Environment-friendly sand paper and preparation method thereof

Abstract

The present application relates to the technical field of coated abrasive manufacturing, and particularly relates to an environment-friendly sandpaper and a preparation method thereof, which comprises a water-resistant base paper substrate, a primer layer, an abrasive layer and a top size layer which are sequentially stacked from bottom to top; the primer layer is made by coating an environment-friendly water-based primer, and the environment-friendly water-based primer comprises a lignin-modified water-based PUA emulsion, a biomass silane coupling agent and an environment-friendly multifunctional crosslinking agent. During the curing process of the environment-friendly water-based primer, one end of the biomass silane coupling agent is coupled with the hydroxyl groups on the surface of the water-resistant base paper substrate, and the other end is subjected to free radical and covalent crosslinking reaction with the acrylate and polyurethane segments in the emulsion, so as to improve the bonding strength between the primer layer and the water-resistant base paper substrate; meanwhile, the environment-friendly multifunctional crosslinking agent establishes a network interpenetrating structure inside the primer layer, effectively inhibits the penetration and swelling of water molecules on the primer layer, so that the sandpaper exhibits excellent chemical sand-fixing force and wet grinding swelling resistance under wet grinding conditions.

Description

Technical Field

[0001] This invention relates to the field of coated abrasive manufacturing technology, specifically to an environmentally friendly sandpaper and its preparation method. Background Technology

[0002] Traditional coated abrasives, such as ordinary sandpaper, typically use high-grammage insulating paper as the base material and extensively employ phenol-formaldehyde resin (phenolic resin) or epoxy resin as the primer and top coat. During the production, baking, and curing process, phenolic resin releases large amounts of free formaldehyde, phenol, and other toxic and harmful gases. Furthermore, organic solvents such as toluene and xylene are usually added to adjust the coating viscosity, causing serious air pollution and occupational health hazards. In addition, after traditional sandpaper is discarded, its highly cross-linked resin layer cannot be naturally degraded, often requiring landfill or incineration for disposal, which is highly inconsistent with current carbon neutrality and green environmental protection development strategies.

[0003] To eliminate harmful volatile organic compounds at the source, some manufacturers in the industry are currently trying to replace traditional phenolic resins with ordinary water-based acrylic emulsions or water-based polyurethanes. However, after the hydrophilic groups of these conventional water-based resins are dehydrated, their molecular chains still contain a large number of hydrophilic sites. This causes water molecules to easily penetrate the adhesive layer when sandpaper is used for both dry and wet sanding (especially in wet sanding scenarios such as automotive paint and fine hardware), leading to swelling and softening of the adhesive layer. This results in large-scale abrasive shedding (commonly known as "abrasive shedding"). The base paper also loses strength due to water absorption, resulting in paper tears and breakage, completely failing to meet the requirements of heavy-duty, high-intensity industrial sanding. Therefore, there is an urgent need to develop an environmentally friendly sandpaper and its preparation method that possesses both green, low-carbon, and environmentally friendly characteristics throughout the entire process, as well as high strength and high water resistance comparable to traditional phenolic sandpaper, in order to overcome the above-mentioned technical bottlenecks. Summary of the Invention

[0004] The purpose of this invention is to provide an environmentally friendly sandpaper and its preparation method, which can at least solve some of the defects in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is an environmentally friendly sandpaper, comprising a water-resistant base paper substrate, a base adhesive layer, an abrasive layer, and a top adhesive layer stacked sequentially from bottom to top; the base adhesive layer is made by coating with an environmentally friendly water-based base adhesive, which includes a lignin-modified water-based PUA emulsion, a biomass silane coupling agent, and an environmentally friendly multifunctional crosslinking agent. The amount of the biomass silane coupling agent is 1.5% to 3.5% of the total mass of the lignin-modified water-based PUA emulsion, and the amount of the environmentally friendly multifunctional crosslinking agent is 2% to 5% of the total mass of the lignin-modified water-based PUA emulsion.

[0006] As one embodiment, the lignin-modified waterborne PUA emulsion is prepared by epoxidizing alkali lignin, grafting it with polyurethane prepolymer, and then polymerizing it with acrylate monomers after reverse emulsification.

[0007] As one embodiment, the specific preparation method of the lignin-modified aqueous PUA emulsion includes the following steps:

[0008] A. Dissolve 8-12 parts of alkali lignin and add 2-4 parts of epichlorohydrin. React at 70℃-80℃ for 3-5 hours to obtain modified lignin.

