High-performance bio-based pressure-sensitive adhesive and preparation method thereof

Abstract

The invention relates to the field of water-based pressure-sensitive adhesives, and particularly discloses a high-performance bio-based pressure-sensitive adhesive and a preparation method thereof. The preparation method of the high-performance bio-based pressure-sensitive adhesive comprises the following steps: (1) preparing a pre-emulsion; (2) preparing an initiator solution; (3) preparing an additional solution; and (4) preparing a polymer emulsion, namely the pressure-sensitive adhesive. The high-performance bio-based pressure-sensitive adhesive can keep low viscosity under high solid content.

Description

Technical Field

[0001] This application relates to the field of water-based pressure-sensitive adhesives, and more specifically, to a high-performance bio-based pressure-sensitive adhesive and its preparation method. Background Technology

[0002] Water-based pressure-sensitive adhesives (PSA) are favored by the industry for their environmental friendliness (free of volatile organic compounds, VOCs), safety, and wide range of applications. These adhesives are widely used in products such as labels, tapes, and notebooks, offering advantages including ease of use, rapid drying, cost-effectiveness, and good durability.

[0003] However, traditional water-based pressure-sensitive adhesives still have some problems. For example, when the solid content of the emulsion exceeds 50%, the viscosity of the emulsion system increases sharply during the emulsion polymerization process. This increased viscosity leads to problems in monomer mixing and heat transfer during the reaction, making the emulsion polymerization unstable, resulting in a large amount of agglomerates, which is detrimental to production and may even cause experimental failure. Therefore, preparing pressure-sensitive adhesives with high solid content and low viscosity has always been a research hotspot both domestically and internationally, and it is technically quite challenging. Summary of the Invention

[0004] In order to enable pressure-sensitive adhesives to maintain low viscosity at high solid content, this application provides a high-performance bio-based pressure-sensitive adhesive and its preparation method.

[0005] In a first aspect, this application provides a method for preparing a high-performance bio-based pressure-sensitive adhesive, employing the following technical solution: A method for preparing a high-performance bio-based pressure-sensitive adhesive includes the following steps: (1) Preparation of preemulsion: 220-230 parts by weight of deionized water and 53-62 parts by weight of emulsifier are stirred and mixed, then 20-77 parts by weight of styrene, 42-459 parts by weight of alkyl methacrylate, 30-62 parts by weight of vinyl acetate, 532-1000 parts by weight of tetrahydrofurfuryl acrylate, 4-7 parts by weight of acid, and 0.15-0.4 parts by weight of chain transfer agent are added, and stirring is continued to obtain preemulsion; (2) Preparation of initiator solution: Dissolve the free radical initiator in deionized water to prepare an initiator solution with a mass concentration of 3% to 10%; (3) Preparation of additional solutions: Dissolve the oxidizing and reducing agent in deionized water to prepare the first additional solution with a mass concentration of 5% to 30%; dissolve tert-butyl hydroperoxide in deionized water to prepare the second additional solution with a mass concentration of 5% to 35%. (4) Preparation of polymer emulsion: 120-160 parts by weight of deionized water, 1-1.5 parts by weight of buffer, 3-10 parts by weight of emulsifier, 5-16 parts by weight of alkyl methacrylate, 50-116 parts by weight of tetrahydrofurfuryl acrylate and 0.3-0.6 parts by weight of acid are added to the reactor, mixed and stirred, heated, and a portion of the initiator solution is added to the reactor for reaction. The pre-emulsion and the remaining initiator solution are added separately, and the reaction continues. The total amount of initiator solution added is 97-98.5 parts by weight, and the total amount of pre-emulsion added is 1387-1504 parts by weight. Then, while lowering the temperature, 34-56 parts by weight of additional solution are added. Finally, when the temperature drops to 30°C, 0.3-1 parts by weight of preservative is added until the reaction is completed, and the polymer emulsion, i.e. pressure-sensitive adhesive, is obtained.

[0006] By adopting the above technical solution, due to the use of a semi-continuous emulsion polymerization process, multiple functional monomers undergo copolymerization reactions in an aqueous medium in the presence of free radical initiators and buffers, forming an acrylic copolymer particle system with multiphase structural characteristics.

