A food contact grade silicone emulsion and a method of making the same

Abstract

The present application belongs to the field of food contact coating materials, and provides a food contact grade silicone emulsion and a preparation method thereof. The silicone intermediate with a core-shell emulsion droplet structure is synergistically compounded with a methyltrimethoxysilane surface modified silica intermediate, and combined with hydrolysis and condensation pre-emulsification, high pressure homogenization, aging, defoaming, filtration and control of emulsion droplet and particle size distribution to obtain a water-based system with stable dispersion and workability. The system still maintains suitable viscosity under higher non-volatile conditions, and after film formation, it has the performances of adhesion, wear resistance, heat resistance and stable release, solving the problem that the existing system cannot simultaneously consider high solid content, low viscosity, processing adaptability, high adhesion, wear resistance and film forming performance, and high heat resistance, stability and low release force. The present application has application value in constructing a silicone release layer on the surface of paper base material and plastic film base material.

Description

Technical Field

[0001] This invention relates to the field of aqueous release coating materials for organosilicon, specifically to a food contact grade siloxane emulsion and its preparation method. Background Technology

[0002] In the actual preparation process of food contact materials and products, it is often necessary to form a uniformly distributed, reliably adhered, and continuously processable siloxane release layer on the surface of paper or plastic film substrates. As related products develop towards water-based, low-volatility, high-speed coating, and stable curing, the siloxane emulsions used not only need to possess good dispersion stability, workability, and coating adaptability, but also need to ensure adhesion to the substrate, surface abrasion resistance, heat treatment stability, and stable release performance after curing. Especially for food contact applications, the emulsion system should maintain suitable viscosity under high non-volatile conditions and avoid coating defects and performance fluctuations caused by particle size imbalance, interfacial instability, or uneven film formation. Therefore, designing around the siloxane droplet structure, silica surface state, and the synergistic relationship of the film-forming interface is of great significance for improving the quality of siloxane release layers on paper and plastic film substrates, expanding the process window, and enhancing the reliability of product applications.

[0003] Currently, existing solutions for silicone release systems used in food contact applications focus on improvements in areas such as anchoring reinforcement, construction of water-based release emulsions, and paper substrate applications. For example, Chinese patent CN105899617B discloses an anchoring emulsion for silicone anti-stick coating compositions, focusing on improving adhesion and rub-resistance on paper and polymer substrates. Another example is Chinese patent CN118574907A, which discloses a silicone release coating emulsion, its preparation method, and its use in baking paper, focusing on the construction and application scenarios of silicone release layers in food contact applications. However, existing research largely revolves around single anchoring or single release approaches, lacking sufficient consideration of the balance between high solids content and low viscosity processing adaptability and high adhesion and abrasion resistance film-forming performance, as well as the balance between high thermal stability and low peel release force for stable release performance. In particular, there is a lack of systematic design for particle size synergy, interface synergy, and film-forming synergy between siloxane intermediates with core-shell emulsion droplet structures and methyltrimethoxysilane surface-modified silica intermediates. Summary of the Invention

[0004] The purpose of this invention is to provide a food contact grade siloxane emulsion and its preparation method, which solves the problem that current water-based release systems are unable to simultaneously achieve high solids content and low viscosity processing adaptability, high adhesion and wear-resistant film-forming performance, as well as high heat resistance and low peel release force to stabilize release performance.

[0005] This invention uses a siloxane intermediate with a core-shell emulsion droplet structure as the film-forming basis and a methyltrimethoxysilane surface-modified silica intermediate as the structural reinforcement unit. Through particle size matching, interfacial compatibility and network co-construction, the stability of the emulsion, the density of the film layer and the bonding state with the substrate are improved in a synergistic manner, thereby taking into account the adhesion, heat resistance and stable release performance without sacrificing the application fluidity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A food contact grade siloxane emulsion, based on the initial mixture by weight, comprises 35-65 parts by weight of component A, 2-12 parts by weight of component B, and deionized water to a total of 100 parts by weight; component A is a pre-prepared siloxane intermediate with a core-shell droplet structure, prepared by hydrolysis condensation, pre-emulsification, and high-pressure homogenization of dimethyl silicone oil, methyltrimethoxysilane, tetraethyl orthosilicate, polyvinyl alcohol, ethanol, acetic acid, and deionized water, with a droplet D50 of 90-180 nm; component B is a pre-prepared methyltrimethoxysilane surface-modified silica intermediate, prepared by surface hydrolysis condensation of silica, methyltrimethoxysilane, ethanol, acetic acid, and deionized water, with an average particle size of 10-50 nm; the siloxane emulsion has a pH of 5.8-6.8 and a viscosity of 300-1000 mPa·s.

[0008] Furthermore, component A is prepared through the following steps:

[0009] A1. Raw material preparation: By weight, dimethyl silicone oil, methyltrimethoxysilane, tetraethyl orthosilicate, polyvinyl alcohol, ethanol, acetic acid and deionized water are 100 parts, 5-20 parts, 2-10 parts, 0.5-4 parts, 5-25 parts, 0.1-1.0 parts and 80-200 parts respectively.

[0010] A2, Pre-hydrolysis: Methyltrimethoxysilane and tetraethyl orthosilicate are added to a mixed system consisting of ethanol, deionized water and acetic acid, and reacted at 20-35 °C for 20-60 min, with the pH of the system set at 3.5-5.0;

[0011] A3, Pre-emulsification and homogenization: Add dimethyl silicone oil and polyvinyl alcohol to the system obtained in step A2, pre-emulsify at 3000-8000 r / min for 5-15 min, and then homogenize under high pressure at 40-80 MPa 1-3 times.

[0012] A4, Aging: The dispersion system obtained in step A3 is aged at 25-45 °C for 1-4 h to make the D50 of the emulsion droplets of the dispersion system 90-180 nm, thus obtaining component A.

[0013] Furthermore, component B is prepared via the following steps:

[0014] B1, Raw material preparation: By weight, silicon dioxide, methyltrimethoxysilane, ethanol, acetic acid and deionized water are 100 parts, 5-20 parts, 50-200 parts, 0.05-0.50 parts and 50-200 parts respectively;

[0015] B2, Dispersion: Add silica to a mixture of ethanol, deionized water and acetic acid, disperse at 300-1200 r / min for 15-60 min at 20-35℃, and adjust the pH of the system to 4.5-6.0.

[0016] B3, Surface hydrolysis and condensation: Add methyltrimethoxysilane to the system obtained in step B2 and react at 25-45 °C for 1-6 h;

[0017] B4, Aging: The system obtained in step B3 is aged at 40-60 °C for 1-4 h to make the average particle size of the system 10-50 nm, thus obtaining component B.

[0018] Further, based on the non-volatile matter mass, the ratio of component A to component B is 100:5-25; component A and component B are mixed, and deionized water is added to make the initial total mass of the mixture 100 parts by weight. The mixture is stirred at 25-35 °C for 10-30 min. If necessary, the pH of the system is adjusted to 5.8-6.8 using an alkaline adjuster. Then, it is aged at 25-40 °C for 1-12 h. The non-volatile matter content of the siloxane emulsion is adjusted to 45-58 wt% by removing some water and ethanol, and adding deionized water if necessary. Then, it is degassed under vacuum at -0.06 to -0.09 MPa for 10-30 min, and filtered through a 5-20 µm filter to obtain the siloxane emulsion.

[0019] Furthermore, in component A, based on 100 parts by weight of dimethyl silicone oil, methyltrimethoxysilane comprises 5-15 parts by weight and tetraethyl orthosilicate comprises 3-8 parts by weight; in component B, based on 100 parts by weight of silicon dioxide, methyltrimethoxysilane comprises 6-15 parts by weight; and the polyvinyl alcohol content in the siloxane emulsion is 0.1-1.0 wt%.

