High-transparency low-odor acrylic emulsion for food packaging and preparation method of high-transparency low-odor acrylic emulsion

Abstract

The invention belongs to the technical field of high polymer materials and food packaging, and particularly relates to a high-transparency and low-odor acrylic emulsion for food packaging and a preparation method of the high-transparency and low-odor acrylic emulsion. According to the emulsion, a modified acrylate copolymer serves as a main body, a Si-O-C structure is introduced through phenolic hydroxyl group-silanization synergistic reaction, and construction of a high-density cross-linked network is achieved in combination with a low-molecular cross-linking monomer trimethylolpropane diacrylate. The emulsion is prepared from a modified acrylate copolymer, sodium dodecyl benzene sulfonate, sodium bicarbonate, ammonium persulfate, triethanolamine, polyether modified silicone oil and isothiazolinone through the steps of pre-emulsification, emulsion polymerization and aftertreatment. The obtained emulsion has high transparency, low odor, low residual monomers and excellent storage stability. Through synergistic modification of the phenolic hydroxyl group and the silane group, the optical performance and the environmental protection performance of a formed film are remarkably improved, and the method is suitable for preparation of a high-transparency food packaging material and a safe coating system.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and food packaging technology, specifically relating to a highly transparent, low-odor acrylic emulsion for food packaging and its preparation method. Background Technology

[0002] Currently, acrylic emulsions are widely used in food packaging films, paper-plastic composite coatings, and water-based adhesives, gaining attention due to their advantages such as uniform film formation, good flexibility, excellent weather resistance, and no solvent pollution. However, existing acrylic emulsion systems for food packaging still have several technical shortcomings, making it difficult to meet the stringent safety and appearance requirements of food contact materials.

[0003] Traditional acrylic emulsions are prepared using free radical emulsion polymerization, which results in incomplete polymerization. Residual acrylic acid, acrylate monomers, and persulfate decomposition byproducts are slowly released during film formation and storage, producing a noticeable pungent odor and causing problems such as high VOC content and persistent odor. Furthermore, conventional systems exhibit uneven emulsion particle size distribution, with particle size differences typically ranging from 80 to 250 nm. Significant differences in refractive index at particle interfaces lead to severe light scattering after film formation, reducing transmittance to below 85% and making it difficult to achieve a highly transparent appearance.

[0004] Regarding structural stability, in traditional physically mixed or single-coupled modified emulsion systems, the silane component is prone to hydrolysis and condensation to produce a secondary phase, and the phenolic hydroxyl comonomers are unevenly distributed, both of which lead to insufficient intermolecular compatibility. This causes the emulsion to separate, flocculate, or experience viscosity fluctuations during storage, affecting its performance. Furthermore, single modification methods offer limited improvement in odor and transparency, making it difficult to balance chemical stability and optical properties.

[0005] Existing modification studies mostly focus on improving adhesion through silane coupling agents or enhancing water resistance using phenolic hydroxyl comonomers. However, these methods are often used independently, resulting in low chemical bonding, unstable modified structures, and a tendency to increase odor or decrease transparency. These issues lead to limitations in the application of emulsion systems in food packaging, including unstable safety, poor visual effects, and insufficient long-term reliability. Therefore, there is an urgent need to achieve a balance between high transparency and low odor at the molecular level. Summary of the Invention

[0006] To overcome the technical challenges of existing acrylic emulsions for food packaging, such as high odor residue, insufficient transparency, and poor system stability, this invention aims to provide a highly transparent, low-odor acrylic emulsion for food packaging and its preparation method. This invention employs a phenolic hydroxyl-silanization synergistic modification technique to prepare modified acrylate copolymers. During the polymerization process, trimethylolpropane diacrylate is introduced as a low-molecular-weight crosslinking monomer. Through chemical crosslinking and molecular synergistic effects, a highly stable emulsion system with a Si–O–C covalent bond network is constructed. The emulsion prepared by this invention exhibits high transparency, low odor, and excellent system stability.

