A solvent-free polymerization preparation method for preparing UV-cured pressure-sensitive adhesive
The preparation of UV-curable pressure-sensitive adhesives by solvent-free polymerization solves the problems of long production cycles and solvent residues in existing technologies, achieving environmentally friendly and energy-saving high-efficiency production and meeting the VOC requirements of high-end products.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN LIHE BOHUI PHOTOSENSITIVE MATERIAL CO LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-30
Smart Images
Figure CN122302777A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pressure-sensitive adhesive technology, specifically to a solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesives. Background Technology
[0002] Current technologies for producing UV-curable hot-melt pressure-sensitive adhesives all employ solvent polymerization. First, a photocurable acrylate copolymer containing photocurable functional groups is synthesized in an organic solvent, or a photoinitiator is added to formulate a photocurable pressure-sensitive adhesive. Then, the solvent is removed through drying and vacuuming to produce a solvent-free photocurable pressure-sensitive adhesive, which becomes a commercial product. The main drawbacks of this technology are its long production cycle, high waste (due to significant solvent waste), and the fact that the final product always contains a small amount of residual solvent (approximately 5000 ppm). However, many electronic products, automotive brands, and high-end buildings increasingly require reduced residual VOCs in their products. For example, high-end automobiles in Europe and America generally require VOCs of less than 50 ppm for pressure-sensitive adhesives used in automotive interiors. Currently available photocurable pressure-sensitive adhesives cannot be directly used in these high-end products. Additional production processes are usually required to further reduce VOC content. Summary of the Invention
[0003] This invention provides a solvent-free polymerization method for preparing UV-curable pressure-sensitive adhesives, thereby solving the technical problems mentioned in the background section.
[0004] To address the aforementioned technical problems, this invention discloses a solvent-free polymerization method for preparing UV-curable pressure-sensitive adhesives, comprising the following steps: Step 1: Mix the acrylate monomers, tackifying resin, polyol, thermal initiator and polymerization inhibitor evenly; then carry out the thermal polymerization reaction at 80℃~130℃ under a protective atmosphere to obtain the prepolymer; Step 2: Add photoinitiator and antioxidant to the prepolymer, stir and mix, and then coat it into a pressure-sensitive adhesive film; Step 3: The pressure-sensitive adhesive film is cured by ultraviolet irradiation under a nitrogen atmosphere to obtain UV-cured pressure-sensitive adhesive.
[0005] Preferably, the raw materials include, by weight: 50-80 parts of acrylate monomers; 10-30 parts of tackifying resin; 5-20 parts of polyol; 0.1-1 part of thermal initiator; 0.5-3 parts of photoinitiator; 0.005-0.08 parts of polymerization inhibitor; and 0.1-1 part of antioxidant.
[0006] Preferably, the acrylate monomers include soft monomers and hard monomers, with a mass ratio of soft monomers to hard monomers of (6-9):1.
[0007] Preferably, the soft monomers include one or more of butyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate, and the hard monomers include one or more of methyl acrylate, methyl methacrylate, and hydroxyethyl acrylate.
[0008] Preferably, the stirring speed in step 2 is 450-550 rpm and the mixing temperature is 40-60℃.
[0009] Preferably, based on the experimental analysis of the initiator dropwise addition pre-analysis stage and historical production data, a configuration rule of "stirring viscosity change coefficient - initiator dropwise addition rate" is determined; Step 1 includes: Step 11: Purge and replace the reactor with nitrogen gas while it is empty; Step 12: Under stirring conditions and at room temperature, first mix the acrylate monomer with the tackifying resin, then add the polyol and the polymerization inhibitor in sequence. After the polymerization inhibitor is added, stir and mix for a longer period of time. Measure the viscosity of the mixture before and after adding the polymerization inhibitor, and measure the temperature of the mixture after mixing for a longer period of time. Step 13: Based on the viscosity and temperature detection values of the mixture in Step 12, determine the actual redundant temperature and the actual stirring viscosity change coefficient. Based on the actual redundant temperature and the actual stirring viscosity change coefficient, determine the initiator dripping rate and drip the heated initiator at the initiator dripping rate. The temperature of the entire raw material mixing process is less than or equal to 40℃. Step 14: Under a protective atmosphere, a thermal polymerization reaction is carried out at 80℃~130℃ to obtain the prepolymer.
[0010] Preferably, the stirring speed in step 12 is in the range of 350 to 450 r / min; and the remixing time is 10 to 15 min.
[0011] Preferably, the initiator dripping rate is in the range of 3 ml / min to 4.5 ml / min.
[0012] Preferably, the process of determining the light reference parameters predetermines the reference light parameters and the light time-reference pressure-sensitive adhesive temperature curve under the reference light parameters, as well as the reference effective oxygen concentration change rate and the reference effective temperature change rate during the induction period; based on the light time-reference pressure-sensitive adhesive temperature curve, several light characteristic processes are divided, and the light characteristic processes are continuous in time; Step 3 of the current verification process includes: Step 31: Send the coated pressure-sensitive adhesive film to the curing chamber and purge the air inside the curing chamber with nitrogen gas; Step 32: Start the UV curing process during the induction period with UV irradiation at 0.85 to 0.9 times the reference light intensity, and periodically monitor the temperature and oxygen concentration of the pressure-sensitive adhesive. Take a fixed time window before the end of the induction period and construct an analysis matrix covering the curing time, temperature of the pressure-sensitive adhesive, and oxygen concentration. Step 33: Determine the temperature and oxygen change lag factor based on the analysis matrix. If the temperature and oxygen change lag factor does not meet the preset lag factor range (value range 0 to 0.01; calibrated by multiple batches of mass production data), issue an early warning. If no early warning is issued, determine the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period based on the analysis matrix. The target light intensity for each light characteristic process is determined based on the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period, the reference effective oxygen concentration change rate during the induction period, and the reference effective temperature change rate during the induction period. Step 33: Verify the qualification of target illumination intensity based on the target illumination intensity of the residual illumination characteristic process; When performing batch UV curing of pressure-sensitive adhesive films, UV curing is carried out for each light characteristic process based on the target light intensity that has passed the verification of the light characteristic process.