[0007] Among them, styrene monomers have a high rigidity structure, and their introduction can improve the cohesive strength and creep resistance of the copolymer, while also helping to maintain the structural stability of the emulsion particles under high solids content conditions. Alkyl methacrylate, as the main film-forming monomer, can effectively control the glass transition temperature by adjusting the side chain structure while ensuring good film-forming performance, thus maintaining a low system viscosity under high solids content conditions. Vinyl acetate can improve the flexibility and film-forming continuity of the copolymer system, which is beneficial to improving the adaptability of pressure-sensitive adhesives to various substrates. Tetrahydrofurfuryl acrylate is derived from bio-based raw materials. Its molecular structure contains a large-volume cyclic structure, which helps to reduce the effective entanglement density between polymer chains, thereby achieving low viscosity under high solids content conditions, while also taking into account excellent initial tack and peel performance. Acidic monomers provide carboxyl functional groups, which can improve the surface charge stability of emulsion particles and enhance the dispersion stability of the emulsion under high solids content conditions.

[0008] The synergistic effect of the above monomers in terms of structure and function enables the pressure-sensitive adhesive prepared in this application to maintain a low system viscosity and good processing stability even with a significant increase in solid content.

[0009] In addition, the supplemental solution is added after the main polymerization reaction is essentially complete. This post-polymerization treatment helps to consume residual monomers, thereby improving polymer uniformity, adhesive properties, and product stability. The addition of preservatives inhibits microbial growth and ensures the storage stability of high-solids-content, low-viscosity pressure-sensitive adhesives.

[0010] The overall preparation process is simple, economical and efficient, and the pressure-sensitive adhesive obtained can maintain low viscosity under high solid content.

[0011] Optionally, the emulsifier is one or more of the following: ethoxylated alcohol ammonium sulfate, secondary alcohol polyoxyethylene ether, sodium diisooctyl sulfosuccinate, and sodium C10-C14 sulfonate.

[0012] By adopting the above technical solution, the emulsifier is free of APE and is environmentally friendly, minimizing the generation of harmful chemicals and thus reducing the potential environmental burden.

[0013] Optionally, in step (4), styrene needs to be added to the reactor in a weight of 1 to 2 parts; a buffer solution also needs to be prepared, and the buffer solution needs to be added dropwise when adding the pre-emulsion and initiator solution, with a weight of 25 to 26 parts.

[0014] By employing the above technical solution and adding a small amount of styrene monomer, the structural integrity and cohesive strength of polymer particles can be further improved in the early stages or during polymerization. Styrene has a high glass transition temperature, and its introduction into the copolymer system helps to form relatively rigid polymer segments, thereby suppressing excessive flow of polymer chains under high solids content conditions and reducing the sharp increase in viscosity of the emulsion system caused by particle deformation or aggregation.

[0015] Simultaneous addition of a buffer solution during the dropwise addition of the preemulsion and initiator solution can effectively control pH fluctuations in the polymerization system, preventing excessive pH changes caused by the accumulation of acidic monomers or initiator decomposition. A stable pH environment helps maintain the charge balance on the surface of emulsion particles, reducing agglomerate formation and thus significantly improving the stability and controllability of the polymerization reaction under high solids content conditions.

[0016] Optionally, the buffer solution is prepared by dissolving a buffer in deionized water, with a mass concentration of 7% to 10%, and the buffer is one or more of sodium pyrophosphate, sodium citrate, and sodium bicarbonate.

[0017] Optionally, the alkyl methacrylate is one or more of methyl methacrylate, citronellol methacrylate, isobornyl methacrylate, and menthyl methacrylate.

[0018] By employing the above technical solution and selecting one or more of methyl methacrylate, citronellol methacrylate, isobornyl methacrylate, and menthyl methacrylate as alkyl methacrylate monomers, a side-chain structure with steric hindrance effect can be introduced while adjusting the glass transition temperature of the copolymer. Citronellol, isobornyl, and menthyl methacrylate monomers are derived from bio-based raw materials and have a larger molecular volume, which helps to reduce the tight packing between polymer chain segments, thereby effectively reducing the viscosity of the system under high solids content conditions. Furthermore, these monomers can improve the flexibility and surface wetting properties of the pressure-sensitive adhesive while ensuring good initial tack and peel performance, resulting in excellent adhesion performance on various substrates.

[0019] Optionally, the acid is acrylic acid or itaconic acid.

[0020] By adopting the above technical solution and selecting acrylic acid or itaconic acid as acidic monomers, carboxyl functional groups can be introduced into the copolymer molecular chain to increase the surface charge density of emulsion particles, thereby enhancing the electrostatic stability of the emulsion under high solid content conditions.

[0021] Compared to systems that rely solely on emulsifiers for stability, the introduction of acidic monomers helps reduce the emulsion's dependence on emulsifier dosage and decreases the nonlinear viscosity increase under high solids content conditions. Simultaneously, itaconic acid, as a dicarboxylic acid, can enhance intermolecular interactions to some extent through its molecular structure, thereby improving the cohesive strength and shear resistance of the pressure-sensitive adhesive.