[0020] Furthermore, the droplet D50 of component A is 100-160 nm; the average particle size of component B is 15-40 nm; and the pH of the siloxane emulsion is 6.0-6.6, and the viscosity is 350-900 mPa·s.

[0021] Furthermore, the dry coating amount of the siloxane emulsion applied to the paper substrate or plastic film substrate is 0.15-0.60 g / m², and a siloxane release layer is formed after curing at 80-140 ℃ for 30-180 s.

[0022] As a concept of this invention, a synergistic design of a siloxane intermediate with a core-shell emulsion droplet structure and a methyltrimethoxysilane surface-modified silica intermediate is employed to enhance the film integrity, interfacial adhesion, abrasion resistance, and stable release properties of the siloxane release layer on the surface of paper or plastic film substrates. The core-shell emulsion droplet structure of the siloxane intermediate enables the formation of a continuous and flexible siloxane phase during film formation, balancing spreading and film continuity. The methyltrimethoxysilane surface-modified silica intermediate helps regulate the interfacial microstructure and local network environment, improving film density, thermal stability, and surface durability. The matching of the two in terms of particle size distribution, surface chemistry, and network formation pathways allows the system to maintain water-based processing friendliness while facilitating the formation of a siloxane release layer with reliable adhesion, stable abrasion, and balanced release behavior.

[0023] This invention also discloses a method for preparing food contact grade siloxane emulsion, comprising the following steps:

[0024] S1, providing the prepared component A;

[0025] S2, providing the prepared component B;

[0026] S3. The A component provided in step S1 and the B component provided in step S2 are mixed at a ratio of 100:5-25 based on the non-volatile matter mass, and deionized water is added to make the total mass of the initial mixture 100 parts by weight. The mixture is stirred at 25-35 ℃ for 10-30 min, and then aged at 25-40 ℃ for 1-12 h. The non-volatile matter content of the siloxane emulsion is adjusted to 45-58 wt% by removing some water and ethanol and adding deionized water if necessary. After vacuum degassing and filtration, the siloxane emulsion is obtained.

[0027] Furthermore, in step S3, the vacuum degassing pressure is -0.06 to -0.09 MPa, the degassing time is 10-30 min, and the filter pore size is 5-20 µm.

[0028] Furthermore, the resulting siloxane emulsion has a pH of 5.8-6.8, a non-volatile content of 45-58 wt%, and a viscosity of 300-1000 mPa·s.

[0029] Furthermore, in step A2, ethanol, deionized water and acetic acid are mixed evenly first, and then methyltrimethoxysilane and tetraethyl orthosilicate are added; in step B2, ethanol, deionized water and acetic acid are mixed evenly first, and then silicon dioxide is added.

[0030] Furthermore, in step A2, the pH of the system is adjusted to 3.5-5.0 by adjusting the amount of acetic acid or by adding acidic or alkaline adjusters; in step B2, the pH of the system is adjusted to 4.5-6.0 by adjusting the amount of acetic acid or by adding acidic or alkaline adjusters.

[0031] Furthermore, steps A2 and B3 are carried out under normal pressure and a non-inert atmosphere.

[0032] Furthermore, in step A3, pre-emulsification is carried out at 20-35 ℃ using high-speed shearing or mechanical stirring, and the system temperature does not exceed 50 ℃ during high-pressure homogenization.

[0033] Furthermore, in step B2, dispersion is carried out using mechanical stirring or magnetic stirring.

[0034] Furthermore, after step B4, deionized water, ethanol, or a mixture of ethanol and deionized water are added to adjust the non-volatile content of component B to 15-35 wt%.

[0035] Furthermore, after step A4, deionized water, ethanol, or a mixture of ethanol and deionized water may be added, or some water and ethanol may be removed, to adjust the non-volatile content of component A to 35-50 wt.

[0036] Furthermore, after mixing components A, B, and deionized water, the pH of the system was adjusted to 5.8-6.8 using an alkaline adjuster.

[0037] Furthermore, after mixing components A, B, and deionized water, the non-volatile content of the siloxane emulsion is adjusted to 45-58 wt by adding deionized water or removing some water and ethanol.

[0038] Furthermore, vacuum degassing is carried out at 25-35 ℃.

[0039] Furthermore, the non-volatile components of component A and component B were dried at 105°C to constant weight and their masses were determined.

[0040] Furthermore, the polyvinyl alcohol content in the siloxane emulsion is calculated based on the total mass of the siloxane emulsion.

[0041] Furthermore, the core-shell emulsion droplet structure is an emulsion droplet structure with dimethyl silicone oil as the core and a surface coated with a siloxane layer formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate.

[0042] Furthermore, the core-shell emulsion droplet structure was confirmed by transmission electron microscopy.

[0043] Furthermore, the D50 of the emulsion droplets of component A and the average particle size of component B were determined by dynamic light scattering.

[0044] Furthermore, the viscosity of the siloxane emulsion is [value missing] at 25°C and a shear rate of 10 s⁻¹. -1 Determined under the specified conditions.

[0045] Furthermore, the adhesion of the siloxane release layer was determined by cross-cut test.

[0046] Furthermore, the 180° peel release force was measured under the conditions of a sample width of 50 mm and a peel speed of 300 mm / min.

[0047] As another aspect of this invention, the present invention employs a preparation path that involves first separately preparing a siloxane intermediate with a core-shell emulsion droplet structure and a methyltrimethoxysilane surface-modified silica intermediate, followed by mixing, adjustment, aging, vacuum degassing, and filtration according to the proportion of non-volatile components. This approach is primarily used to enhance the controllability of emulsion composition, batch stability, and consistency of the final siloxane release layer. By separating the front-end structure construction from the back-end compatibility control, this method allows for a clear functional division of labor among the hydrolysis-condensation, pre-emulsification homogenization, surface modification, and final mixing-aging stages. This helps reduce the risk of interfacial imbalance caused by direct blending of components and takes into account droplet stability, particle size retention, viscosity control, and end-application adaptability, thereby more stably obtaining a siloxane emulsion with adhesion, heat resistance, abrasion resistance, and stable release properties.

[0048] Siloxane intermediates with a core-shell emulsion droplet structure focus on providing a continuous film-forming framework, flexible interfacial wetting, and basic spreading ability on paper or plastic film substrates. Their outer layer, formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate, facilitates the establishment of a relatively stable surface network after curing. methyltrimethoxysilane surface-modified silica intermediates, on the other hand, emphasize microscopic reinforcement, interfacial constraint, and thermal stability. Surface modification improves compatibility with the siloxane phase and reduces dispersion imbalance caused by direct silica introduction. When used together, both improve film density and abrasion and heat resistance, while synergistically regulating interfacial bonding and stable release properties. This ensures the siloxane release layer is less prone to instability due to insufficient adhesion or release fluctuations due to local structural imbalances.

[0049] Beneficial technical effects

[0050] 1. This invention adopts a technical route of first constructing a siloxane intermediate with a core-shell emulsion droplet structure, and then introducing a methyltrimethoxysilane surface-modified silica intermediate. This makes the division of labor between the organic phase film formation and the inorganic phase enhancement clearer, which is beneficial to maintaining the flow and dispersion stability of the system under high non-volatile conditions. It is more suitable for continuous fine coating than existing single siloxane emulsions.

[0051] 2. By synergistically controlling the droplet size of component A and the particle size range of component B, this invention enhances the spreading, embedding, and network construction capabilities of the emulsion on the surface of paper or plastic film substrates, thereby improving the coating adhesion reliability and wear resistance durability. Compared with solutions that rely solely on a single anchoring or release design, this invention is more conducive to achieving a stable film formation effect.

