Preparation method of peelable acrylic emulsion and peelable acrylic emulsion

Abstract

The embodiment of the invention provides a preparation method of a peelable acrylic emulsion and the peelable acrylic emulsion, and relates to the technical field of acrylic emulsion and peelable coatings, the method comprises the following steps: dissolving a modified 2-ureido-4 [1H] pyrimidone (UPy) monomer and a cross-linking agent in dimethyl sulfoxide to obtain a functional monomer solution; mixing the functional monomer solution with the mixed monomer to obtain a first solution, dividing the first solution into a first sub-solution and a second sub-solution, fully mixing the first sub-solution with the emulsifier solution, and uniformly dispersing to obtain a pre-emulsion; dividing the ammonium persulfate aqueous solution into a third sub-solution and a fourth sub-solution, stirring the third sub-solution and the pre-emulsion at a first temperature, and carrying out heat preservation to prepare a seed emulsion; dropwise adding the second sub-solution and the fourth sub-solution into the seed emulsion for full reaction, and keeping the temperature at the first temperature to obtain a second solution; and adjusting the pH value of the second solution to a target value at a second temperature, continuously stirring, and filtering to obtain the acrylic emulsion.

Description

Technical Field

[0001] The disclosed embodiments relate to the technical field of acrylic emulsions and strippable coatings, and more particularly to a method for preparing a strippable acrylic emulsion and the strippable acrylic emulsion. Background Art

[0002] Electronic parts, precision instruments, weapons and equipment may suffer from scratches, abrasions, wear, pollution and other surface damage during production, processing, storage and transportation, which may affect their appearance and even reduce their performance. In order to reduce these damages and extend the service life of the product, a temporary protective coating, namely a peelable coating, can be applied to the surface of the product. As a temporary coating, the peelable coating can not only protect the substrate from any type of damage, such as mechanical, physical, chemical and other surface damage, but also will not penetrate the substrate and can be peeled off from the surface after its service life ends or when the purpose of use is achieved.

[0003] The high cohesion and low adhesion of the peelable coating are the key factors to ensure that it is easy to peel and does not leave residue. Tensile strength and elongation at break are usually used as indicators to measure the cohesion of the peelable film. However, the mechanical properties of the current acrylic emulsion peelable film are poor, and its cohesion is difficult to meet the peeling requirements, making it difficult to peel the film completely. Summary of the invention

[0004] The purpose of the present disclosure is to provide a method for preparing a peelable acrylic emulsion and a peelable acrylic emulsion, thereby overcoming at least to a certain extent the problems of poor mechanical properties and difficulty in complete peeling of acrylic emulsion-type peelable films caused by limitations and defects of related technologies.

[0005] According to one aspect of the present disclosure, a method for preparing a strippable acrylic emulsion is provided, comprising: dissolving a modified UPy monomer and a cross-linking agent in dimethyl sulfoxide to obtain a functional monomer solution; mixing the functional monomer solution with a mixed monomer to obtain a first solution, and dividing the first solution into a first sub-solution and a second sub-solution, and fully mixing and uniformly dispersing the first sub-solution with an emulsifier solution to obtain a pre-emulsion; dividing an ammonium persulfate aqueous solution into a third sub-solution and a fourth sub-solution, and mechanically stirring and heat-keeping the third sub-solution and the pre-emulsion at a first temperature to obtain a seed emulsion; dropping the second sub-solution and the fourth sub-solution into the seed emulsion to fully react and heat-keeping at the first temperature to obtain a second solution; adjusting the pH value of the second solution to a target value at a second temperature and continuing stirring to obtain a mixed solution, and filtering the obtained mixed solution to obtain a strippable acrylic emulsion; wherein the second temperature is lower than the first temperature.

[0006] In an exemplary embodiment of the present disclosure, the mass fraction of the functional monomer solution is 20%~30%; wherein the mass ratio of the cross-linking agent to the modified UPy monomer is 1:(1.5~2).

[0007] In an exemplary embodiment of the present disclosure, the steps of preparing the modified UPy monomer include: 2-Amino-4-hydroxy-6-methylpyrimidine was fully dissolved in dimethyl sulfoxide, and isocyanoethyl methacrylate was added and then cooled to room temperature. The modified UPy monomer was obtained by washing, filtering and drying.

[0008] In an exemplary embodiment of the present disclosure, the mass ratio of 2-amino-4-hydroxy-6-methylpyrimidine to isocyanoethyl methacrylate is 1:(1.3-1.8).

[0009] In an exemplary embodiment of the present disclosure, the cross-linking agent is one or more of N,N'-methylenebisacrylamide, 1,5-pentanediol dimethacrylate, and triethylene glycol dimethacrylate; the mixed monomer includes methyl methacrylate, butyl acrylate, methacrylic acid, and styrene, and the mass ratio of methyl methacrylate, butyl acrylate, methacrylic acid, and styrene is 1:2: (0.08~0.16): (0.16~0.23); wherein the added amount of the functional monomer solution is 7.4%~8.9% of the mass of the mixed monomer.