[0013] Preferably, the light irradiation process includes an induction period, a rapid polymerization exothermic period, and a curing temperature period; the heating rate during the induction period is ≤0.3℃ / s, the heating rate during the curing stabilization period is ≤0.1℃ / s, and the light irradiation time between the induction period and the curing stabilization period is the rapid polymerization exothermic period.
[0014] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The excellent flowability of tackifying resin and polyol under high temperature conditions helps the thermal polymerization of acrylate monomers, replacing the organic solvents used in the existing process of producing pressure-sensitive adhesives. This not only saves solvents and reduces costs, but also makes the production technology more environmentally friendly, energy-saving and low-carbon.
[0016] (2) By utilizing the influence of tackifying resin and polyol on the glass transition temperature of pressure-sensitive adhesive, the performance of pressure-sensitive adhesive can be further improved to make it suitable for more application scenarios.
[0017] (3) Polyols can further participate in the UV curing reaction of pressure-sensitive adhesives, thereby increasing the UV curing speed of pressure-sensitive adhesives.
[0018] (4) By selecting different polyols, the bonding strength to special surfaces can be increased.
[0019] (5) First, mix the acrylate monomer with the tackifying resin to fully dissolve and disperse the solid tackifying resin in the monomer, forming a homogeneous basic system. This avoids agglomeration or uneven dispersion when polyols and polymerization inhibitors are added later, laying the foundation for the stability of the entire system. After the basic system is homogenized, add the polyol to ensure that it is evenly dispersed in the system. As a chain segment extender, it participates in the subsequent thermal polymerization, ensuring the uniformity of the crosslinking density of the prepolymer and avoiding performance fluctuations caused by excessive or insufficient local crosslinking.
[0020] (6) Adding the polymerization inhibitor after the other raw materials are completely dispersed has the following key advantages: Precision Coverage System: The polymerization inhibitor can uniformly cover the entire mixture, forming a complete free radical buffer layer, which effectively inhibits monomer self-polymerization during the mixing stage and before the initiator is added, thus preventing local gelation from the source; To avoid interference with dispersion: If the polymerization inhibitor is added in advance, it will interfere with the dispersion process of the tackifying resin and polyol, affecting the uniformity of the system; adding it last will completely avoid this problem. It does not affect the initiation of polymerization: The polymerization inhibitor only plays a stabilizing role in the mixing stage. When the thermal initiator is added dropwise, the system temperature and initiator concentration can overcome the inhibitory effect of the polymerization inhibitor, ensuring that the thermal polymerization reaction starts normally and there will be no problem of "excessive polymerization inhibition leading to failure to polymerize". Attached Figure Description
[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation
[0022] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0023] Furthermore, in this invention, the use of terms such as "first" and "second" is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the invention. They are merely used to distinguish components or operations described using the same technical terms and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions and features of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If a combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.
[0024] The present invention provides the following embodiments: Example 1: This embodiment of the invention provides a solvent-free polymerization method for preparing UV-curable pressure-sensitive adhesives, such as... Figure 1 As shown, the steps include: Step 1: Mix the acrylate monomers, tackifying resin, polyol, thermal initiator and polymerization inhibitor evenly; then carry out the thermal polymerization reaction at 80℃~130℃ under a protective atmosphere to obtain the prepolymer; Step 2: Add photoinitiator and antioxidant to the prepolymer, stir and mix, and then coat it into a pressure-sensitive adhesive film; Step 3: The pressure-sensitive adhesive film is cured by ultraviolet irradiation under a nitrogen atmosphere to obtain UV-cured pressure-sensitive adhesive.
[0025] The raw materials include, by weight: 50-80 parts of acrylate monomers; 10-30 parts of tackifying resin; 5-20 parts of polyol; 0.1-1 part of thermal initiator; 0.5-3 parts of photoinitiator; 0.005-0.08 parts of polymerization inhibitor; and 0.1-1 part of antioxidant.
[0026] The acrylate monomers include soft monomers and hard monomers, with a mass ratio of soft monomers to hard monomers of (6-9):1.
[0027] The soft monomers include one or more of butyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate, while the hard monomers include one or more of methyl acrylate, methyl methacrylate, and hydroxyethyl acrylate.
[0028] In step 2, the stirring speed is 450-550 rpm and the mixing temperature is 40-60℃.
[0029] The tackifying resin includes one or more combinations of rosin resin, terpene resin, petroleum resin or its hydrogenated modified products (preferably hydrogenated rosin resin / terpene phenolic resin). Polyols include one or more of 1,4-butanediol, propylene glycol, polyether polyols (molecular weight 200-1000) or polyester polyols; they participate in the thermal polymerization reaction as crosslinking regulators / segment extenders to adjust the molecular weight distribution and crosslinking density of the prepolymer and improve the mechanical properties and temperature resistance of the pressure-sensitive adhesive.
[0030] Thermal initiators include one or more of the following: azo initiators (such as azobisisobutyronitrile AIBN, azobisisoheptanenitrile ABVN) or peroxide initiators (such as benzoyl peroxide BPO, di-tert-butyl peroxide DTBP); Photoinitiators include: free radical photoinitiators (such as 2-hydroxy-2-methyl-1-phenyl-1-propanone 1173, 1-hydroxycyclohexylphenyl ketone 184, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide TPO) or any one or more thereof.
[0031] Polymerization inhibitors include one or more of the following: hydroxyanisole, hydroquinone, and phenothiazine.
[0032] Antioxidants include one or more of phenolic antioxidants (such as 2,6-di-tert-butyl-p-cresol BHT and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and phosphite antioxidants (such as tris[2,4-di-tert-butylphenyl]phosphite).
