A strippable protective coating and a method for its preparation

Abstract

This invention relates to the field of coatings and discloses a peelable protective coating and its preparation method. The peelable protective coating comprises: a polyurethane mother liquor: 5-10 parts diisocyanate, 90-110 parts diol, 1-3 parts catalyst, 1-8 parts chain extender, 40-70 parts solvent, 2-5 parts triethylamine, and 45-55 parts deionized water; 15-30 parts reinforcing filler; and 3-10 parts production aids. This invention's coating can achieve excellent isolation and protection of the substrate with a dry film thickness of only 20-40 μm. The coating formed by this invention is acid and alkali resistant, and after protection, it can be peeled off entirely by hand without damaging the substrate or leaving any marks. Furthermore, the polyurethane mother liquor used in this invention is solvent-free, and the solvent can be recovered by vacuum distillation, making it practical and environmentally friendly. The coating preparation process is simple, and the curing method does not require high-temperature sintering, thus eliminating site limitations.

Description

Technical Field

[0001] This invention relates to the field of coatings, and more specifically, to a peelable protective coating and a method for preparing the same. Background Technology

[0002] Metal surfaces frequently require temporary protection, most commonly during transportation. Examples include the surface protection used on aluminum alloy and PVC windows and doors at the factory to prevent scratches and maintain aesthetics, thus reducing product quality. Besides transportation, temporary protection is also needed during intermediate processing at the factory, such as metal stamping, brushed aluminum sheets, and sputtering processes. This requires temporary shielding of the substrate metal surface to ensure the final product quality and appearance are not affected. Generally, a temporary protective film is used to temporarily protect the metal surface, which is then peeled off after protection is complete.

[0003] In the non-stick cookware industry, it is often necessary to treat the inside of aluminum pots with a non-stick coating, namely by spraying a polytetrafluoroethylene (PTFE) coating or a ceramic coating. For the outside of the aluminum pot, it is desirable to maintain the appearance of the aluminum itself. In order to enhance corrosion resistance and heat resistance, anodizing is required. The current process is to first spray a PTFE coating or ceramic coating on the inside and then perform anodizing on the outside. However, since the anodizing process requires acid washing and alkali washing of the aluminum pot surface to remove the oxide layer and contaminants, it inevitably damages the surface of the internal coating. Therefore, during the anodizing process, the internal coating of the aluminum pot needs to be temporarily shielded for protection.

[0004] Currently, the most common method is to use a cover plate for protection, but this method is complex, time-consuming, and labor-intensive. In contrast, spraying a peelable protective film onto the coating surface is simple, convenient, and provides excellent protection. This peelable protective film typically needs to have the following characteristics: 1. It should have good adhesion to the substrate and not peel off during processing; 2. It should have good barrier properties, protecting the non-stick coating from contamination and contact with acids and alkalis; 3. It should be easy to peel off, allowing the entire protective film to be removed by hand without damaging the coating or leaving any residue.

[0005] Patent CN102863888B discloses a peelable heat-resistant and rust-proof protective film coating. This coating is obtained by curing a hydroxyl-containing linear polyester resin or acrylic resin with an isocyanate polymer. The coating is solvent-free and possesses high water resistance, oil resistance, temperature resistance, abrasion resistance, and peelability. However, this coating uses a two-component curing method, involving multiple preparation steps, and the isocyanate polymer used poses safety risks. Patent CN103360931A discloses a water-based peelable coating with waterborne polyurethane and styrene-acrylic emulsion as the main components. It exhibits excellent water resistance, salt resistance, and corrosion resistance. However, this coating requires 3-4 coats and 7 days of drying before performance testing. The dry film thickness is 80-90 μm, making the process complex, time-consuming, and labor-intensive, and the film thickness is still relatively large, requiring a large amount of coating. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a peelable protective coating and its preparation method. The coating of this invention can provide excellent isolation and protection to the substrate with a dry film thickness of only 20-40 μm; the coating formed by this invention is acid and alkali resistant, and after protection is completed, it can be peeled off entirely by hand without damaging the substrate or leaving any marks.