[0010] In an exemplary embodiment of the present disclosure, the preparation step of the emulsifier solution includes: mechanically stirring the emulsifier and deionized water to obtain an emulsifier solution; wherein the emulsifier is one or more of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; the mass ratio of the emulsifier to deionized water is 1: (28~40), and the amount of the emulsifier added is 2.8%~3.6% of the mass of the mixed monomer.

[0011] In an exemplary embodiment of the present disclosure, the preparation step of the ammonium persulfate aqueous solution includes: fully dissolving ammonium persulfate in deionized water to obtain the ammonium persulfate aqueous solution; wherein the mass ratio of ammonium persulfate to deionized water is 1:(16~20), and the amount of ammonium persulfate added is 1.7%~2.1% of the mass of the mixed monomer.

[0012] In an exemplary embodiment of the present disclosure, the first temperature is 73-83°C, and the second temperature is lower than 40°C.

[0013] In an exemplary embodiment of the present disclosure, the target value is 7-8.

[0014] According to one aspect of the present disclosure, a strippable acrylic emulsion is provided. The strippable acrylic emulsion is prepared by any one of the above methods for preparing a strippable acrylic emulsion.

[0015] In the technical solution provided in the embodiment of the present disclosure, a chemical crosslinking agent is added to the modified UPy monomer, and a peelable acrylic emulsion is prepared by emulsion polymerization. After the emulsion is formed into a film, it has a double crosslinking network of physical crosslinking and chemical crosslinking, so it has higher mechanical strength. When it is peeled off under the action of external force, the physical crosslinking (hydrogen bond) inside the film breaks to offset the external tension, and the chemical crosslinking serves as the rigid skeleton of the film, thereby improving the mechanical strength of the film and ensuring that the peelable film can be completely peeled off.

[0016] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0018] Figure 1 A flow chart schematically shows a method for preparing a strippable acrylic emulsion according to an embodiment of the present disclosure.

[0019] Figure 2 The schematic diagram schematically shows the results of a film formed by a peelable acrylic emulsion prepared in an embodiment of the present disclosure before and after peeling on tinplate.

[0020] Figure 3 The schematic diagram shows the results of the film formed by the peelable acrylic emulsion prepared in Comparative Example 2 before and after peeling on tinplate.

[0021] Figure 4 A schematic diagram of a double network structure of a film formed by a strippable acrylic emulsion prepared in an embodiment of the present disclosure is schematically shown.

[0022] Figure 5 A diagram schematically shows the energy dissipation mechanism of a film formed by a strippable acrylic emulsion prepared according to an embodiment of the present disclosure when it is stripped.

[0023] Figure 6 The hydrogen nuclear magnetic resonance spectrum of a modified UPy monomer prepared in an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0024] The following is an explanation of the implementation of the present disclosure by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification.

[0025] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0026] In addition, it should be understood that one or more method steps mentioned in the present disclosure do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present disclosure does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. Changes or adjustments in their relative relationships, without substantial changes in the technical content, should also be regarded as the scope of the present disclosure.

[0027] The high cohesion and low adhesion of the peelable coating are the key factors to ensure that it is easy to peel and does not leave residue. Tensile strength and elongation at break are usually used as indicators to measure the cohesion of the peelable film. However, the mechanical properties of the current acrylic emulsion peelable film are poor, and its cohesion is difficult to meet the peeling requirements. It is easy to break during peeling, making it difficult to peel the film completely.

[0028] It should be noted that the strippable acrylic emulsion prepared in the embodiment of the present disclosure can be used as a temporary coating, and can be coated on the surface of electronic parts, precision instruments, weapons and equipment during production, processing, storage, transportation, etc. to protect the substrate from damage, and can be completely stripped from the surface of the product after its service life ends or when the purpose of use is achieved. Of course, the strippable acrylic emulsion prepared in the embodiment of the present disclosure can also be used in other application scenarios that require a strippable coating, without limitation.

[0029] In order to solve the technical problems in the related art, the present disclosure provides a method for preparing a high-strength peelable acrylic emulsion, which aims to give the peelable film high mechanical strength and improve its cohesion so that it can be completely peeled off. Figure 1 A flow chart showing a method for preparing a strippable acrylic emulsion may include: In step S110 , the modified UPy monomer and the cross-linking agent are dissolved in dimethyl sulfoxide to obtain a functional monomer solution.

[0030] In step S120, the functional monomer solution is mixed with the mixed monomer to obtain a first solution, and the first solution is divided into a first sub-solution and a second sub-solution. The first sub-solution is fully mixed with the emulsifier solution and dispersed uniformly to obtain a pre-emulsion.

[0031] In step S130, the ammonium persulfate aqueous solution is divided into a third sub-solution and a fourth sub-solution, and the third sub-solution and the pre-emulsion are mechanically stirred and kept warm at a first temperature to obtain a seed emulsion.