[0033] The beneficial effects of this invention are as follows: (1) The excellent flowability of tackifying resin and polyol under high temperature conditions helps the thermal polymerization of acrylate monomers, replacing the organic solvents used in the existing process of producing pressure-sensitive adhesives. This not only saves solvents and reduces costs, but also makes the production technology more environmentally friendly, energy-saving and low-carbon.
[0034] (2) By utilizing the influence of tackifying resin and polyol on the glass transition temperature of pressure-sensitive adhesive, the performance of pressure-sensitive adhesive can be further improved to make it suitable for more application scenarios.
[0035] (3) Polyols can further participate in the UV curing reaction of pressure-sensitive adhesives, thereby increasing the UV curing speed of pressure-sensitive adhesives.
[0036] (4) By selecting different polyols, the bonding strength to special surfaces can be increased.
[0037] (5) First, mix the acrylate monomer with the tackifying resin to fully dissolve and disperse the solid tackifying resin in the monomer, forming a homogeneous basic system. This avoids agglomeration or uneven dispersion when polyols and polymerization inhibitors are added later, laying the foundation for the stability of the entire system. After the basic system is homogenized, add the polyol to ensure that it is evenly dispersed in the system. As a chain segment extender, it participates in the subsequent thermal polymerization, ensuring the uniformity of the crosslinking density of the prepolymer and avoiding performance fluctuations caused by excessive or insufficient local crosslinking.
[0038] (6) Adding the polymerization inhibitor after the other raw materials are completely dispersed has the following key advantages: Precision Coverage System: The polymerization inhibitor can uniformly cover the entire mixture, forming a complete free radical buffer layer, which effectively inhibits monomer self-polymerization during the mixing stage and before the initiator is added, thus preventing local gelation from the source; To avoid interference with dispersion: If the polymerization inhibitor is added in advance, it will interfere with the dispersion process of the tackifying resin and polyol, affecting the uniformity of the system; adding it last will completely avoid this problem. It does not affect the initiation of polymerization: The polymerization inhibitor only plays a stabilizing role in the mixing stage. When the thermal initiator is added dropwise, the system temperature and initiator concentration can overcome the inhibitory effect of the polymerization inhibitor, ensuring that the thermal polymerization reaction starts normally and there will be no problem of "excessive polymerization inhibition leading to failure to polymerize".
[0039] (7) The present invention adopts a solvent-free polymerization process, which completely abandons the traditional solvent polymerization route, eliminates the problem of organic solvent residue from the source, and eliminates the need for solvent removal processes such as drying and vacuuming. The production cycle is greatly shortened and no solvent waste is generated. The final product has no organic solvent residue and the VOC content can be controlled below 50ppm, which fully meets the stringent requirements of ultra-low VOC in high-end automobiles, precision electronic products, high-end buildings and other fields.
[0040] Example 2, based on Example 1, and based on the experimental analysis of the initiator dropwise addition pre-analysis stage and historical production data, determines the configuration rule of "stirring viscosity change coefficient - initiator dropwise addition rate"; Step 1 includes: Step 11: Purge and replace the reactor with nitrogen gas while it is empty; Step 12: Under stirring conditions and at room temperature, first mix the acrylate monomer with the tackifying resin, then add the polyol and the polymerization inhibitor in sequence. After the polymerization inhibitor is added, stir and mix for a longer period of time. Measure the viscosity of the mixture before and after adding the polymerization inhibitor, and measure the temperature of the mixture after mixing for a longer period of time. Step 13: Based on the viscosity and temperature detection values of the mixture in Step 12, determine the actual redundant temperature and the actual stirring viscosity change coefficient. Based on the actual redundant temperature and the actual stirring viscosity change coefficient, determine the initiator dripping rate and drip the heated initiator at the initiator dripping rate. The temperature of the entire raw material mixing process is less than or equal to 40℃. Step 14: Under a protective atmosphere, a thermal polymerization reaction is carried out at 80℃~130℃ to obtain the prepolymer.
[0041] In step 12, the stirring speed range is 350–450 r / min (this speed range was optimized and determined through multiple batches of mixing tests to ensure uniform dispersion of the system and to prevent the introduction of air bubbles); the remixing time is 10–15 min.
[0042] The drop rate of the initiator is set between 3 ml / min and 4.5 ml / min (this drop rate range was determined through multiple batches of thermal polymerization stability tests to avoid localized burst polymerization while ensuring production efficiency).
[0043] Related explanations: Based on the experimental analysis during the initiator dropwise addition pre-analysis stage and historical production data, a configuration rule of "stirring viscosity change coefficient - initiator dropwise addition rate" was determined, specifically as follows: I. Pre-analysis stage: Establishing initial correspondence rules: Fix the stirring speed at 350-450 r / min, and set multiple sets of different initial viscosities (i.e., the viscosity of the mixture before the addition of the polymerization inhibitor) by adjusting the raw material ratio, etc. For each initial viscosity group, the viscosity of the mixture before the addition of the polymerization inhibitor and after mixing for 10-15 minutes was measured to quantify the degree of viscosity change during stirring (i.e., the viscosity change coefficient, which reflects the overall dispersion and mixing ability of the system). The smaller the coefficient, the more gradual the viscosity change after the addition of the material under stirring conditions, indicating strong dispersion ability, good mixing uniformity, and stable system state. The larger the coefficient, the more significant the viscosity fluctuation after the addition of the material under stirring conditions, indicating weak dispersion ability, poor mixing uniformity, and low system stability.
[0044] For each group of stirring viscosity changes, the reaction state was tested under different initiator dropping rates. The dropping rate / speed range with no local premature polymerization, no gelation, and qualified prepolymer performance was screened out, and an initial correspondence table of "stirring viscosity change - initiator dropping rate" was formed as the guide for the first batch of production.