[0007] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a peelable protective coating comprising the following raw materials in parts by weight: Polyurethane mother liquor: 5-10 parts diisocyanate, 90-110 parts diol, 1-3 parts catalyst, 1-8 parts chain extender, 40-70 parts solvent, 2-5 parts triethylamine, and 45-55 parts deionized water.

[0008] 15-30 parts of reinforcing filler.

[0009] 3-10 parts of production aids.

[0010] This invention's peelable protective coating consists of three parts: a polyurethane masterbatch, reinforcing fillers, and production aids. The polyurethane masterbatch, as the main structural component of the coating, provides excellent film-forming properties and firmly fixes the reinforcing fillers within it. It also exhibits excellent chemical corrosion resistance, ensuring the protected substrate is protected from acid, alkali, and salt corrosion. Furthermore, it possesses good flexural strength, preventing cracking and exposure even when applied to substrates subject to frequent bending. The addition of reinforcing fillers provides a strengthening effect to the coating. It not only increases the surface hardness of the coating, better protecting the substrate from impacts from hard objects, but also increases the tensile strength of the coating, thereby improving its peelability. Simultaneously, reinforcing fillers such as calcium stearate and calcium carbonate also act as peeling agents. During the coating drying and film formation process, calcium stearate accumulates at the bottom of the coating, acting as a lubricant between the coating and the substrate, further increasing the coating's peelability.

[0011] Specifically, in the polyurethane mother liquor, the polyol and isocyanate of this invention serve as the main raw materials. Under the action of a catalyst, the NCO group of an isocyanate molecule contacts the hydroxyl (OH) group of a polyol molecule, undergoing nucleophilic attack to form an unstable complex. Subsequently, this complex loses carbon dioxide, forming a new urethane (-NHCOO-), and this cycle repeats, gradually forming a long-chain polymer. Furthermore, under the influence of a chain extender, the polyurethane chains can further react with additional OH groups via NCO to form a network structure, increasing the degree of crosslinking and mechanical strength of the polymer. After curing, fillers are interspersed throughout, increasing the hardness and wear resistance of the coating. The fillers enriched at the bottom also act as a lubricant, improving the peelability of the coating.

[0012] Further preferably, the diisocyanate is selected from toluene diisocyanate, isoflurane diisocyanate, and diphenylmethane diisocyanate; the diol is selected from polypropylene carbonate diol, polydimethylsiloxane diol, polyether diol, polyester diol, and polybutadiene diol; the catalyst is selected from triethylamine, dibutyltin dilaurate, and N,N-dimethylcyclohexylamine; the chain extender is selected from 1,4-butanediol, dimethylolpropionic acid, and ethylenediamine; and the solvent is selected from acetone and tetrahydrofuran.

[0013] Preferably, the reinforcing filler is selected from nano-calcium carbonate, calcium stearate, titanium dioxide, mica powder, and talc powder; the production aids include one or more of wetting and dispersing agents, defoamers, and leveling agents. The wetting and dispersing agent is selected from BYK-151 and BYK-161; the defoamer is selected from BYK-011, DF-89, and BYK-065; and the leveling agent is selected from BYK-333, BYK-306, and BYK-322.

[0014] Secondly, the present invention provides a method for preparing a polyurethane mother liquor, which specifically includes the following steps: Diisocyanate was first added to a four-necked flask and vacuumed. The mixture was then heated to dry, cooled, and diol was added. Stirring was started, and a catalyst was added after stirring. After maintaining the temperature, a chain extender was added to extend the polymer chain. The mixture was then kept at the same temperature, cooled, and solvent and triethylamine were added. After stirring until homogeneous, deionized water was added and stirred until homogeneous to obtain a prepolymer. The prepolymer was then poured into a high-speed emulsifier for emulsification. After emulsification, a chain extender was added to carry out a post-chain extension reaction. After the reaction, acetone in the system was removed by vacuum distillation to obtain a polyurethane mother liquor.