[0032] In step S140, the second sub-solution and the fourth sub-solution are added dropwise to the seed emulsion to fully react and kept warm at the first temperature to obtain a second solution.

[0033] In step S150, the pH value of the second solution is adjusted to a target value at a second temperature and stirring is continued to obtain a mixed solution, and the obtained mixed solution is filtered to obtain an acrylic emulsion; wherein the second temperature is lower than the first temperature.

[0034] Next, the preparation method of the strippable acrylic emulsion in the embodiment of the present disclosure is specifically described.

[0035] In step S110 , the modified UPy monomer and the cross-linking agent are dissolved in dimethyl sulfoxide to obtain a functional monomer solution.

[0036] In the disclosed embodiment, the modified UPy monomer and the cross-linking agent can be dissolved in dimethyl sulfoxide at 40-50°C to obtain a functional monomer solution. Optionally, the modified UPy monomer and the cross-linking agent are dissolved in dimethyl sulfoxide at 40°C, so that the modified UPy monomer and the cross-linking agent are fully dissolved in dimethyl sulfoxide. Of course, the temperature of dimethyl sulfoxide can also be adjusted according to actual needs to ensure that the modified UPy monomer and the cross-linking agent are fully dissolved.

[0037] The mass fraction of the functional monomer solution is 20% to 30%, and the mass ratio of the crosslinker to the modified UPy monomer is 1:(1.5 to 2). Optionally, the mass ratio of the crosslinker to the modified UPy monomer is 1:2, 1:1.78 or 1:1.5.

[0038] In the disclosed embodiment, the cross-linking agent is one or more of N,N'-methylenebisacrylamide, 1,5-pentanediol dimethacrylate, and triethylene glycol dimethacrylate.

[0039] In the disclosed embodiment, the mixed monomer includes methyl methacrylate, butyl acrylate, methacrylic acid, and styrene, and the mass ratio of methyl methacrylate, butyl acrylate, methacrylic acid, and styrene is 1:2:(0.08-0.16):(0.16-0.23). The amount of the functional monomer solution added is 7.4%-8.9% of the mass of the mixed monomer.

[0040] In the disclosed embodiment, the steps of preparing the modified UPy monomer include: 2-Amino-4-hydroxy-6-methylpyrimidine was fully dissolved in dimethyl sulfoxide, and isocyanoethyl methacrylate was added and then cooled to room temperature. The modified UPy monomer was obtained by washing, filtering and drying.

[0041] Among them, 2-amino-4-hydroxy-6-methylpyrimidine can be dissolved in dimethyl sulfoxide at 170~180°C to fully dissolve 2-amino-4-hydroxy-6-methylpyrimidine, and then isocyanoethyl methacrylate is added, and the mixture is brought to room temperature through an ice-water bath, and finally washed and filtered through cyclohexane, and dried to obtain a modified UPy monomer.

[0042] Optionally, other organic solvents for washing may be used, without any special limitation. The drying temperature may be selected according to actual needs, without any special limitation.

[0043] Among them, the mass ratio of 2-amino-4-hydroxy-6-methylpyrimidine to the isocyanoethyl methacrylate is 1:(1.3~1.8), optionally, the mass ratio of 2-amino-4-hydroxy-6-methylpyrimidine to the isocyanoethyl methacrylate is 1:1.3, 1:1.36 or 1:1.8.

[0044] In step S120, the functional monomer solution is mixed with the mixed monomer to obtain a first solution, and the first solution is divided into a first sub-solution and a second sub-solution. The first sub-solution is fully mixed with the emulsifier solution and dispersed uniformly to obtain a pre-emulsion.

[0045] In the disclosed embodiment, the preparation step of the emulsifier solution includes: mechanically stirring the emulsifier and deionized water to obtain an emulsifier solution. Optionally, the emulsifier is one or more of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; the mass ratio of the emulsifier to deionized water is 1: (28-40), and the amount of the emulsifier added is 2.8%-3.6% of the mass of the mixed monomer.

[0046] Among them, the emulsifier and deionized water can be added into the reaction kettle and stirred evenly to obtain an emulsifier solution. The embodiment of the present disclosure does not impose any special restriction on the stirring rate, which can be flexibly adjusted according to actual needs.

[0047] In the embodiment of the present disclosure, the mixed monomer and the functional monomer solution are fully mixed to obtain a first solution. Alternatively, one tenth of the first solution can be taken as a first sub-solution, and the first sub-solution can be fully mixed with an emulsifier solution and dispersed uniformly to obtain a pre-emulsion, and the remaining nine tenths of the first solution can be taken as a second sub-solution. Of course, other division methods can also be selected according to actual conditions.

[0048] In the disclosed embodiment, the first sub-solution can be added into the reaction kettle to be fully mixed with the emulsifier solution and evenly dispersed. The rotation speed of the dispersion kettle can be adjusted according to actual needs to ensure that the first sub-solution can be fully and evenly dispersed to obtain a pre-emulsion.