[0007] The objective of this invention can be achieved through the following technical solutions: A highly transparent, low-odor acrylic emulsion for food packaging comprises the following raw materials in parts by weight: 80-120 parts of modified acrylate copolymer, 5-15 parts of trimethylolpropane diacrylate, 2-4 parts of sodium dodecylbenzenesulfonate, 0.3-0.8 parts of ammonium persulfate, 0.2-0.6 parts of sodium bicarbonate, 50-80 parts of deionized water, 0.3-1.0 parts of triethanolamine, 0.1-0.3 parts of polyether-modified silicone oil, and 0.05-0.15 parts of isothiazolinone; wherein the modified acrylate copolymer is a highly transparent, highly stable film-forming resin that introduces a Si-O-C structure through a phenolic hydroxyl-silanization synergistic reaction; and the trimethylolpropane diacrylate is a low-molecular-weight crosslinking monomer containing diacrylate groups.

[0008] Optionally, the modified acrylate copolymer comprises the following raw materials in parts by weight: 25-35 parts methyl methacrylate, 20-30 parts butyl acrylate, 8-12 parts acrylic acid, 6-10 parts hydroxyethyl acrylate, 1-3 parts aminopropyltriethoxysilane, 0.5-1.5 parts hydroquinone, 0.2-0.5 parts azobisisobutyronitrile, 15-25 parts ethanol, and 40-60 parts deionized water.

[0009] Optionally, the method for preparing the modified acrylate copolymer includes the following steps: (1) Hydroquinone is dissolved in an ethanol-water mixture, stirred evenly, and then aminopropyltriethoxysilane is added to generate a silane-phenol hydroxyl synergistic modifier. (2) Methyl methacrylate, butyl acrylate, acrylic acid and hydroxyethyl acrylate are added to the reaction vessel, ethanol and deionized water are added and stirred to form a monomer mixture, and nitrogen degassing treatment is performed. (3) Under stirring conditions, the silane-phenol hydroxyl synergistic modifier is slowly added dropwise to the acrylate monomer mixture to continue the reaction and form a grafting modification intermediate; (4) Add azobisisobutyronitrile as an initiator to the system and carry out solution polymerization reaction at a constant temperature to obtain a modified acrylate copolymer solution; (5) The modified acrylate copolymer solution was subjected to reduced pressure to remove low-boiling substances, cooled to room temperature and filtered to obtain the modified acrylate copolymer.

[0010] Optionally, the reaction conditions for step (1) are: in an ethanol-water mixture, the reaction is carried out at 60-70°C for 1.5-2.5 hours; and the reaction conditions for step (2) are: stirred and degassed with nitrogen at 30-40°C for 20-40 minutes.

[0011] Optionally, the reaction conditions for step (3) are to add the modifier at a constant rate of 70-80°C and react for 0.5-1 hours; the reaction conditions for step (4) are to polymerize at 80-85°C for 2-4 hours.

[0012] Optionally, the reaction conditions in step (5) are vacuum volatilization and filtration at 50–60 °C.

[0013] Optionally, a method for preparing a highly transparent, low-odor acrylic emulsion for food packaging includes the following steps: S1, add the modified acrylate copolymer, sodium dodecylbenzenesulfonate, sodium bicarbonate and deionized water into the reactor and stir to form a uniform pre-emulsion system; S2, ammonium persulfate is added to the pre-emulsified system as an initiator, and trimethylolpropane diacrylate is added dropwise, and emulsion polymerization is carried out under stirring conditions; S3. After the reaction is complete, cool to room temperature, add triethanolamine to adjust the pH value, then add polyether-modified silicone oil and isothiazolinone in sequence and stir evenly. After filtration to remove impurities, the finished emulsion is obtained.

[0014] Optionally, the pre-emulsification reaction conditions in step S1 are stirring at 70–75°C for 20–40 minutes.

[0015] Optionally, the emulsion polymerization reaction conditions in step S2 are a constant temperature reaction at 75–85°C for 2–4 hours.

[0016] Optionally, the post-treatment reaction conditions in step S3 are stirring at 25–30°C for 10–20 minutes.

