Film-forming replenishing liquid for teaching blackboard writing and preparation method of film-forming replenishing liquid

Abstract

The invention relates to the technical field of teaching supplies, and discloses a film-forming replenisher for teaching blackboard writing and a preparation method thereof.The replenisher comprises, by mass, 40%-55% of biological fermentation ethyl alcohol, 1%-5% of ethyl acetate, 1%-5% of 1, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate and the balance water. The water-based polyurethane composite material is prepared from, by weight, 1%-4% of 1, 2-propylene glycol, 30%-45% of PVB-PLA composite resin, 1%-5% of waterborne polyurethane, 5%-12% of nanoscale modified special carbon black, 0.3%-1.0% of sulfonated-grafted lignin derivatives, 0.2%-1.0% of polyether modified silicone oil, 0.1%-0.8% of microencapsulated paraffin, 0.15%-0.3% of silanized TiO2 (at) Ag nanometer materials, 0.1%-0.5% of citric acid-starch compounds and the balance deionized water. The method comprises the steps of resin premixing, gradient solvent adding, pigment dispersing, functional mixing, aftertreatment and the like. The replenishing liquid can quickly and stably form a film, is easy to wipe, and is green and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of teaching supplies, and particularly relates to a film-forming replenishing liquid for teaching blackboard writing and a preparation method thereof. Background Art

[0002] Currently, chalk is mainly used for blackboard writing in classrooms. The history of chalk has exceeded one hundred years. As a teaching tool, while bringing people knowledge, chalk dust poses hazards to the health of teachers and students as well as the classroom environment. A lot of fine dust can float in the air for up to six hours, and various heavy metal elements in chalk are highly harmful to the human body. The health of teachers is often related to the harm of chalk dust. What most people don't notice is that the health of students is also closely related to chalk dust.

[0003] In order to fundamentally solve the problem of dust-free blackboard writing, various dust-free board writing liquids have emerged on the market. They inject the writing liquid into a special writing pen and write on a special board, which can replace chalk for teaching and has the advantages of smooth writing and dust-free. However, these writing liquids use organic solvents as the medium, are somewhat toxic, are volatile and flammable, pollute the environment and are harmful to health, and the pen tip is prone to drying and cannot be wiped clean, and the film-forming speed is slow. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a film-forming replenishing liquid for teaching blackboard writing and a preparation method thereof.

[0005] On the one hand, a film-forming replenishing liquid for teaching blackboard writing according to the present invention, by mass percentage, includes: bio-fermented ethanol 40%-55%, ethyl acetate 1%-5%, 1,2-propanediol 1%-4%, PVB-PLA composite resin 30%-45%, waterborne polyurethane 1%-5%, nano-modified special carbon black 5%-12%, sulfonated-grafted lignin derivative 0.3%-1.0%, polyether-modified silicone oil 0.2%-1.0%, microencapsulated paraffin 0.1%-0.8%, silanized TiO2@Ag nanomaterial 0.15%-0.3%, citric acid-starch complex 0.1%-0.5%, and the balance deionized water.

[0006] Preferably, the molar ratio of PVB to PLA in the PVB-PLA composite resin is (2:1)-(5:1);

[0007] The molecular weight of the waterborne polyurethane is 30000Da-100000Da.

[0008] Preferably, the nano-modified special carbon black is special carbon black particles coated with silica particles on the surface, with a particle size of 30-100nm and a silica coating thickness of 2-10nm.

[0009] Preferably, the pH buffering range of the citric acid-starch complex is 6.0 - 7.5.

[0010] Preferably, the particle size of the microcapsule paraffin wax is 0.5 - 10 μm, and the coating rate is 80% - 95%;

[0011] The surface tension of the polyether-modified silicone oil is 20 - 30 mN / m.

[0012] Preferably, the silver loading amount in the silanized TiO2@Ag nanomaterial is 3% - 10 wt%.

[0013] Preferably, the degree of substitution of the sulfonated-grafted lignin derivative is 0.5 - 1.5, and the sulfonation rate is 50% - 90%.

[0014] On the other hand, the present invention also discloses a preparation method of a film-forming replenishing liquid for teaching blackboard writing, comprising the following steps:

[0015] Dissolve the PVB-PLA composite resin and the waterborne polyurethane in biological fermentation ethanol at 50 - 65 °C and under an inert gas, and stir until completely dissolved;

[0016] Add ethyl acetate and 1,2-propanediol in sequence, and stir and mix;

[0017] Add nanoscale modified special carbon black and sulfonated-grafted lignin derivative, stir and disperse, and sand mill until the fineness of the slurry is ≤10 μm;

[0018] Add the polyether-modified silicone oil, microcapsule paraffin wax and silanized TiO2@Ag in stages, and mix under light avoidance and inert gas protection;

[0019] Add the citric acid-starch complex to adjust the pH to 6.0 - 7.5, add deionized water to make the viscosity 12.5 - 13.2 FPS, and filter and package.

[0020] Preferably, the adding of the polyether-modified silicone oil, microcapsule paraffin wax and silanized TiO2@Ag in stages and mixing under light avoidance includes:

[0021] Add the polyether-modified silicone oil and microcapsule paraffin wax, and stir at 20 - 40 °C and 500 rpm for 20 min;

[0022] Add the silanized TiO2@Ag under light avoidance conditions, and stir at 300 rpm for 15 min.

[0023] Preferably, the medium for sand milling is zirconia beads or alumina beads, the particle size is 0.1 - 0.5 mm, and the filling rate is 60% - 85%.