[0049] In step S130, the ammonium persulfate aqueous solution is divided into a third sub-solution and a fourth sub-solution, and the third sub-solution and the pre-emulsion are mechanically stirred and kept warm at a first temperature to obtain a seed emulsion.

[0050] In the embodiments of the present disclosure, ammonium persulfate is used as an initiator, and ammonium persulfate can be fully dissolved in deionized water to obtain an ammonium persulfate aqueous solution; wherein the mass ratio of ammonium persulfate to deionized water is 1:(16~20), and the amount of ammonium persulfate added is 1.7%~2.1% of the mass of the mixed monomer.

[0051] Optionally, one third of the ammonium persulfate aqueous solution can be taken as the third sub-solution, and the remaining two thirds of the ammonium persulfate aqueous solution can be taken as the fourth sub-solution. Of course, the division method can also be adjusted according to actual needs, including but not limited to this distribution method.

[0052] In the disclosed embodiment, the reactor can be heated to a first temperature, and then the third sub-solution and the pre-emulsion are sequentially added to the reactor, stirred evenly and kept warm for a first period of time to obtain a seed emulsion.

[0053] Optionally, the first temperature is 73-83° C., and the first time period is 30-40 minutes. For example, the mixture may be kept warm for 30 minutes after being stirred evenly.

[0054] Optionally, the rotation speed of the reactor can be adjusted according to actual needs to ensure sufficient reaction, and there is no special limitation on this.

[0055] In step S140, the second sub-solution and the fourth sub-solution are added dropwise to the seed emulsion to fully react and kept warm at the first temperature to obtain a second solution.

[0056] In the disclosed embodiment, the second sub-solution and the fourth sub-solution can be uniformly added to the seed emulsion for 200 to 220 minutes to allow the second sub-solution and the fourth sub-solution to fully react in the seed emulsion. Optionally, the second sub-solution and the fourth sub-solution can be uniformly added to the seed emulsion for 2 to 10 minutes, or any other time that can ensure that the second sub-solution and the fourth sub-solution fully react in the seed emulsion.

[0057] In the embodiment of the present disclosure, after the second sub-solution and the fourth sub-solution are added dropwise, the first temperature may be kept for 2 to 2.5 hours to obtain the second solution. Optionally, the second solution may be obtained after keeping the temperature at 73 to 83° C. for 2 hours.

[0058] In step S150, the pH value of the second solution is adjusted to a target value at a second temperature and stirring is continued to obtain a mixed solution, and the obtained mixed solution is filtered to obtain a strippable acrylic emulsion; wherein the second temperature is lower than the first temperature.

[0059] In the disclosed embodiment, the second temperature is lower than 40° C., and the target value is 7-8, that is, pH=7-8.

[0060] After obtaining the second solution, the temperature of the reactor is lowered to below 40°C, and an appropriate amount of ammonia water is added to adjust the pH value of the second solution to 7-8, and the mixture is continuously stirred for 30-40 minutes and then filtered to obtain a strippable acrylic emulsion. Optionally, an appropriate amount of ammonia water is added to adjust the pH value of the second solution to 7-8, and the mixture is continuously stirred for 30 minutes and then filtered to obtain a strippable acrylic emulsion. The pH value can also be adjusted to other alkaline solutions, which can be selected according to needs.

[0061] Furthermore, the present disclosure also provides a strippable acrylic emulsion, which is prepared by the method for preparing the strippable acrylic emulsion of the exemplary embodiment described above. For details, please refer to the above embodiment, which will not be described in detail here.

[0062] The preparation method of the strippable acrylic emulsion disclosed in the present invention is described in detail below through specific examples.

[0063] Example 1

[0064] The method for preparing a strippable acrylic emulsion comprises the following steps: Step 1: Dissolve 5.9 g of 2-amino-4-hydroxy-6-methylpyrimidine in dimethyl sulfoxide at 170° C., add 7.7 g of isocyanoethyl methacrylate, and immediately cool to room temperature in an ice-water bath; wash with cyclohexane, filter, and dry to obtain 13 g of modified UPy monomer.

[0065] Step 2: 3 g of modified UPy monomer and 1.5 g of N,N'-methylenebisacrylamide were dissolved in 15 g of dimethyl sulfoxide at 40° C. to prepare a functional monomer solution A.

[0066] Step 3: Add 7.5g of sodium dodecyl sulfate and 225g of deionized water into a reactor, stir evenly to obtain an emulsifier solution, then mix 65g of methyl methacrylate, 130g of butyl acrylate, 10g of methacrylic acid, 15g of styrene, and 19.5g of functional monomer solution A to obtain solution B, take one tenth of solution B (the first sub-solution) and add it into the reactor to fully mix with the emulsifier solution, and disperse it evenly at high speed to obtain a pre-emulsion.