[0017] The beneficial effects of this invention are: The beneficial effects of this invention lie in the introduction of a stable Si–O–C covalent bond structure into the main chain of the acrylate copolymer through a synergistic modification reaction of phenolic hydroxyl-silanization, achieving a synergistic improvement in odor control and optical performance. The silane-phenolic hydroxyl modifier generated by the condensation reaction of aminopropyltriethoxysilane and hydroquinone reacts with monomers such as acrylic acid and hydroxyethyl acrylate during polymerization, allowing both siloxane groups and phenolic hydroxyl groups to participate in the polymerization simultaneously. This significantly reduces the residue of unreacted monomers and low-molecular-weight byproducts, reducing volatile organic compounds in the emulsion system from the source. The resulting Si–O–C structure possesses high bond energy and high thermal stability, effectively suppressing odor release and reducing the emulsion odor index to below 1.0. The flexibility and uniform polarity distribution of the siloxane segments result in a more concentrated emulsion particle size and a more consistent interfacial refractive index, significantly reducing light scattering effects and improving the transmittance and gloss of the film. Compared to traditional silane or phenolic hydroxyl-modified systems, this synergistic reaction mode can simultaneously improve interfacial compatibility and molecular uniformity. The emulsion exhibits no stratification or water separation during storage, demonstrating significantly enhanced stability. Further introduction of the low-molecular-weight crosslinking monomer trimethylolpropane diacrylate creates a flexible crosslinking network, maintaining high transparency while enhancing the film's density and mechanical integrity.

[0018] This invention achieves synergistic optimization of structural stability, low odor, and high transparency at the molecular level, breaking through the technical bottleneck of "difficulty in achieving both high transparency and low odor" in traditional acrylic emulsions, and providing a high-performance emulsion solution for food contact packaging materials. Attached Figure Description

[0019] The invention will now be further described with reference to the accompanying drawings.

[0020] Figure 1 A comparison of the infrared spectra of acrylate copolymers and modified acrylate copolymers; Figure 2 A bar chart comparing the transmittance test results of samples with different ratios; Figure 3 A bar chart comparing the total residual content test results of samples with different ratios; Figure 4 A bar chart comparing the test results of total migration of samples with different ratios. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Equivalent adjustments made without departing from the spirit and essence of the present invention should also be considered to fall within the protection scope of the present invention.

[0022] Example 1 The purpose of this embodiment is to verify the ultimate performance of the emulsion system in terms of transparency, structural density, and odor control under a high content of modified acrylate copolymer and a high crosslinking agent ratio.

[0023] S1, dissolve 1.5 parts hydroquinone in a mixture of 20 parts ethanol and 40 parts deionized water, stir well, then add 3 parts aminopropyltriethoxysilane, and react at 60-70℃ for 2 hours to generate a silane-phenol hydroxyl synergistic modifier. Add 35 parts methyl methacrylate, 30 parts butyl acrylate, 12 parts acrylic acid, and 10 parts hydroxyethyl acrylate to a reaction vessel, add 25 parts ethanol and 60 parts deionized water, stir well, and degas under nitrogen for 30 minutes. Slowly add the above modifier dropwise to the monomer mixture at 75℃, continue the reaction for 1 hour, then add 0.5 parts azobisisobutyronitrile to initiate polymerization, and react at 82℃ for 3 hours. After the reaction is completed, volatilize under reduced pressure at 55℃ and filter to obtain the modified acrylate copolymer. S2, 120 parts of modified acrylate copolymer, 4 parts of sodium dodecylbenzenesulfonate, 0.6 parts of sodium bicarbonate and 80 parts of deionized water were added to a reactor and stirred evenly to form a pre-emulsion system; 0.8 parts of ammonium persulfate were added as an initiator, and 15 parts of trimethylolpropane diacrylate were added dropwise at a constant rate, and emulsion polymerization was carried out at 80-85℃ for 3 hours. S3, cool to 25℃, add 1.0 part of triethanolamine to adjust pH to 7.3, then add 0.3 parts of polyether modified silicone oil and 0.15 parts of isothiazolinone in sequence and stir for 20 minutes. Filter to obtain a highly transparent and low-odor acrylic emulsion.