[0024] The film-forming replenishing liquid for teaching blackboard writing and the preparation method thereof of the present invention have the advantages that:

[0025] (1) The solvent of the present invention is selected from bio-fermented ethanol, ethyl acetate, and 1,2-propylene glycol, which can better ensure the stability of film formation. Bio-fermented ethanol is a polar solvent. Ethanol can effectively dissolve PVB-PLA composite resin and waterborne polyurethane (WPU) to form a homogeneous solution, ensure that the resin molecular chain is fully extended, and provide a basis for film formation. The ethanol has a moderate volatilization rate (boiling point 78°C), which can not only avoid the supplementary liquid from drying too quickly and causing poor writing, but also prevent the residual stains caused by too slow drying. Bio-fermented ethanol comes from renewable resources (such as corn and sugarcane), and the VOCs content is extremely low (<5ppm), which meets the requirements of green chemistry. Ethyl acetate is a fast-evaporating solvent, and its low boiling point (77°C) makes it evaporate quickly. After the supplementary liquid is applied, it quickly forms a surface "skeleton" and shortens the film formation time; ethyl acetate and bio-fermented ethanol form a gradient volatilization system, which accelerates film formation in the early stage, and the pores are filled by bio-fermented ethanol in the middle stage to ensure a uniform film layer. 1,2-propylene glycol has strong hygroscopicity, which slows down the drying speed of the replenisher edge, prevents cracking, reduces the crystallization tendency of the system at low temperature (-20°C), maintains the flexibility of the film layer, slightly thickens through hydrogen bonding, and improves the leveling of the ink.

[0026] (2) The present invention uses PVB-PLA composite resin and WPU to form a film-forming resin group, which has a short film-forming time and high stability. PVB (polyvinyl butyral) provides excellent adhesion and flexibility, ensuring that the film layer is tightly attached to the substrate and is not easy to break. PLA (polylactic acid) imparts degradability and decomposes into CO2 and H2O under the action of soil microorganisms, with a degradation rate of >95% in 28 days. PVB-PLA composite resin forms an interpenetrating network structure through copolymerization, so that it has both the toughness of PVB and the environmental protection of PLA, avoiding the limitations of a single resin. The hydrophilic groups (such as carboxylic acid groups) in the WPU molecular chain are rapidly cross-linked after the water evaporates, shortening the film-forming time to 5-10 seconds, and its soft segment (polyether / polyester) enhances the flexibility of the film layer at low temperature (-20°C), prevents brittle cracking, and ensures the stability of the film. The rapid volatilization of ethyl acetate and the cross-linking effect of WPU allow the replenisher to form a film in 5-10 seconds.

[0027] (3) Special carbon black particles have a high specific surface area and light absorption property, providing a deep black color; the SiO2 coating layer reflects ultraviolet light, reducing fading caused by photooxidation (ΔE < 1.5 after UV aging). The SiO2 coating layer (2 - 10 nm) reduces the van der Waals force between particles through steric hindrance effects, preventing agglomeration, and the nano - particle size (30 - 100 nm) ensures uniform dispersion. Sulfonated - grafted lignin derivatives introduce sulfonic acid groups (-SO3H), enhancing water solubility and electronegativity, stabilizing the pigment suspension through electrostatic repulsion, and grafting hydrophobic chains (such as long alkyl groups) to form a stable adsorption layer on the surface of special carbon black, replacing traditional synthetic dispersants (such as polyethylene glycol).

[0028] (4) Polyether - modified silicone oil reduces the surface tension. The polyether segment endows amphiphilicity, reducing the surface tension from 32 mN / m to 25 mN / m and decreasing the wiping resistance. The silicone oil molecules of polyether - modified silicone oil form a lubricating layer on the whiteboard surface, avoiding scratching the substrate during wiping. Micro - encapsulated paraffin provides a rolling effect: after film - forming, the micro - capsules rupture to release paraffin particles (particle size 0.5 - 10 μm), reducing the actual contact area between the film layer and the substrate, and being easily peeled off as a whole during wiping. The hydrophobicity of paraffin enhances the low - temperature stability of the film layer. Using the combined action of polyether - modified silicone oil and micro - encapsulated paraffin, ΔE ≤ 0.2 after one dry - wipe.

[0029] (5) In the silanized TiO2@Ag nanomaterial, nano - silver (Ag particle size 10 - 20 nm) releases Ag + ions, destroying the bacterial cell membrane and inhibiting enzyme activity, with a bacteriostatic rate > 99.8% in 24 hours. TiO2 absorbs UV - A / B and converts it into heat energy, protecting carbon black and resin from photodegradation. The silane coupling agent coats TiO2@Ag, enhancing its compatibility with the resin and preventing agglomeration. The tricarboxylic acid groups of citric acid in the citric acid - starch complex neutralize the acid - base fluctuations in the system, maintaining a stable pH (6.0 - 7.5), preventing resin hydrolysis or pigment sedimentation. Starch forms a three - dimensional network through hydrogen bonds, slightly increasing the viscosity; synergistically with the resin, it enhances the brittleness of the film layer, facilitating wiping and shedding. Both citric acid and starch are natural biodegradable substances, enhancing the environmental friendliness of the replenishing solution.

[0030] (6) The method of the present invention optimizes the film-forming efficiency, wiping performance, and long-term stability of the ink through staged addition and inert gas protection, while ensuring the activity and dispersibility of functional additives (such as Ag and TiO2). By adding gradient solvents (i.e., successively adding bio-fermented ethanol, ethyl acetate, and 1,2-propanediol), ethyl acetate and bio-fermented ethanol form a gradient volatilization system. In the initial stage, it accelerates surface curing. In the middle stage, ethanol fills the pores to ensure a uniform and defect-free film layer. Adding ethyl acetate utilizes its rapid volatility to lay the foundation for film formation. After adding ethyl acetate, 1,2-propanediol is added to balance the volatilization gradient and avoid uneven film layers caused by excessive drying. Polyether-modified silicone oil is added after the resin system is initially formed to avoid affecting resin dissolution or dispersion by premature addition. Adding it in the later stage ensures its uniform distribution on the surface and maximizes the lubrication effect. Microencapsulated paraffin is added after the resin and pigment dispersion are completed to avoid the rupture and failure of microcapsules during the grinding process. Mixing in the later stage ensures that paraffin particles are evenly embedded in the film layer rather than being wrapped by the resin. The light-shielding operation of silanized TiO2@Ag nanomaterials avoids the premature photolysis failure of ultraviolet absorbers and is added after the resin system is stable to ensure the uniform dispersion of nanomaterials in the film layer.