[0045] II. Production Stage: Applying Corresponding Rules: In actual production, at a fixed stirring speed of 350-450 r / min, the viscosity of the mixture before and after the addition of the current batch of polymerization inhibitor is measured to obtain the actual stirring viscosity change coefficient. By referring to the initial correspondence table formed in the pre-analysis stage, the corresponding initiator to be added at the drop rate is obtained, and the drop operation is performed. If the actual viscosity change coefficient exceeds the range of the initial correspondence table: using the current actual viscosity change coefficient as a benchmark, find the known viscosity change coefficient range with the closest value in the initial correspondence table. Based on the dropping rate in this range and the variation law of "viscosity change degree - dropping rate" (such as the trend that the greater the viscosity change degree, the slower the dropping rate), lock the candidate dropping rate within a narrow range of ±15% to 20% of the dropping rate in this known range to avoid large-scale experiments without basis.
[0046] Take samples from the current batch of mixture and conduct small-scale tests in a laboratory simulating production conditions (same stirring speed, temperature, and material ratio) within the aforementioned narrowed safety range, setting a gradient dropping rate: Test the reaction state at different dropping rates (whether local premature polymerization, gelation, abnormal molecular weight distribution, etc. occur). The dropping rate that is free of abnormalities and meets the prepolymer quality requirements is selected as the actual dropping rate for the current batch.
[0047] III. Iterative Optimization Phase: Update and Supplement Rules: After each batch of production is completed, the actual stirring viscosity change coefficient, initiator dropping rate, and reaction results (such as whether polymerization was carried out in advance, molecular weight distribution of prepolymer, conversion rate, etc.) are entered into the production database. Once enough batch data has been accumulated, the initial correspondence table is optimized and updated: the range of viscosity variation is refined, the corresponding dropwise acceleration value is adjusted, and new rules for viscosity variation ranges are added to make the rules more consistent with actual production; the updated rules are used for subsequent batch production.
[0048] Step 11: Use high-purity nitrogen (≥99.99%) to continuously purge; reduce the oxygen content inside the reactor to ≤50ppm, and maintain a slight positive pressure of 0.01~0.02MPa after replacement to prevent backflow of outside air.
[0049] Step 12: Stirring speed 350-450 r / min; Monomer + Resin first: Using acrylate as the base, disperse the solid resin first; Polyol next: Introduce UV curing crosslinking sites, and adjust the viscosity of the system without interfering with the resin dispersion; Polymerization inhibitor: Add after other materials are mixed evenly to ensure that the polymerization inhibitor evenly covers the entire system and forms a free radical buffer layer; Initiator is only added dropwise after the mixture is stable to avoid premature initiation.
[0050] Remixing time: 10-15 min; ensure sufficient diffusion of the polymerization inhibitor to prevent localized polymerization vacancies / accumulation of the inhibitor in the mixture and avoid premature polymerization in localized areas when adding the initiator; allow the temperature and viscosity of the mixture to stabilize, providing a stable baseline for subsequent additions.
[0051] Step 13: First determine: Redundancy temperature = 40 - temperature detection value of mixture after remixing time; Coefficient of viscosity change during stirring = ; The base time is the total time for adding the polymerization inhibitor, all in minutes; the base time is 1 minute. By referring to the latest "stirring viscosity change coefficient - initiator dropwise addition rate" configuration rules, a baseline dropwise addition rate (range 3 ml / min to 4.5 ml / min) was obtained: The viscosity of the polymerization inhibitor itself is a fixed value that is tested before the raw materials are put into storage, or the operation of "testing the viscosity of the polymerization inhibitor raw materials" is added simultaneously in step 12.
[0052] If the actual viscosity change coefficient during stirring is within the coverage range of the initial corresponding table: directly take the dropping rate of the corresponding interval in the table as the reference dropping rate; If the actual viscosity change coefficient exceeds the range of the initial corresponding table: First, take the closest known viscosity change coefficient range as the benchmark, lock the drop rate to be selected within a narrow range of ±15% to 20% of the drop rate in that range, then take a sample from the current batch of mixture, simulate the production conditions in the laboratory (same stirring speed, temperature, and material ratio), set a gradient drop rate within the narrow range to conduct a small-scale test, test the reaction state under different drop rates (whether there is local premature polymerization, gelation, abnormal molecular weight distribution, etc.), and screen out the drop rate that has no abnormalities and meets the prepolymer quality requirements as the benchmark drop rate.
[0053] Margin fine-tuning (based on actual redundancy temperature): Based on the baseline dropping rate, perform safe fine-tuning in conjunction with the actual redundancy temperature. When the actual redundant temperature is greater than 10℃, the reference dropping rate can be increased by 5% to 10% (the upper limit is no more than 4.5 ml / min) to obtain the initiator dropping rate, thereby improving production efficiency while ensuring safety. When the actual redundant temperature is between 5℃ and 10℃: directly use the reference dropping rate as the dropping rate of the initiator; When the actual redundant temperature is less than 5℃: reduce the reference dropping rate by 5% to 10% (the lower limit is not less than 3 ml / min) to obtain the initiator dropping rate, so as to avoid the system heating up too quickly and the temperature exceeding 40℃.
[0054] Step 14: Under a protective atmosphere, a thermal polymerization reaction is carried out at 80℃~130℃ to obtain the prepolymer, specifically as follows: Maintain the stirring speed of step 13. When the initiator is to be added at a rate of 3 ml / min to 4 ml / min (the upper limit is less than 4 ml / min), increase the temperature at a rate of 1 to 1.5 °C / min (greater than or equal to 1 and less than or equal to 1.5 °C / min). When the initiator is to be added at a rate of 4 ml / min to 4.5 ml / min (the lower limit is 4 ml / min), increase the temperature at a rate of 1.5 to 2 °C / min (greater than 1.5 and less than or equal to 1.5 °C / min), and finally raise the temperature to 80 to 130 °C for thermal polymerization. First, maintain the temperature at 80 to 100 °C for 1 to 2 hours, and then raise the temperature to 100 to 130 °C and maintain it for 2 to 4 hours. React until the viscosity of the system is stable and the monomer conversion rate is not less than 98%, and obtain the prepolymer.