[0022] Optionally, the chain transfer agent is 1-dodecyl mercaptan.

[0023] By employing the above technical solution and selecting 1-dodecyl mercaptan as a chain transfer agent, the molecular weight and distribution of the polymer can be effectively controlled, preventing excessive molecular weight growth during polymerization and thus avoiding a sharp increase in system viscosity. In high-solids-content emulsion polymerization systems, an appropriate amount of chain transfer agent helps reduce the degree of entanglement between polymer chain segments, thereby achieving a balance between low viscosity and high solids content without significantly affecting the adhesive properties of the pressure-sensitive adhesive.

[0024] Optionally, the free radical initiator is ammonium persulfate or sodium persulfate.

[0025] Optionally, in step (3), the second additional solution also includes ammonium persulfate.

[0026] Secondly, this application provides a high-performance bio-based pressure-sensitive adhesive, employing the following technical solution: A high-performance bio-based pressure-sensitive adhesive, prepared by the above method, has a solid content of 65%–72%, a viscosity of 300–600 mPa·s, and a pH value of 4–6 after filtration through a 100-mesh nylon filter.

[0027] By adopting the above technical solution, the pressure-sensitive adhesive produced has high solids content and low viscosity, making it suitable for a wide range of applications, especially for preparing various self-adhesive products such as sheets, labels, tapes, and protective films. The pressure-sensitive adhesive has a low content of volatile substances, posing minimal risk to human health and the environment, thus ensuring safety during production and use.

[0028] Pressure-sensitive adhesive is a milky white liquid with blue fluorescent properties. After drying, it can form a colorless and transparent film. Its main performance advantages include: high initial tack, fast drying speed, and excellent peel strength. In summary, this application has the following beneficial effects: The preparation method of the high-performance bio-based pressure-sensitive adhesive provided in this application is simpler and more efficient, effectively reducing energy consumption and manpower requirements, and minimizing the generation of harmful chemicals, thereby reducing the potential environmental impact.

[0029] The pressure-sensitive adhesive provided in this application is particularly suitable for the preparation of labels, tapes, and protective films. This pressure-sensitive adhesive possesses excellent initial tack and rapid drying properties, ensuring efficient and automated production line operation. Its environmentally friendly properties directly address the industry's urgent need for sustainable alternatives.

[0030] The core technological innovation of this application lies in successfully solving the technical challenge of maintaining low viscosity of pressure-sensitive adhesives at high solids content. Through a simplified process, while significantly improving the performance of the final product (such as bond strength and stability) and reducing production costs, it still maintains the core advantages of traditional water-based pressure-sensitive adhesives, such as rapid drying and environmental protection characteristics. Detailed Implementation

[0031] The present application will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments shall be performed under conventional conditions or conditions recommended by the manufacturer, and the raw materials used in the following embodiments shall be commercially available unless otherwise specified.

[0032] Kathan™ LX, purchased from Dow Chemical Company.

[0033] Reasop SR-1025, alkylphenol-free polyoxyethylene ether (APEO), purchased from Nanjing Qinghai Trading Co., Ltd.

[0034] Rhodapex® AB 20U, 29% solids content, manufactured by Shanghai Jin Chemical Co., Ltd., is free of APEO (alkylphenol polyoxyethylene ether) and formaldehyde.

[0035] ABEX 2515 (50% solids content) was purchased from Shanghai Kaiyin Chemical Co., Ltd.

[0036] Aerosol® OT-75 (75% solids content), purchased from HJUNKEL (Foshan) Co., Ltd.

[0037] DowfaX™ 2A1, purchased from Shanghai Kaiyin Chemical Co., Ltd.

[0038] Tergitol 15-S-9 was purchased from Shanghai Kaiyin Chemical Co., Ltd.

[0039] Reasop S-10, purchased from Nanjing Qinghai Trading Co., Ltd.

[0040] Tetrahydrofurfuryl acrylate was purchased from Shandong Changhong Chemical Co., Ltd.

[0041] Methyl methacrylate was purchased from Mitsubishi Chemical Group.

[0042] Isoborneol methacrylate was purchased from Mitsubishi Chemical Group.

[0043] Menthyl methacrylate was purchased from Wuhan Fengtai Weiyuan Technology Co., Ltd.