[0031] On the one hand, since PVB and PLA may undergo oxidative degradation in the presence of high temperature or oxygen, resulting in the breakage of molecular chains and affecting film-forming performance, and nano silver (Ag) is easily oxidized to form Ag2O when exposed to oxygen, reducing antibacterial activity. After adding inert gas, the oxidation of PVB and PLA resins and nano silver can be prevented, ensuring the stability of the replenishing liquid.

[0032] On the other hand, the silane coupling agent in silanized TiO2@Ag may undergo hydrolysis side reactions in the presence of oxygen and moisture, affecting its bonding effect with the resin. After adding inert gas (such as nitrogen), the occurrence of side reactions can be inhibited.

[0033] On yet another hand, although bio-fermented ethanol and ethyl acetate are highly volatile, trace amounts of peroxides may be generated during high-temperature stirring. Inert gas (such as nitrogen) can inhibit such reactions.

[0034] During the encapsulation stage, nitrogen filling encapsulation avoids performance degradation (such as inactivation of antibacterial agents and oxidation of resins) in the long-term storage of the replenishing liquid caused by residual oxygen.

[0035] All raw materials in the present invention are commercially available products or self-made from commercially available raw materials (such as silanized TiO2@Ag nanomaterials, PVB-PLA composite resins, etc.). Detailed implementation mode

[0036] Example 1

[0037] On the one hand, this example discloses a film-forming replenishing liquid for teaching blackboard writing. The blackboard liquid includes, by mass percentage:

[0038] Solvent group: Bioethanol (40%), Ethyl acetate (3%), 1,2 - Propylene glycol (2%);

[0039] Resin group: PVB - PLA composite resin (38%), WPU (2%), where PVB:PLA = 2:1, and the molecular weight of WPU is 30000Da;

[0040] Pigment and dispersion system: Nano - modified special carbon black (8%), Sulfonated - grafted lignin derivative (0.5%). The particle size of the special carbon black is 30nm, the thickness of the silica coating layer is 2nm, the substitution degree of the sulfonated - grafted lignin derivative is 0.5, and the sulfonation rate is 50%;

[0041] Wiping aid group: Polyether - modified silicone oil (0.5%), Micro - encapsulated paraffin wax (0.8%). The particle size of the micro - encapsulated paraffin wax is 0.5μm, the coating rate is 80%, and the surface tension of the polyether - modified silicone oil is 20mN / m;

[0042] Additive group: Silanized TiO2@Ag (0.15%), Citric acid - starch (0.3%). The silver loading in the silanized TiO2@Ag nanomaterial is 3wt%;

[0043] Deionized water (4.75%).

[0044] On the other hand, this embodiment discloses a preparation method of the blackboard writing liquid, including the following steps:.

[0045] Resin premixing: Add bio - fermented ethanol into a high - shear dispersion kettle with a nitrogen inlet, then add PVB - PLA composite resin and WPU in sequence. Set the temperature at 50°C, the rotation speed at 2000rpm, and simultaneously charge nitrogen for protection, and stir for 40min until the resin is completely dissolved. Detect the transparency of the solution to ensure that there are no undissolved particles (by visual inspection or turbidimeter).

[0046] Gradient solvent addition: Slowly dropwise add ethyl acetate, maintain at 50°C, stir at a rotation speed of 1000rpm for 5min, add 1,2 - propylene glycol, and continue to stir for 5min under the same conditions.

[0047] Pigment dispersion: Add nano - modified carbon black and sulfonated - grafted lignin derivative, and pre - disperse at a rotation speed of 800rpm for 10min;

[0048] Transfer the pre - dispersed mixture to a sand mill, and add zirconia beads (particle size 0.1mm, filling rate 60%);

[0049] Set the temperature at 25°C, the rotation speed at 1500rpm, and wet - grind for 180min;

[0050] End point control: The fineness of the slurry ≤ 5 μm (detected by laser particle size analyzer).

[0051] Functional mixing: Transfer the ground mixture into a stirring kettle with a nitrogen inlet, add polyether modified silicone oil and microencapsulated paraffin wax, stir for 20 min at 20 °C and a rotation speed of 500 rpm, and add silanized TiO2@Ag under light-shielding and nitrogen protection conditions, then stir for 15 min at a rotation speed of 300 rpm.

[0052] Post-treatment: Add citric acid-starch complex, adjust the pH of the system to 6.0 (monitored in real time by pH meter), and add deionized water to make the viscosity 12.5 FPS (Ford cup method, 25 °C);

[0053] Filter through a 5-μm nylon filter membrane to remove undispersed particles, encapsulate with nitrogen into a light-shielding container, and the oxygen content ≤ 0.5% (detected by oxygen concentration sensor).

[0054] For the above PVB-PLA composite resin, sulfonated-grafted lignin derivative, polyether modified silicone oil, silanized TiO2@Ag nanomaterial, microencapsulated paraffin wax, nano-modified special carbon black, citric acid-starch complex, etc., the following methods can also be used for preparation.

[0055] 1. Preparation of PVB-PLA composite resin

[0056] Raw materials:

[0057] Polyvinyl butyral (PVB) powder

[0058] Polylactic acid (PLA) particles

[0059] Mixed solvent of dichloromethane (DCM) and tetrahydrofuran (THF) (volume ratio 1:1)

[0060] Stannous octoate (catalyst, dosage 0.1%)

[0061] Process steps:

[0062] Dissolution:

[0063] Add PVB and PLA to the mixed solvent at a mass ratio of 3:1, and control the total solid content at 15-20%.

[0064] Mechanically stir at 40 °C for 4-6 hours until completely dissolved to form a transparent solution.