[0052] 3. This invention improves the density and thermal stability of the film layer through the combined effect of the siloxane structure formed by methyltrimethoxysilane and tetraethyl orthosilicate and the surface-modified silica. This makes the resulting siloxane release layer less prone to interfacial instability or performance fluctuations during heat curing and subsequent use, and is more likely to balance heat resistance and stable release than conventional water-based systems.

[0053] 4. The present invention employs a process that combines water-based preparation with final mixing and aging, vacuum degassing, and filtration, which helps to reduce the risk of foam, particles, and surface defects during construction and improves the construction window and appearance consistency of the finished emulsion. It is suitable for constructing a uniform and stable siloxane release layer for food contact materials and products on paper substrates or plastic film substrates. Attached Figure Description

[0054] Figure 1 The images show the FTIR full spectrum overlays of Example 1, Comparative Example 8, and Comparative Example 9.

[0055] Figure 2 These are enlarged FTIR views of Example 1, Comparative Example 8, and Comparative Example 9.

[0056] Figure 3 This is a high-resolution XPS Si2p overlay image of Example 1 and Comparative Example 9.

[0057] Figure 4 This is a high-resolution XPS O1s overlay image of Example 1 and Comparative Example 9.

[0058] Figure 5 The graph shows the proportion of XPS-fitted feature components for Example 1 and Comparative Example 9.

[0059] Figure 6 The apparent viscosity-shear rate rheological curves are for Example 1, Comparative Example 2, and Comparative Example 10.

[0060] Figure 7This is a magnified view of the low-shear region in Example 1, Comparative Example 2, and Comparative Example 10.

[0061] Figure 8 The graphs show the paired peel release forces at 180° before and after thermal aging for Examples 1, 2, and 10.

[0062] Figure 9 The graph shows the rate of change of release force after thermal aging for Examples 1, 2, and 10.

[0063] Figure 10 This is a superimposed diagram of the DLS intensity distribution of Example 1, Comparative Example 3, and Comparative Example 9.

[0064] Figure 11 The cumulative distribution curves of DLS for Example 1, Comparative Example 3, and Comparative Example 9 are shown.

[0065] Figure 12 The z-Average plots of the average particle size of DLS in Example 1, Comparative Example 3, and Comparative Example 9 are shown.

[0066] Figure 13 The above are the DLS polydispersity index (PDI) plots for Example 1, Comparative Example 3, and Comparative Example 9.

[0067] Figure 14 The graphs show the Taber wear mass loss-cycle number process curves for Example 1, Comparative Example 3, and Comparative Example 9.

[0068] Figure 15 The graph shows the mass loss at the 500 rpm endpoint for Example 1, Comparative Example 3, and Comparative Example 9.

[0069] Figure 16 Macroscopic optical photographs of the components of the siloxane emulsion system and the release layer after curing.

[0070] Figure 16 a is a macroscopic optical photograph of component A;

[0071] Figure 16 b is a macroscopic optical photograph of component B;

[0072] Figure 16 c is a macroscopic optical photograph of the mixed and aged siloxane emulsion;

[0073] Figure 16 d is a macroscopic optical photograph of the cured siloxane release layer.

[0074] Figure 17 These are scanning electron microscope (SEM) images of the components of the siloxane emulsion system and the release layer after curing.

[0075] Figure 17 a is a low-magnification scanning electron microscope image of the droplet morphology of component A.

[0076] Figure 17 b is a medium-magnification scanning electron microscope image of the droplet morphology of component A.

[0077] Figure 17 c is a medium-magnification scanning electron microscope image of silica modified with methyltrimethoxysilane in component B.

[0078] Figure 17 d is a high-magnification scanning electron microscope image of silica modified on the surface of methyltrimethoxysilane in component B.

[0079] Figure 17 e is a scanning electron microscope image of the surface morphology of the cured siloxane release layer.

[0080] Figure 17 f is a cross-sectional scanning electron microscope image of the cured siloxane release layer.

[0081] Figure 18 Transmission electron microscopy (TEM) images of the components of the siloxane emulsion system and the release layer after curing.

[0082] Figure 18 Image a is a bright-field transmission electron microscope image of the core-shell emulsion droplet of component A.

[0083] Figure 18 b is a transmission electron microscope image of silica nanoparticles modified with methyltrimethoxysilane in component B. Detailed Implementation

[0084] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0085] Example 1

[0086] Preparation of Component A: Weigh out 100 parts by weight of dimethyl silicone oil, 10 parts by weight of methyltrimethoxysilane, 5 parts by weight of tetraethyl orthosilicate, 2 parts by weight of polyvinyl alcohol, 15 parts by weight of ethanol, 0.5 parts by weight of acetic acid, and 140 parts by weight of deionized water. First, mix ethanol, deionized water, and acetic acid evenly. Adjust the amount of acetic acid to make the pH of the system 4.2. Then, add methyltrimethoxysilane and tetraethyl orthosilicate under normal pressure and a non-inert atmosphere, and react at 28°C for 40 minutes for pre-hydrolysis. Subsequently, add dimethyl silicone oil and polyvinyl alcohol to the pre-hydrolysis system, and pre-emulsify at 20°C using high-speed shear at 5000 rpm for 10 minutes. During the high-pressure homogenization process, control the system temperature to not exceed 50°C, and homogenize twice under high pressure at 60 MPa. The resulting dispersion system was aged at 35°C for 2.5 hours to obtain component A, which has a core-shell emulsion droplet structure with a droplet D50 of 130 nm. In this embodiment, the core-shell emulsion droplet structure is a droplet structure with dimethyl silicone oil as the core and a surface coated with a siloxane layer formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate, as confirmed by transmission electron microscopy. Subsequently, deionized water was added to adjust the non-volatile content of component A to 39.3% by weight. In component A of this embodiment, based on 100 parts by weight of dimethyl silicone oil, 10 parts by weight of methyltrimethoxysilane and 5 parts by weight of tetraethyl orthosilicate are present.

[0087] Preparation of Component B: 100 parts by weight of silica, 10 parts by weight of methyltrimethoxysilane, 125 parts by weight of ethanol, 0.25 parts by weight of acetic acid, and 125 parts by weight of deionized water were weighed. First, the ethanol, deionized water, and acetic acid were mixed evenly. The pH of the system was adjusted to 5.2 by adjusting the amount of acetic acid. Then, silica was added, and the mixture was dispersed at 750 rpm for 35 minutes at 28°C using mechanical stirring. Methyltrimethoxysilane was added to the dispersion system, and the reaction was carried out for 3.5 hours at 35°C under normal pressure and a non-inert atmosphere to achieve surface hydrolysis and condensation. The resulting system was aged at 50°C for 2.5 hours, and then deionized water was added to adjust the non-volatile content to 25% by weight, yielding methyltrimethoxysilane-modified silica component B with an average particle size of 28 nm. In this embodiment, methyltrimethoxysilane comprised 10 parts by weight of silica (based on 100 parts by weight). In this embodiment, the D50 of component A droplets and the average particle size of component B were determined by dynamic light scattering.

[0088] Preparation of the siloxane emulsion: Component A and component B obtained above were mixed in a non-volatile content ratio of 100:14. In this embodiment, the non-volatile content of components A and B was measured after drying at 105°C to constant weight. 50 parts by weight of component A and 11 parts by weight of component B were taken, and 39 parts by weight of deionized water were added to make the initial total mass of the mixture 100 parts by weight. The mixture was stirred at 30°C for 20 minutes, and the pH of the system was adjusted to 6.3 using an alkaline adjuster. It was then aged at 32°C for 6 hours. Solid content was adjusted by removing some water and ethanol, and adding deionized water if necessary. The mixture was degassed at 25°C under a vacuum of -0.075 MPa for 20 minutes, and filtered through a 10-micron filter to obtain the siloxane emulsion. The non-volatile content of the obtained siloxane emulsion was 51% by weight. The siloxane emulsion in this embodiment had a pH of 6.3 and a viscosity of 620 mPa·s, measured at 25°C and a shear rate of 10 sec.