[0009] B. Mix 30-40 parts of isophorone diisocyanate, 45-55 parts of polycarbonate diol and 4-6 parts of dimethylolpropionic acid, add a diluent, and react at 75℃-85℃ for 2.5-4 hours under the action of a catalyst to obtain a polyurethane prepolymer; then cool to 45℃-55℃, add 2-4 parts of the above-mentioned modified lignin and 4-6 parts of the end-capping agent, and continue to react for 1.5-3 hours to obtain a lignin-modified polyurethane prepolymer;

[0010] C. After neutralizing the lignin-modified polyurethane prepolymer, reverse emulsification is carried out in deionized water to obtain an aqueous polyurethane emulsion; then 15-25 parts of methyl methacrylate and 10-20 parts of butyl acrylate are added to the aqueous polyurethane emulsion, and a polymerization reaction is carried out at 75℃-85℃ for 3-5 hours using ammonium persulfate as an initiator to obtain the lignin-modified aqueous PUA emulsion.

[0011] As one embodiment, the biomass silane coupling agent is citric acid esterified modified γ-aminopropyltriethoxysilane, which is prepared by partial ethyl esterification of citric acid monohydrate and then reacting it with γ-aminopropyltriethoxysilane via an amidation reaction.

[0012] As one embodiment, the environmentally friendly multifunctional crosslinking agent is one or a mixture of two of polyaziridine and water-dispersible polyisocyanate; the adhesive layer is made by coating with an environmentally friendly water-based adhesive, which is a self-crosslinking water-based acrylic emulsion.

[0013] As one embodiment, the water-resistant base paper substrate includes base paper and a biomass-based waterproof barrier layer disposed on the front and back of the base paper, and the base adhesive layer is disposed on the biomass-based waterproof barrier layer on the front side.

[0014] As one embodiment, the biomass-based waterproof barrier layer is made by coating with a biomass-based waterproof barrier liquid. The biomass-based waterproof barrier liquid is prepared by mixing a chitosan acetate solution with a mass fraction of 2% to 5% and a nanocellulose crystal aqueous suspension with a mass fraction of 1% to 3% at a volume ratio of 2:1 to 4:1. The base paper is made by blending bamboo fiber pulp and hardwood pulp at a mass ratio of 3:1 to 1:1.

[0015] The present invention also provides a method for preparing the environmentally friendly sandpaper described in any one of the above claims, comprising the following steps:

[0016] S1. Preparation of water-resistant base paper substrate;

[0017] S2. Apply an environmentally friendly water-based primer to the front side of the water-resistant base paper substrate to form a primer layer;

[0018] S3. Abrasives are implanted into the base adhesive layer to form an abrasive layer;

[0019] S4. Perform initial curing on the substrate after sand application;

[0020] S5. Spray a coating adhesive onto the surface of the initially cured abrasive layer to form a coating adhesive layer;

[0021] S6. The substrate after coating and adhesive is cured, and then post-processed to obtain the environmentally friendly sandpaper.

[0022] As one of the implementation methods, in step S1, the method for preparing the water-resistant base paper substrate is as follows: providing base paper, coating the front and back sides with biomass-based waterproof barrier liquid respectively, and drying the paper to obtain the water-resistant base paper substrate.

[0023] As one implementation method, in step S4, the initial curing conditions are: treatment at a temperature of 55℃~65℃ for 15~25 minutes; in step S6, the main curing adopts a stepped curing process, specifically: the first stage temperature is 60℃~65℃, and the holding time is 25~40 minutes; the second stage temperature is increased to 75℃~80℃, and the holding time is 35~50 minutes; the third stage temperature is increased to 90℃~95℃, and the holding time is 50~70 minutes.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The environmentally friendly water-based primer of the present invention uses lignin-modified water-based PUA emulsion and adds biomass silane coupling agent and environmentally friendly multifunctional crosslinking agent. During the curing process, one end of the biomass silane coupling agent undergoes a coupling reaction with the hydroxyl groups on the surface of the water-resistant base paper substrate, and the other end undergoes a free radical and covalent crosslinking reaction with the acrylate and polyurethane segments in the emulsion, thereby improving the bonding strength between the primer layer and the water-resistant base paper substrate. At the same time, the environmentally friendly multifunctional crosslinking agent establishes a network interpenetrating structure inside the adhesive layer, effectively inhibiting the penetration and swelling of water molecules into the adhesive layer, so that the sandpaper exhibits excellent chemical sand-fixing force and wet-grind swelling resistance under wet grinding conditions.

[0026] (2) The present invention uses chitosan and nanocellulose crystals to form a dense three-dimensional network waterproof barrier on the surface of the base paper. It can form a dense waterproof barrier on both sides of the base paper, thereby effectively blocking the penetration of external moisture and moisture in the base layer, avoiding the decrease in strength of the base paper due to water absorption under wet grinding conditions, so that the water-resistant base paper substrate has excellent wet tensile strength while maintaining degradability.