[0065] Copolymerization reaction:

[0066] Add stannous octoate catalyst and raise the temperature to 60 °C.

[0067] React under nitrogen protection for 12-24 hours to promote the cross-linking of PVB and PLA molecular chains.

[0068] Post-treatment:

[0069] The reaction solution was slowly dropped into excessive ethanol to precipitate the copolymer.

[0070] After filtration and washing, it was dried in vacuum at 50 °C for 24 hours to obtain white granular PVB-PLA composite resin.

[0071] 2. Preparation of sulfonated-grafted lignin derivative

[0072] Raw materials:

[0073] Lignin powder (extracted from paper-making black liquor, purity ≥ 85%)

[0074] Concentrated sulfuric acid (H2SO4) and sodium sulfite (Na2SO3)

[0075] Butyl acrylate (BA) monomer

[0076] Ammonium persulfate (APS, initiator)

[0077] Process steps:

[0078] Sulfonation reaction:

[0079] Lignin was stirred and reacted with the H2SO4 / Na2SO3 mixture (molar ratio 2:1) at 80 °C for 3 hours.

[0080] Sulfonic acid groups substituted the hydroxyl groups on the benzene ring of lignin, and the sulfonation degree reached 0.8 - 1.2.

[0081] Grafting modification:

[0082] The sulfonated lignin was dispersed in water, and BA monomer (10 - 15% of the lignin mass) and APS (1% of the monomer amount) were added.

[0083] It was reacted at 70 °C under nitrogen protection for 6 hours to form a graft copolymer.

[0084] Purification:

[0085] Dialysis was used to remove unreacted monomers and salts (cut-off molecular weight 3500 Da).

[0086] After freeze-drying, sulfonated-grafted lignin derivative powder was obtained.

[0087] 3. Preparation of polyether-modified silicone oil

[0088] Raw materials:

[0089] Hydroxyl silicone oil (viscosity 500 - 1000 mPa·s)

[0090] Ethylene oxide (EO) or propylene oxide (PO)

[0091] Potassium hydroxide (KOH, catalyst)

[0092] Process steps:

[0093] Ring-opening polymerization:

[0094] Mix silicone oil with KOH (0.5% of the mass of silicone oil) and heat to 100 - 120 °C.

[0095] Introduce EO or PO gas with a pressure of 0.2 - 0.5 MPa and react until the degree of polymerization of the polyether chain segment reaches 5 - 10.

[0096] Neutralization and purification:

[0097] Add phosphoric acid to neutralize the catalyst and filter to remove salts.

[0098] Dehydrate under vacuum at 80 °C for 4 hours to obtain polyether-modified silicone oil (surface tension 25 - 30 mN / m).

[0099] Preparation of silanized TiO2@Ag nanomaterials

[0100] Raw materials:

[0101] Silver nitrate (AgNO3)

[0102] Tetrabutyl titanate (TTIP)

[0103] Silane coupling agent (KH-550)

[0104] Sodium citrate (reducing agent)

[0105] Process steps:

[0106] Preparation of nano silver:

[0107] React the AgNO3 solution with sodium citrate at 80 °C for 1 hour to generate silver particles with a size of 10 - 20 nm.

[0108] TiO2 coating:

[0109] Disperse the Ag particles in ethanol, add TTIP, adjust the pH to 9 - 10, and hydrolyze to form a TiO2 gel layer.

[0110] Age at 60 °C for 12 hours and calcine at 400 °C for 2 hours to obtain anatase TiO2@Ag.

[0111] Silanization treatment:

[0112] Disperse TiO2@Ag in a KH-550 ethanol solution (3%) and react at 60 °C for 6 hours.

[0113] After centrifugal washing and drying, silanized TiO2@Ag (Ag loading 3-10%) was obtained.

[0114] 5. Preparation of microencapsulated paraffin wax

[0115] Raw materials:

[0116] Paraffin wax (melting point 50-60°C)

[0117] Gelatin (wall material)

[0118] Glutaraldehyde (crosslinking agent)

[0119] Process steps:

[0120] Emulsification:

[0121] The molten paraffin wax was mixed with an aqueous gelatin solution (5%) and emulsified at high speed (10,000 rpm) to form an O / W emulsion.

[0122] Crosslinking and curing:

[0123] Glutaraldehyde (0.5% of the amount of gelatin) was added and stirred at 50°C for 2 hours to form crosslinked microcapsules.

[0124] Separation and drying:

[0125] The microcapsules were collected by centrifugation and freeze-dried to obtain microencapsulated paraffin wax with a particle size of 0.5-10 μm.

[0126] 6. Preparation of nano-modified special carbon black

[0127] Raw materials:

[0128] Special carbon black (particle size 200-500 nm)

[0129] Tetraethyl orthosilicate (TEOS)

[0130] Ammonia water (catalyst)

[0131] Process steps:

[0132] SiO2 coating:

[0133] The special carbon black was dispersed in an ethanol / water mixture, TEOS and ammonia water were added, and the reaction was carried out at 50°C for 6 hours to form an SiO2 coating layer (thickness 2-10 nm).

[0134] Purification:

[0135] After centrifugal washing and drying at 60°C, nano-modified carbon black (particle size 30-100 nm) was obtained.

[0136] 7. Preparation of citric acid-starch complex

[0137] Raw materials:

[0138] Corn starch

[0139] Citric acid (CA)

[0140] Epichlorohydrin (crosslinking agent)

[0141] Process steps:

[0142] Esterification reaction:

[0143] The starch and citric acid (mass ratio 10:1) are reacted dry at 120 °C for 2 hours to produce esterified starch.

[0144] Crosslinking:

[0145] Add epichlorohydrin (0.5% of the starch amount), react at 60 °C for 1 hour to form a three-dimensional network structure.

[0146] Purification:

[0147] Wash with water to remove unreacted citric acid, dry and crush to obtain a citric acid-starch complex.