[0015] Preferably, the temperature for the heating and drying process is 100-120℃ for 1-2 hours; the first cooling process is to reduce the temperature to 80-85℃ and hold it for 2-3 hours; the second holding process is to hold the temperature for 1-1.5 hours and the second cooling process is to reduce the temperature to 60-70℃.

[0016] Preferably, the stirring speed is 100-200 rpm; the chain extension reaction time is 1-1.5 h.

[0017] Thirdly, the present invention provides a method for preparing and using the above-mentioned peelable protective coating, comprising the following steps: adding reinforcing fillers and production aids to a polyurethane mother liquor, pouring it into a grinding kettle, adding zirconium beads, turning on a grinding and dispersing machine for grinding, and filtering with a filter cloth to obtain the peelable protective coating. Then, the metal plate substrate is cleaned with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from the substrate surface, and dried. The peelable protective coating is brushed onto the metal plate and dried at room temperature to form a film.

[0018] Preferably, the amount of zirconium beads added is 40-60% of the coating mass; the rotation speed of the grinding mill is 400-500 rpm; and the filter cloth is a filter cloth with a pore size of 300-500 mesh.

[0019] In the method of this invention, the preparation process of polyurethane mother liquor and peelable protective coating is simple and easy to implement, the raw materials are readily available, and the amount used per unit area is small. It has a low content of volatile organic compounds (VOCs), causes no environmental pollution during preparation and use, and the coating has strong peelability while also possessing certain strength and abrasion resistance, thus effectively protecting the substrate.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) The polyurethane mother liquor used in this invention is a non-solvent type. The solvent used in the preparation process can be recovered by vacuum distillation, which is practical and environmentally friendly. The coating preparation process is simple, and the curing method does not require high-temperature sintering, so there are no site restrictions.

[0021] (2) The present invention introduces a stripping agent into the coating, which can not only increase the peelability of the coating, but also enhance the hardness and wear resistance of the coating, thereby protecting the substrate more effectively.

[0022] (3) The coating of the present invention can provide excellent isolation and protection to the substrate when the dry film thickness is only 20-40 μm; the coating obtained by curing the coating is acid and alkali resistant, and can be peeled off by hand after protection is completed without damaging the substrate or leaving any marks. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments.

[0024] General Implementation Examples First, a peelable protective coating comprising a polyurethane masterbatch, reinforcing fillers, and manufacturing aids. Specifically: The polyurethane mother liquor comprises the following raw materials in parts by weight: 5-10 parts diisocyanate, 90-110 parts diol, 1-3 parts catalyst, 1-8 parts chain extender, 40-70 parts solvent, 2-5 parts triethylamine, and 45-55 parts deionized water.

[0025] 15-30 parts of reinforcing filler.

[0026] 3-10 parts of production aids.

[0027] In some preferred embodiments, the diisocyanate is selected from toluene diisocyanate, isoflurone diisocyanate, and diphenylmethane diisocyanate.

[0028] In some preferred embodiments, the diol is selected from polypropylene carbonate diol, polydimethylsiloxane diol, polyether diol, polyester diol, and polybutadiene diol.

[0029] In some preferred embodiments, the catalyst is selected from triethylamine, dibutyltin dilaurate, and N,N-dimethylcyclohexylamine.

[0030] In some preferred embodiments, the chain extender is selected from 1,4-butanediol, dimethylolpropionic acid, and ethylenediamine; the solvent is selected from acetone and tetrahydrofuran.

[0031] In some preferred embodiments, the reinforcing filler is selected from nano-calcium carbonate, calcium stearate, titanium dioxide, mica powder, and talc powder.

[0032] In some preferred embodiments, the production aids include wetting and dispersing agents, defoamers, and leveling agents; in some more preferred embodiments, the wetting and dispersing agents are selected from BYK-151 and BYK-161; in some more preferred embodiments, the defoamers are selected from BYK-011, DF-89, and BYK-065; in some more preferred embodiments, the leveling agents are selected from BYK-333, BYK-306, and BYK-322.