[0027] (3) The environmentally friendly water-based base adhesive and the environmentally friendly water-based composite adhesive used in this invention both use water as the dispersion medium and do not add any organic solvents. This can achieve ultra-low VOC release, and the water-resistant base paper substrate is completely degradable. It also has excellent wet abrasion water resistance performance, thus achieving green, low-carbon and environmentally friendly whole process. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This embodiment provides an environmentally friendly sandpaper, comprising, from bottom to top, a water-resistant base paper substrate, a base adhesive layer, an abrasive layer, and a top adhesive layer; the base adhesive layer is made by coating with an environmentally friendly water-based base adhesive, which includes a lignin-modified water-based PUA (polyurethane-acrylate) emulsion, a biomass silane coupling agent, and an environmentally friendly multifunctional crosslinking agent. The amount of the biomass silane coupling agent is 1.5% to 3.5% of the total mass of the lignin-modified water-based PUA emulsion, and the amount of the environmentally friendly multifunctional crosslinking agent is 2% to 5% of the total mass of the lignin-modified water-based PUA emulsion. This embodiment of the environmentally friendly water-based primer uses a lignin-modified water-based PUA emulsion, with the addition of a biomass silane coupling agent and an environmentally friendly multifunctional crosslinking agent. During the curing process, one end of the biomass silane coupling agent undergoes a coupling reaction with the hydroxyl groups on the surface of the water-resistant base paper substrate, while the other end undergoes free radical and covalent crosslinking reactions with the acrylate and polyurethane segments in the emulsion, thereby improving the bonding strength between the primer layer and the water-resistant base paper substrate. At the same time, the environmentally friendly multifunctional crosslinking agent establishes a network interpenetrating structure inside the primer layer, effectively inhibiting the penetration and swelling of water molecules into the primer layer. This results in the sandpaper exhibiting excellent chemical sand-fixing power and resistance to wet abrasion swelling under wet abrasion conditions. Furthermore, the environmentally friendly water-based primer uses water as the dispersion medium and does not contain any organic solvents, which can greatly reduce air pollution.

[0030] Furthermore, the lignin-modified waterborne PUA emulsion is prepared by epoxidizing alkali lignin, grafting it with a polyurethane prepolymer, and then polymerizing it with acrylate monomers after phase inversion emulsification. By first epoxidizing alkali lignin to enable it to react with the polyurethane prepolymer, and simultaneously introducing acrylate monomers, the hydrophobicity and crosslinking density of the primer layer can be improved.

[0031] Furthermore, the preparation method of the lignin-modified aqueous PUA emulsion specifically includes the following steps:

[0032] A. Dissolve 8-12 parts of alkali lignin and add 2-4 parts of epichlorohydrin. React at 70℃-80℃ for 3-5 hours to obtain modified lignin.

[0033] B. Mix 30-40 parts of isophorone diisocyanate, 45-55 parts of polycarbonate diol and 4-6 parts of dimethylolpropionic acid, add a diluent, and react at 75℃-85℃ for 2.5-4 hours under the action of a catalyst to obtain a polyurethane prepolymer; then cool to 45℃-55℃, add 2-4 parts of the above-mentioned modified lignin and 4-6 parts of the end-capping agent, and continue to react for 1.5-3 hours to obtain a lignin-modified polyurethane prepolymer;

[0034] C. After neutralizing the lignin-modified polyurethane prepolymer, reverse emulsification is carried out in deionized water to obtain an aqueous polyurethane emulsion; then 15-25 parts of methyl methacrylate and 10-20 parts of butyl acrylate are added to the aqueous polyurethane emulsion, and a polymerization reaction is carried out at 75℃-85℃ for 3-5 hours using ammonium persulfate as an initiator to obtain the lignin-modified aqueous PUA emulsion.

[0035] In step A, the method for dissolving alkali lignin is as follows: alkali lignin is added to NaOH solution and stirred at 60°C for 2 hours to dissolve; after alkali lignin reacts with epichlorohydrin, the pH is adjusted to neutral with dilute hydrochloric acid, and modified lignin is obtained after dialysis and freeze-drying.

[0036] In step B, the diluent can be an appropriate amount of acetone, the catalyst can be dibutyl stannate, and the capping agent can be hydroxyethyl acrylate.

[0037] In step C, after neutralizing the lignin-modified polyurethane prepolymer, reverse emulsification is performed in deionized water. Specifically, triethylamine is added to the lignin-modified polyurethane prepolymer to neutralize the carboxyl groups, and then deionized water is slowly added under high-speed stirring to perform reverse emulsification. After the aqueous polyurethane emulsion reacts with methyl methacrylate and butyl acrylate, acetone is removed by vacuum distillation to obtain the lignin-modified aqueous PUA emulsion.

[0038] Furthermore, the biomass silane coupling agent is citric acid esterified modified γ-aminopropyltriethoxysilane, which is prepared by partially esterifying citric acid monohydrate and then reacting it with γ-aminopropyltriethoxysilane via an amidation reaction. By first partially esterifying citric acid monohydrate and then subjecting it to an amidation reaction with γ-aminopropyltriethoxysilane, the functional groups of the silane coupling agent are retained while allowing it to react with polyurethane-acrylate.