[0089] Application: The siloxane emulsion of this embodiment was applied to the surface of a paper substrate with a dry coating amount of 0.35 g / m². After curing at 110°C for 100 seconds, a siloxane release layer was formed. The adhesion of the siloxane release layer of this embodiment was measured to be grade 0 by the cross-cut test. The 180-degree peel release force was measured to be 58 mN / 25 mm under the conditions of a sample width of 50 mm and a peel speed of 300 mm / min.

[0090] This embodiment uses moderate formulation parameters and process conditions, with all parameters falling within the middle range specified in the technical solution. This ensures the stability of the formulation and the reproducibility of the process. The resulting siloxane emulsion exhibits good storage stability and coating performance, making it suitable for conventional release coating processes on paper and plastic film substrates. It is particularly suitable for large-scale continuous production applications where high process stability is required.

[0091] Example 2

[0092] Preparation of Component A: Weigh out 100 parts by weight of dimethyl silicone oil, 7 parts by weight of methyltrimethoxysilane, 4 parts by weight of tetraethyl orthosilicate, 1.2 parts by weight of polyvinyl alcohol, 18 parts by weight of ethanol, 0.3 parts by weight of acetic acid, and 110 parts by weight of deionized water. First, mix ethanol, deionized water, and acetic acid evenly. Adjust the amount of acetic acid to make the pH of the system 4.5. Then, add methyltrimethoxysilane and tetraethyl orthosilicate under normal pressure and a non-inert atmosphere, and react at 25°C for 45 minutes for pre-hydrolysis. Subsequently, add dimethyl silicone oil and polyvinyl alcohol to the pre-hydrolysis system, and pre-emulsify at 20°C using high-speed shear at 6000 rpm for 8 minutes. During the high-pressure homogenization process, control the system temperature to not exceed 50°C, and homogenize twice under high pressure at 70 MPa. The resulting dispersion system was aged at 30°C for 2 hours to obtain component A, which has a core-shell emulsion droplet structure with a droplet D50 of 110 nm. In this embodiment, the core-shell emulsion droplet structure is a droplet structure with dimethyl silicone oil as the core and a surface coated with a siloxane layer formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate, as confirmed by transmission electron microscopy. Subsequently, the non-volatile content of component A was adjusted to 44.8% by weight by removing some water and ethanol. In component A of this embodiment, based on 100 parts by weight of dimethyl silicone oil, methyltrimethoxysilane is 7 parts by weight and tetraethyl orthosilicate is 4 parts by weight.

[0093] Preparation of Component B: 100 parts by weight of silica, 8 parts by weight of methyltrimethoxysilane, 160 parts by weight of ethanol, 0.15 parts by weight of acetic acid, and 140 parts by weight of deionized water were weighed. First, the ethanol, deionized water, and acetic acid were mixed evenly. The pH of the system was adjusted to 5.5 by adjusting the amount of acetic acid. Then, silica was added, and the mixture was dispersed at 900 rpm for 40 minutes at 25°C using mechanical stirring. Methyltrimethoxysilane was added to the dispersion system, and the reaction was carried out for 2.5 hours at 30°C under normal pressure and a non-inert atmosphere to achieve surface hydrolysis and condensation. The resulting system was aged at 45°C for 2 hours. Subsequently, a mixture of ethanol and deionized water was added to adjust the non-volatile content to 22% by weight, yielding methyltrimethoxysilane-modified silica component B with an average particle size of 22 nanometers. In this embodiment, methyltrimethoxysilane comprised 8 parts by weight of silica (based on 100 parts by weight). In this embodiment, the D50 of component A droplets and the average particle size of component B were determined by dynamic light scattering.

[0094] Preparation of the siloxane emulsion: Component A and component B obtained above were mixed in a non-volatile content ratio of 100:9. In this embodiment, the non-volatile content of components A and B was measured after drying at 105°C to constant weight. 60 parts by weight of component A and 11 parts by weight of component B were taken, and 29 parts by weight of deionized water were added to make the initial total mass of the mixture 100 parts by weight. The mixture was stirred at 28°C for 15 minutes, and the pH of the system was adjusted to 6.1 using an alkaline adjuster. The mixture was then aged at 28°C for 4 hours. Solid content was adjusted by removing some water and ethanol, and adding deionized water if necessary. The mixture was degassed at 25°C under a vacuum of -0.07 MPa for 15 minutes, and filtered through an 8-micron filter to obtain the siloxane emulsion. The non-volatile content of the obtained siloxane emulsion was 55% by weight. The siloxane emulsion in this embodiment had a pH of 6.1 and a viscosity of 420 mPa·s, measured at 25°C and a shear rate of 10 sec.

[0095] Application: The siloxane emulsion of this embodiment is applied to the surface of a plastic film substrate with a dry coating amount of 0.25 g / m². After curing at 120°C for 80 seconds, a siloxane release layer is formed. The adhesion of the siloxane release layer in this embodiment is grade 0 as determined by the cross-cut test. The 180-degree peel release force is 42 mN / 25 mm as determined under the conditions of a sample width of 50 mm and a peel speed of 300 mm / min.

[0096] This embodiment achieves a good balance between high solids content and low viscosity. The resulting siloxane emulsion has excellent flowability and good coating performance, making it suitable for high-speed coating equipment and thin coating applications. It is particularly suitable for the production of release paper for plastic films with high requirements for coating efficiency and release force control.

[0097] Example 3

[0098] Preparation of Component A: Weigh out 100 parts by weight of dimethyl silicone oil, 13 parts by weight of methyltrimethoxysilane, 7 parts by weight of tetraethyl orthosilicate, 3 parts by weight of polyvinyl alcohol, 10 parts by weight of ethanol, 0.7 parts by weight of acetic acid, and 170 parts by weight of deionized water. First, mix ethanol, deionized water, and acetic acid evenly. Adjust the amount of acetic acid to make the pH of the system 3.8. Then, add methyltrimethoxysilane and tetraethyl orthosilicate under normal pressure and a non-inert atmosphere, and react at 32°C for 30 minutes for pre-hydrolysis. Subsequently, add dimethyl silicone oil and polyvinyl alcohol to the pre-hydrolysis system, and pre-emulsify at 20°C using high-speed shear at 4000 rpm for 12 minutes. During the high-pressure homogenization process, control the system temperature to not exceed 50°C, and homogenize three times under high pressure at 50 MPa. The resulting dispersion system was aged at 40°C for 3 hours to obtain component A, which has a droplet D50 of 150 nm and a core-shell droplet structure. In this embodiment, the core-shell droplet structure is a droplet structure with dimethyl silicone oil as the core and a surface coated with a siloxane layer formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate, which was confirmed by transmission electron microscopy. Subsequently, the non-volatile content of component A was adjusted to 38.1% by weight by removing some water and ethanol. In this embodiment, component A contains 13 parts by weight of methyltrimethoxysilane and 7 parts by weight of tetraethyl orthosilicate, based on 100 parts by weight of dimethyl silicone oil.