[0033] Secondly, a method for preparing a peelable protective coating specifically includes the following steps: 1) Preparation of polyurethane mother liquor: Diisocyanate was first added to a four-necked flask and vacuum-sealed, then heated to dry. After cooling, diol was added and stirring was started. After stirring, a catalyst was added, and the mixture was kept at this temperature for a period of time. Then, a chain extender was added to extend the polymer chains. The mixture was kept at this temperature for another period of time, then cooled, and solvent and triethylamine were added. After stirring until homogeneous, deionized water was added and stirred until homogeneous to obtain a prepolymer. The prepolymer was poured into a high-speed emulsifier for emulsification. After emulsification, a chain extender was added to initiate a post-chain extension reaction. After one stage of reaction, acetone in the system was removed by vacuum distillation to obtain the polyurethane mother liquor.

[0034] In some preferred embodiments, the temperature for heating and drying is 100-120°C, and the time is 1-2 hours.

[0035] In some preferred implementation cases, the first cooling is to a temperature of 80-85℃, and the first holding time is 2-3 hours; the second holding time is 1-1.5 hours, and the second cooling is to a temperature of 60-70℃.

[0036] In some preferred embodiments, the stirring speed is 100-110 rpm.

[0037] In some preferred embodiments, the chain extension reaction takes 1-1.5 hours.

[0038] 2) Add the reinforcing filler and production aids to the polyurethane mother liquor, pour it into the grinding kettle, add zirconium beads, turn on the grinding and dispersing machine and grind for a period of time, and filter with filter cloth to obtain a peelable protective coating.

[0039] In some preferred embodiments, the amount of zirconium beads added is 40-60% of the coating mass; the speed of the grinder is 400-500 rpm; and the filter cloth is a filter cloth with a pore size of 300-500 mesh.

[0040] Finally, the application of a peelable protective coating in the preparation of a peelable protective coating includes the following steps: cleaning the substrate with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from the substrate surface, and drying it. The peelable protective coating is then brushed onto the substrate and dried at room temperature to form a film, thus obtaining the peelable protective coating.

[0041] In some preferred embodiments, the substrate is a metal plate substrate.

[0042] Specific embodiments and comparative examples Example 1 Step 1: Preparation of polyurethane mother liquor: 8.7g of toluene diisocyanate was first added to a four-necked flask and vacuum-sealed. The temperature was raised to 105℃ and dried for 1.5h. After cooling to 85℃, 97.3g of polypropylene carbonate diol was added and stirred at 150rpm for 5min. Then, 0.5g of dibutyltin dilaurate was added and kept at this temperature for 3h. 1.2g of 1,4-butanediol and 1.6g of dimethylolpropionic acid were added to extend the polymer chain. The temperature was maintained for another 1.5h, then cooled to 65℃ and 45g of acetone and 0.7g of triethylamine were added. After stirring evenly, 50g of deionized water was added and stirred evenly to obtain the prepolymer. The prepolymer was poured into a high-speed emulsifier for emulsification. After emulsification, 0.55g of ethylenediamine was added for further chain extension. After reacting for 0.5h, the acetone in the system was removed by vacuum distillation to obtain the polyurethane mother liquor.

[0043] Step 2: Preparation of peelable protective coating: Add 8g of composite reinforcing filler (the mass ratio of titanium dioxide: mica powder: nano calcium carbonate is 2:2:1) and 3g of production aid (the mass ratio of BYK-151: BYK-065: BYK-306 is 6:1:3) to 50g of polyurethane mother liquor, pour into a grinding kettle, add 30g of zirconium beads, turn on the grinding and dispersing machine and grind at 500rpm for 2h, filter with 400 mesh filter cloth to obtain peelable protective coating.