[0039] Furthermore, the preparation method of the citrate-modified γ-aminopropyltriethoxysilane specifically includes the following steps:

[0040] a. Dissolve 0.08–0.12 mol of citric acid monohydrate in 80–120 mL of anhydrous ethanol, add a catalyst, and reflux and stir at 75–85 °C for 2–4 hours to partially ethyl esterify some of the carboxyl groups of citric acid, and remove ethanol and water generated in the reaction.

[0041] b. Redissolve the obtained product in 120-180 mL of organic solvent, slowly add 0.08-0.12 mol of γ-aminopropyltriethoxysilane, reflux at 105℃-115℃ for 4-6 hours, and remove the by-products generated in the reaction.

[0042] c. After the reaction is complete, the organic solvent is completely removed, and the resulting high-viscosity transparent liquid is citrate-modified γ-aminopropyltriethoxysilane.

[0043] In step a, p-toluenesulfonic acid is used as the catalyst, and ethanol and water generated in the reaction are removed by vacuum distillation after the reaction is completed; in step b, anhydrous toluene is used as the organic solvent, and byproducts generated in the reaction are continuously removed by a water separator after the reaction is completed; in step c, the organic solvent is completely removed by vacuum distillation after the reaction is completed.

[0044] Furthermore, the environmentally friendly multifunctional crosslinking agent is one or a mixture of two of polyaziridine and water-dispersible polyisocyanate (WDI).

[0045] In some embodiments, the adhesive layer is formed by coating with an environmentally friendly water-based adhesive, which is a self-crosslinking water-based acrylic emulsion. The adhesive layer uses a self-crosslinking water-based acrylic emulsion, which can undergo intermolecular crosslinking reactions during curing to form a three-dimensional network structure, exhibiting high strength and water resistance.

[0046] In some embodiments, the water-resistant base paper substrate includes base paper and biomass-based waterproof barrier layers disposed on the front and back surfaces of the base paper, with the primer layer disposed on the biomass-based waterproof barrier layer on the front surface. This embodiment, by providing biomass-based waterproof barrier layers on the front and back surfaces of the base paper, can form a dense waterproof barrier on both sides of the base paper, thereby effectively blocking the penetration of external moisture and moisture in the primer layer. This prevents the base paper from losing strength due to water absorption under wet abrasion conditions, allowing the water-resistant base paper substrate to maintain degradability while possessing excellent wet tensile strength. Preferably, the base paper is a fully degradable biomass base paper with a basis weight of 120–220 g / m².

[0047] Furthermore, the biomass-based waterproof barrier layer is formed by coating with a biomass-based waterproof barrier liquid. This liquid is prepared by mixing a 2%–5% (w / w) chitosan acetate solution with a 1%–3% (w / w) nanocellulose crystal (NCC) aqueous suspension at a volume ratio of 2:1–4:1. The base paper is made by blending bamboo fiber pulp and hardwood pulp at a mass ratio of 3:1–1:1. The chitosan and nanocellulose crystals in the biomass-based waterproof barrier liquid work synergistically to form a dense three-dimensional network waterproof barrier on the surface of the base paper, preventing water molecule penetration. The base paper is made by blending bamboo fiber pulp (with longer fiber length) and hardwood pulp (with shorter fiber length) at a specific mass ratio, which can reduce the internal porosity of the base paper and improve its surface smoothness while ensuring its tensile strength. Moreover, the chitosan acetate, nanocellulose, bamboo fiber pulp, and hardwood pulp are completely degradable after disposal, thus ensuring the sandpaper's environmental friendliness.

[0048] The present invention also provides a method for preparing the environmentally friendly sandpaper described in any one of the above claims, comprising the following steps:

[0049] S1. Preparation of water-resistant base paper substrate;

[0050] S2. Apply an environmentally friendly water-based primer to the front side of the water-resistant base paper substrate to form a primer layer;

[0051] S3. Abrasives are implanted into the base adhesive layer to form an abrasive layer;

[0052] S4. Perform initial curing on the substrate after sand planting, so that the base adhesive layer is in a semi-cured state to fix the root of the abrasive.

[0053] S5. Spray a coating onto the surface of the abrasive layer after initial curing to form a coating layer, which then wraps the waist and root of the abrasive a second time.

[0054] S6. The substrate after coating and adhesive is subjected to primary curing to completely dehydrate and initiate a cross-linking reaction; after post-treatment, the environmentally friendly sandpaper is obtained.

[0055] Furthermore, in step S1, the method for preparing the water-resistant base paper substrate is as follows: providing base paper, coating its front and back sides with biomass-based waterproof barrier liquid respectively, and drying it to obtain the water-resistant base paper substrate.

[0056] Furthermore, in step S2, the solid content of the environmentally friendly water-based primer is 40%–55%, and the coating amount is 40–90 g / m².