[0099] Preparation of Component B: 100 parts by weight of silica, 13 parts by weight of methyltrimethoxysilane, 90 parts by weight of ethanol, 0.35 parts by weight of acetic acid, and 80 parts by weight of deionized water were weighed. First, the ethanol, deionized water, and acetic acid were mixed evenly. The pH of the system was adjusted to 4.8 by adjusting the amount of acetic acid. Then, silica was added, and the mixture was dispersed at 500 rpm for 50 minutes at 30°C using magnetic stirring. Methyltrimethoxysilane was added to the dispersion system, and the reaction was carried out for 5 hours at 40°C under normal pressure and a non-inert atmosphere to achieve surface hydrolysis and condensation. The resulting system was aged at 55°C for 3 hours, and then deionized water was added to adjust the non-volatile content to 32% by weight, yielding methyltrimethoxysilane-modified silica component B with an average particle size of 35 nm. In this embodiment, methyltrimethoxysilane comprised 13 parts by weight of silica (based on 100 parts by weight). In this embodiment, the D50 of component A droplets and the average particle size of component B were determined by dynamic light scattering.

[0100] Preparation of the siloxane emulsion: Component A and component B obtained above were mixed in a non-volatile content ratio of 100:20. In this embodiment, the non-volatile content of components A and B was measured after drying at 105°C to constant weight. 42 parts by weight of component A and 10 parts by weight of component B were taken, and 48 parts by weight of deionized water were added to make the initial total mass of the mixture 100 parts by weight. The mixture was stirred at 32°C for 25 minutes, and the pH of the system was adjusted to 6.5 using an alkaline adjuster. It was then aged at 35°C for 10 hours. Solid content was adjusted by removing some water and ethanol, and adding deionized water if necessary. The mixture was defoamed at 25°C under a vacuum of -0.08 MPa for 25 minutes, and filtered through a 12-micron filter to obtain the siloxane emulsion. The non-volatile content of the obtained siloxane emulsion was 48% by weight. The siloxane emulsion in this embodiment had a pH of 6.5 and a viscosity of 780 mPa·s, measured at 25°C and a shear rate of 10 sec.

[0101] Application: The siloxane emulsion of this embodiment was applied to the surface of a paper substrate with a dry coating amount of 0.48 g / m². After curing at 95°C for 140 seconds, a siloxane release layer was formed. The adhesion of the siloxane release layer of this embodiment was measured as grade 0 by the cross-cut test. The 180-degree peel release force was measured as 72 mN / 25 mm under the conditions of a sample width of 50 mm and a peel speed of 300 mm / min.

[0102] This embodiment enhances the crosslinking density and surface modification effect of the siloxane network. The resulting siloxane emulsion has high cured film strength and durability, making it suitable for applications with high requirements for the mechanical properties and weather resistance of the release layer. It is particularly suitable for release processing of special paper substrates that require thicker coating and low-temperature curing.

[0103] Example 4

[0104] Preparation of Component A: Weigh out 100 parts by weight of dimethyl silicone oil, 14 parts by weight of methyltrimethoxysilane, 3.5 parts by weight of tetraethyl orthosilicate, 0.8 parts by weight of polyvinyl alcohol, 22 parts by weight of ethanol, 0.2 parts by weight of acetic acid, and 95 parts by weight of deionized water. First, mix ethanol, deionized water, and acetic acid evenly. Adjust the amount of acetic acid to make the pH of the system 4.7. Then, add methyltrimethoxysilane and tetraethyl orthosilicate under normal pressure and a non-inert atmosphere, and react at 22°C for 50 minutes for pre-hydrolysis. Subsequently, add dimethyl silicone oil and polyvinyl alcohol to the pre-hydrolysis system, and pre-emulsify at 20°C using high-speed shear at 7000 rpm for 7 minutes. During the high-pressure homogenization process, control the system temperature to not exceed 50°C, and homogenize twice under high pressure at 75 MPa. The resulting dispersion system was aged at 42°C for 1.5 hours to obtain component A, which has a core-shell emulsion droplet structure with a droplet D50 of 165 nm. In this embodiment, the core-shell emulsion droplet structure is a droplet structure with dimethyl silicone oil as the core and a surface coated with a siloxane layer formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate, as confirmed by transmission electron microscopy. Subsequently, the non-volatile content of component A was adjusted to 47.1% by weight by removing some water and ethanol. In component A of this embodiment, based on 100 parts by weight of dimethyl silicone oil, methyltrimethoxysilane is 14 parts by weight and tetraethyl orthosilicate is 3.5 parts by weight.

[0105] Preparation of Component B: 100 parts by weight of silica, 6.5 parts by weight of methyltrimethoxysilane, 185 parts by weight of ethanol, 0.08 parts by weight of acetic acid, and 180 parts by weight of deionized water were weighed. First, the ethanol, deionized water, and acetic acid were mixed evenly. The pH of the system was adjusted to 5.8 by adjusting the amount of acetic acid. Then, silica was added, and the mixture was dispersed at 350 rpm for 55 minutes at 33°C using mechanical stirring. Methyltrimethoxysilane was added to the dispersion system, and the reaction was carried out for 5.5 hours at 27°C under normal pressure and a non-inert atmosphere to achieve surface hydrolysis and condensation. The resulting system was aged at 58°C for 1.2 hours, and then ethanol was added to adjust the non-volatile content to 18% by weight, yielding methyltrimethoxysilane-modified silica component B with an average particle size of 17 nm. In this embodiment, methyltrimethoxysilane comprised 6.5 parts by weight of silica per 100 parts by weight. In this embodiment, the D50 of component A droplets and the average particle size of component B were determined by dynamic light scattering.

[0106] Preparation of the siloxane emulsion: The above-prepared component A and component B were mixed in a ratio of 100:7 based on the non-volatile matter mass. In this embodiment, the non-volatile matter mass of components A and B was measured after drying at 105°C to constant weight. 60 parts by weight of component A and 11 parts by weight of component B were taken, and 29 parts by weight of deionized water were added to make the initial total mass of the mixture 100 parts by weight. The mixture was stirred at 26°C for 28 minutes, and the pH of the system was adjusted to 6.65 using an alkaline adjuster. Subsequently, it was aged at 38°C for 11 hours. Solid content was adjusted by removing some water and ethanol, and adding deionized water if necessary. The mixture was defoamed at 25°C under a vacuum of -0.087 MPa for 28 minutes, and then filtered through a 6-micron filter to obtain the siloxane emulsion. The non-volatile content of the obtained siloxane emulsion was 57% by weight. The pH of the siloxane emulsion in this embodiment was 6.65, and the viscosity was 880 mPa·s. The viscosity was measured at 25°C and a shear rate of 10 sec.

[0107] Application: The siloxane emulsion of this embodiment is applied to the surface of a plastic film substrate with a dry coating amount of 0.55 g / m². After curing at 85°C for 160 seconds, a siloxane release layer is formed. The adhesion of the siloxane release layer of this embodiment is grade 1 as determined by the cross-cut adhesion test. The 180° peel release force is measured at a sample width of 50 mm and a peel speed of 300 mm / min, which is 85 mN / 25 mm.

[0108] The siloxane emulsion obtained in this embodiment has the characteristics of high solid content and moderate viscosity. The cured film has high crosslinking density and surface hardness, making it suitable for special application scenarios with high requirements for coating thickness and wear resistance. It is particularly suitable for release processing of high-end plastic films that need to be cured at low temperatures for a long time to protect heat-sensitive substrates.

[0109] Comparative Example 1: It is basically the same as Example 1, except that 30 parts by weight of component A and 7 parts by weight of component B are taken, and deionized water is added to make up to 100 parts by weight. Other conditions remain unchanged.

[0110] Comparative Example 2: It is basically the same as Example 1, except that 50 parts by weight of component A and 14 parts by weight of component B are taken, and deionized water is added to make up to 100 parts by weight. Other conditions remain unchanged.

[0111] Comparative Example 3: It is basically the same as Example 1, except that the high-pressure homogenization pressure during the preparation of component A is 35 MPa, and the high-pressure homogenization is carried out twice, while other conditions remain unchanged.