[0055] The beneficial effects of the above scheme are as follows: 1. First, mix the acrylate monomers and tackifying resin: Using the liquid monomers as a base, first fully disperse the solid resin to avoid resin agglomeration and ensure that the resin is uniformly swollen and dispersed in the monomers, providing a uniform matrix for the subsequent crosslinking reaction; then add the polyol: while introducing UV-curable crosslinking sites, adjust the viscosity of the system without interfering with the initial resin dispersion, and avoid uneven crosslinking sites caused by local enrichment of polyols; finally, add the polymerization inhibitor: add it after the other materials are mixed evenly to ensure that the polymerization inhibitor uniformly covers the entire system, forming a "free radical buffer layer", which precisely inhibits premature local initiation and provides a safe buffer for the controlled dropwise addition of the initiator.
[0056] Stirring speed of 350-450 r / min: This balances shear force and mixing efficiency, ensuring sufficient dispersion of the high-viscosity system while avoiding material degradation or bubble introduction due to excessive shearing; Remixing time of 10-15 min: This ensures sufficient diffusion of the polymerization inhibitor, eliminates local inhibitor vacancies / accumulations, and avoids localized uncontrolled polymerization caused by uneven distribution of the inhibitor when adding the initiator; At the same time, it allows the temperature and viscosity of the mixed system to stabilize, providing a reliable benchmark for accurate calculation of the subsequent initiator drop rate.
[0057] By detecting the viscosity of the mixture before and after the addition of the polymerization inhibitor and the temperature of the system after remixing, the dispersion state and heat capacity of the system are quantitatively characterized, providing data support for the precise control of the subsequent initiator droplet acceleration rate.
[0058] 2. Dual-factor control logic of "stirring viscosity change coefficient - redundant temperature": Viscosity variation coefficient: This coefficient is calculated by quantifying the viscosity difference before and after adding the polymerization inhibitor, remixing time, the duration of inhibitor addition, and the system's own viscosity. It accurately reflects the system's ability to disperse and mix materials. A smaller coefficient indicates stronger dispersion and greater stability; a larger coefficient indicates poorer mixing uniformity and lower stability. Based on this coefficient and matching the initiator drop rate, the dispersion characteristics of different batches of materials can be specifically adapted, avoiding excessively fast (local gelation) or excessively slow (low production efficiency) drop addition due to viscosity fluctuations. Redundancy temperature: With 40℃ as the safety upper limit, the system's thermal buffer capacity is calculated using "40℃ - remixing temperature." The baseline drop rate is then fine-tuned based on the redundancy temperature: when the redundancy temperature is >10℃, the drop rate is moderately increased (to improve efficiency); between 5 and 10℃, the baseline is maintained; and when <5℃, the drop rate is decreased (to avoid overheating), achieving a dynamic balance between safety and efficiency. Dropping rate range limitation: The initiator dropping rate is strictly controlled within 3 to 4.5 ml / min to ensure production efficiency while avoiding excessive local exothermic reaction and gelation risk caused by excessively fast dropping rate, or prolonged production cycle caused by excessively slow dropping rate.
[0059] 3. Differentiated control of heating rate: The heating rate is matched with different rates according to the initiator dropping rate - when the dropping rate is 3-4 ml / min, the heating rate is 1-1.5℃ / min, and when the dropping rate is 4-4.5 ml / min, the heating rate is 1-2℃ / min. This accurately matches the free radical generation rate corresponding to the initiator dropping rate, avoiding exothermic runaway caused by excessive heating or reaction lag caused by excessively slow heating, and ensuring the smooth progress of the polymerization reaction.
[0060] Two-stage heat preservation process: First, heat preservation at 80-100℃ for 1-2 hours: Gently start polymerization, control the initial heat release rate, avoid the rapid conversion of a large amount of monomers and the resulting temperature rise, and ensure the uniform molecular weight distribution of the prepolymer; then heat preservation at 100-130℃ for 2-4 hours: Deeply advance polymerization, increase monomer conversion rate to ≥98%, ensure the degree of crosslinking and mechanical properties of the prepolymer meet the standards, and at the same time avoid the risk of yellowing and degradation of the adhesive layer caused by long-term heat preservation at high temperature.
[0061] Example 3, based on Example 1 or Example 2, pre-determines the reference illumination parameters and the reference illumination time-reference pressure-sensitive adhesive temperature curve under the reference illumination parameters, as well as the reference effective oxygen concentration change rate and the reference effective temperature change rate during the induction period; based on the reference illumination time-reference pressure-sensitive adhesive temperature curve, several illumination characteristic processes are divided, and the illumination characteristic processes are continuous in time; In the current pre-curing verification process before batch curing of pressure-sensitive adhesives, step 3 includes: Step 31: Send the coated pressure-sensitive adhesive film to the curing chamber and purge the air inside the curing chamber with nitrogen gas; Step 32: Begin UV curing during the induction period with a light intensity of 0.85–0.9 times the baseline intensity (the induction period is the initial reaction initiation stage of UV curing, a critical window for the simultaneous establishment of free radical generation, exothermic reaction, and oxygen consumption. Directly using the baseline intensity for initiation may lead to overreaction due to differences in pressure-sensitive adhesives; if the intensity is too low, it will slow down production efficiency. Therefore, setting it to 0.85–0.9 times the baseline intensity (slightly lower than the baseline) is the optimal compromise between "safe initiation + accurate verification + efficient production"). Periodically monitor the pressure-sensitive adhesive temperature and oxygen concentration, and construct an analytical matrix covering curing time, pressure-sensitive adhesive temperature, and oxygen concentration within a fixed time window before the end of the induction period. Step 33: Determine the temperature and oxygen change lag factor based on the analysis matrix. If the temperature and oxygen change lag factor does not meet the preset lag factor range (value range 0 to 0.01, less than 0 and greater than 0.01 are unqualified; this threshold range is determined based on the statistical analysis of actual production batch data and can effectively identify abnormal temperature and oxygen synchronicity), an early warning is issued. If no warning is issued, determine the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period based on the analysis matrix. The target light intensity for each light characteristic process is determined based on the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period, the reference effective oxygen concentration change rate during the induction period, and the reference effective temperature change rate during the induction period. Step 34: Verify the target light intensity qualification based on the residual light intensity characteristics process; the quality of the pressure-sensitive adhesive after curing meets the requirements (gel rate ≥ formula preset value (e.g. ≥ 95%); 180° peel strength and tackiness meet the requirements, ensuring stable bonding performance; the adhesive layer has no defects such as yellowing, cracking, or bubbles, and the appearance is qualified). If the verification fails, suspend the batch production plan and initiate root cause analysis of the deviation: investigate the problems in the light intensity adjustment logic, the judgment of the reaction status during the induction period, and the consistency of process conditions, return to the corresponding step (step 32 or step 33) to optimize and adjust the parameters / process, and then conduct small-scale verification again until the verification is successful; if the same type of failure occurs multiple times, enter the actual data into the production database and iteratively optimize the baseline configuration rules. When performing batch UV curing of pressure-sensitive adhesive films, UV curing is carried out for each light characteristic process based on the target light intensity that has passed the verification of the light characteristic process.
