAILED DESCRIPTION The present invention is further described by the following examples, which are not intended to limit the scope of the present invention. Changes and modifications made by those skilled in the art within the scope of the claims should also be considered to fall within the scope of the present invention.

[0033] The following describes the embodiments of the present invention in detail. In this specification, "%" indicating a ratio refers to a mass basis unless otherwise specified, and content refers to the mass % of the constituent components based on the mass of the aqueous ink. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] The present invention uses distilled water, which can reduce the mixing of bacteria in the formula and extend the shelf life.

[0035] Example 1, oil-in-water formaldehyde-free memory microcapsule pigment Example 1-1: Preparation of oil-in-water formaldehyde-free memory microcapsule pigment

[0036] a. Prepare a 1.5% polyvinyl alcohol (PVA) distilled water solution: Add 98.5 parts of distilled water to a reaction kettle. Start the agitator and add the PVA while stirring. Stir for 20 minutes without heating. Then slowly heat to 90°C. Maintain this temperature for 3 hours to completely dissolve the PVA. Cool down and set aside.

[0037] b. Prepare a 1.5% SMA distilled water solution: Add 98.5 parts of distilled water to a reactor. Start the agitator and add SMA while stirring. Stir for 20 minutes without heating. Then slowly heat to 90°C. Maintain this temperature for 3 hours to completely dissolve the SMA. Cool down and set aside.

[0038] c. Take the PVA solution and SMA solution prepared in a and b respectively, stir at 70°C for 10 minutes to construct the aqueous phase; d. The chitosan, temperature-sensitive red material, bisphenol AF are mixed in order and melted for later use; e. Add the polyurethane prepolymer to coconut oil and heat to 70°C for end-capping; f. Mix d and e to construct the oil phase; g. Inject the oil phase into the water phase at 70°C and stir and emulsify for 60 to 70 minutes; h. After emulsification is completed, dibutyltin dilaurate is added and reacted for 30 minutes to form an oil-in-water type formaldehyde-free memory microcapsule pigment.

[0039] In some embodiments, the temperature-sensitive red material may be other temperature-sensitive materials, including 4-benzyloxyphenylethyldecanoate, 4,4'-(2-ethylhexane-1,1-diyl)biphenol, and other materials commonly used in the industry.

[0040] Example 1-2:

[0041] The preparation method is the same as that of Example 1-1.

[0042] Comparative Example 1-1:

[0043] The preparation method is the same as that of Example 1-1.

[0044] Comparative Example 1-2:

[0045] The preparation method is the same as that of Example 1-1.

[0046] Comparative Examples 1-3:

[0047] The preparation method is the same as that of Example 1-1.

[0048] Comparative Examples 1-4

[0049] The preparation method is the same as that of Example 1-1.

[0050] Comparative Examples 1-5:

[0051] The preparation method is the same as that of Example 1-1.

[0052] Comparative Examples 1-6:

[0053] The preparation method is the same as that of Example 1-1.

[0054] Comparative Examples 1-7:

[0055] The preparation method is the same as that of Example 1-1.

[0056] The PVA used in Comparative Example 1-1 has a higher degree of polymerization of 2699, while the PVA used in Comparative Example 1-2 has a lower degree of polymerization of 0588, with the rest remaining unchanged. It was found that the microcapsules synthesized in Comparative Examples 1-1 and 1-2 separated into water and oil after a period of time, indicating that the emulsion system was unstable.

[0057] In Comparative Examples 1-3, the accelerator dosage was 4%, while the remaining ingredients remained unchanged. Observation of the products revealed that the microcapsules synthesized in Comparative Examples 1-3 were significantly lighter in color than those in Examples 1-1 and 1-2. This may be due to the excessive amount of accelerator, which caused rapid polymerization and released a large amount of heat in a short period of time, leading to discoloration of the thermochromic material.

[0058] In Comparative Examples 1-4, the accelerator dosage was only 0.1%, while the remaining contents remained unchanged. Viscometer testing of the microcapsules synthesized in Comparative Examples 1-4 revealed a significantly higher viscosity than that of the microcapsules synthesized in Examples 1-1 and 1-2. Consequently, when formulated into ink, the viscosity of the ink obtained with the same microcapsule dosage was higher than that of the ink in Example 1, affecting the writing experience.