[0148] Example 2

[0149] On the one hand, this example discloses a film-forming replenishing liquid for teaching blackboard writing. The blackboard writing liquid includes by mass percentage:

[0150] Solvent group: bioethanol (55%), ethyl acetate (2%), 1,2-propanediol (1%);

[0151] Resin group: PVB-PLA composite resin (30%), WPU (1%), where PVB:PLA = 3:1 and the molecular weight of WPU is 50000 Da;

[0152] Pigment and dispersion system: nano-scale modified special carbon black (6%), sulfonated-grafted lignin derivative (0.8%). The particle size of the special carbon black is 50 nm, the thickness of the silica coating layer is 5 nm, the substitution degree of the sulfonated-grafted lignin derivative is 0.8, and the sulfonation rate is 75%;

[0153] Wiping aid group: polyether-modified silicone oil (0.3%), microcapsule paraffin (0.3%). The particle size of the microcapsule paraffin is 2 μm, the coating rate is 85%, and the surface tension of the polyether-modified silicone oil is 25 mN / m;

[0154] Additive group: silanized TiO2@Ag (0.3%), citric acid-starch (0.1%). The silver loading in the silanized TiO2@Ag nanomaterial is 6% wt%;

[0155] Deionized water (3.2%).

[0156] On the other hand, this embodiment discloses a preparation method of the blackboard writing liquid, which includes the following steps:

[0157] Resin premixing: Add bio-fermented ethanol into a high-shear dispersion kettle with a nitrogen inlet, and then sequentially add PVB-PLA composite resin and WPU. Set the temperature at 55°C and the rotation speed at 2000 rpm. At the same time, charge nitrogen for protection and stir for 40 min until the resin is completely dissolved. Detect the transparency of the solution to ensure that there are no undissolved particles (visual method or turbidimeter).

[0158] Gradient solvent addition: Slowly dropwise add ethyl acetate, maintain at 55°C, stir at a rotation speed of 1000 rpm for 5 min, add 1,2-propanediol, and continue to stir for 5 min under the same conditions.

[0159] Pigment dispersion: Add nano-modified carbon black and sulfonated-grafted lignin derivatives, and pre-disperse at a rotation speed of 800 rpm for 10 min;

[0160] Transfer the pre-dispersed mixture to a sand mill, and add alumina beads (particle size 0.2 mm, filling rate 65%);

[0161] Set the temperature at 25°C, the rotation speed at 1500 rpm, and wet grind for 180 min;

[0162] Endpoint control: The fineness of the slurry ≤ 6 μm (detected by a laser particle size analyzer).

[0163] Functional mixing: Transfer the ground mixture into a stirring kettle with a nitrogen inlet, add polyether-modified silicone oil and microcapsule paraffin, stir at 25°C and a rotation speed of 500 rpm for 20 min, and add silanized TiO2@Ag under the conditions of avoiding light and nitrogen protection, and stir at a rotation speed of 300 rpm for 15 min.

[0164] Post-treatment: Add citric acid-starch complex, adjust the pH of the system to 6.5 (real-time monitoring with a pH meter), and supplement deionized water to a viscosity of 12.8 FPS (Ford cup method, 25°C);

[0165] Filter through a 5-μm nylon filter membrane to remove undispersed particles, fill with nitrogen and encapsulate into a light-proof container, and the oxygen content ≤ 0.5% (detected by an oxygen concentration sensor).

[0166] Example 3

[0167] On the one hand, this embodiment discloses a film-forming replenishing liquid for teaching blackboard writing. The blackboard writing liquid includes, by mass percentage:

[0168] Solvent group: Bio-ethanol (40%), ethyl acetate (1%), 1,2-propanediol (2%);

[0169] Resin group: PVB-PLA composite resin (45%), WPU (2%), where PVB:PLA = 4:1, and the molecular weight of WPU is 100000 Da;

[0170] Pigment and dispersion system: nano-modified special carbon black (6%), sulfonated-grafted lignin derivative (0.3%), the particle size of the special carbon black is 100 nm, the thickness of the silica coating layer is 10 nm, and the substitution degree of the sulfonated-grafted lignin derivative is 1.0, and the sulfonation rate is 90%;

[0171] Wiping aid group: polyether-modified silicone oil (0.5%), microcapsule paraffin (0.1%), the particle size of the microcapsule paraffin is 10 μm, the coating rate is 95%, and the surface tension of the polyether-modified silicone oil is 30 mN / m;

[0172] Additive group: silanized TiO2@Ag (0.2%), citric acid-starch (0.5%), and the silver loading in the silanized TiO2@Ag nanomaterial is 10% wt%;

[0173] Deionized water (2.4%).

[0174] On the other hand, this embodiment discloses a preparation method of the blackboard writing liquid, including the following steps:.

[0175] Resin premixing: Add bio-fermented ethanol into a high-shear dispersion kettle with a nitrogen inlet, and then add PVB-PLA composite resin and WPU in sequence. Set the temperature at 65°C and the rotation speed at 2000 rpm. At the same time, charge nitrogen for protection and stir for 40 min until the resin is completely dissolved. Detect the transparency of the solution to ensure that there are no undissolved particles (visual inspection method or turbidimeter).

[0176] Gradient solvent addition: Slowly drop ethyl acetate, keep the temperature at 65°C, stir at a rotation speed of 1000 rpm for 5 min, add 1,2-propanediol, and continue to stir for 5 min under the same conditions.

[0177] Pigment dispersion: Add nano-modified carbon black and sulfonated-grafted lignin derivative, and pre-disperse at a rotation speed of 800 rpm for 10 min;

[0178] Transfer the pre-dispersed mixture to a sand mill, and add zirconia beads (particle size 0.5 mm, filling rate 85%);

[0179] Set the temperature at 25°C, the rotation speed at 1500 rpm, and wet grind for 180 min;

[0180] Endpoint control: The fineness of the slurry ≤ 7 μm (detected by a laser particle size analyzer).