[0062] The photo-irradiation process includes the induction period, the rapid polymerization exothermic period, and the curing temperature period; the heating rate during the induction period is ≤0.3℃ / s, the heating rate during the curing stabilization period is ≤0.1℃ / s, and the photo-irradiation time between the induction period and the curing stabilization period is the rapid polymerization exothermic period.
[0063] (1) The process of determining the reference illumination parameters predetermines the reference illumination parameters and the illumination time-reference pressure-sensitive adhesive temperature curve under the reference illumination parameters; based on the illumination time-pressure-sensitive adhesive temperature curve, several illumination characteristic processes are divided, specifically: First, during the research and development experimental phase, a process of determining the light reference parameters must be carried out to establish a set of reference light parameters (reference ultraviolet wavelength, reference light intensity) as control / reference parameters for subsequent tests; specifically: Based on the performance and application of pressure-sensitive adhesives, the initial range of ultraviolet light wavelength and light intensity parameters was determined according to industry experience. At the same time, the process conditions were fixed, the coating substrate, coating method and typical film thickness of the pressure-sensitive adhesive were standardized, and the nitrogen replacement treatment for industrial standard pressure-sensitive adhesive curing was uniformly adopted to ensure the curing foundation. Only the ultraviolet light wavelength and light intensity were used as the core optimization parameters. Subsequently, the comprehensive performance of the pressure-sensitive adhesive after curing (the qualified threshold of the core evaluation index can be: gel rate ≥95%, 180° peel strength not less than 95% of the benchmark formulation, tackiness not less than 24h (GB / T 4851 standard), and no yellowing, cracking, or bubbles in the adhesive layer appearance) was used as the core evaluation index. Through single-factor variable experiments combined with multiple parallel verifications, the optimal range of ultraviolet light wavelength and light intensity was gradually screened out (this range not only meets the requirements for qualified curing quality, but also meets the production needs of comprehensive performance, reliable process stability, and qualified curing efficiency; the typical value range of the optimal range is: ultraviolet wavelength 350~380nm, light intensity 150~250mW / cm²; this intensity range was determined by multiple batches of curing tests with different film thicknesses, taking into account both curing depth and adhesive layer appearance stability); then, a comprehensive comparison was carried out on the parameter combinations within this optimal range, and finally, the ultraviolet wavelength and light intensity combination suitable for all commonly used film thicknesses was determined.
[0064] Under these illumination reference parameters, the pressure-sensitive adhesive film was irradiated with ultraviolet light, and the illumination time and corresponding pressure-sensitive adhesive temperature data were recorded simultaneously. An illumination time-reference pressure-sensitive adhesive temperature curve was plotted. Based on the slope of the curve, the entire illumination cycle was divided into several characteristic illumination processes, including the induction period (heating rate ≤ 0.3℃ / s), the rapid polymerization exothermic period, and the curing stabilization period (heating rate ≤ 0.1℃ / s). The illumination characteristic processes were continuous in time; the heating rate during the induction period was ≤ 0.3℃ / s, and the heating rate during the curing stabilization period was ≤ 0.1℃ / s. The illumination time between the induction period and the curing stabilization period was defined as the rapid polymerization exothermic period. (2) Use nitrogen with a purity of 99.5% to 99.99% to replace the air in the curing chamber by continuous purging, control the oxygen content in the curing chamber to ≤500ppm, the replacement time to 3 to 10 minutes, and maintain a slight positive pressure of 0.01 to 0.03MPa; (3) Effective temperature change rate and effective oxygen concentration change rate during the induction period: A fixed time window (a fixed value, which can be 10 seconds, or the last 10% of the time interval) before the end of the induction period is taken to construct the analysis matrix: First column: The curing time corresponding to the current sampling time; Second column: Temperature value of pressure-sensitive adhesive detected at the current sampling time; The third column: the oxygen concentration value detected at the current sampling time; Fourth column: Instantaneous temperature change rate calculated based on the current sampling point and the previous sampling point; Fifth column: Instantaneous oxygen concentration change rate calculated based on the current sampling point and the previous sampling point; Preset thresholds for temperature change rate and oxygen concentration change rate (each set to 0.7 times the baseline effective temperature change rate and oxygen concentration change rate during the induction period, respectively). In the instantaneous temperature change rate in the fourth column of the matrix, locate the first sampling moment that exceeds the temperature change rate threshold and record it as the first trigger moment of the temperature change rate. In the instantaneous oxygen concentration change rate in the fifth column of the matrix, locate the first sampling moment that exceeds the oxygen concentration change rate threshold and record it as the first trigger moment of the oxygen concentration change rate. Calculate the time difference between the two first trigger moments, and use the ratio of this time difference to the duration of the fixed window as the temperature and oxygen change lag factor to characterize the order and degree of lag between exothermic initiation and oxygen consumption initiation.