[0059] When too much polyvinyl alcohol and styrene-maleic anhydride are added in Comparative Examples 1-5 and too little polyvinyl alcohol and styrene-maleic anhydride are added in Comparative Examples 1-6, the synthesized microcapsules will separate into water and oil after a period of time, that is, the emulsion system is unstable.

[0060] The particle size of the oil-in-water type formaldehyde-free memory microcapsule pigments of Examples 1-1 and 1-2 of the present invention was measured to be 0.5 to 2 μm using a BT-9300ST fully automatic laser particle size analyzer.

[0061] Example 2, a specific example of heat-erasable formaldehyde-free water-based ink: The formaldehyde-free memory microcapsules can be selected from a variety of colors such as red, yellow, blue, purple, green, black, etc. This embodiment is described using red as an example.

[0062] The oil-in-water formaldehyde-free memory microcapsule pigment of Example 1-1 was used to prepare heat-erasable formaldehyde-free water-based ink.

[0063] Example 2-1: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0064] The method comprises the following steps: firstly adding distilled water into a pre-dispersing pot, adding sodium molybdate under stirring, and then sequentially adding a polyacrylic acid dispersant, ethylene glycol, polyacrylamide, and Tween-80 after the sodium molybdate is completely dissolved, and finally adding red formaldehyde-free memory microcapsules after uniform dispersion, stirring for 30 minutes, and filtering to obtain the heat-erasable formaldehyde-free water-based ink of the present invention.

[0065] Example 2-2: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0066] The preparation method is the same as that of Example 2-1.

[0067] Example 2-3: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0068] The preparation method is the same as that of Example 2-1.

[0069] Example 2-4: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0070] The preparation method is the same as that of Example 2-1.

[0071] Comparative Example 2-1: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0072] The preparation method is the same as that of Example 2-1.

[0073] Comparative Example 2-2: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0074] The preparation method is the same as that of Example 2-1.

[0075] Comparative Example 2-3: The heat-erasable formaldehyde-free water-based ink of the present invention has the following material formula by weight:

[0076] The conventional indicators of the inks prepared in Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-3 were tested, and the test results are shown in the following table:

[0077] In Examples 2-1 to 2-4, all physical indicators meet the requirements.

[0078] While all indicators in Comparative Example 2-1 met the requirements, the insufficient amount of microcapsule pigment resulted in a light color after writing. In Comparative Example 2-2, the excessive amount of water-soluble organic solvent and insufficient specific gravity adjuster resulted in slightly higher ink viscosity, resulting in choppy writing and breakage. The pen also exhibited storage instability, with the color becoming lighter after several days at room temperature. In Comparative Example 2-3, the insufficient amount of flocculant and excessive amount of surfactant resulted in storage instability, ink stratification, and severe bleeding during writing. Table 1 below compares the performance of the formaldehyde-free inks prepared in Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-3 with existing heat-erasable inks on the market. Comparative Examples 2-4 and 2-5 are both commercially available heat-erasable inks prepared using conventional methods, with excess formaldehyde added during the encapsulation process to ensure complete polymerization.

[0079] Table 1 Comparison of performance of the embodiments of the present invention, comparative examples and existing erasable inks on the market

[0080] As can be seen from the above table, in terms of stability and writing feel, the ink of the present invention is significantly superior to commercially available inks.

[0081] Commercially available inks, after being left for a period of time, will continue to polymerize formaldehyde, resulting in excessive viscosity, broken lines, choppy writing, a poor writing experience, and decreased storage stability. However, the ink of the present invention, which does not contain formaldehyde, avoids the subsequent increase in ink viscosity, maintaining excellent writing quality and storage stability.

[0082] The result of manual marking is as follows Figure 1 As shown, Examples 2-1 to 2-4 have moderate viscosities and relatively uniform writing effects. In Comparative Example 2-1, a small amount of microcapsules is added, and the color is light. In Comparative Example 2-2, the viscosity is large, the writing ink is uneven, and the color varies in depth.