[0044] Citronellol methacrylate is prepared as follows: 78.14g citronellol, 51.64g methacrylic acid, 13g NKC-9 resin acid (esterification catalyst), composite polymerization inhibitor (0.26g 4-methoxyphenol and 0.065g phenothiazine), and 130ml toluene are added to a reaction vessel. Stirring is started, and nitrogen gas is slowly introduced into the system (flow rate approximately 1-2 bubbles / second). Heating is initiated, and the reaction solution is slowly heated to 112℃ for azeotropic dehydration. This continues until 9ml of water is discharged. The mixture is then cooled to 85℃, and the reaction mixture is hot-filtered through a preheated sintered glass funnel or filter cloth to separate the solid catalyst. The reaction flask and catalyst filter cake are washed 2-3 times with a small amount of hot toluene (approximately 20mL), and the filtrates are combined. The mixture is heated to 110℃ under normal pressure, and toluene is distilled off at boiling point. Then, 0.005g of polymerization inhibitor 4-methoxyphenol was added to the receiving bottle, and a vacuum of 0.5 kPa was applied. After the vacuum stabilized, the mixture was heated to 100°C to distill off citronellol methacrylate.

[0045] Acrylic acid, CAS No.: 79-10-7, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0046] Itaconic acid was purchased from Zhejiang Guoguang Biochemical Co., Ltd.

[0047] 1-Dodecyl mercaptan, brand: Arkema, France.

[0048] Bruggolite® FF6M is a formaldehyde-free sulfur-based reducing agent manufactured by Brüggemann. Example Example 1

[0049] The polymerization reaction takes place in a 2-liter jacketed reactor connected to a water bath thermostat, with nitrogen gas introduced into the reactor. The reactor is equipped with a reflux condenser, thermocouples, two tilting turbine stirrers, and three feed lines connected to a pump.

[0050] (1) Preparation of preemulsion: 220g deionized water, 14g Reasop SR-1025 (emulsifier), 0.15g 1-dodecyl mercaptan (chain transfer agent), 22g Rhodapex® AB 20U (emulsifier), 15g ABEX 2515 (50% solids content) (emulsifier) ​​and 2g Aerosol® OT-75 (75% solids content) (emulsifier) ​​were added to a 2L mixer and stirred at 600rpm for 10 minutes. While stirring, 32g styrene, 200g methyl methacrylate (alkyl methacrylate), 62g vinyl acetate, 930g tetrahydrofurfuryl acrylate and 6.5g acrylic acid (acid) were added to the mixer. All materials were stirred at 500rpm for 45 minutes to form a uniform preemulsion.

[0051] (2) Preparation of initiator solution: Dissolve 3.5g of ammonium persulfate in 95g of deionized water to form an initiator solution.

[0052] (3) Preparation of additional solution: Dissolve 3.6g Bruggolite® FF6M (oxidizing and reducing agent) in 10g deionized water to prepare the first additional solution; take 1.2g ammonium persulfate and 6g tert-butyl hydroperoxide and dissolve them in 14g deionized water to prepare the second additional solution.

[0053] (4) Preparation of polymer emulsion: Add 120g deionized water, 0.5g sodium pyrophosphate (buffer), 1g sodium citrate (buffer), 1g Rhodapex® AB20U (29% solids) (emulsifier), 3g ABEX® 2515 (50% solids) (emulsifier), 16g menthyl methacrylate (alkyl methacrylate), 73g tetrahydrofurfuryl acrylate and 0.3g acrylic acid to the reactor and mix for 45 minutes.

[0054] The reactor was heated to 80°C, and 11g of initiator solution was added. The reaction was allowed to proceed for 20 minutes. When the temperature reached 85°C, a homogeneous preemulsion was added at a rate of 8g / min, and the initiator solution was added at a rate of 0.3g / min. The reactor temperature was maintained at 85°C for 180 minutes, and then the temperature was increased to 88°C. The addition rates of the preemulsion and initiator solution were adjusted to 5.1g / min and 0.36g / min, respectively.

[0055] Over 60 minutes, additional solution is added to the reactor while the temperature is lowered. When the temperature drops to 30°C, 0.5 g of Kathan™ LX (preservative) is added. The reaction continues until completion, yielding a polymer emulsion, i.e., pressure-sensitive adhesive.

[0056] The obtained pressure-sensitive adhesive has a solid content of 71.6% (by weight), a viscosity of 550 mPa·s, and a pH value of 4.3 after filtration through a 100-mesh nylon filter. Example 2

[0057] The polymerization reaction was carried out in the same reactor as in Example 1.