[0065] Actual effective temperature change rate: the arithmetic mean of all instantaneous temperature change rates within a fixed time window, from the moment the temperature change rate is first triggered to the moment the window ends; Actual effective oxygen concentration change rate: is the arithmetic mean of all instantaneous oxygen concentration change rates within a fixed time window, from the moment the oxygen concentration change rate is first triggered to the end of the window.
[0066] The target illumination intensity for each illumination characteristic process is determined based on the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period, as well as the reference effective oxygen concentration change rate and the reference effective temperature change rate during the induction period. Specifically: Determine the temperature change rate factor as follows: Actual effective temperature change rate during the induction period ÷ Reference effective temperature change rate during the induction period. Oxygen concentration change rate factor = Actual effective oxygen concentration change rate during induction period ÷ Reference effective oxygen concentration change rate during induction period; Take max(|1-temperature change rate factor|, |1-oxygen concentration change rate factor|) as the equivalent deviation factor; If the equivalent deviation factor is ≤0.1: the target light intensity during the induction period remains unchanged from the reference light intensity; during the rapid polymerization exothermic period, the light intensity is slightly adjusted by ±1% based on the reference light intensity; during the curing and stabilization period, the light intensity is slightly adjusted by ±0.5% based on the reference light intensity. If the equivalent deviation factor > 0.1: When the actual reaction rate is faster than the baseline (i.e., temperature change rate factor > 1 and oxygen concentration change rate factor > 1), the target light intensity during the induction period = baseline light intensity × (1 - equivalent deviation factor); the target light intensity during the rapid polymerization exothermic period is reduced by 3% based on the target light intensity during the induction period; the target light intensity during the curing and stabilization period is reduced by 1% based on the target light intensity during the induction period. When the actual reaction rate is slower than the baseline, the target light intensity during the induction period is equal to the baseline light intensity multiplied by (1 + equivalent deviation factor); the target light intensity during the rapid polymerization exothermic period is increased by 3% based on the target light intensity during the induction period; and the target light intensity during the curing and stabilization period is reduced by 1% based on the target light intensity during the induction period.
[0067] The beneficial effects of the above-described embodiments are as follows: 1. The baseline illumination parameters were determined by using fixed process conditions, single-factor variables, and multiple parallel verifications. Only ultraviolet wavelength and light intensity were used as core optimization parameters, eliminating interference from variables such as coating substrate, film thickness, and nitrogen purging. A typical thickness was fixed to ensure that the selected optimal range (350–380 nm wavelength, 150–250 mW / cm² intensity) simultaneously met the requirements of qualified curing quality, optimal overall performance, and best process stability. A comprehensive comparison was conducted within the optimal range to identify the ultraviolet wavelength and light intensity combination suitable for all commonly used film thicknesses. This broke the limitations of a single film thickness parameter, improved the process's adaptability to different product specifications, and reduced line changeover and debugging costs. Based on the temperature curve slope changes under the baseline illumination parameters, the curing cycle was precisely divided into an induction period, a rapid polymerization exothermic period, and a curing stabilization period. This enabled staged and refined management of the curing process, providing clear stage boundaries and control targets for differentiated control of light intensity in subsequent stages (e.g., induction period heating rate ≤ 0.3℃ / s, curing stabilization period ≤ 0.1℃ / s).
[0068] A baseline illumination parameter system (including baseline illumination parameters, illumination time-temperature curves, and baseline effective temperature change rate and oxygen concentration change rate during the induction period) was pre-established, and continuous illumination characteristic processes were defined. This provided a unified reference and stage division basis for subsequent curing verification and dynamic control, avoiding process confusion under different batches and operating conditions, and ensuring the consistency of the curing logic. The induction period was started with 0.85 to 0.9 times the baseline illumination intensity. This avoided the risk of excessive reaction caused by directly using the baseline intensity (such as excessively rapid local exothermic reaction and temperature-oxygen imbalance), while also avoiding the decrease in production efficiency caused by too low an intensity. This achieved a balance between "safe start-up + accurate verification + efficient production," providing a stable initial reaction state for subsequent temperature and oxygen change analysis.
[0069] 2. During the induction period, an illumination intensity of 0.85–0.9 times the baseline is used to initiate the process. The temperature and oxygen concentration of the pressure-sensitive adhesive are periodically monitored. A five-column analysis matrix is constructed, including curing time, temperature, oxygen concentration, instantaneous temperature change rate, and instantaneous oxygen concentration change rate. This provides a complete and reliable data carrier for calculating the temperature-oxygen change lag factor, the actual effective temperature change rate, and the actual effective oxygen concentration change rate, avoiding analytical distortion caused by fragmented data. By setting preset thresholds for temperature change rate and oxygen concentration change rate (0.7 times the baseline rate), the "first trigger time of temperature change rate" and the "first trigger time of oxygen concentration change rate" are located. The ratio of the time difference between these two times to the fixed window duration is calculated as the temperature-oxygen change lag factor, quantifying the order and degree of lag between exothermic initiation and oxygen consumption initiation. If the lag factor exceeds the preset range of 0–0.01, an early warning is issued to identify potential reaction imbalance risks (such as localized gelation due to excessively rapid exothermic / lagging oxygen consumption, or insufficient curing due to excessive oxygen residue), preventing quality defects during mass production. The arithmetic mean of the instantaneous rates within the interval from the first trigger time to the end of the window is taken to calculate the actual effective temperature change rate and the actual effective oxygen concentration change rate. Invalid data interference from non-triggered reactions within the window is eliminated to ensure the accuracy and representativeness of the calculation.