[0057] Furthermore, in step S3, the abrasive is one of calcined corundum, white corundum, silicon carbide, or mixed ceramic abrasive, and the particle size of the abrasive is P120 to P2000 mesh. Specifically, an electrostatic sand-planting process is used to implant the abrasive into the base adhesive layer. The electrostatic sand-planting process uses an electrostatic sand-planting device to vertically implant the abrasive into the uncured base adhesive layer. The process parameters are: high voltage electrostatic field voltage of 25 to 50 kV, electrode spacing of 80 to 150 mm, and relative humidity of the sand-planting environment maintained at 50% to 60%.

[0058] Furthermore, the solid content of the self-crosslinking waterborne acrylic emulsion is 35% to 45%, and the spray coating amount is 30 to 70 g / m².

[0059] As one implementation method, in step S4, the initial curing conditions are: treatment at a temperature of 55℃~65℃ for 15~25 minutes; in step S6, the main curing adopts a stepped curing process, specifically: the first stage temperature is 60℃~65℃, and the holding time is 30 minutes; the second stage temperature is increased to 75℃~80℃, and the holding time is 40 minutes; the third stage temperature is increased to 90℃~95℃, and the holding time is 60 minutes.

[0060] Furthermore, in step S6, the post-processing includes sequential cooling, winding, constant temperature and moisture-proof curing, and slitting. The constant temperature and moisture-proof curing conditions are: placing the product in a sealed curing chamber at a temperature of 40℃±2℃ and a relative humidity of less than 30% for 48 to 72 hours to allow the cross-linked network to reach a thermodynamically stable state.

[0061] The sandpaper in this embodiment has a total VOC (volatile organic compound) release of less than 10 mg / m³, a tensile strength retention rate of more than 85% after being soaked in water at 25°C for 24 hours, and a biodegradation rate or high fragmentation rate of more than 75% within 180 days after being buried in the soil and subjected to the action of micro-ecology.

[0062] The performance of the environmentally friendly sandpaper of the present invention will be further illustrated below with reference to specific embodiments and comparative examples.

[0063] Example 1

[0064] This embodiment provides an environmentally friendly sandpaper, the preparation method of which includes the following steps:

[0065] S1. Preparation of water-resistant base paper substrate: 75 wt% bamboo fiber pulp and 25 wt% hardwood pulp are blended to make a base paper of 150 g / m². Then, a biomass-based waterproof barrier liquid prepared by mixing 3 wt% chitosan acetate solution and 1.5 wt% NCC suspension at a volume ratio of 3:1 is uniformly coated on both sides of the base paper. The coating amount is 8 g / m² on one side. After drying, it is ready for use.

[0066] S2. Applying the primer: An environmentally friendly water-based primer is roller-coated onto the front side of the water-resistant base paper substrate to form a primer layer. The environmentally friendly water-based primer includes a lignin-modified water-based PUA emulsion with a solid content of 45%, a citric acid ester-modified γ-aminopropyltriethoxysilane, and a polyazidopropylidin crosslinking agent. The amount of citric acid ester-modified γ-aminopropyltriethoxysilane is 2.0% of the total mass of the lignin-modified water-based PUA emulsion, and the amount of polyazidopropylidin crosslinking agent (model: SaC-100, purchased from Shanghai Zeheng Chemical Co., Ltd.) is 3.0% of the total mass of the lignin-modified water-based PUA emulsion. The coating amount of the environmentally friendly water-based primer is 55 g / m².

[0067] S3. Electrostatic sand planting: Under the conditions of high voltage electric field voltage of 35 kV, electrode spacing of 100 mm and relative humidity of 55%, P400 mesh silicon carbide abrasive is electrostatically and directionally implanted into the base adhesive layer to form an abrasive layer.

[0068] S4. Initial curing: Enter the No. 1 drying tunnel and bake at a low temperature of 60℃ for 20 minutes to make the base adhesive layer semi-cured and fix the root of the abrasive.

[0069] S5. Coating and backing: Spray a self-crosslinking waterborne acrylic emulsion (model: WL-91, purchased from Guangzhou Badefu Industrial Co., Ltd.) with a solid content of 40% onto the surface of the abrasive layer after initial curing to form a backing layer; the coating amount of the self-crosslinking waterborne acrylic emulsion is 45 g / m².

[0070] S6. Main curing: Step curing is carried out in the No. 2 drying tunnel. First, it is kept at 62℃ for 30 minutes, then at 78℃ for 40 minutes, and finally at 95℃ for 60 minutes. After cooling and winding, it is placed in a closed curing room at a temperature of 40℃±2℃ and a relative humidity of less than 30% for 48 hours for constant temperature and moisture-proof curing. After that, it is slit to obtain P400 mesh environmentally friendly water-resistant sandpaper.

[0071] The preparation method of lignin-modified waterborne PUA emulsion with a solid content of 45% includes the following steps:

[0072] A. Weigh 10 parts of alkali lignin (available from Shandong Longli Biotechnology Co., Ltd.) and add it to 90 parts of a 5% NaOH solution. Stir and dissolve at 60°C for 2 hours. Then add 3 parts of epichlorohydrin and react at 75°C for 4 hours. Adjust the pH to neutral with dilute hydrochloric acid. After dialysis and freeze-drying, obtain activated lignin.