[0181] Functional mixing: Transfer the ground mixture into a stirring kettle with a nitrogen inlet, add polyether-modified silicone oil and microencapsulated paraffin wax, stir for 20 min at 30 °C and a rotation speed of 500 rpm, and add silanized TiO2@Ag under light-shielding and nitrogen protection conditions, then stir for 15 min at a rotation speed of 300 rpm.

[0182] Post-treatment: Add citric acid-starch complex, adjust the pH of the system to 7.0 (monitored in real time with a pH meter), and make up deionized water to a viscosity of 13.2 FPS (Ford cup method, 25 °C);

[0183] Filter through a 5-μm nylon filter membrane to remove undispersed particles, fill with nitrogen and seal in a light-shielding container, with an oxygen content ≤ 0.5% (detected by an oxygen concentration sensor).

[0184] Example 4

[0185] On the one hand, this example discloses a film-forming supplementary liquid for teaching blackboard writing. The blackboard writing liquid includes, by mass percentage:

[0186] Solvent group: bioethanol (45%), ethyl acetate (3%), 1,2-propanediol (2%);

[0187] Resin group: PVB-PLA composite resin (32%), WPU (3%), where PVB:PLA = 5:1 and the molecular weight of WPU is 80000 Da;

[0188] Pigment and dispersion system: nano-scale modified special carbon black (9%), sulfonated-grafted lignin derivative (0.6%), the particle size of the special carbon black is 40 nm, the thickness of the silica coating layer is 6 nm, the substitution degree of the sulfonated-grafted lignin derivative is 1.5, and the sulfonation rate is 85%;

[0189] Wiping aid group: polyether-modified silicone oil (0.6%), microencapsulated paraffin wax (0.4%), the particle size of the microencapsulated paraffin wax is 6 μm, the coating rate is 90%, and the surface tension of the polyether-modified silicone oil is 24 mN / m;

[0190] Additive group: silanized TiO2@Ag (0.2%), citric acid-starch (0.3%), and the silver loading in the silanized TiO2@Ag nanomaterial is 5 wt%;

[0191] Deionized water (3.9%).

[0192] On the other hand, this example discloses a preparation method of the blackboard writing liquid, including the following steps:.

[0193] Resin premixing: Add bio-fermented ethanol into a high-shear dispersion kettle with a nitrogen inlet, then sequentially add PVB-PLA composite resin and WPU. Set the temperature to 60°C and the rotation speed to 2000 rpm. At the same time, charge nitrogen for protection and stir for 40 min until the resin is completely dissolved. Detect the transparency of the solution to ensure that there are no undissolved particles (by visual inspection or turbidimeter).

[0194] Gradient solvent addition: Slowly dropwise add ethyl acetate, maintain at 60°C, stir at a rotation speed of 1000 rpm for 5 min, add 1,2-propanediol, and continue to stir for 5 min under the same conditions.

[0195] Pigment dispersion: Add nano-modified carbon black and sulfonated-grafted lignin derivatives, and pre-disperse at a rotation speed of 800 rpm for 10 min;

[0196] Transfer the pre-dispersed mixture to a sand mill, and add zirconia beads (particle size 0.5 mm, filling rate 85%);

[0197] Set the temperature to 25°C, the rotation speed to 1500 rpm, and wet grind for 180 min;

[0198] Endpoint control: The fineness of the slurry ≤ 7 μm (detected by laser particle size analyzer).

[0199] Functional mixing: Transfer the ground mixture into a stirring kettle with a nitrogen inlet, add polyether-modified silicone oil and microcapsule paraffin, stir at 40°C and a rotation speed of 500 rpm for 20 min, and add silanized TiO2@Ag under the conditions of avoiding light and nitrogen protection, and stir at a rotation speed of 300 rpm for 15 min.

[0200] Post-treatment: Add citric acid-starch complex, adjust the pH of the system to 7.5 (monitored in real time by pH meter), and add deionized water to make the viscosity 13.0 FPS (Ford cup method, 25°C);

[0201] Filter through a 5-μm nylon filter membrane to remove undispersed particles, fill with nitrogen and encapsulate into a light-proof container, and the oxygen content ≤ 0.5% (detected by oxygen concentration sensor).

[0202] Example 5

[0203] On the one hand, this example discloses a film-forming replenishing liquid for teaching blackboard writing. The blackboard writing liquid includes, by mass percentage:

[0204] Solvent group: Bio-ethanol (41%), ethyl acetate (5%), 1,2-propanediol (1%);

[0205] Resin group: PVB-PLA composite resin (30%), WPU (5%), where PVB:PLA = 3:1 and the molecular weight of WPU is 80000 Da;

[0206] Pigments and dispersion system: Nanoscale modified special carbon black (12%), sulfonated-grafted lignin derivative (1.0%). The particle size of the special carbon black is 40 nm, the thickness of the silica coating layer is 6 nm, the degree of substitution of the sulfonated-grafted lignin derivative is 1.5, and the sulfonation rate is 85%;

[0207] Wiping aid group: Polyether-modified silicone oil (0.8%), microcapsule paraffin (0.6%). The particle size of the microcapsule paraffin is 5 μm, the coating rate is 85%, and the surface tension of the polyether-modified silicone oil is 26 mN / m;

[0208] Additive group: Silanized TiO2@Ag (0.15%), citric acid-starch (0.5%). The silver loading in the silanized TiO2@Ag nanomaterial is 8% wt%;

[0209] Deionized water (2.5%).

[0210] On the other hand, this embodiment discloses a preparation method of the blackboard writing liquid, including the following steps:.

[0211] Resin premixing: Add bio-fermented ethanol into a high-shear dispersion kettle with a nitrogen inlet, and then add PVB-PLA composite resin and WPU in sequence. Set the temperature at 55 °C and the rotation speed at 2000 rpm. At the same time, charge nitrogen for protection and stir for 40 min until the resin is completely dissolved. Detect the transparency of the solution to ensure that there are no undissolved particles (visual method or turbidimeter).