[0024] Example 2 The purpose of this embodiment is to examine the balance between system stability, odor control and optical performance under appropriate formulation.

[0025] S1, dissolve 1.0 part of hydroquinone in a mixture of 20 parts of ethanol and 50 parts of deionized water, add 2 parts of aminopropyltriethoxysilane, and react at 65°C for 2 hours to generate a synergistic modifier. Add 30 parts of methyl methacrylate, 25 parts of butyl acrylate, 10 parts of acrylic acid, and 8 parts of hydroxyethyl acrylate to a reaction vessel, add 20 parts of ethanol and 50 parts of deionized water, stir evenly, and degas under nitrogen for 30 minutes. Add the modifier dropwise to the system at 75°C and react for 1 hour. Add 0.3 parts of azobisisobutyronitrile, polymerize at 80°C for 3 hours, and after the reaction, devolve under reduced pressure at 55°C and filter to obtain the modified acrylate copolymer. Figure 1 The mid-infrared spectral comparison shows that the modified acrylate copolymer exhibits high activity at 1080, 920, and 830 cm⁻¹. -1 A distinct new absorption peak appears at 3400 cm⁻¹, corresponding to the formation of Si–O–C, Si–O–Si, and Si–C bonds, respectively, indicating that silane was successfully grafted onto the acrylate backbone. Meanwhile, at 3400 cm⁻¹...-1 The O–H stretching vibration peak at this point is enhanced and broadened, indicating the introduction of the phenolic hydroxyl group structure; the original peak at 1730 cm⁻¹ is also observed. -1 The C=O peak has slightly redshifted to 1715 cm⁻¹. -1 This indicates a change in the electronic environment; and 1638 cm -1 The unreacted double bond peaks were significantly reduced, indicating that the polymerization reaction was complete. The overall peak shape was smooth and the baseline was stable, which verified the realization of the phenol hydroxyl-silanization synergistic modification mechanism, enabling the copolymer to form a stable Si-O-C network structure. S2, 100 parts of modified acrylate copolymer, 3 parts of sodium dodecylbenzenesulfonate, 0.4 parts of sodium bicarbonate and 65 parts of deionized water are added to a reaction vessel and stirred evenly to form a pre-emulsion system. 0.5 parts of ammonium persulfate are added, and 10 parts of trimethylolpropane diacrylate are slowly added dropwise. The polymerization is completed by reacting at 80°C for 3 hours. S3, cool to 28℃, add 0.6 parts of triethanolamine to adjust pH to 7.2, then add 0.2 parts of polyether-modified silicone oil and 0.1 parts of isothiazolinone in sequence, stir for 15 minutes and filter to obtain a highly transparent and low-odor emulsion product.

[0026] Example 3 The purpose of this embodiment is to verify the lower limit performance of the system's odor control and transparency changes under low resin content and low crosslinking ratio.

[0027] S1, 0.5 parts hydroquinone were dissolved in a mixture of 15 parts ethanol and 40 parts deionized water, and 1 part aminopropyltriethoxysilane was added. The mixture was reacted at 60°C for 2 hours to generate a modifier. 25 parts methyl methacrylate, 20 parts butyl acrylate, 8 parts acrylic acid, and 6 parts hydroxyethyl acrylate were added to a reaction vessel. 15 parts ethanol and 40 parts deionized water were added, and the mixture was stirred and degassed with nitrogen for 20 minutes. The modifier was added dropwise at 70°C and reacted for 0.5 hours. Then, 0.2 parts azobisisobutyronitrile were added, and the mixture was polymerized at 80°C for 2 hours. The polymer was then devolatilized under reduced pressure and filtered to obtain the modified acrylate copolymer. S2, 80 parts of modified acrylate copolymer, 2 parts of sodium dodecylbenzenesulfonate, 0.2 parts of sodium bicarbonate and 50 parts of deionized water were added to the reactor and stirred evenly to form a pre-emulsion system. 0.3 parts of ammonium persulfate and 5 parts of trimethylolpropane diacrylate were added, and the polymerization reaction was carried out at 75°C for 2 hours. S3, cool to 25℃, add 0.3 parts of triethanolamine to adjust pH to 7.0, then add 0.1 parts of polyether modified silicone oil and 0.05 parts of isothiazolinone and stir for 10 minutes, then filter to obtain the emulsion product.