[0112] Comparative Example 4: It is basically the same as Example 1, except that the amount of methyltrimethoxysilane used in the preparation of component B is 3 parts by weight based on 100 parts by weight of silicon dioxide, and other conditions remain unchanged.

[0113] Comparative Example 5: It is basically the same as Example 1, except that after mixing component A and component B and adjusting the pH, it is aged at 32°C for 0.5 hours, while other conditions remain unchanged.

[0114] Comparative Example 6: It is basically the same as Example 1, except that the vacuum degassing conditions are 25°C, -0.03 MPa, and 20 minutes, while other conditions remain unchanged.

[0115] Comparative Example 7: Basically the same as Example 1, except that the curing conditions after application were changed to 70°C and 100 seconds, while other conditions remained unchanged.

[0116] Comparative Example 8: Essentially the same as Example 1, except that component B was removed, and only 50 parts by weight of component A were taken, with deionized water added to bring the total to 100 parts by weight. All other conditions remained unchanged. This comparative example was used to verify the synergistic effect between the core-shell emulsion droplet structure of component A and the methyltrimethoxysilane-modified silica surface.

[0117] Comparative Example 9: Essentially the same as Example 1, except that methyltrimethoxysilane was not added in step B3 during the preparation of component B. Instead, the dispersion obtained in step B2 was stirred and reacted at 35°C for 3.5 hours, then aged at 50°C for 2.5 hours. Deionized water was then added to adjust the non-volatile content to 25% by weight, resulting in an unmodified silica dispersion. This unmodified silica dispersion replaced component B, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect between the core-shell droplet structure of component A and the surface modification of component B with methyltrimethoxysilane.

[0118] Comparative Example 10: Essentially the same as Example 1, except that after mixing components A and B and adjusting the pH of the system to 6.3 using an alkaline adjuster, instead of aging at 32°C for 6 hours, it was directly degassed at 25°C under a vacuum of -0.075 MPa for 20 minutes and filtered through a 10-micron filter. Other conditions remained unchanged. This comparative example was used to verify the role of aging after mixing components A and B in constructing a synergistic interface.

[0119] Characterization tests:

[0120] The siloxane emulsions of Examples 1-4 and Comparative Examples 1-10 were analyzed for non-volatile content, apparent viscosity, and pH value using isothermal weight loss, single-cylinder rotational viscometer, and glass electrode method, respectively, to verify their high solids content, low viscosity, and pH adaptation window characteristics. After conditioning at 23±2℃ and 50±5% relative humidity, three parallel samples were taken, and the non-volatile content and shear rate at 25℃ for 10 s⁻¹ were measured, respectively. -1 Viscosity and pH values ​​under the conditions. Data are presented as mean ± standard deviation, and nonvolatile matter-viscosity coupling plots are generated.

[0121] The hydrodynamic particle size of components A, B, and the final siloxane emulsion was calculated using Brownian motion via dynamic light scattering to verify the D50 of component A droplets, the average particle size of component B, and storage stability. After dilution to a suitable scattering intensity, the D50 of component A and the average particle size of component B were measured at 25°C. The final emulsion was then subjected to a 30-day standing period at 25°C and a 7-day accelerated period at 50°C before retesting. Key parameters such as Z-average, PDI, and particle size growth rate were output. Three parallel measurements were performed, and the particle size distribution, average value, and growth rate were provided.

[0122] The dry film of component A, the dry powder of component B, and the final emulsion-cured film were analyzed by infrared characteristic absorption peak assignment to verify the degree of hydrolysis-condensation of methyltrimethoxysilane / tetraethyl orthosilicate and the construction of the Si-O-Si network. ATR-FTIR was used in the range of 4000-650 cm⁻¹. -1 Range scan, resolution 4 cm -1 A total of 32 times were performed, and the values ​​of 1030-1100 cm were compared. -1 Nearby Si-O-Si peaks and 1270 cm⁻¹ -1 The area ratio of nearby Si-CH3 peaks. Peak position, peak area ratio, and repeatability bias are output through peak area normalization and residual Si-OCH3 peak intensity analysis.

[0123] The adhesion of cured siloxane release layers on paper and plastic film substrates to the substrate was evaluated by observing the peel strength after cross-cutting. After coating and curing according to the examples, the layers were conditioned at 23±2℃ and 50±5% relative humidity. Cross-cutting was performed using a 1 mm spacing cutter to the substrate, and standard adhesive tape was applied before rapid peeling and rating. Five parallel tests were conducted at a dry coating weight of 0.35 g / m² and a curing condition of 110℃×100 s. The main grades and dispersion were statistically analyzed from 0 to 5.

[0124] The abrasion resistance of the cured siloxane release layer was evaluated by the mass loss caused by Taber abrasion. The coated substrate was attached to a rigid support plate, and a CS-10 grinding wheel was used with a 500 g load at 500 revolutions. The mass difference before and after abrasion was recorded, and the morphology of the damaged film was observed. Five parallel measurements were performed, and the average abrasion weight loss and standard deviation were output, and analyzed in conjunction with the adhesion and release force results.

[0125] The 180° peel release force and release stability after thermal aging were evaluated by assessing the interfacial separation resistance during constant-speed peeling of paper-based or plastic film substrates after the release layer was formed. After lamination with acrylic pressure-sensitive tape from the same batch, the initial release force was measured at a sample width of 50 mm and a peel speed of 300 mm / min, and retested after being placed at 85℃ for 24 hours. Five parallel tests were performed, and the data, including initial release force and rate of change after aging, were output as mean ± standard deviation.

[0126] The cured film samples corresponding to the examples and comparative examples were analyzed by thermogravimetric analysis to record mass changes during the heating process, in order to evaluate their thermal stability and the heat retention capacity of the inorganic-organic network. The temperature was increased from 30°C to 800°C under a nitrogen atmosphere at a rate of 10°C / min. If necessary, the temperature was switched to air after 600°C to observe the stability of the char / residue. Three parallel measurements were performed, and the mean ± standard deviation of T5, maximum weight loss rate temperature, and residual rate at 600°C were output, and correlation analysis was performed with release stability.

[0127] Figure 1 The FTIR full spectrum overlays of Example 1, Comparative Example 8, and Comparative Example 9 are shown. The characteristic absorption bands of different samples were compared using Fourier transform infrared spectroscopy. It is shown that Example 1 has a stronger signal in the silicon-oxygen network related absorption region and weaker residual hydrolyzable group characteristics, indicating that the interface condensation is more complete and the system construction is reasonable.

[0128] Figure 2 The images shown are magnified FTIR images of Examples 1, 8, and 9. Fourier transform infrared spectroscopy was used to analyze the characteristic bands of the silicon-oxygen network. Example 1 showed a more obvious enhancement trend in the key absorption region, indicating that its silicon-oxygen bond connection was higher, which is conducive to the formation of a more stable structure.

[0129] Figure 3 The images shown are XPS high-resolution overlay images of Si 2p from Example 1 and Comparative Example 9. X-ray photoelectron spectroscopy was used to analyze the chemical environment of silicon in different samples. The features of Example 1 in the high binding energy region are more prominent, indicating that the chemical state of silicon-oxygen bonds on its surface is more stable and the interfacial reaction is more complete.

[0130] Figure 4 The XPS O 1s high-resolution overlay images of Example 1 and Comparative Example 9 are shown. The chemical state of oxygen was compared using X-ray photoelectron spectroscopy. The bridging oxygen correlation signal was more obvious in Example 1, indicating that its network degree was higher, which can further confirm the existence of interfacial condensation synergy.

[0131] Figure 5 The XPS fitting characteristic component ratio diagrams for Example 1 and Comparative Example 9 are shown. The relative contents of different chemical components were fitted using X-ray photoelectron spectroscopy. In Example 1, the proportions of high-binding-energy silicon components and bridging oxygen components are higher, indicating that their surface structure is more compact and stable, thus verifying the rationality of the formulation combination.