[0058] (1) Preparation of preemulsion: 220g deionized water, 7g Reasop SR-1025 (emulsifier), 0.4g 1-dodecyl mercaptan (chain transfer agent), 29g Rhodapex AB 20U (emulsifier), 18g ABEX 2515 (50% solids content) (emulsifier) ​​and 1.8g Aerosol OT-75 (75% solids content) (emulsifier) ​​were added to a 2L mixer and stirred at 600rpm for 10 minutes. While stirring, 77g styrene, 433g isobornyl methacrylate (alkyl methacrylate), 39g vinyl acetate, 26g citronellol methacrylate (alkyl methacrylate), 532g tetrahydrofurfuryl acrylate and 4.5g itaconic acid (acid) were added to the mixer and all materials were stirred at 500rpm for 45 minutes to form a uniform preemulsion.

[0059] (2) Preparation of initiator solution: Dissolve 5.5g of ammonium persulfate in 93g of deionized water to form an initiator solution.

[0060] (3) Preparation of additional solution: Dissolve 3.5g Bruggolite® FF6M (oxidizing and reducing agent) in 10g deionized water to prepare the first additional solution; take 1.2g ammonium persulfate and 6g tert-butyl hydroperoxide and dissolve them in 14g deionized water to prepare the second additional solution.

[0061] (4) Preparation of polymer emulsion: Add 120g deionized water, 0.5g sodium pyrophosphate (buffer), 1g sodium citrate (buffer), 5g Rhodapex® AB20U (29% solids) (emulsifier), 5g ABEX® 2515 (50% solids) (emulsifier), 10g isobornyl methacrylate (alkyl methacrylate), 116g tetrahydrofurfuryl acrylate and 0.6g itaconic acid (acid) to the reactor and mix for 45 minutes.

[0062] The reactor was heated to 75°C, and the initiator solution was added to the reactor at a rate of 0.24 g / min for 45 minutes. The temperature was then raised to 85°C, and after 30 minutes, the preemulsion was added at a rate of 8 g / min, and the initiator solution was added at a rate of 0.3 g / min. The reactor temperature was maintained at 85°C for 120 minutes. Then, the temperature was raised to 88°C, and the addition rates of the preemulsion and initiator solution were changed to 5.1 g / min and 0.36 g / min, respectively.

[0063] Over 60 minutes, additional solution is added to the reactor while the temperature is lowered. When the temperature drops to 30°C, 0.5 g of Kathan™ LX (preservative) is added. The reaction continues until completion, yielding a polymer emulsion, i.e., pressure-sensitive adhesive.

[0064] The obtained pressure-sensitive adhesive has a solid content of 70.8% (by weight), a viscosity of 570 mPa·s, and a pH value of 4.1 after filtration through a 100-mesh nylon filter. Example 3

[0065] The polymerization reaction was carried out in the same reactor as in Example 1.

[0066] (1) Preparation of pre-emulsion: Add 230g deionized water, 30g Reasop S-10 (emulsifier), 0.15g 1-dodecyl mercaptan (chain transfer agent), 30g DowfaX™ 2Al (emulsifier), and 2g Tergitol 15-S-9 (emulsifier) ​​to a 2L mixer and stir at 600rpm for 10 minutes. While stirring, add 20g menthyl methacrylate (alkyl methacrylate), 20g styrene, 30g vinyl acetate, 22g citronellol methacrylate (alkyl methacrylate), 1000g tetrahydrofurfuryl acrylate, and 5.6g acrylic acid to the mixer in sequence, and stir the mixture at 350rpm for 30 minutes until a homogeneous pre-emulsion is formed.

[0067] (2) Preparation of initiator solution: Dissolve 9g of sodium persulfate in 88g of deionized water to form an initiator solution.

[0068] (3) Preparation of additional solution: Dissolve 1.4g Bruggolite® FF6M (oxidizing and reducing agent) in 26.2g deionized water to prepare the first additional solution; take 1.4g tert-butyl hydroperoxide and dissolve it in 26.2g deionized water to prepare the second additional solution.

[0069] (4) Preparation of polymer emulsion: Dissolve 2g of sodium citrate (buffer) in 23.6g of deionized water to prepare a buffer solution.

[0070] Add 160g deionized water, 1g sodium pyrophosphate (buffer), 1g DowfaX™ 2Al (emulsifier), and 2g Tergitol 15-S-9 (emulsifier) ​​to the reactor and mix thoroughly. Next, add 50g tetrahydrofurfuryl acrylate, 5g methyl methacrylate (alkyl methacrylate), 0.3g acrylic acid, and 1.15g styrene to the reactor and mix for 10 minutes.