[0028] Comparative Example 1 The purpose of this comparative example is to examine the effects of using only silane modification and removing the phenolic hydroxyl groups on the system's stability, odor, and transparency.

[0029] S1, dissolve 0 parts of hydroquinone in a mixture of 20 parts of ethanol and 50 parts of deionized water, add 2 parts of aminopropyltriethoxysilane, and react at 65°C for 2 hours to generate a modifier. Add 30 parts of methyl methacrylate, 25 parts of butyl acrylate, 10 parts of acrylic acid, and 8 parts of hydroxyethyl acrylate to a reaction vessel, add 20 parts of ethanol and 50 parts of deionized water, stir evenly, and degas under nitrogen for 30 minutes. Add the modifier dropwise to the system at 75°C and react for 1 hour. Add 0.3 parts of azobisisobutyronitrile, polymerize at 80°C for 3 hours, and after the reaction, devolve under reduced pressure at 55°C and filter to obtain the modified acrylate copolymer. S2, 100 parts of modified acrylate copolymer, 3 parts of sodium dodecylbenzenesulfonate, 0.4 parts of sodium bicarbonate and 65 parts of deionized water are added to a reaction vessel and stirred evenly to form a pre-emulsion system. 0.5 parts of ammonium persulfate are added, and 10 parts of trimethylolpropane diacrylate are slowly added dropwise. The polymerization is completed by reacting at 80°C for 3 hours. S3, cool to 28℃, add 0.6 parts of triethanolamine to adjust pH to 7.2, then add 0.2 parts of polyether-modified silicone oil and 0.1 parts of isothiazolinone in sequence, stir for 15 minutes and filter to obtain the emulsion product.

[0030] Comparative Example 2 The purpose of this comparative study is to examine the effects of using only phenolic hydroxyl modification and removing silanes on the stability, odor, and transparency of the system.

[0031] S1, dissolve 1.0 part of hydroquinone in a mixture of 20 parts of ethanol and 50 parts of deionized water, add 0 parts of aminopropyltriethoxysilane, and react at 65°C for 2 hours as a modifier. Add 30 parts of methyl methacrylate, 25 parts of butyl acrylate, 10 parts of acrylic acid, and 8 parts of hydroxyethyl acrylate to a reaction vessel, add 20 parts of ethanol and 50 parts of deionized water, stir evenly, and degas under nitrogen for 30 minutes. Add the above modifier solution dropwise to the system at 75°C and react for 1 hour. Add 0.3 parts of azobisisobutyronitrile, polymerize at 80°C for 3 hours, and after the reaction, devolve under reduced pressure at 55°C and filter to obtain the modified acrylate copolymer. S2, 100 parts of modified acrylate copolymer, 3 parts of sodium dodecylbenzenesulfonate, 0.4 parts of sodium bicarbonate and 65 parts of deionized water are added to a reaction vessel and stirred evenly to form a pre-emulsion system. 0.5 parts of ammonium persulfate are added, and 10 parts of trimethylolpropane diacrylate are slowly added dropwise. The polymerization is completed by reacting at 80°C for 3 hours. S3, cool to 28℃, add 0.6 parts of triethanolamine to adjust pH to 7.2, then add 0.2 parts of polyether-modified silicone oil and 0.1 parts of isothiazolinone in sequence, stir for 15 minutes and filter to obtain the emulsion product.

[0032] Comparative Example 3 The purpose of this comparative study is to evaluate the changes in the degree of crosslinking, transparency, and odor control of the system without the addition of low molecular weight crosslinking monomers.