[0212] Gradient solvent addition: Slowly dropwise add ethyl acetate, keep the temperature at 55 °C, stir at a rotation speed of 1000 rpm for 5 min, add 1,2-propanediol, and continue to stir for 5 min under the same conditions.

[0213] Pigment dispersion: Add nanoscale modified carbon black and sulfonated-grafted lignin derivative, and pre-disperse at a rotation speed of 800 rpm for 10 min;

[0214] Transfer the pre-dispersed mixture to a sand mill, and add zirconia beads (particle size 0.5 mm, filling rate 85%);

[0215] Set the temperature at 25 °C, the rotation speed at 1500 rpm, and wet grind for 180 min;

[0216] Endpoint control: The fineness of the slurry ≤ 10 μm (detected by a laser particle size analyzer).

[0217] Functional mixing: Transfer the ground mixture into a stirring kettle with a nitrogen inlet, add polyether-modified silicone oil and microcapsule paraffin, stir at 35 °C and a rotation speed of 500 rpm for 20 min, and add silanized TiO2@Ag under the conditions of light avoidance and nitrogen protection, and stir at a rotation speed of 300 rpm for 15 min.

[0218] Post-treatment: Add citric acid-starch complex, adjust the pH of the system to 7.0 (monitored in real time by a pH meter), and add deionized water to make the viscosity reach 13.2 FPS (Ford cup method, 25 °C);

[0219] Filter through a 5-μm nylon filter membrane to remove undispersed particles, encapsulate with nitrogen into a light-proof container, and the oxygen content ≤ 0.5% (detected by an oxygen concentration sensor).

[0220] Example 6

[0221] On the one hand, this example discloses a film-forming supplementary liquid for teaching blackboard writing. The blackboard writing liquid includes, by mass percentage:

[0222] Solvent group: bioethanol (45%), ethyl acetate (2%), 1,2-propanediol (4%);

[0223] Resin group: PVB-PLA composite resin (32%), WPU (2%), where PVB: PLA = 3:1, and the molecular weight of WPU is 50000 Da;

[0224] Pigment and dispersion system: nano-modified special carbon black (8%), sulfonated-grafted lignin derivative (0.8%). The particle size of the special carbon black is 40 nm, the thickness of the silica coating layer is 6 nm, the substitution degree of the sulfonated-grafted lignin derivative is 0.8, and the sulfonation rate is 85%;

[0225] Wiping aid group: polyether-modified silicone oil (1.0%), microcapsule paraffin (0.6%). The particle size of the microcapsule paraffin is 6 μm, the coating rate is 83%, and the surface tension of the polyether-modified silicone oil is 27 mN / m;

[0226] Additive group: silanized TiO2@Ag (0.2%), citric acid-starch (0.3%). The silver loading in the silanized TiO2@Ag nanomaterial is 5% wt%;

[0227] Deionized water (4.1%).

[0228] On the other hand, this example discloses a preparation method of the blackboard writing liquid, including the following steps:.

[0229] Resin premixing: Add bio-fermented ethanol to a high-shear dispersion kettle with a nitrogen inlet, then add PVB-PLA composite resin and WPU in sequence. Set the temperature at 50 °C and the rotation speed at 2000 rpm. At the same time, charge nitrogen for protection and stir for 40 min until the resin is completely dissolved. Detect the transparency of the solution to ensure that there are no undissolved particles (by visual inspection or turbidimeter).

[0230] Gradient solvent addition: Slowly drip ethyl acetate, maintain at 50 °C, stir at 1000 rpm for 5 min, add 1,2-propanediol, and continue stirring for 5 min under the same conditions.

[0231] Pigment dispersion: Add nano-modified carbon black and sulfonated-grafted lignin derivatives, and pre-disperse at 800 rpm for 10 min;

[0232] Transfer the pre-dispersed mixture to a sand mill, and add zirconia beads (particle size 0.3 mm, filling rate 80%);

[0233] Set the temperature at 25 °C, rotate at 1500 rpm, and wet grind for 180 min;

[0234] Endpoint control: The fineness of the slurry ≤ 10 μm (detected by a laser particle size analyzer).

[0235] Functional mixing: Transfer the ground mixture into a stirring kettle with a nitrogen inlet, add polyether-modified silicone oil and microcapsule paraffin, stir at 30 °C and 500 rpm for 20 min, and add silanized TiO2@Ag under the conditions of avoiding light and nitrogen protection, and stir at 300 rpm for 15 min.

[0236] Post-treatment: Add citric acid-starch complex, adjust the pH of the system to 6.7 (monitored in real time by a pH meter), and supplement deionized water to a viscosity of 12.9 FPS (Ford cup method, 25 °C);

[0237] Filter through a 5-μm nylon filter membrane to remove undispersed particles, fill with nitrogen and encapsulate into a light-proof container, and the oxygen content ≤ 0.5% (detected by an oxygen concentration sensor).

[0238] Comparative example:

[0239] Commercially available petroleum-based whiteboard pen ink.

[0240] Perform antibacterial rate detection (Escherichia coli / Staphylococcus aureus), wiping performance detection, low-temperature stability detection, film-forming time detection, VOCs content detection, anti-ultraviolet detection, degradation rate detection, initial contrast, initial color difference, and 12-meter viewing distance recognizability detection on the replenishing liquids of the above Examples 1-6 and the ink in the comparative example. The test standards are as follows:

[0241] Antibacterial rate: ISO 22196 (Escherichia coli / Staphylococcus aureus);

[0242] Wiping performance: ASTM D2486 (dry wipe 3 times or wet wipe 1 time);

[0243] Low-temperature stability: The ΔE value of the wiping residue after freezing at -20 °C for 24 hours;

[0244] Film formation time: The time from coating until there is no flowing gloss on the surface;

[0245] Degradation rate: ISO 17556 (28-day soil burial);

[0246] VOCs: Tested according to the standard of GB / T 23986;

[0247] UV resistance: Color difference ΔE value after 1000 hours of QUV accelerated aging.