[0073] B. Mix 35 parts of isophorone diisocyanate (IPDI), 50 parts of polycarbonate diol (PCDL, molecular weight 2000), and 5 parts of dimethylolpropionic acid (DMPA), add an appropriate amount of acetone as a diluent, and react at 80°C for 3 hours under the catalysis of dibutylstannate. Then cool to 50°C, add 3 parts of the above-mentioned activated lignin and 5 parts of hydroxyethyl acrylate (HEA), and continue the reaction for 2 hours to obtain lignin-modified polyurethane prepolymer;

[0074] C. Triethylamine is added to neutralize the carboxyl groups in the prepolymer, followed by slow addition of deionized water under high-speed stirring for reverse emulsification to obtain an aqueous polyurethane emulsion. Finally, 20 parts of methyl methacrylate (MMA) and 15 parts of butyl acrylate (BA) are added to the emulsion, and emulsion polymerization is carried out at 80°C for 4 hours using ammonium persulfate as an initiator. Acetone is removed by vacuum distillation to obtain a lignin-modified aqueous PUA emulsion with a solid content of 45%.

[0075] The preparation method of citric acid esterified modified γ-aminopropyltriethoxysilane specifically includes the following steps:

[0076] a. Dissolve 21.0 g (0.1 mol) of citric acid monohydrate in 100 mL of anhydrous ethanol, add 0.5 g of p-toluenesulfonic acid as a catalyst, reflux and stir at 80 °C for 3 hours to partially ethyl esterify some of the carboxyl groups of citric acid, and then remove ethanol and water generated in the reaction by vacuum distillation.

[0077] b. Dissolve the obtained product in 150 mL of anhydrous toluene, and slowly add 22.1 g (0.1 mol) of γ-aminopropyltriethoxysilane (KH-550, available from Nanjing Shuguang Chemical Group). Reflux the reaction at 110 °C for 5 hours, and continuously remove the byproducts generated by the reaction using a water separator.

[0078] c. After the reaction is complete, the toluene solvent is completely removed by vacuum distillation. The resulting high-viscosity transparent liquid is the citric acid esterified modified γ-aminopropyltriethoxysilane.

[0079] Example 2

[0080] The remaining steps and materials of the preparation method of the environmentally friendly sandpaper provided in this embodiment are the same as those in Embodiment 1, except that: in step S1, 180 g / m² base paper is prepared by blending 60 wt% bamboo fiber pulp and 40 wt% hardwood pulp; in step S2, the polyazidopropylidyl crosslinking agent is replaced with water-dispersible polyisocyanate (WDI, model: Bayhydur 302, purchased from Covestro), and the amount used is 4.0% of the total mass of the lignin-modified waterborne PUA emulsion, and the coating amount of the environmentally friendly waterborne primer is 70 g / m²; in step S3, the P400 mesh silicon carbide abrasive is replaced with P240 mesh brown corundum abrasive, and the high voltage electric field voltage is adjusted to 40 kV.

[0081] Example 3

[0082] The remaining steps and materials of the preparation method of the environmentally friendly sandpaper provided in this embodiment are the same as those in Embodiment 1, except that: in step S2, the amount of citric acid esterified modified γ-aminopropyltriethoxysilane is 3.5% of the total mass of lignin-modified waterborne PUA emulsion, and polyaziridine is replaced by a 1:1 mixture of polyaziridine and water-dispersible polyisocyanate, and the amount is 4.5% of the total mass of lignin-modified waterborne PUA emulsion; in step S3, P400 mesh silicon carbide abrasive is replaced by P800 mesh white corundum abrasive, and the high voltage field voltage is adjusted to 30kV; in step S5, the coating amount of the self-crosslinking waterborne acrylic emulsion is 35 g / m².

[0083] Example 4

[0084] The remaining steps and materials of the preparation method of the environmentally friendly sandpaper provided in this embodiment are the same as those in Embodiment 1, except that: the amount of biomass-based waterproof barrier liquid coating on one side of the base paper in step S1 is increased to 15 g / m²; in step S3, the P400 mesh silicon carbide abrasive is replaced with P1200 mesh fine ceramic abrasive, and the high voltage electric field voltage is adjusted to 28kV; in step S6, the stepped curing is adjusted to first be kept at 62℃ for 30 minutes, then kept at 78℃ for 40 minutes, and finally kept at 95℃ for 80 minutes.

[0085] Comparative Example 1

[0086] The remaining steps and materials of the sandpaper preparation method are the same as in Example 1, except that: in step S2, the environmentally friendly water-based primer only includes lignin-modified water-based PUA emulsion with a solid content of 45%, and does not add citric acid esterified modified γ-aminopropyltriethoxysilane and polyaziridine.