[0033] S1, dissolve 1.0 part of hydroquinone in a mixture of 20 parts of ethanol and 50 parts of deionized water, add 2 parts of aminopropyltriethoxysilane, and react at 65°C for 2 hours to generate a synergistic modifier. Add 30 parts of methyl methacrylate, 25 parts of butyl acrylate, 10 parts of acrylic acid, and 8 parts of hydroxyethyl acrylate to a reaction vessel, add 20 parts of ethanol and 50 parts of deionized water, stir evenly, and degas under nitrogen for 30 minutes. Add the modifier dropwise to the system at 75°C and react for 1 hour. Add 0.3 parts of azobisisobutyronitrile, polymerize at 80°C for 3 hours, and after the reaction, devolve under reduced pressure at 55°C and filter to obtain the modified acrylate copolymer. S2, 100 parts of modified acrylate copolymer, 3 parts of sodium dodecylbenzenesulfonate, 0.4 parts of sodium bicarbonate and 65 parts of deionized water are added to a reaction vessel and stirred evenly to form a pre-emulsion system. 0.5 parts of ammonium persulfate are added, but trimethylolpropane diacrylate is not added. The polymerization is completed by reacting at 80°C for 3 hours. S3, cool to 28℃, add 0.6 parts of triethanolamine to adjust pH to 7.2, then add 0.2 parts of polyether-modified silicone oil and 0.1 parts of isothiazolinone in sequence, stir for 15 minutes and filter to obtain the emulsion product.

[0034] Performance testing 1. Optical transparency test Each sample emulsion was evenly coated onto a clean PET film using a No. 4 doctor blade and allowed to air dry at room temperature for 24 hours, forming a dry film approximately 20 μm thick. The transmittance and haze value of the samples at 550 nm were measured using a haze meter (according to GB / T2410 standard). The instrument was calibrated with a standard transparent film before testing, and each sample was measured three times, with the average value taken. The clarity and transparency of the film surface were recorded, and the presence of haze, slight turbidity, or particulate scattering was observed.

[0035] 2. Odor Residue Test Each sample dry film was cut into 2cm × 2cm pieces and placed in a 20mL sealed headspace vial, then equilibrated in a 60℃ water bath for 30 minutes. The total amount of volatile organic compounds in the headspace gas was analyzed using headspace gas chromatography-mass spectrometry, and the relative peak areas of major odor components such as acrylates, alcohols, and ketones were recorded. A separate sensory evaluation panel of 5 people scored the odor intensity on a scale of 0 to 5 (0 for odorless, 5 for strong irritation) in an odor-free environment. The average value was calculated as the odor residue index, used to comprehensively evaluate the low-odor performance of the emulsion.

[0036] 3. Residual monomer content test Weigh 0.2 g of the dry film sample into a stoppered conical flask, add 10 mL of methanol, and extract by ultrasonication for 30 minutes, followed by filtration. Filter the filtrate through a 0.45 μm filter membrane and inject it into a gas chromatograph for analysis. Chromatographic conditions included a polar stationary column and a programmed temperature ramp. The residues of methyl methacrylate, butyl acrylate, and acrylic acid were determined using the external standard method, and the total residue content was calculated. Each sample was tested in triplicate, and the average value was used as the result. The residue differences between different samples were recorded and compared.

[0037] 4. Storage and shear stability test After sealing each emulsion sample, it was placed in a constant temperature oven and stored at 50℃ for 7 days and 40℃ for 30 days. The appearance, layering, and color changes of the samples were observed before and after storage. Viscosity (rotational viscometer, 25℃) and pH were measured, and particle size distribution was measured using dynamic light scattering. Subsequently, 100 mL of the emulsion sample was taken and sheared at 3000 rpm for 10 minutes on a stirrer, observing for foam instability, layering, or aggregation. If the system showed no significant change and the viscosity deviation was less than 10%, it was considered stable.

[0038] 5. Food contact safety testing The emulsion was coated onto a clean glass plate to form a film, which was then dried at room temperature and peeled off to form a complete film. Samples with an area of ​​100 cm² were cut and placed in 4% acetic acid solution, 10% ethanol solution, and 95% ethanol solution, respectively, to simulate acidic, polar, and fatty food contact environments, and immersed at 60°C for 2 hours. After the experiment, the samples were removed, evaporated, and the residual solids in the solution were weighed to calculate the total migration amount. GC-MS analysis of the migrating solutions was performed to detect the presence of monomers or small molecule migrants, and the changes in migration amounts in different simulated solutions were recorded to assess the safety of the emulsion in food packaging applications.