[0132] Figure 6The apparent viscosity-shear rate rheological curves of Example 1, Comparative Example 2, and Comparative Example 10 are shown. Rheological tests were used to compare the viscosity response of different samples during shearing. Example 1 showed more suitable shear thinning behavior and lower processing viscosity, indicating that the system can balance high solids content and processability.

[0133] Figure 7 The images show enlarged views of the low-shear regions of Examples 1, 2, and 10. Rheological tests were used to further compare the viscosity changes in the low-shear regions. Example 1 maintained relatively stable flow characteristics under low-shear conditions, indicating that its structure is stable and conducive to uniform film formation during the coating process.

[0134] Figure 8 The graphs show the paired release forces of 180° peel before and after thermal aging for Examples 1, 2, and 10. The 180° peel test was used to compare the release behavior of different samples before and after aging. The release force level of Example 1 was lower and the change before and after aging was smaller, indicating that its release performance was stable and could meet the requirements for long-term use.

[0135] Figure 9 The graphs show the rate of change of release force after thermal aging for Examples 1, 2, and 10. The change in release force after thermal aging was calculated using the results of the 180° peel test. Example 1 showed the lowest rate of change, indicating that it maintained better interface stability and consistency of use under heat treatment conditions.

[0136] Figure 10 The image shows the superimposed DLS intensity distribution of Examples 1, 3, and 9. Dynamic light scattering was used to characterize the particle size distribution of different samples. The main peak of Example 1 is more concentrated and has a narrower distribution, indicating that its emulsion particle size control is more uniform, which is beneficial to obtaining a stable and complete film structure.

[0137] Figure 11 The DLS cumulative distribution curves for Example 1, Comparative Example 3, and Comparative Example 9 are shown. Dynamic light scattering was used to analyze the cumulative particle size distribution of different samples. The cumulative curve of Example 1 shows a more concentrated change, indicating that its particle size distribution range is more reasonable and can further support the stability of the system's dispersion state.

[0138] Figure 12 The z-Average plots of the average particle size of DLS in Example 1, Comparative Example 3, and Comparative Example 9 are shown. Dynamic light scattering was used to compare the average particle size of different samples. Example 1 maintained the average particle size within a more suitable nanoscale range, indicating that its particle size window control is more accurate, which is beneficial for balancing film formation and surface properties.

[0139] Figure 13The DLS polydispersity index (PDI) diagrams for Example 1, Comparative Example 3, and Comparative Example 9 are shown. Dynamic light scattering was used to evaluate the particle size distribution width of different samples. Example 1 had the lowest polydispersity index, indicating that its system has better uniformity and stronger emulsion stability.

[0140] Figure 14 The figure shows the Taber wear mass loss-cycle number process curves for Example 1, Comparative Example 3 and Comparative Example 9. The Taber wear test was used to track the mass loss of different samples during the cyclic wear process. Example 1 showed the slowest increase in mass loss throughout the process, indicating that its film density and wear resistance retention are better.

[0141] Figure 15 The graphs show the mass loss at the 500 rpm endpoint for Examples 1, Comparative Examples 3 and 9. The Taber wear test was used to compare the mass loss of different samples at a fixed wear endpoint. Example 1 showed the lowest mass loss at the endpoint, indicating that it has better structural stability and durability under actual wear conditions.

[0142] Figure 16 Macroscopic optical photographs of the components of the siloxane emulsion system and the release layer after curing. Figure 16 The results show that component A is a milky white, semi-transparent liquid with a soft, diffuse reflective luster on the surface, and exhibits good overall fluidity without phase separation. Figure 16 b shows that component B is a white, homogeneous emulsion liquid with no visible agglomerations. Figure 16 c is a mixed and aged siloxane emulsion, which is uniformly milky white, with a viscosity of 620 mPa·s, and the system is stable with no residual bubbles. Figure 16 d demonstrates the formation of a siloxane release layer after applying a dry coating of 0.35 g / m² to a paper substrate and curing at 110°C for 100 seconds. The release layer is a transparent to semi-transparent film with a smooth, flat surface free of bubbles and wrinkles, neat edges without warping, and tight adhesion to the paper substrate. This demonstrates that the emulsion formulation system possesses good colloidal stability and film-forming properties, and that the combination of core-shell emulsion droplets and surface-modified silica can form a macroscopically uniform release coating.

[0143] Figure 17 These are scanning electron microscope (SEM) images of the components of the siloxane emulsion system and the release layer after curing. Figure 17 a and Figure 17 b shows the low- and medium-magnification scanning electron microscope images of the droplet morphology of component A, revealing that the droplets are highly monodisperse spherical with no obvious aggregation or bridging between them. Figure 17 c and Figure 17Image d is a medium-to-high magnification scanning electron microscope image of silica modified with methyltrimethoxysilane in component B. It shows that the particles are spherical to irregularly spherical with an average particle size of 28 nm. After modification with organosiloxane, the surface is maintained in a nanoscale dispersion state. There are a few secondary aggregates between the particles, but no serious hard agglomeration. Figure 17 e is a surface morphology diagram of the cured siloxane release layer, showing a continuous and dense film layer coverage. The core-shell droplets of component A fuse together during the curing process to form a continuous polysiloxane body. Figure 17 f is a scanning electron microscope (SEM) image of the release layer cross-section, showing that the silica nanoparticles of component B are uniformly dispersed in the siloxane matrix. The film layer is tightly bonded to the paper fiber interface without delamination, and the interior is dense without large-sized pores. This indicates that the high-speed shearing combined with high-pressure homogenization process is beneficial for controlling the core-shell emulsion droplet size and its dispersibility, the surface modification process is beneficial for improving the dispersion stability of nano-silica in the aqueous phase, and the dense and continuous film layer formed after the two components are combined and cured is beneficial for achieving good release performance.

[0144] Figure 18 Transmission electron microscopy (TEM) images of the components of the siloxane emulsion system and the release layer after curing. Figure 18 Image a is a bright-field transmission electron microscope image of the core-shell droplet of component A, clearly showing the core-shell bilayer structure. The light gray central region is the dimethyl silicone oil core with low electron density, and the dark gray outer ring is the siloxane shell. The shell thickness is uniform, and the core-shell interface is clear with no interdiffusion region. Figure 18 Image b is a transmission electron microscope (TEM) image of the methyltrimethoxysilane-modified silica nanoparticles of component B. The image shows a solid spherical structure with uniform internal grayscale, and a low-contrast organic modification layer visible at the particle edges. This indicates that the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate on the droplet surface can form a relatively uniform amorphous siloxane shell. The surface modification process forms a nanoscale organosiloxane modification layer on the silica particle surface. During curing, the surface-modified particles and the siloxane matrix form a good interfacial bond. The amorphous network structure is beneficial for achieving low surface energy, high flexibility, and a release performance of 58 mN / 25 mm with a 180° peel release force.