[0087] Comparative Example 2

[0088] The remaining steps and materials of the sandpaper preparation method are the same as in Example 1, except that in step S2, the environmentally friendly water-based primer is replaced with the same self-crosslinking water-based acrylic emulsion (without coupling agent and polyaziridine) as the top coat, and the coating amount is kept at 55 g / m².

[0089] Comparative Example 3

[0090] The remaining steps and materials of the sandpaper preparation method are the same as in Example 1, except that in step S1, 75 wt% bamboo fiber pulp and 25 wt% hardwood pulp are blended to make a base paper of 150 g / m² and then dried directly for later use, without coating the front and back sides with biomass-based waterproof barrier liquid.

[0091] Comparative Example 4

[0092] The remaining steps and materials of the sandpaper preparation method are the same as in Example 1, except that: in step S2, the environmentally friendly water-based primer is replaced with conventional industrial solvent-based phenolic resin (containing 15% xylene diluent by mass), and the coating amount is 55 g / m²; in step S4, the initial curing is carried out by conventional high-temperature baking (110°C, 30 minutes); in step S5, the self-crosslinking water-based acrylic emulsion is replaced with conventional industrial solvent-based phenolic resin; in step S6, the main curing is carried out by industrial standard high-temperature curing process (first held at 90°C for 1 hour, then heated to 145°C for 4 hours).

[0093] The sandpaper prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to rigorous quantitative testing. The testing standards are as follows:

[0094] Total VOC emissions: The amount of harmful gases emitted per unit area at the end of the baking production line and the finished product was tested using gas chromatography-mass spectrometry (GC-MS) in accordance with GB / T 35462 standard.

[0095] Wet tensile strength retention rate: The sandpaper sample was completely immersed in distilled water at 25°C for 24 hours. Immediately after removal, its longitudinal tensile strength was measured and the percentage of its wet tensile strength to that of the dry tensile strength was calculated.

[0096] Wet abrasive loss rate: The sandpaper sample is mounted on a wet reciprocating friction tester, a vertical load of 1.5 kg is applied, and water is sprayed onto the surface of a standard marble slab and reciprocated for 500 cycles. After drying, the percentage of abrasive mass lost is measured.

[0097] Soil biodegradation rate: Sandpaper was cut into pieces and buried in natural active soil (15 cm deep). The samples were kept at room temperature and regularly moistened for 180 days, and the total mass loss rate of the samples was measured.

[0098] The test results are shown in Table 1:

[0099] Table 1. Test results of total VOC release, wet tensile strength retention rate, wet grinding sand removal rate, and soil biodegradation rate.

[0100]

[0101] As can be seen from the quantitative performance indicators in Table 1, the environmentally friendly sandpaper prepared in Examples 1-4 of this invention has extremely low VOC emissions (all below 2.5 mg / m³), which is far superior to traditional phenolic resin (145.8 mg / m³ in Comparative Example 4), completely eliminating the risk of air toxicity during factory production and user use. At the end of its entire life cycle, the sandpaper of this invention can achieve a degradation rate of 76.5% to 84.2% in soil after 180 days, while the highly cross-linked resin curing material of traditional phenolic sandpaper (Comparative Example 4) is almost impossible to biodegrade (only 4.2%).

[0102] In terms of sanding performance, Comparative Example 1, lacking the chemical bonding of biomass silane coupling agents and the chemical locking of environmentally friendly multifunctional crosslinking agents, experienced severe hydrolysis and softening of the primer after water molecule intrusion, resulting in a wet sanding loss rate as high as 34.5%, and the sandpaper quickly became ineffective. Comparative Example 2 used a conventional self-crosslinking acrylic emulsion as the primer, but due to its insufficient interlayer adhesion to the base paper and silicon carbide abrasive and insufficient water-resistant crosslinking density, the wet sanding loss rate was still as high as 24.8%, which could not meet the needs of industrial sanding. However, Examples 1-4 of this invention, through the synergistic effect of additives, controlled the wet sanding loss rate to within 1.3%, which has reached or even surpassed the sanding fixation level of traditional high-pollution phenolic resin (Comparative Example 4).

[0103] Regarding the strength of the substrate, Comparative Example 3, which lacked a biomass-based waterproof barrier layer, allowed moisture to rapidly penetrate the fiber paper base, resulting in a sharp drop in wet strength retention to 45.6% after 24 hours of immersion. This made the paper extremely prone to tearing during actual sanding. In contrast, the wet strength retention of the base paper in this embodiment of the invention reached over 87.5%, fully demonstrating the superior effectiveness of the chitosan / nanocellulose water barrier.