[0071] The reactor was heated to 78°C. An initiator solution, comprising 10% of the total weight of the initiator solution, was added to the reactor. After a brief induction period, an exothermic polymerization reaction was initiated. After 10 minutes, the temperature stabilized at 80°C. Then, the pre-emulsion, initiator solution, and buffer solution were added to the reactor at rates of 5.9 g / min, 0.4 g / min, and 0.1 g / min, respectively. The temperature was maintained at 85°C for 240 minutes.

[0072] Over 60 minutes, additional solution is added to the reactor while the temperature is lowered. When the temperature drops to 30°C, 0.5 g of Kathan™ LX (preservative) is added. The reaction continues until completion, yielding a polymer emulsion, i.e., pressure-sensitive adhesive.

[0073] The obtained pressure-sensitive adhesive has a solid content of 67.2% (by weight), a viscosity of 420 mPa·s, and a pH value of 5.1 after filtration through a 100-mesh nylon filter. Example 4

[0074] The polymerization reaction was carried out in the same reactor as in Example 1.

[0075] (1) Preparation of preemulsion: Add 230g deionized water, 30g Reasop S-10 (emulsifier), 0.15g 1-dodecyl mercaptan (chain transfer agent), 30g DowfaX™ 2Al (emulsifier), and 2g Tergitol 15-S-9 (emulsifier) ​​to a 2L mixer and stir at 600rpm for 10 minutes. While stirring, add 31g methyl methacrylate (alkyl methacrylate), 20g styrene, 30g vinyl acetate, 18g citronellol methacrylate (alkyl methacrylate), 993g tetrahydrofurfuryl acrylate, and 5.6g acrylic acid to the mixer and stir the mixture at 350rpm for 30 minutes until a homogeneous preemulsion is formed.

[0076] (2) Preparation of initiator solution: Dissolve 9g of sodium persulfate in 88g of deionized water to form an initiator solution.

[0077] (3) Preparation of additional solution: Dissolve 1.4g Bruggolite® FF6M (oxidizing and reducing agent) in 26.2g deionized water to prepare the first additional solution; take 1.4g tert-butyl hydroperoxide and dissolve it in 26.2g deionized water to prepare the second additional solution.

[0078] (4) Preparation of polymer emulsion: Dissolve 2g of sodium bicarbonate (buffer) in 23.6g of deionized water to prepare a buffer solution.

[0079] Add 160g deionized water, 1g sodium pyrophosphate (buffer), 1g DowfaX™ 2Al (emulsifier), and 2g Tergitol 15-S-9 (emulsifier) ​​to the reactor and mix thoroughly. Next, add 50g tetrahydrofurfuryl acrylate, 5g methyl methacrylate (alkyl methacrylate), 0.3g acrylic acid, and 1.15g styrene to the reactor and mix for 10 minutes.

[0080] The reactor was heated to 78°C. An initiator solution, comprising 15% of the total weight of the initiator solution, was added to the reactor. After a brief induction period, an exothermic polymerization reaction was initiated. After 10 minutes, the temperature stabilized at 80°C. Then, the pre-emulsion, initiator solution, and buffer solution were added to the reactor at rates of 5.9 g / min, 0.4 g / min, and 0.1 g / min, respectively. The temperature was maintained at 85°C for 240 minutes.

[0081] Over 60 minutes, additional solution is added to the reactor while the temperature is lowered. When the temperature drops to 30°C, 0.5 g of Kathan™ LX (preservative) is added. The reaction continues until completion, yielding a polymer emulsion, i.e., pressure-sensitive adhesive.

[0082] The obtained pressure-sensitive adhesive has a solid content of 65.8% (by weight), a viscosity of 380 mPa·s, and a pH value of 5.6 after filtration through a 100-mesh nylon filter. Comparative Example

[0083] Comparative Example 1 Purchased from the market, high-solids acrylic system, Henkel's AQUENCE BG 9032 LM.

[0084] Comparative Example 2 Purchased from the market, water-based polyacrylate resin, Opaldi AC75022.

[0085] Comparative Example 3 Purchased from the market, water-based polyacrylate resin, Opaldi AC75063. Performance testing Detection methods

[0086] 1. Peel test: The peel test is used to measure the peel strength of pressure-sensitive adhesives. This test, according to the international peel strength testing guideline PSTC-101, evaluates the force required to peel the adhesive from a substrate at a specific speed. The test is conducted under controlled conditions (23±1℃ and 50±5% relative humidity) at a fixed peel rate and angle.

[0087] During testing, pressure-sensitive adhesives (24 mm wide, 300 mm long) prepared for each example and comparative example were pressed onto a clean stainless steel plate (3 inches x 6 inches) using a 10-pound roller to ensure constant pressure. The tapes were allowed to stand for 30 minutes, then peeled at a rate of 12 inches per minute. Peel force and displacement were recorded during this process, with results expressed in pounds per inch (lbs / inch). Peel strength was measured using an Instron universal testing system (4411 / 4464). Test results are detailed in Table 1.