[0067] Step 4: Dissolve 4.5 g of ammonium persulfate in 76 g of deionized water to obtain an aqueous solution of ammonium persulfate, and take one-third of the aqueous solution of ammonium persulfate as solution C (the third sub-solution), and take two-thirds of the aqueous solution of ammonium persulfate as solution D (the fourth sub-solution).

[0068] Step 5: After the temperature in the reactor is raised to 75°C, solution C and pre-emulsion are added in sequence, and the seed emulsion is obtained after high-speed stirring and heat preservation for 30 minutes. Then, the remaining nine-tenths of solution B (the second sub-solution) and solution D are uniformly added dropwise for 210 minutes; after the remaining solution B and solution D are added dropwise, the mixture is kept warm at 80°C for 2 hours. After the heat preservation is completed, the temperature in the reactor is lowered to 35°C, and an appropriate amount of ammonia water is added to adjust the pH of the liquid in the reactor to 7. After stirring for 30 minutes, the liquid in the reactor is filtered to obtain a strippable acrylic emulsion.

[0069] Example 2

[0070] The method for preparing a strippable acrylic emulsion comprises the following steps: Step 1: Dissolve 6 g of 2-amino-4-hydroxy-6-methylpyrimidine in dimethyl sulfoxide at 170°C, add 10.8 g of isocyanoethyl methacrylate, and immediately cool to room temperature in an ice-water bath; wash with cyclohexane, filter, and dry to obtain 15.5 g of modified UPy monomer.

[0071] Step 2: 2.5 g of modified UPy monomer and 1.4 g of N,N'-methylenebisacrylamide were dissolved in 13 g of dimethyl sulfoxide at 40° C. to prepare a functional monomer solution A.

[0072] Step 3: Add 7g of sodium dodecyl sulfate and 220g of deionized water into a reactor, stir evenly to obtain an emulsifier solution, then mix 62g of methyl methacrylate, 124g of butyl acrylate, 8g of methacrylic acid, 12g of styrene, and 16.9g of functional monomer solution A to obtain solution B, take one tenth of solution B (the first sub-solution) and add it into the reactor to fully mix with the emulsifier solution, and disperse it evenly at high speed to obtain a pre-emulsion.

[0073] Step 4: Dissolve 3.7 g of ammonium persulfate in 69 g of deionized water to obtain an ammonium persulfate aqueous solution, and take one-third of the ammonium persulfate aqueous solution as solution C (the third sub-solution), and take two-thirds of the ammonium persulfate aqueous solution as solution D (the fourth sub-solution).

[0074] Step 5: After the temperature in the reactor is raised to 75°C, solution C and pre-emulsion are added in sequence, and the seed emulsion is obtained after high-speed stirring and heat preservation for 30 minutes. Then, the remaining nine-tenths of solution B (the second sub-solution) and solution D are uniformly added dropwise for 210 minutes; after the remaining solution B and solution D are added dropwise, the mixture is kept warm at 75°C for 2 hours. After the heat preservation is completed, the temperature in the reactor is lowered to 40°C, and an appropriate amount of ammonia water is added to adjust the pH of the liquid in the reactor to 7. After stirring for 30 minutes, the liquid in the reactor is filtered to obtain a strippable acrylic emulsion.

[0075] Example 3

[0076] The method for preparing a strippable acrylic emulsion comprises the following steps: Step 1: Dissolve 6 g of 2-amino-4-hydroxy-6-methylpyrimidine in dimethyl sulfoxide at 170° C., add 8.2 g of isocyanoethyl methacrylate, and immediately cool to room temperature in an ice-water bath; wash with cyclohexane, filter, and dry to obtain 13.5 g of modified UPy monomer.

[0077] Step 2: Take 2 g of modified UPy monomer and 1.3 g of triethylene glycol dimethacrylate and dissolve them in 13 g of dimethyl sulfoxide at 40° C. to prepare a functional monomer solution A.

[0078] Step 3: Add 6g of sodium dodecylbenzene sulfonate and 216g of deionized water into a reactor, stir evenly to obtain an emulsifier solution, then mix 60g of methyl methacrylate, 120g of butyl acrylate, 7g of methacrylic acid, 10g of styrene, and 16.3g of functional monomer solution A to obtain solution B, take one tenth of solution B (the first sub-solution) and add it into the reactor to fully mix with the emulsifier solution, and disperse it evenly at high speed to obtain a pre-emulsion.

[0079] Step 4: Dissolve 4.1 g of ammonium persulfate in 72 g of deionized water to obtain an aqueous solution of ammonium persulfate, and take one-third of the aqueous solution of ammonium persulfate as solution C (the third sub-solution), and take two-thirds of the aqueous solution of ammonium persulfate as solution D (the fourth sub-solution).