[0070] Based on the deviation factor between the actual effective rate and the reference rate, target light intensity is set for each illumination characteristic process in different scenarios: When the equivalent deviation factor is ≤0.1: only the rapid polymerization exothermic period is finely adjusted by ±1%, and the curing stabilization period by ±0.5%, ensuring stable curing quality while minimizing parameter fluctuations; when the equivalent deviation factor is >0.1: according to the actual reaction rate and the reference rate, differentiated adjustment ranges are set for the induction period, rapid polymerization exothermic period, and curing stabilization period (e.g., increasing the induction period intensity when the reaction is slower than the reference, and decreasing the induction period intensity when the reaction is faster than the reference), accurately adapting to the reaction rate differences of different batches and ensuring curing quality. The adjustment range for the rapid polymerization exothermic period is larger to adapt to its violent exothermic reaction characteristics; the adjustment range for the curing stabilization period is smaller to ensure uniform curing in the later stages; this improves curing efficiency and optimizes the adhesive and mechanical properties of the pressure-sensitive adhesive.
[0071] The traditional experience-dependent UV curing process has been upgraded to a specific solution of "benchmark establishment → gentle start-up → quantitative analysis → dynamic control", which solves the problems of "parameter dependence on experience, large batch differences, and unstable curing quality" in the traditional process, while improving production efficiency.
[0072] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A solvent-free polymerization process for the preparation of UV-cured pressure sensitive adhesives, characterized in that: Including the following steps: Step 1: Mix the acrylate monomers, tackifying resin, polyol, thermal initiator and polymerization inhibitor evenly; then carry out the thermal polymerization reaction at 80℃~130℃ under a protective atmosphere to obtain the prepolymer; Step 2: Add photoinitiator and antioxidant to the prepolymer, stir and mix, and then coat it into a pressure-sensitive adhesive film; Step 3: The pressure-sensitive adhesive film is cured by ultraviolet irradiation under a nitrogen atmosphere to obtain UV-cured pressure-sensitive adhesive.
2. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 1, characterized in that: The raw materials include the following by weight: acrylate monomers: 50-80 parts; tackifying resin: 10-30 parts; polyol: 5-20 parts; thermal initiator: 0.1-1 parts; photoinitiator: 0.5-3 parts; polymerization inhibitor: 0.005-0.08 parts; antioxidant: 0.1-1 parts.
3. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 2, characterized in that: The acrylate monomers include soft monomers and hard monomers, with a mass ratio of soft monomers to hard monomers of (6-9):
1.
4. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 3, characterized in that: The soft monomers include one or more of butyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate, while the hard monomers include one or more of methyl acrylate, methyl methacrylate, and hydroxyethyl acrylate.
5. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 1, characterized in that: The stirring speed in step 2 is 450-550 rpm, and the mixing temperature is 40-60℃.
6. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 1, characterized in that: Based on the experimental analysis of the initiator dropwise addition pre-analysis stage and historical production data, the configuration rule of "stirring viscosity change coefficient - initiator dropwise addition rate" was determined; Step 1 includes: Step 11: Purge and replace the reactor with nitrogen gas while it is empty; Step 12: Under stirring conditions and at room temperature, first mix the acrylate monomer with the tackifying resin, then add the polyol and the polymerization inhibitor in sequence. After the polymerization inhibitor is added, stir and mix for a longer period of time. Measure the viscosity of the mixture before and after adding the polymerization inhibitor, and measure the temperature of the mixture after mixing for a longer period of time. Step 13: Based on the viscosity and temperature detection values of the mixture in Step 12, determine the actual redundant temperature and the actual stirring viscosity change coefficient. Based on the actual redundant temperature and the actual stirring viscosity change coefficient, determine the initiator dripping rate and drip the heated initiator at the initiator dripping rate. The temperature of the entire raw material mixing process is less than or equal to 40℃. Step 14: Under a protective atmosphere, a thermal polymerization reaction is carried out at 80℃~130℃ to obtain the prepolymer.
7. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 6, characterized in that: Step 12: The stirring speed range is 350–450 r / min; the remixing time is 10–15 min.
8. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 6, characterized in that: The initiator dripping rate should be in the range of 3 ml / min to 4.5 ml / min.
9. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 1, characterized in that: The process of determining the light reference parameters involves pre-determining the reference light parameters, the light time-reference pressure-sensitive adhesive temperature curve under the reference light parameters, the rate of change of the reference effective oxygen concentration during the induction period, and the rate of change of the reference effective temperature during the induction period. Based on the light exposure time-pressure-sensitive adhesive temperature curve, several light exposure characteristic processes are defined. The illumination characteristic process is continuous in time; In the current pre-curing verification process before batch curing of pressure-sensitive adhesives, step 3 includes: Step 31: Send the coated pressure-sensitive adhesive film to the curing chamber and purge the air inside the curing chamber with nitrogen gas; Step 32: Start the UV curing process during the induction period with UV irradiation at 0.85 to 0.9 times the reference light intensity, and periodically monitor the temperature and oxygen concentration of the pressure-sensitive adhesive. Take a fixed time window before the end of the induction period and construct an analysis matrix covering the curing time, temperature of the pressure-sensitive adhesive, and oxygen concentration. Step 33: Determine the temperature and oxygen change lag factor based on the analysis matrix. If the temperature and oxygen change lag factor does not meet the preset lag factor range, issue an early warning. If no early warning is issued, determine the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period based on the analysis matrix. The target light intensity for each light characteristic process is determined based on the actual effective temperature change rate and the actual effective oxygen concentration change rate during the induction period, the reference effective oxygen concentration change rate during the induction period, and the reference effective temperature change rate during the induction period. Step 33: Verify the qualification of target illumination intensity based on the target illumination intensity of the residual illumination characteristic process; When performing batch UV curing of pressure-sensitive adhesive films, UV curing is carried out for each light characteristic process based on the target light intensity that has passed the verification of the light characteristic process.
10. The solvent-free polymerization preparation method for UV-curable pressure-sensitive adhesive according to claim 9, characterized in that: The photo-irradiation process includes the induction period, the rapid polymerization exothermic period, and the curing temperature period; the heating rate during the induction period is ≤0.3℃ / s, the heating rate during the curing stabilization period is ≤0.1℃ / s, and the photo-irradiation time between the induction period and the curing stabilization period is the rapid polymerization exothermic period.