[0088] 2. Shear test Shear adhesion tests were conducted on a standard steel plate. The pressure-sensitive adhesives prepared in each embodiment and comparative example were applied to the steel plate surface using a controlled rolling motion. The contact area was 1 inch x 1 inch. The steel plate was placed vertically and allowed to stand for 30 minutes to allow the tape to adhere. Then, a 1 kg object was attached to the free end of the tape. The failure time was then recorded. The test results are detailed in Table 1.

[0089] 3. Ring viscosity test The ring tack test is used to measure the pressure-sensitive adhesive properties of pressure-sensitive adhesives, particularly those that bond quickly upon contact and can be cleanly removed without leaving residue. The test involves applying a load for a specified time at a specific temperature, and then measuring the force required to peel the pressure-sensitive adhesive from the surface. During the test, a probe moves at a constant speed to contact the pressure-sensitive adhesive, maintains this force for 2 seconds, and then peels off at the same speed.

[0090] The pressure-sensitive adhesives prepared in each embodiment and comparative example were directly coated onto a 2-mil thick polyester film and tested on a stainless steel plate to evaluate the performance of the pressure-sensitive adhesives. The thickness of the pressure-sensitive adhesive film was approximately 1 mil. The test results are detailed in Table 1. Failure modes are indicated in parentheses.

[0091] 4. Drying speed The drying rate was evaluated by surface drying time test.

[0092] The pressure-sensitive adhesives prepared in each embodiment and comparative example were uniformly coated on a 2-mil polyester film with a wet film thickness of about 50 μm, and allowed to dry under static conditions of 23±1℃ and 50±5% relative humidity.

[0093] From the time the coating is completed, lightly touch the surface of the film with your finger every 30 seconds. When the surface of the film is no longer sticky to your finger and there is no obvious stringing, record the time as the surface drying time.

[0094] Each sample was tested three times, and the average value was taken. The test results are detailed in Table 1.

[0095] 5. The pressure-sensitive adhesives prepared in each embodiment and comparative example were tested for peel strength on stainless steel (SS), high-density polyethylene (HDPE) and corrugated cardboard (CC). The pressure-sensitive adhesives showed different adhesion to different substrates, reflecting the applicability of different substrates. The test results are detailed in Table 2.

[0096] Table 1. Comparison of basic performance of each embodiment and comparative example Sample source Solid content (wt%) Viscosity at 25℃ (mPa·s) Peel strength (lb / in, SS) Shearing (h, 1kg) Ring viscosity (lb / in) Surface drying time (min) Example 1 71.6 550 3.0 (Cohesion Failure) 13 2.8 3.5 Example 2 70.8 570 2.9 (Cohesion Failure) 16 2.7 3.6 Example 3 67.2 420 2.6 18 2.5 3.2 Example 4 65.8 380 2.4 20 2.3 3 Comparative Example 1 68.5 3000 3.1 15 2.6 6.5 Comparative Example 2 67 1500 2.2 14 2.1 4.8 Comparative Example 3 65 3000 2.5 12 2.3 5.6 Table 2. Peel performance of each sample on different substrates (lb / in) Sample source SS HDPE CC Example 1 3 2.4 2.7 Example 2 2.9 2.3 2.6 Example 3 2.6 2.1 2.4 Example 4 2.4 2 2.3 Comparative Example 1 3.1 1.9 2.1 Comparative Example 2 2.2 1.7 1.9 Comparative Example 3 2.5 1.8 2 Combining Examples 1-4 with Comparative Example 1, and referring to Tables 1 and 2, it can be seen that although the traditional high-solids water-based pressure-sensitive adhesive (Comparative Example 1) can provide high peel strength and shear performance, its system viscosity is significantly high and its drying speed is slow, which is not conducive to high-speed coating and industrial continuous processing. This application, by introducing bio-based bulk monomers, a Non-APE emulsion system, and a semi-continuous multiphase polymerization process, significantly reduces the system viscosity and significantly shortens the surface drying time under conditions of comparable or even higher solids content, demonstrating excellent processing adaptability.

[0097] Combining Example 1 and Comparative Example 2, and referring to Table 1, it can be seen that, under the premise of keeping the polymerization process and emulsion system consistent, after removing tetrahydrofurfuryl acrylate (Comparative Example 2), the viscosity of the pressure-sensitive adhesive system increased significantly, and the peel strength and ring tack both decreased. This indicates that bio-based bulky side-chain monomers have a significant effect on reducing molecular chain entanglement density, improving rheological properties under high solids content conditions, and enhancing pressure-sensitive adhesion performance.