[0248] Initial contrast: ISO 2835, measuring the brightness difference between the writing area and the whiteboard background using a color difference meter (X-Rite i1Pro 3);

[0249] Initial color difference: CIE 1976Lab color difference formula, comparing the writing color with standard black, ΔE < 2.0 is excellent;

[0250] Recognizability at a viewing distance of 12 meters: In a standard classroom environment (illumination 500 lux), 5 testers evaluate the clarity of the handwriting at a distance of 12 meters.

[0251] The test results are shown in the following table:

[0252]

[0253] Compared with traditional inks, the advantages of the refill prepared by the present invention are as follows:

[0254] Better environmental performance: The total VOCs content of the refill of the present invention is less than 5 ppm, while the VOCs content of traditional inks is greater than 50 ppm, reducing more than 90% of VOCs, meeting the green chemistry standard; the 28-day degradation rate of the refill of the present invention is about 95%, while the degradation rate of traditional inks is 27.5%, and the degradation efficiency is increased by 260%, meeting the compostability certification (EN 13432).

[0255] Better writing performance: The film formation time of the present invention is 6 - 10 s, while the film formation time of traditional inks is greater than 20 s, and the speed is increased by more than 150%, avoiding writing sagging. The contrast of the present invention is greater than 95%, improving the long-distance visibility and being clear at a viewing distance of 12 meters.

[0256] Wiping performance: The present invention can be completely wiped clean after dry-wiping 1 - 2 times, while after wiping traditional inks 3 times, ΔE = 1.8, and the wiping efficiency is increased by 100% - 200%, reducing the maintenance cost.

[0257] Function expansion: The antibacterial rate of the present invention is above 99%, while the antibacterial rate of traditional inks is only 12.3%, greatly improving the bacteriostatic rate and being able to inhibit the growth of microorganisms for a long time. The UV resistance of the present invention is also significantly improved, which can delay fading and greatly improve the durability of the handwriting.

[0258] Low-temperature stability: The present invention does not crack at -20°C, while the traditional ink film layer cracks (ΔE = 2.5). The present invention can be used in cold regions and extend the life of the whiteboard.

Claims

1. A film-forming replenishing liquid for teaching blackboard writing, characterized in that: Calculated by mass percentage, it includes: 40%-55% bio-fermentation ethanol, 1%-5% ethyl acetate, 1%-4% 1,2-propylene glycol, 30%-45% PVB-PLA composite resin, 1%-5% water-based polyurethane, 5%-12% nano-modified special carbon black, 0.3%-1.0% sulfonated-grafted lignin derivatives, 0.2%-1.0% polyether modified silicone oil, 0.1%-0.8% microencapsulated paraffin, 0.15%-0.3% silanized TiO2@Ag nanomaterials, 0.1%-0.5% citric acid-starch complex and the balance deionized water.

2. The film-forming replenishing liquid for teaching blackboard writing according to claim 1, characterized in that: The molar ratio of PVB to PLA in the PVB-PLA composite resin is (2:1)-(5:1); The molecular weight of the waterborne polyurethane is 30000Da-100000Da.

3. The film-forming replenishing liquid for teaching blackboard writing according to claim 1, characterized in that: The nano-scale modified special carbon black is a special carbon black particle with silicon dioxide particles coated on the surface, with a particle size of 30-100 nm and a silicon dioxide coating layer thickness of 2-10 nm.

4. The film-forming replenishing liquid for teaching blackboard writing according to claim 3, characterized in that: The pH buffer range of the citric acid-starch complex is 6.0-7.

5.

5. The film-forming replenishing liquid for teaching blackboard writing according to claim 1, characterized in that: The particle size of the microencapsulated paraffin is 0.5-10 μm, and the coverage rate is 80%-95%; The surface tension of the polyether-modified silicone oil is 20-30 mN / m.

6. The film-forming replenishing liquid for teaching blackboard writing according to claim 1, characterized in that: The silver loading amount in the silanized TiO2@Ag nanomaterial is 3%-10wt%.

7. The film-forming replenishing liquid for teaching blackboard writing according to claim 1, characterized in that: The substitution degree of the sulfonated-grafted lignin derivative is 0.5-1.5, and the sulfonation rate is 50%-90%.

8. A method for preparing the film-forming replenishing liquid for teaching blackboard writing according to any one of claims 1 to 7, characterized in that: The following steps are involved: Dissolve the PVB-PLA composite resin and waterborne polyurethane in biofermentation ethanol at 50-65°C under inert gas protection, and stir until completely dissolved; Add ethyl acetate and 1,2-propylene glycol in sequence and stir to mix; Add nano-scale modified special carbon black and sulfonated-grafted lignin derivatives, stir and disperse, and sand grind to a slurry fineness of ≤10μm; Add polyether-modified silicone oil, microcapsule paraffin and silanized TiO2@Ag in stages and mix them under light-proof and inert gas protection; Add citric acid-starch complex to adjust the pH to 6.0-7.5, add deionized water to a viscosity of 12.5-13.2 FPS, and filter and package.

9. The method for preparing the film-forming replenishing liquid for teaching blackboard writing according to claim 8, characterized in that: The step of adding polyether-modified silicone oil, microcapsule paraffin and silanized TiO2@Ag in stages and mixing in the dark comprises: Add polyether-modified silicone oil and microcapsule paraffin, and stir at 20-40°C and 500 rpm for 20 min; Silylated TiO2@Ag was added under light-protected conditions and stirred at 300 rpm for 15 min.

10. The method for preparing the film-forming replenishing liquid for teaching blackboard writing according to claim 8, characterized in that: The sand milling medium is zirconium oxide beads or aluminum oxide beads, with a particle size of 0.1-0.5 mm and a filling rate of 60%-85%.

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