[0044] Step 3: Preparation of the peelable protective coating: Using tinplate as the metal substrate, the tinplate is cleaned with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from its surface, and then dried. The peelable protective coating is brushed onto the tinplate surface and dried at room temperature to form a film, thus obtaining the peelable protective coating.

[0045] Comparative Example 1 The only difference from Example 1 is that, in preparing the peelable protective coating, the composite reinforcing filler in Example 1 is replaced with an equal mass of nano-calcium carbonate. The remaining steps, materials, and composition are the same as in Example 1, specifically including the following steps: Step 1: Preparation of polyurethane mother liquor: 8.7g of toluene diisocyanate was first added to a four-necked flask and vacuum-sealed. The temperature was raised to 105℃ and dried for 1.5h. After cooling to 85℃, 97.3g of polypropylene carbonate diol was added and stirred at 150rpm for 5min. Then, 0.5g of dibutyltin dilaurate was added and kept at this temperature for 3h. 1.2g of 1,4-butanediol and 1.6g of dimethylolpropionic acid were added to extend the polymer chain. The temperature was maintained for another 1.5h, then cooled to 65℃ and 45g of acetone and 0.7g of triethylamine were added. After stirring evenly, 50g of deionized water was added and stirred evenly to obtain the prepolymer. The prepolymer was poured into a high-speed emulsifier for emulsification. After emulsification, 0.55g of ethylenediamine was added for further chain extension. After reacting for 0.5h, the acetone in the system was removed by vacuum distillation to obtain the polyurethane mother liquor.

[0046] Step 2: Preparation of peelable protective coating: Add 8g of nano calcium carbonate and 3g of production aid (BYK-151:BYK-065:BYK-306 in a mass ratio of 6:1:3) to 50g of polyurethane mother liquor, pour into a grinding kettle, add 30g of zirconium beads, turn on the grinding and dispersing machine and grind at 500rpm for 2 hours, filter with 400-mesh filter cloth to obtain peelable protective coating.

[0047] Step 3: Preparation of the peelable protective coating: Using tinplate as the metal substrate, the tinplate is cleaned with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from its surface, and then dried. The peelable protective coating is brushed onto the tinplate surface and dried at room temperature to form a film, thus obtaining the peelable protective coating.

[0048] Comparative Example 2 The only difference from Example 1 is that the amount of composite reinforcing filler added in Example 1 is reduced from 8g to 4g when preparing the peelable protective coating. The remaining steps, materials, and composition are the same as in Example 1, specifically including the following steps: Step 1: Preparation of polyurethane mother liquor: 8.7g of toluene diisocyanate was first added to a four-necked flask and vacuum-sealed. The temperature was raised to 105℃ and dried for 1.5h. After cooling to 85℃, 97.3g of polypropylene carbonate diol was added and stirred at 150rpm for 5min. Then, 0.5g of dibutyltin dilaurate was added and kept at this temperature for 3h. 1.2g of 1,4-butanediol and 1.6g of dimethylolpropionic acid were added to extend the polymer chain. The temperature was maintained for another 1.5h, then cooled to 65℃ and 45g of acetone and 0.7g of triethylamine were added. After stirring evenly, 50g of deionized water was added and stirred evenly to obtain the prepolymer. The prepolymer was poured into a high-speed emulsifier for emulsification. After emulsification, 0.55g of ethylenediamine was added for further chain extension. After reacting for 0.5h, the acetone in the system was removed by vacuum distillation to obtain the polyurethane mother liquor.

[0049] Step 2: Preparation of peelable protective coating: Add 4g of composite reinforcing filler (the mass ratio of titanium dioxide: mica powder: nano calcium carbonate is 2:2:1) and 3g of production aid (the mass ratio of BYK-151: BYK-065: BYK-306 is 6:1:3) to 50g of polyurethane mother liquor, pour into a grinding kettle, add 30g of zirconium beads, turn on the grinding and dispersing machine and grind at 500rpm for 2h, filter with 400 mesh filter cloth to obtain peelable protective coating.