[0104] In summary, this invention achieves the green and environmentally friendly goals of low energy consumption, ultra-low VOC, and full degradation throughout the entire process while ensuring excellent industrial grinding life and wet abrasion resistance. It overcomes the core technical contradictions that have long plagued the abrasive industry. Moreover, the technical solution is reasonably designed and the process is highly reproducible, possessing broad market promotion potential and profound technological leadership.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An environmentally friendly sandpaper, characterized in that: The material comprises, from bottom to top, a water-resistant base paper substrate, a base adhesive layer, an abrasive layer, and a top adhesive layer. The base adhesive layer is made by coating with an environmentally friendly water-based base adhesive, which includes a lignin-modified water-based PUA emulsion, a biomass silane coupling agent, and an environmentally friendly multifunctional crosslinking agent. The amount of the biomass silane coupling agent is 1.5% to 3.5% of the total mass of the lignin-modified water-based PUA emulsion, and the amount of the environmentally friendly multifunctional crosslinking agent is 2% to 5% of the total mass of the lignin-modified water-based PUA emulsion.

2. The environment-friendly abrasive paper according to claim 1, wherein: The lignin-modified waterborne PUA emulsion is prepared by epoxidation modification of alkali lignin, grafting reaction with polyurethane prepolymer, and then polymerizing with acrylate monomers after reverse emulsification.

3. The environment-friendly abrasive paper according to claim 2, wherein: The specific preparation method of the lignin-modified aqueous PUA emulsion includes the following steps: A. Dissolve 8-12 parts of alkali lignin and add 2-4 parts of epichlorohydrin. React at 70℃-80℃ for 3-5 hours to obtain modified lignin. B. Mix 30-40 parts of isophorone diisocyanate, 45-55 parts of polycarbonate diol and 4-6 parts of dimethylolpropionic acid, add a diluent, and react at 75℃-85℃ for 2.5-4 hours under the action of a catalyst to obtain a polyurethane prepolymer; then cool to 45℃-55℃, add 2-4 parts of the above-mentioned modified lignin and 4-6 parts of the end-capping agent, and continue to react for 1.5-3 hours to obtain a lignin-modified polyurethane prepolymer; C. After neutralizing the lignin-modified polyurethane prepolymer, reverse emulsification is carried out in deionized water to obtain an aqueous polyurethane emulsion; then 15-25 parts of methyl methacrylate and 10-20 parts of butyl acrylate are added to the aqueous polyurethane emulsion, and a polymerization reaction is carried out at 75℃-85℃ for 3-5 hours using ammonium persulfate as an initiator to obtain the lignin-modified aqueous PUA emulsion.

4. The environment-friendly abrasive paper according to claim 1, wherein: The biomass silane coupling agent is citric acid esterified modified γ-aminopropyltriethoxysilane, which is prepared by partial ethyl esterification of citric acid monohydrate and then reacting it with γ-aminopropyltriethoxysilane via an amidation reaction.

5. The environment-friendly abrasive paper according to claim 1, wherein: The environmentally friendly multifunctional crosslinking agent is one or a mixture of two of polyaziridine and water-dispersible polyisocyanate; the adhesive layer is made by coating with an environmentally friendly water-based adhesive, which is a self-crosslinking water-based acrylic emulsion.

6. The environment-friendly abrasive paper according to claim 1, wherein: The water-resistant base paper substrate includes base paper and biomass-based waterproof barrier layers disposed on the front and back of the base paper, and the base adhesive layer is disposed on the biomass-based waterproof barrier layer on the front side.

7. The environment-friendly abrasive paper according to claim 6, wherein: The biomass-based waterproof barrier layer is made by coating with a biomass-based waterproof barrier liquid, which is prepared by mixing a 2%–5% chitosan acetate solution and a 1%–3% nanocellulose crystal aqueous suspension at a volume ratio of 2:1–4:1; the base paper is made by blending bamboo fiber pulp and hardwood pulp at a mass ratio of 3:1–1:

1.

8. A method for preparing environmentally friendly sandpaper according to any one of claims 1-7, characterized in that, The steps include the following: S1. Preparation of water-resistant base paper substrate; S2. Apply an environmentally friendly water-based primer to the front side of the water-resistant base paper substrate to form a primer layer; S3. Abrasives are implanted into the base adhesive layer to form an abrasive layer; S4. Perform initial curing on the substrate after sand application; S5. Spray a coating adhesive onto the surface of the initially cured abrasive layer to form a coating adhesive layer; S6. The substrate after coating and adhesive is cured, and then post-processed to obtain the environmentally friendly sandpaper.

9. The preparation method according to claim 8, characterized in that, In step S1, the method for preparing the water-resistant base paper substrate is as follows: provide base paper, and coat the front and back sides with biomass-based waterproof barrier liquid respectively, and after drying treatment, the water-resistant base paper substrate is obtained.

10. The production method according to claim 8, wherein In step S4, the initial curing conditions are: treatment at a temperature of 55℃~65℃ for 15~25 minutes; in step S6, the main curing adopts a stepped curing process, specifically: the first stage temperature is 60℃~65℃, and the holding time is 25~40 minutes; the second stage temperature is increased to 75℃~80℃, and the holding time is 35~50 minutes; the third stage temperature is increased to 90℃~95℃, and the holding time is 50~70 minutes.

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