[0080] Step 5: After the temperature in the reactor is raised to 80°C, solution C and pre-emulsion are added in sequence, and the seed emulsion is obtained after high-speed stirring and heat preservation for 30 minutes. Then, the remaining nine-tenths of solution B (the second sub-solution) and solution D are uniformly added dropwise for 210 minutes; after the remaining solution B and solution D are added dropwise, the mixture is kept warm at 80°C for 2 hours. After the heat preservation is completed, the temperature in the reactor is lowered to 35°C, and an appropriate amount of ammonia water is added to adjust the pH of the liquid in the reactor to 8. After stirring for 30 minutes, the liquid in the reactor is filtered to obtain a strippable acrylic emulsion.

[0081] Example 4

[0082] The method for preparing a strippable acrylic emulsion comprises the following steps: Step 1: Dissolve 6 g of 2-amino-4-hydroxy-6-methylpyrimidine in dimethyl sulfoxide at 170°C, add 8 g of isocyanoethyl methacrylate, and immediately cool to room temperature in an ice-water bath; wash with cyclohexane, filter, and dry to obtain 13 g of modified UPy monomer.

[0083] Step 2: 1.5 g of modified UPy monomer and 1 g of 1,5-pentanediol dimethacrylate were dissolved in 12 g of dimethyl sulfoxide at 40° C. to prepare a functional monomer solution A.

[0084] Step 3: Add 5.5g of sodium dodecyl sulfate and 215g of deionized water into a reactor, stir evenly to obtain an emulsifier solution, then mix 60g of methyl methacrylate, 120g of butyl acrylate, 5g of methacrylic acid, 10g of styrene, and 14.5g of functional monomer solution A to obtain solution B, take one tenth of solution B (the first sub-solution) and add it into the reactor to fully mix with the emulsifier solution, and disperse it evenly at high speed to obtain a pre-emulsion.

[0085] Step 4: Dissolve 3.5 g of ammonium persulfate in 70 g of deionized water to obtain an aqueous solution of ammonium persulfate, and take one-third of the aqueous solution of ammonium persulfate as solution C (the third sub-solution), and take two-thirds of the aqueous solution of ammonium persulfate as solution D (the fourth sub-solution).

[0086] Step 5: After the temperature in the reactor is raised to 78°C, solution C and pre-emulsion are added in sequence, and the seed emulsion is obtained after high-speed stirring and heat preservation for 30 minutes. Then, the remaining nine-tenths of solution B (the second sub-solution) and solution D are uniformly added dropwise for 210 minutes; after the remaining solution B and solution D are added dropwise, the mixture is kept warm at 80°C for 2 hours. After the heat preservation is completed, the temperature in the reactor is lowered to 35°C, and an appropriate amount of ammonia water is added to adjust the pH of the liquid in the reactor to 8. After stirring for 30 minutes, the liquid in the reactor is filtered to obtain a strippable acrylic emulsion.

[0087] Comparative Example 1 The preparation method of acrylic emulsion comprises the following steps: Step 1: Add 7.5g of sodium dodecyl sulfate and 225g of deionized water into a reactor, stir evenly, then mix 68g of methyl methacrylate, 130g of butyl acrylate, 10g of methacrylic acid, 15g of styrene, and 1.5g of N,N'-methylenebisacrylamide to prepare solution A, take one tenth of solution A and add it into the reactor, disperse evenly at high speed to prepare a pre-emulsion.

[0088] Step 2: Dissolve 4.5 g of ammonium persulfate in 76 g of deionized water to obtain an aqueous solution of ammonium persulfate, and take one-third of the aqueous solution of ammonium persulfate as solution B, and take two-thirds of the aqueous solution of ammonium persulfate as solution C.

[0089] Step 3: After the temperature in the reactor is raised to 75°C, solution B and pre-emulsion are added in sequence, and the seed emulsion is obtained after high-speed stirring and heat preservation for 30 minutes. Then, the remaining nine-tenths of solution A and solution C are uniformly added dropwise for 210 minutes; after the remaining solution A and solution C are added dropwise, the mixture is kept warm at 80°C for 2 hours. After the heat preservation is completed, the temperature in the reactor is lowered to 35°C, and an appropriate amount of ammonia water is added to adjust the pH of the liquid in the reactor to 7. After stirring for 30 minutes, the liquid in the reactor is filtered to obtain a strippable acrylic emulsion.

[0090] Comparative Example 2 The preparation method of acrylic emulsion comprises the following steps: Step 1: Dissolve 5.9 g of 2-amino-4-hydroxy-6-methylpyrimidine in dimethyl sulfoxide at 170° C., add 7.7 g of isocyanoethyl methacrylate, and immediately cool to room temperature in an ice-water bath; wash with cyclohexane, filter, and dry to obtain 13 g of modified UPy monomer.

[0091] Step 2: 3 g of modified UPy monomer was dissolved in 15 g of dimethyl sulfoxide at 40° C. to prepare solution A.

[0092] Step 3: Add 7.5g of sodium dodecyl sulfate and 225g of deionized water into a reactor, stir evenly, then mix 65g of methyl methacrylate, 130g of butyl acrylate, 10g of methacrylic acid, 15g of styrene and solution A to obtain solution B, take one tenth of solution B and add it into the reactor, disperse evenly at high speed to obtain a pre-emulsion.