[0050] Step 3: Preparation of the peelable protective coating: Using tinplate as the metal substrate, the tinplate is cleaned with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from its surface, and then dried. The peelable protective coating is brushed onto the tinplate surface and dried at room temperature to form a film, thus obtaining the peelable protective coating.

[0051] Comparative Example 3 The only difference from Example 1 is that the amount of composite reinforcing filler added in Example 1 is increased from 8g to 12g when preparing the peelable protective coating. The remaining steps, materials, and composition are the same as in Example 1, specifically including the following steps: Step 1: Preparation of polyurethane mother liquor: 8.7g of toluene diisocyanate was first added to a four-necked flask and vacuum-sealed. The temperature was raised to 105℃ and dried for 1.5h. After cooling to 85℃, 97.3g of polypropylene carbonate diol was added and stirred at 150rpm for 5min. Then, 0.5g of dibutyltin dilaurate was added and kept at this temperature for 3h. 1.2g of 1,4-butanediol and 1.6g of dimethylolpropionic acid were added to extend the polymer chain. The temperature was maintained for another 1.5h, then cooled to 65℃ and 45g of acetone and 0.7g of triethylamine were added. After stirring evenly, 50g of deionized water was added and stirred evenly to obtain the prepolymer. The prepolymer was poured into a high-speed emulsifier for emulsification. After emulsification, 0.55g of ethylenediamine was added for further chain extension. After reacting for 0.5h, the acetone in the system was removed by vacuum distillation to obtain the polyurethane mother liquor.

[0052] Step 2: Preparation of peelable protective coating: Add 12g of composite reinforcing filler (the mass ratio of titanium dioxide: mica powder: nano calcium carbonate is 2:2:1) and 3g of production aid (the mass ratio of BYK-151: BYK-065: BYK-306 is 6:1:3) to 50g of polyurethane mother liquor, pour into a grinding kettle, add 30g of zirconium beads, turn on the grinding and dispersing machine and grind at 500rpm for 2h, filter with 400 mesh filter cloth to obtain peelable protective coating.

[0053] Step 3: Preparation of the peelable protective coating: Using tinplate as the metal substrate, the tinplate is cleaned with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from its surface, and then dried. The peelable protective coating is brushed onto the tinplate surface and dried at room temperature to form a film, thus obtaining the peelable protective coating.

[0054] Comparative Example 4 The only difference from Example 1 is that the polyurethane mother liquor in Example 1 is replaced with an equal mass of acrylic emulsion (commercially available) when preparing the protective coating. The remaining steps, materials, and composition are the same as in Example 1, specifically including the following steps: Step 1: Preparation of protective coating: Add 12g of composite reinforcing filler (the mass ratio of titanium dioxide: mica powder: nano calcium carbonate is 2:2:1) and 3g of production aid (the mass ratio of BYK-151: BYK-065: BYK-306 is 6:1:3) to 50g of acrylic emulsion (commercially available), pour into a grinding kettle, add 30g of zirconium beads, turn on the grinding and dispersing machine and grind at 500rpm for 2 hours, filter with 400 mesh filter cloth to obtain the protective coating.

[0055] Step 2: Preparation of the protective coating: Using tinplate as the metal substrate, the tinplate is cleaned with alkali and water to remove soluble salts, oils, greases, water, and other contaminants from its surface, and then dried. A peelable protective coating is then brushed onto the tinplate surface and dried at room temperature to form a film, thus obtaining the protective coating.