[0083] The inks prepared in Comparative Examples 1-7 according to the method of Example 2-1 were manually drawn and compared with those in Example 2-1. Figure 2 As shown, the base color of Example 2-1 with chitosan added is very light after wiping, while the color-removing effect of the product without chitosan added is slightly worse.

[0084] In summary, the ink of the present invention does not contain formaldehyde, solves the problem of adverse effects on human health, and has the advantage of being environmentally friendly; and the provided ink is significantly superior to the prior art in terms of writing feel and storage stability.

Claims

1. An oil-in-water type formaldehyde-free memory microcapsule pigment, characterized in that: The invention comprises the following components by mass fraction: polyvinyl alcohol 5% to 20%, styrene-maleic anhydride 1.25% to 10%, chitosan 5% to 10%, thermochromic pigment 7.5% to 17.5%, bisphenol AF 5% to 10%, polyurethane prepolymer 5% to 10%, oil phase solvent 12% to 20%, accelerator 0.25% to 2%, and the balance is water.

2. The oil-in-water type formaldehyde-free memory microcapsule pigment according to claim 1, characterized in that: The degree of polymerization of polyvinyl alcohol is 1700≤≤2400, and the degree of alcoholysis is ≥88.

3. The oil-in-water type formaldehyde-free memory microcapsule pigment according to claim 1, characterized in that: The accelerator is a fatty amine accelerator, a tin accelerator, ferric chloride or p-chlorobenzoic acid. The fatty amine accelerator is selected from DMP-30 and triethanolamine. The tin accelerator is selected from dibutyltin dilaurate or stannous octoate.

4. The method for preparing the oil-in-water type formaldehyde-free memory microcapsule pigment according to claim 1, characterized in that: The steps include: a. dissolving polyvinyl alcohol in water to prepare an aqueous solution of polyvinyl alcohol; b. The styrene - maleic anhydride copolymer resin is dissolved in water to prepare an aqueous solution of a styrene - maleic anhydride copolymer resin; c. Mix the solutions obtained in a and b, stir and heat to construct an aqueous phase; d. The chitosan, thermochromic pigment, bisphenol AF are mixed in order and melted for later use; e. adding the polyurethane prepolymer to the oil phase solvent and heating it for end-capping; f. Mix d and e to construct the oil phase; g. Inject the oil phase into the water phase and stir to emulsify; h. After emulsification is completed, add accelerator to complete the cross-linking and curing of the wall material to form water-in-oil type formaldehyde-free memory microcapsule pigment.

5. The method for preparing the oil-in-water type formaldehyde-free memory microcapsule pigment according to claim 4, characterized in that: In step c, the mass ratio of polyvinyl alcohol to styrene-maleic anhydride copolymer resin in the mixed solution is 4:1 to 2:

1.

6. Use of the oil-in-water formaldehyde-free memory microcapsule pigment according to claim 1 in the preparation of inks for the following products: a, water-based ballpoint pen; b, watercolor pen; c, pen; d, marker pen.

7. A heat-erasable formaldehyde-free water-based ink, characterized in that: The invention comprises: 10-30% microcapsule pigment, 0.5-3% dispersant, 10-40% water-soluble organic solvent, 5-20% specific gravity regulator, 0.1-2% flocculant, 0.1-2% surfactant, and the rest is water. The microcapsule pigment is the oil-in-water formaldehyde-free memory microcapsule pigment according to claim 1.

8. The method for preparing the heat-erasable formaldehyde-free water-based ink according to claim 7, characterized in that: First, add water into the pre-dispersion pot, add the specific gravity regulator under stirring, and after the specific gravity regulator is completely dissolved, then add the dispersant, water-soluble organic solvent, flocculant, and surfactant in sequence. Finally, add the microcapsule pigment after uniform dispersion, stir, and filter to obtain the product.

9. A replacement refill, characterized in that: The heat-erasable formaldehyde-free water-based ink according to claim 7 is built in.

10. A water-based ballpoint pen, characterized in that: The heat-erasable formaldehyde-free water-based ink according to claim 7 is built in.

Images