[0093] Step 4: dissolving 4.5 g of ammonium persulfate in 76 g of deionized water to obtain an aqueous solution of ammonium persulfate, and taking one third of the aqueous solution of ammonium persulfate as solution C, and taking two thirds of the aqueous solution of ammonium persulfate as solution D; Step 5: After the temperature in the reactor is raised to 75°C, solution C and pre-emulsion are added in sequence, and the seed emulsion is obtained after high-speed stirring and heat preservation for 30 minutes. Then, the remaining nine-tenths of solution B and solution D are uniformly added dropwise for 210 minutes; after the remaining solution B and solution D are added dropwise, the mixture is kept warm at 80°C for 2 hours. After the heat preservation is completed, the temperature in the reactor is lowered to 35°C, and an appropriate amount of ammonia water is added to adjust the pH of the liquid in the reactor to 7. After stirring for 30 minutes, the liquid in the reactor is filtered to obtain a strippable acrylic emulsion.

[0094] After the peelable acrylic emulsion is prepared by Examples 1 to 4 and Comparative Examples 1 and 2, the peelable acrylic emulsion prepared in Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 can be uniformly coated on tinplate. After curing, the tensile strength and elongation at break of the peelable film are tested according to GB / T 1040.3-2006, and the peelability of the peelable film is tested according to GB / T 2790-1995. The test results are shown in Table 1: Table 1

[0095] It can be seen from Table 1 that, with Comparative Examples 1 to 2 as controls, the peelable films prepared according to the method for preparing the peelable acrylic emulsion proposed in the embodiments of the present disclosure (corresponding to Examples 1 to 4) all have a tensile strength of 7 to 9 MPa, which is significantly higher than that of the comparative examples. With the reduction of the chemical crosslinking agent and the physical crosslinking agent (modified UPy monomer) (from Example 1 to Example 3), the tensile strength of the peelable film also decreases slightly.

[0096] As shown in Table 1, with Comparative Examples 1 to 2 as controls, the elongation at break of the peelable film (corresponding to Examples 1 to 4) prepared by the method for preparing the peelable acrylic emulsion proposed in the embodiments of the present disclosure is less than 500%. Since the greater the elongation at break, the longer the stretching and the softer the film, the external force that should be used to peel the film is used to stretch and deform the film because the film is too soft, so more external force is required, resulting in increased difficulty in peeling. It can be seen that the embodiments of the present disclosure improve the tensile strength while making the film easier to peel, thus avoiding the problems of fracture and residue caused by difficult peeling to a certain extent.

[0097] Figure 2 Schematic diagram showing the results of a film formed by a peelable acrylic emulsion prepared in an embodiment of the present disclosure before and after peeling on tinplate (the upper part is the unpeeled area, and the lower part is the peeled area), as shown in FIG. Figure 2 As shown, the prepared peelable film can be completely peeled off from the tinplate without any residual film. Figure 3 The results of the film formed by the peelable acrylic emulsion prepared in Comparative Example 2 before and after peeling on tinplate are shown. Although the film can be peeled, there are many broken parts, that is, the film is difficult to peel completely. It can be seen that the film made of the peelable acrylic emulsion prepared in the embodiment of the present disclosure can be completely peeled and has high mechanical strength.

[0098] For this, see Figure 4 The double network structure diagram of the film formed by the peelable acrylic emulsion prepared in the embodiment of the present disclosure is shown and Figure 5The energy dissipation mechanism diagram of the peelable acrylic emulsion film prepared according to the embodiment of the present disclosure when peeling is shown. Since the peelable film prepared according to the embodiment of the present disclosure has a double network structure of physical crosslinking and chemical crosslinking, the chemical crosslinking serves as the skeleton structure of the film, and the physical crosslinking can dissipate external energy by breaking, the peelable film has high tensile strength and can be completely peeled without breaking. At the same time, you can also refer to Figure 6 The H NMR spectrum of the modified UPy monomer prepared in the embodiment of the present disclosure is shown (the abscissa is the chemical shift, the ordinate is the absorption peak intensity). Figure 6 It can be seen that there are double bond signal peaks at 6.17 ppm and 5.54 ppm, so the double bonds with high polymerization activity are successfully grafted onto the UPy group, so that physical crosslinking (multiple hydrogen bonds) can be provided for the film formed by the strippable acrylic emulsion. However, since Comparative Examples 1 and 2 only contain one network structure, namely a chemical crosslinking network or a physical crosslinking network, their tensile strength is low, and they are easy to break when peeled and the number of breaks is large.

[0099] In addition, the disclosed embodiment also provides an application method of a peelable acrylic emulsion, wherein the peelable acrylic emulsion is coated on the surface of a product to form a peelable layer; after the peelable layer has reached the end of its service life or when the purpose of use has been achieved, it can be completely peeled off from the surface of the product to reduce various damages to the product and extend the service life of the product. The products include but are not limited to electronic parts, precision instruments, weapons and equipment, etc., which may have surface damage such as scratches, abrasions, wear, and contamination during production, processing, storage, and transportation.