[0056] Comparative Example 5 The only difference from Example 1 is that the composite reinforcing filler prepared in Example 1 is not added when preparing the peelable protective coating. The remaining steps, materials, and composition are the same as in Example 1, specifically including the following steps: Step 1: Preparation of polyurethane mother liquor: 8.7g of toluene diisocyanate was first added to a four-necked flask and vacuum-sealed. The temperature was raised to 105℃ and dried for 1.5h. After cooling to 85℃, 97.3g of polypropylene carbonate diol was added and stirred at 150rpm for 5min. Then, 0.5g of dibutyltin dilaurate was added and kept at this temperature for 3h. 1.2g of 1,4-butanediol and 1.6g of dimethylolpropionic acid were added to extend the polymer chain. The temperature was maintained for another 1.5h, then cooled to 65℃ and 45g of acetone and 0.7g of triethylamine were added. After stirring evenly, 50g of deionized water was added and stirred evenly to obtain the prepolymer. The prepolymer was poured into a high-speed emulsifier for emulsification. After emulsification, 0.55g of ethylenediamine was added for further chain extension. After reacting for 0.5h, the acetone in the system was removed by vacuum distillation to obtain the polyurethane mother liquor.

[0057] Step 2: Preparation of peelable protective coating: Add 3g of production aid (BYK-151:BYK-065:BYK-306 in a mass ratio of 6:1:3) to 50g of polyurethane mother liquor, pour into a grinding kettle, add 30g of zirconium beads, turn on the grinding and dispersing machine and grind at 500rpm for 2 hours, filter with 400-mesh filter cloth to obtain peelable protective coating.

[0058] Step 3: Preparation of the peelable protective coating: Using tinplate as the metal substrate, the tinplate is cleaned with alkali and water to remove soluble salts, oils, esters, water, and other contaminants from its surface, and then dried. The peelable protective coating is brushed onto the tinplate surface and dried at room temperature to form a film, thus obtaining the peelable protective coating.

[0059] Performance testing The peelable protective coating prepared in Example 1 and the protective coatings prepared in Comparative Examples 1-5 were tested for properties such as hardness, average tensile strength, average breaking strength, and 180° peel strength. Hardness testing was conducted according to GB / T 6739, and the result was assessed as: paint film scratch. Average tensile strength testing was conducted according to GB / T 10654-2001, and the result was assessed as: sample breakage. Elongation at break testing was conducted according to GB / T 10654-2001, and the result was assessed as: sample breakage. 180° peel strength testing was conducted according to GB / T 10654-2001, and the result was assessed as: coating peeling. The results are shown in Table 1. Table 1: Performance test results of the products in Example 1 and Comparative Examples 1-5 Case hardness Average tensile strength / MPa Elongation at break / % 180° peel strength (N / M) Example 1 H 7.85 184.5 317 Comparative Example 1 H 7.37 154.2 309 Comparative Example 2 HB 6.94 197.6 358 Comparative Example 3 H 8.62 107.2 287 Comparative Example 4 H 7.53 179.4 Unable to be completely peeled Comparative Example 5 B 6.17 233.7 351 As can be seen from the comparison of data in Table 1: Comparative Example 1 uses the same mass of nano-calcium carbonate to replace the composite reinforcing filler. Due to the lack of pigments in the system, the appearance is worse. It also lacks the layered structure of mica powder, which cannot prevent the propagation of cracks caused by external forces. As a result, the tensile strength and elongation at break of the coating will also decrease significantly. However, the amount of calcium carbonate powder enriched at the bottom of the coating will increase, reducing the adhesion between the coating and the substrate, so the peel strength will also decrease.

[0060] The results of Comparative Examples 2, 3, and 5 reveal the influence of the amount of reinforcing filler on the coating performance. With increasing reinforcing filler content, the tensile strength of the peelable protective coating gradually increases, indicating that within a certain range, the reinforcing filler has a certain enhancing effect on the mechanical properties of the peelable protective coating. Simultaneously, the elongation at break of the coating gradually decreases; when the amount of reinforcing filler added is 12g, the elongation at break is already relatively low. With further increases in the amount of reinforcing filler, the peel strength of the coating initially increases and then decreases. This is because initially, the addition of reinforcing filler reduces shrinkage during the drying and film-forming process, thereby improving the coating's adhesion, thus initially increasing the peel strength. However, as the amount of reinforcing filler in the system increases, the adhesion of the coating to the substrate gradually decreases, and the peel strength decreases accordingly. When the amount of reinforcing filler added is 12g, although the coating has high tensile strength and low peel strength, the low elongation at break means that the coating may break during the peeling process and cannot be completely peeled off. Example 1 has a certain degree of hardness, which can effectively protect the substrate. It also has better tensile strength and elongation at break, and moderate peel strength. Therefore, it is an excellent peelable protective coating.