[0098] Combining Example 2 and Comparative Example 3, and referring to Table 1, it can be seen that when the semi-continuous pre-emulsion process is cancelled and a one-time emulsion polymerization method is adopted (Comparative Example 3), the viscosity of the system increases significantly, the drying speed decreases, and the shear performance decreases. This indicates that the semi-continuous multiphase polymerization process plays a key role in controlling particle size distribution, reducing the viscosity of high solids content systems, and achieving a balance in the performance of pressure-sensitive adhesives.

[0099] In summary, this application does not achieve performance improvement through a single factor, but rather through the synergistic effect of bio-based bulk monomers, non-APE emulsion systems, and semi-continuous multiphase polymerization processes, achieving a balance between low viscosity, fast drying, and excellent adhesion performance under high solids content conditions. This has technical effects that are significantly different from traditional water-based pressure-sensitive adhesives and existing industrial products.

[0100] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a high-performance bio-based pressure-sensitive adhesive, characterized in that, Includes the following steps: (1) Preparation of preemulsion: 220-230 parts by weight of deionized water and 53-62 parts by weight of emulsifier are stirred and mixed, and then 20-77 parts by weight of styrene, 42-459 parts by weight of alkyl methacrylate, 30-62 parts by weight of vinyl acetate, 532-1000 parts by weight of tetrahydrofurfuryl acrylate, 4-7 parts by weight of acid, and 0.15-0.4 parts by weight of chain transfer agent are added. Stirring and mixing are continued to obtain preemulsion; (2) Preparation of initiator solution: Dissolve the free radical initiator in deionized water to prepare an initiator solution with a mass concentration of 3% to 10%; (3) Preparation of additional solutions: Dissolve the oxidizing and reducing agent in deionized water to prepare the first additional solution with a mass concentration of 5% to 30%; dissolve tert-butyl hydroperoxide in deionized water to prepare the second additional solution with a mass concentration of 5% to 35%. (4) Preparation of polymer emulsion: 120-160 parts by weight of deionized water, 1-1.5 parts by weight of buffer, 3-10 parts by weight of emulsifier, 5-16 parts by weight of alkyl methacrylate, 50-116 parts by weight of tetrahydrofurfuryl acrylate and 0.3-0.6 parts by weight of acid are added to the reactor, mixed and stirred, heated, and a portion of the initiator solution is added to the reactor for reaction. The pre-emulsion and the remaining initiator solution are added separately, and the reaction continues. The total amount of initiator solution added is 97-98.5 parts by weight, and the total amount of pre-emulsion added is 1387-1504 parts by weight. Then, while lowering the temperature, 34-56 parts by weight of additional solution are added. Finally, when the temperature drops to 30°C, 0.3-1 parts by weight of preservative is added until the reaction is completed, and the polymer emulsion, i.e. pressure-sensitive adhesive, is obtained.

2. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: The emulsifier is one or more of the following: ethoxylated alcohol ammonium sulfate, secondary alcohol polyoxyethylene ether, sodium diisooctyl sulfosuccinate, and sodium C10-C14 sulfonate.

3. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: In step (4), styrene needs to be added to the reactor in a weight ratio of 1 to 2 parts; a buffer solution also needs to be prepared, and the buffer solution needs to be added dropwise when adding the pre-emulsion and initiator solution, with a weight ratio of 25 to 26 parts.

4. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 3, characterized in that: The buffer solution is prepared by dissolving a buffer in deionized water, with a mass concentration of 7% to 10%, and the buffer is one or more of sodium pyrophosphate, sodium citrate, and sodium bicarbonate.

5. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: The alkyl methacrylate is one or more of methyl methacrylate, citronellol methacrylate, isobornyl methacrylate, and menthyl methacrylate.

6. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: The acid is acrylic acid or itaconic acid.

7. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: The chain transfer agent is 1-dodecyl mercaptan.

8. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: The free radical initiator is ammonium persulfate or sodium persulfate.

9. The method for preparing a high-performance bio-based pressure-sensitive adhesive according to claim 1, characterized in that: In step (3), the second additional solution also includes ammonium persulfate.

10. A high-performance bio-based pressure-sensitive adhesive according to any one of claims 1 to 9, characterized in that: The high-performance bio-based pressure-sensitive adhesive prepared by the above method has a solid content of 65% to 72%, a viscosity of 300 to 600 mPa·s, and a pH value of 4 to 6 after filtration through a 100-mesh nylon filter.