[0100] In the technical solution provided in the embodiments of the present disclosure, a structure in which a double bond is grafted to the UPy group is provided by modifying the UPy monomer, and a chemical crosslinking agent is added at the same time, and a strippable acrylic emulsion is prepared by emulsion polymerization. After the emulsion is formed into a film, it has a double crosslinking network of physical crosslinking (multiple hydrogen bonds) and chemical crosslinking, and therefore has higher mechanical strength. When it is stripped under the action of an external force, the physical crosslinking (hydrogen bonds) inside the film breaks to offset the external tension, and the chemical crosslinking serves as a rigid skeleton of the film, thereby improving the mechanical strength of the film and ensuring that the strippable film is completely stripped, that is, a method for preparing a high-strength strippable acrylic emulsion is provided.

[0101] It should be noted that the above embodiments are only illustrative of the principles and effects of the present disclosure, and are not intended to limit the present disclosure. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present disclosure. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present disclosure should still be covered by the claims of the present disclosure.

Claims

1. A method for preparing a strippable acrylic emulsion, characterized in that: include: dissolving the modified UPy monomer and the cross-linking agent in dimethyl sulfoxide to obtain a functional monomer solution; The functional monomer solution and the mixed monomer are fully mixed to obtain a first solution, and the first solution is divided into a first sub-solution and a second sub-solution, and the first sub-solution is fully mixed with an emulsifier solution and dispersed uniformly to obtain a pre-emulsion; The ammonium persulfate aqueous solution is divided into a third sub-solution and a fourth sub-solution, and the third sub-solution and the pre-emulsion are mechanically stirred and kept warm at a first temperature to obtain a seed emulsion; Adding the second sub-solution and the fourth sub-solution dropwise to the seed emulsion to fully react and keeping the mixture at the first temperature to obtain a second solution; The pH value of the second solution is adjusted to a target value at a second temperature and stirring is continued to obtain a mixed solution, and the obtained mixed solution is filtered to obtain a strippable acrylic emulsion; wherein the second temperature is lower than the first temperature.

2. The method for preparing a strippable acrylic emulsion according to claim 1, characterized in that: The mass fraction of the functional monomer solution is 20%~30%; wherein the mass ratio of the cross-linking agent to the modified UPy monomer is 1:(1.5~2).

3. The method for preparing a strippable acrylic emulsion according to claim 1, characterized in that: The steps of preparing the modified UPy monomer include: 2-Amino-4-hydroxy-6-methylpyrimidine is fully dissolved in dimethyl sulfoxide, and isocyanoethyl methacrylate is added and then cooled to room temperature. The modified UPy monomer is obtained by washing, filtering and drying.

4. The method for preparing a strippable acrylic emulsion according to claim 3, characterized in that: The mass ratio of the 2-amino-4-hydroxy-6-methylpyrimidine to the isocyanoethyl methacrylate is 1:(1.3-1.8).

5. The method for preparing a strippable acrylic emulsion according to claim 1, characterized in that: The cross-linking agent is one or more of N,N'-methylenebisacrylamide, 1,5-pentanediol dimethacrylate, and triethylene glycol dimethacrylate; the mixed monomer includes methyl methacrylate, butyl acrylate, methacrylic acid, and styrene, and the mass ratio of methyl methacrylate, butyl acrylate, methacrylic acid, and styrene is 1:2: (0.08-0.16): (0.16-0.23); Wherein, the added amount of the functional monomer solution is 7.4% to 8.9% of the mass of the mixed monomer.

6. The method for preparing a strippable acrylic emulsion according to claim 1, characterized in that: The preparation steps of the emulsifier solution include: Mechanically stirring the emulsifier and deionized water to obtain the emulsifier solution; Wherein, the emulsifier is one or more of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; the mass ratio of the emulsifier to deionized water is 1:(28~40), and the added amount of the emulsifier is 2.8%~3.6% of the mass of the mixed monomer.

7. The method for preparing a strippable acrylic emulsion according to claim 1, characterized in that: The preparation steps of the aqueous ammonium persulfate solution include: Fully dissolving ammonium persulfate in deionized water to obtain the ammonium persulfate aqueous solution; The mass ratio of the ammonium persulfate to deionized water is 1:(16-20), and the amount of the ammonium persulfate added is 1.7%-2.1% of the mass of the mixed monomer.

8. The method for preparing a strippable acrylic emulsion according to any one of claims 1 to 7, characterized in that: The first temperature is 73-83°C, and the second temperature is lower than 40°C.

9. The method for preparing a strippable acrylic emulsion according to any one of claims 1 to 7, characterized in that: The target value is 7~8.

10. A strippable acrylic emulsion, characterized in that: The strippable acrylic emulsion is prepared by the method for preparing a strippable acrylic emulsion according to any one of claims 1 to 9.

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