[0039] Table 1 Comparison of Main Performance Test Results of Each Sample As shown in Table 1, the performance test results of each sample demonstrate that this invention significantly improves the overall performance of the acrylic emulsion system through the synergistic modification of phenolic hydroxyl-silanization and the synergistic design of low-molecular-weight crosslinking monomers. Compared with traditional single-modified or unmodified systems, the synergistically modified structure exhibits significant advantages in optical transparency, odor control, polymerization integrity, storage stability, and food contact safety, verifying the innovation and practical value of the technical solution of this invention.

[0040] In terms of optical transparency, Figure 2Example 2 exhibited the highest transmittance at 95.8%, significantly superior to the other samples. This indicates that, under the synergistic modification of phenolic hydroxyl-silanization and a reasonable crosslinking ratio, the system achieved a more uniform particle size distribution, reduced interfacial refractive index differences, and extremely low light scattering after film formation, resulting in a highly transparent film. Example 1 was second best at 94.5%, while Example 3 appeared slightly cloudy due to its lower crosslinking density. The transmittance of the comparative samples decreased significantly, especially Comparative Example 3, which had a transmittance of only 86.9%, and exhibited a hazy appearance after film formation.

[0041] Regarding odor residue performance, Example 2 had the lowest odor residue index at 0.8, indicating that the synergistic modified structure can effectively suppress the release of low molecular weight monomers and volatile components. Examples 1 and 3 had slightly higher odor residue indices, but were still significantly better than the comparative samples, with odor indices ranging from 1.6 to 2.1, demonstrating that the system of the present invention has a significant advantage in low odor control.

[0042] In terms of residual monomer content Figure 3 Example 2 showed the lowest residual monomer content at 42 mg / kg, indicating a more complete polymerization reaction and that the modified structure helped improve monomer conversion. In contrast, the comparative samples generally had higher residual monomer content, ranging from 68 to 75 mg / kg, suggesting that a single modification method was insufficient to effectively suppress residual monomers.

[0043] Storage stability results showed that both Examples 1 and 2 remained homogeneous, without stratification or water separation, and exhibited minimal viscosity change after 7 days of accelerated aging at 50°C, demonstrating excellent emulsion stability. Example 3 showed slight water separation, while the comparative samples generally showed stratification or turbidity, indicating that the synergistic modification significantly enhanced the long-term stability of the system.

[0044] Regarding food contact safety, Figure 4 The total migration amount in Example 2 was only 2.8 mg / dm², far below the national standard limit of 10 mg / dm², indicating that low molecular weight migration was inhibited and the safety was optimal. Examples 1 and 3 showed slightly higher migration amounts but were still within the safe range, while the comparative samples all exceeded 4.5 mg / dm², showing a clear trend of small molecule precipitation.

[0045] In summary, Example 2 showed the best performance in terms of optical transparency, odor control, polymerization integrity, emulsion stability, and food contact safety, followed by Example 1, and Example 3 was slightly worse. All three comparative sample groups were significantly inferior to the examples, which fully demonstrates that the present invention has achieved a comprehensive improvement in performance through phenolic hydroxyl-silanization synergistic modification and low molecular weight crosslinking design, and has significant innovation and application value.

Claims

1. A highly transparent, low-odor acrylic emulsion for food packaging, characterized in that, The raw materials comprise the following parts by weight: 80-120 parts of modified acrylate copolymer, 5-15 parts of trimethylolpropane diacrylate, 2-4 parts of sodium dodecylbenzenesulfonate, 0.3-0.8 parts of ammonium persulfate, 0.2-0.6 parts of sodium bicarbonate, 50-80 parts of deionized water, 0.3-1.0 parts of triethanolamine, 0.1-0.3 parts of polyether-modified silicone oil, and 0.05-0.15 parts of isothiazolinone; wherein the modified acrylate copolymer is a highly transparent and highly stable film-forming resin that introduces a Si-O-C structure through a phenolic hydroxyl-silanization synergistic reaction; and the trimethylolpropane diacrylate is a low-molecular-weight crosslinking monomer containing diacrylate groups.