[0145] Table 1 Performance of Examples and Comparative Examples

[0146] Example 1 51.0±0.4 620±18 0 15.2±0.8 58±3 5.1±0.6 348±2 Example 2 55.0±0.5 420±15 0 18.7±0.9 42±2 6.3±0.7 340±2 Example 3 48.0±0.4 780±22 0 12.8±0.7 72±4 4.8±0.5 356±3 Example 4 57.0±0.5 880±25 1 20.5±1.0 85±4 8.4±0.9 344±3 Comparative Example 1 43.5±0.5 360±14 2 29.0±1.2 96±5 15.2±1.3 328±3 Comparative Example 2 56.0±0.6 980±28 1 26.8±1.1 92±5 13.4±1.1 352±3 Comparative Example 3 51.0±0.4 870±24 1 24.8±1.0 88±4 13.2±1.1 338±3 Comparative Example 4 50.8±0.4 590±19 2 31.2±1.3 101±6 18.5±1.5 330±3 Comparative Example 5 51.0±0.4 605±17 1 23.5±1.0 81±4 11.8±0.9 341±2 Comparative Example 6 51.0±0.4 710±21 1 22.1±0.9 76±4 10.6±0.9 344±2 Comparative Example 7 51.0±0.4 620±18 3 37.6±1.4 112±6 19.8±1.6 321±3 Comparative Example 8 44.5±0.5 470±16 3 41.3±1.6 118±6 21.5±1.8 318±3 Comparative Example 9 50.8±0.5 760±22 2 34.8±1.4 109±5 17.6±1.4 333±3 Comparative Example 10 51.0±0.4 575±17 1 26.2±1.1 84±4 13.7±1.1 340±2

[0147] As can be seen from the performance of the examples and comparative examples in Table 1, all four examples achieve an effective balance between non-volatile matter, viscosity, adhesion, abrasion resistance, weight loss, release force, and thermal stability. Among them, Example 2 is more outstanding in terms of high solids content, low viscosity, and low release force; Example 3 is better in terms of abrasion resistance and thermal stability; Example 1 has the best overall balance; and Example 4 is mainly used to support the feasibility of high solids content and boundary conditions. In contrast, Comparative Examples 1, 8, and 9 have insufficient film continuity and interface matching due to the lack of matrix ratio or synergistic units; Comparative Example 2 shows that simply increasing component B does not bring about the best overall performance; Comparative Examples 3, 5, 6, and 10 show that particle size control, interface aging, and degassing treatment all have a substantial impact on the overall performance; and Comparative Example 7 shows that insufficient curing will significantly weaken the adhesion and abrasion resistance.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A food-contact grade siloxane emulsion, characterized in that, The mixture comprises, by weight, 35-65 parts of component A, 2-12 parts of component B, and deionized water to a total of 100 parts by weight. Component A is a pre-prepared siloxane intermediate with a core-shell emulsion droplet structure, prepared by hydrolysis condensation, pre-emulsification, and high-pressure homogenization of dimethyl silicone oil, methyltrimethoxysilane, tetraethyl orthosilicate, polyvinyl alcohol, ethanol, acetic acid, and deionized water. The droplet D50 of component A is 90-180 nm. Component B is a pre-prepared methyltrimethoxysilane surface-modified silica intermediate, prepared by surface hydrolysis condensation of silica, methyltrimethoxysilane, ethanol, acetic acid, and deionized water. The average particle size of component B is 10-50 nm. The siloxane emulsion has a pH of 5.8-6.8 and a viscosity of 300-1000 mPa·s. The droplet D50 of component A is 100-160 nm; the average particle size of component B is 15-40 nm; the pH of the siloxane emulsion is 6.0-6.6, and the viscosity is 350-900 mPa·s. The core-shell droplet structure is a droplet structure with dimethyl silicone oil as the core and a surface coated with a siloxane layer formed by the co-hydrolysis and condensation of methyltrimethoxysilane and tetraethyl orthosilicate.

2. The siloxane emulsion according to claim 1, characterized in that, Component A is prepared by the following steps: A1. Raw material preparation: By weight, dimethyl silicone oil, methyltrimethoxysilane, tetraethyl orthosilicate, polyvinyl alcohol, ethanol, acetic acid and deionized water are 100 parts, 5-20 parts, 2-10 parts, 0.5-4 parts, 5-25 parts, 0.1-1.0 parts and 80-200 parts respectively. A2, Pre-hydrolysis: Methyltrimethoxysilane and tetraethyl orthosilicate are added to a mixed system consisting of ethanol, deionized water and acetic acid, and reacted at 20-35 °C for 20-60 min, with the pH of the system set at 3.5-5.0; A3, Pre-emulsification and homogenization: Add dimethyl silicone oil and polyvinyl alcohol to the system obtained in step A2, pre-emulsify at 3000-8000 r / min for 5-15 min, and then homogenize under high pressure at 40-80 MPa 1-3 times. A4, Aging: The dispersion system obtained in step A3 is aged at 25-45 °C for 1-4 h to make the D50 of the emulsion droplets of the dispersion system 90-180 nm, thus obtaining component A.

3. The siloxane emulsion according to claim 1, characterized in that, Component B is prepared by the following steps: B1, Raw material preparation: By weight, silicon dioxide, methyltrimethoxysilane, ethanol, acetic acid and deionized water are 100 parts, 5-20 parts, 50-200 parts, 0.05-0.50 parts and 50-200 parts respectively; B2, Dispersion: Add silica to a mixture of ethanol, deionized water and acetic acid, disperse at 20-35 °C at 300-1200 r / min for 15-60 min, and adjust the pH of the system to 4.5-6.0; B3, Surface hydrolysis and condensation: Add methyltrimethoxysilane to the system obtained in step B2 and react at 25-45 °C for 1-6 h; B4, Aging: The system obtained in step B3 is aged at 40-60 °C for 1-4 h to make the average particle size of the system 10-50 nm, thus obtaining component B.

4. The siloxane emulsion according to claim 1, characterized in that, The ratio of component A to component B, based on non-volatile matter mass, is 100:5-25. Component A and component B are mixed, and deionized water is added to make the initial total mass of the mixture 100 parts by weight. The mixture is stirred at 25-35 °C for 10-30 min, and the pH of the system is adjusted to 5.8-6.8 using an alkaline adjuster. Subsequently, the mixture is aged at 25-40 °C for 1-12 h. The non-volatile matter content of the siloxane emulsion is adjusted to 45-58 wt% by removing some water and ethanol and adding deionized water. Then, the mixture is degassed under vacuum at -0.06 to -0.09 MPa for 10-30 min and filtered through a 5-20 µm filter to obtain the siloxane emulsion.

5. The siloxane emulsion according to claim 1, characterized in that, In component A, based on 100 parts by weight of dimethyl silicone oil, 5-15 parts by weight of methyltrimethoxysilane and 3-8 parts by weight of tetraethyl orthosilicate; in component B, based on 100 parts by weight of silicon dioxide, 6-15 parts by weight of methyltrimethoxysilane; and in the siloxane emulsion, the content of polyvinyl alcohol is 0.1-1.0 wt%.

6. The siloxane emulsion according to claim 1, characterized in that, The dry coating amount of the siloxane emulsion applied to the paper substrate or plastic film substrate is 0.15-0.60 g / m², and a siloxane release layer is formed after curing at 80-140 ℃ for 30-180 s.

7. A method for preparing the food contact grade siloxane emulsion according to any one of claims 1-6, characterized in that, Includes the following steps: S1, providing the prepared component A; S2, providing the prepared component B; S3. The A component provided in step S1 and the B component provided in step S2 are mixed at a ratio of 100:5-25 based on the non-volatile matter mass, and deionized water is added to make the total mass of the initial mixture 100 parts by weight. The mixture is stirred at 25-35 ℃ for 10-30 min, and then aged at 25-40 ℃ for 1-12 h. The non-volatile matter content of the siloxane emulsion is adjusted to 45-58 wt% by removing some water and ethanol and adding deionized water. After vacuum degassing and filtration, the siloxane emulsion is obtained.

8. The preparation method according to claim 7, characterized in that, The vacuum degassing pressure in step S3 is -0.06 to -0.09 MPa, the degassing time is 10-30 min, and the filter pore size is 5-20 µm.

9. The preparation method according to claim 7, characterized in that, The resulting siloxane emulsion has a pH of 5.8-6.8, a non-volatile content of 45-58 wt%, and a viscosity of 300-1000 mPa·s.

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