[0061] Comparative Example 4 used commercially available acrylic emulsion of the same mass to replace the self-made polyurethane emulsion. The resulting coating could not be completely peeled off. This is because the polyurethane coating has strong intermolecular hydrogen bonds and van der Waals forces, which increase the flexibility and resilience of the polymer chain segments. In contrast, the acrylic emulsion is made by free radical polymerization of acrylate monomers, forming a linear or branched network structure that lacks sufficient crosslinking points. Its cohesive force is relatively weak when forming a film, thus affecting its peelability.

[0062] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A strippable protective coating characterized in that Including the following parts by weight of raw materials: Polyurethane mother liquor: 5-10 parts diisocyanate, 90-110 parts diol, 1-3 parts catalyst, 1-8 parts chain extender, 40-70 parts solvent, 2-5 parts triethylamine, and 45-55 parts water. 15-30 parts of reinforcing filler; the reinforcing filler is selected from one or more of calcium stearate, nano calcium carbonate, titanium dioxide, mica powder and talc powder; 3-10 parts of production aids.

2. The strippable protective coating of claim 1, wherein: In the polyurethane mother liquor: The diisocyanate is selected from toluene diisocyanate, isoflurone diisocyanate, and diphenylmethane diisocyanate; The diol is selected from polypropylene carbonate diol, polydimethylsiloxane diol, polyether diol, polyester diol and polybutadiene diol; The catalyst is selected from triethylamine, dibutyltin dilaurate and N,N-dimethylcyclohexylamine; The chain extender is selected from 1,4-butanediol, dimethylolpropionic acid, and ethylenediamine; The solvent is selected from acetone and tetrahydrofuran.

3. The strippable protective coating of claim 1, wherein: The production aids include wetting and dispersing agents, defoamers, and leveling agents.

4. A process for the preparation of a strippable protective coating according to any one of claims 1 to 3, characterized in that include: S1: Preparation of polyurethane mother liquor: Diisocyanate was first added to a container and vacuumed, heated and dried, cooled, diol was added, stirred evenly, catalyst was added, heat was maintained and chain extender was added for chain extension, heat was maintained again and cooled and solvent and triethylamine were added, stirred evenly and water was added, stirred evenly to obtain prepolymer; the prepolymer was emulsified, after emulsification, chain extender was added for post-chain extension reaction, after the reaction was completed, acetone in the system was removed by vacuum distillation to obtain polyurethane mother liquor; S2: Preparation of coating: The reinforcing filler and production aids are mixed with polyurethane mother liquor, ground and dispersed, and filtered with filter cloth to obtain a peelable protective coating.

5. The method of claim 4, wherein: In S1: the temperature for heating and drying is 100-120℃, and the time is 1-2 hours.

6. The method of claim 4, wherein: In S1: The first temperature drop will be to 80-85℃; The first insulation period is 2-3 hours; The second insulation period is 1-1.5 hours; The second temperature drop will bring the temperature down to 60-70℃.

7. The method of claim 4, wherein: In S1: The stirring speed is 100-200 rpm; The chain extension reaction takes 1-1.5 hours.

8. The method of claim 4, wherein: In S2: The grinding and dispersing process uses zirconium beads, which are added at 40-60% of the coating mass. The grinding speed is 400-500 rpm.

9. The method of claim 4, wherein: In S2: The filtration process uses a 300-500 mesh filter cloth.

10. Use of a strippable protective coating according to any one of claims 1-3, characterized in that include: Clean and dry the substrate surface; Apply the peelable protective coating to the substrate surface and allow it to dry into a film.