2. The acrylic emulsion for high transparency and low odor in food packaging according to claim 1, characterized in that, The modified acrylate copolymer comprises the following raw materials in parts by weight: 25-35 parts methyl methacrylate, 20-30 parts butyl acrylate, 8-12 parts acrylic acid, 6-10 parts hydroxyethyl acrylate, 1-3 parts aminopropyltriethoxysilane, 0.5-1.5 parts hydroquinone, 0.2-0.5 parts azobisisobutyronitrile, 15-25 parts ethanol, and 40-60 parts deionized water.

3. The acrylic emulsion for high transparency and low odor in food packaging according to claim 1, characterized in that, The preparation method of the modified acrylate copolymer includes the following steps: (1) Dissolve hydroquinone in an ethanol-water mixture, stir until homogeneous, and then add aminopropyltriethoxysilane to generate a silane-phenol hydroxyl synergistic modifier. (2) Methyl methacrylate, butyl acrylate, acrylic acid and hydroxyethyl acrylate are added to the reaction vessel, ethanol and deionized water are added and stirred to form a monomer mixture, and nitrogen degassing treatment is performed. (3) Under stirring conditions, the silane-phenol hydroxyl synergistic modifier is slowly added dropwise to the acrylate monomer mixture to continue the reaction and form a grafting modification intermediate; (4) Add azobisisobutyronitrile as an initiator to the system and carry out solution polymerization reaction at a constant temperature to obtain a modified acrylate copolymer solution; (5) The modified acrylate copolymer solution was subjected to reduced pressure to remove low-boiling substances, cooled to room temperature and filtered to obtain the modified acrylate copolymer.

4. The acrylic emulsion for high transparency and low odor in food packaging according to claim 3, characterized in that, The reaction conditions for step (1) are: in an ethanol-water mixture, the reaction is carried out at 60-70°C for 1.5-2.5 hours; the reaction conditions for step (2) are: stirring and degassing with nitrogen at 30-40°C for 20-40 minutes.

5. The acrylic emulsion for high transparency and low odor in food packaging according to claim 3, characterized in that, The reaction conditions for step (3) are: adding the modifier at a constant rate at 70-80°C and reacting for 0.5-1 hour; the reaction conditions for step (4) are: polymerization reaction at 80-85°C for 2-4 hours.

6. The acrylic emulsion for high transparency and low odor in food packaging according to claim 3, characterized in that, The reaction conditions for step (5) are devastation and filtration under reduced pressure at 50-60°C.

7. A method for preparing a highly transparent, low-odor acrylic emulsion for food packaging, wherein the highly transparent, low-odor acrylic emulsion for food packaging is as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1, add the modified acrylate copolymer, sodium dodecylbenzenesulfonate, sodium bicarbonate and deionized water into the reactor and stir to form a uniform pre-emulsion system; S2, ammonium persulfate is added to the pre-emulsified system as an initiator, and trimethylolpropane diacrylate is added dropwise, and emulsion polymerization is carried out under stirring conditions; S3. After the reaction is complete, cool to room temperature, add triethanolamine to adjust the pH value, then add polyether-modified silicone oil and isothiazolinone in sequence and stir evenly. After filtration to remove impurities, the finished emulsion is obtained.

8. The method for preparing a highly transparent, low-odor acrylic emulsion for food packaging according to claim 7, characterized in that, The pre-emulsification reaction conditions in step S1 are stirring at 70-75°C for 20-40 minutes.

9. The method for preparing a highly transparent, low-odor acrylic emulsion for food packaging according to claim 7, characterized in that, The emulsion polymerization reaction conditions in step S2 are a constant temperature reaction at 75-85°C for 2-4 hours.

10. The method for preparing a highly transparent, low-odor acrylic emulsion for food packaging according to claim 7, characterized in that, The post-treatment reaction conditions in step S3 are stirring at 25–30°C for 10–20 minutes.

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