Water-based polysiloxane-based environment-friendly functional coating material suitable for frame paper and preparation method of water-based polysiloxane-based environment-friendly functional coating material

Abstract

The invention discloses a water-based polysiloxane-based environment-friendly functional coating material suitable for frame paper and a preparation method of the water-based polysiloxane-based environment-friendly functional coating material, and belongs to the technical field of paper-based functional coatings. The coating material comprises a hydroxyl functionalized aqueous polysiloxane emulsion, a double-shell hybrid perfume microcapsule, hydrophobic modified nano SiO2, a polyether-fluoroalkyl grafted modified epoxy silane coupling agent and other components, wherein the double-shell hybrid microcapsule is of a double-shell structure with an inner layer urea-formaldehyde resin wall and an outer layer polysiloxane hybrid layer. Through collaborative design of core components, the technical problems that existing frame paper coating microcapsules are poor in compatibility with a base body, short in fragrance keeping period, conflict between water resistance and stiffness and the like are solved, and collaborative improvement of water resistance, moisture resistance and long-acting fragrance keeping functions is achieved. The coating material can be widely applied to the field of high-end packaging frame paper.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of paper-based functional coating, and particularly relates to a water-based polysiloxane-based environmentally friendly functional coating material suitable for frame paper and a preparation method thereof. BACKGROUND

[0002] Frame paper, as the core substrate of high-end packaging, is widely used in the outer packaging support structure of food, cosmetics, gifts and other fields. It not only needs to have enough stiffness and mechanical strength to ensure the packaging formability, but also needs to meet the functional requirements of waterproof and moisture-proof, long-acting fragrance retention, and at the same time needs to meet the low VOC and environmental protection development trend of the industry.

[0003] At present, the paper-based waterproof coating mostly uses a water-based polysiloxane system, which can achieve excellent waterproof effect due to its low surface energy characteristics, but the function is single and cannot meet the fragrance retention requirement. The fragrance release coating mostly uses single-shell structure microcapsules of urea-formaldehyde resin and melamine resin, which encapsulate the fragrance core material and then are compounded with the coating matrix to achieve the function of fragrance release and retention. However, in the prior art, the single-shell fragrance microcapsules are simply physically compounded with the water-based polysiloxane coating, which has many technical defects: first, the compatibility is poor. There is a polarity difference between the hydrophobicity of polysiloxane and the hydrophilicity of the wall material of single-shell microcapsules, which leads to the easy agglomeration of microcapsules in the polysiloxane emulsion and uneven dispersion, and further causes the delamination of the coating and the decrease of the adhesion; second, the long-acting property is insufficient. The barrier property of the wall material of single-shell microcapsules is limited, and water vapor and oxygen easily penetrate into the capsule to cause the rapid evaporation of the fragrance, and the microcapsules are easily broken by external force or hot and humid environment during coating and storage, which further shortens the fragrance retention period; third, the functions conflict. In order to improve the waterproof effect, the thickness of the polysiloxane coating often needs to be increased, which leads to the decrease of the stiffness of the frame paper, and reducing the thickness of the coating cannot guarantee the waterproof performance, making it difficult to balance the waterproof and stiffness; fourth, the synergistic effect is missing. The single-shell microcapsules and the polysiloxane coating are only physically mixed and do not form a chemical association, so the waterproof and fragrance retention functions cannot be synergistically improved.

[0004] Search shows that although there are reports of polysiloxane-coated microcapsules in the prior art, they are mostly applied in the fields of phase change materials and self-repairing materials, and the core materials are phase change agents and repair agents, not fragrances, and they are not designed to adapt to the stiffness and adhesion requirements of frame paper. The technical solution of using polysiloxane as a hybrid layer to coat urea-formaldehyde fragrance microcapsules and apply it to frame paper waterproof and fragrance retention coating has not been reported so far. Therefore, it is a technical problem to be solved in the field to develop a water-based coating material for frame paper that can solve the above technical problems, achieve waterproof and moisture-proof, long-acting fragrance retention, stiffness retention, and environmental performance synergy. SUMMARY

[0005] Therefore, the present application provides a water-based polysiloxane-based environmentally friendly functional coating material for frame paper and a preparation method thereof, aiming to solve the technical defects of poor compatibility between microcapsules and the matrix, short fragrance retention period, conflict between water resistance and stiffness, insufficient functional synergy, etc.

[0006] The technical scheme of the present application is as follows: the present application provides a water-based polysiloxane-based environmentally friendly functional coating material for frame paper, which comprises, by mass fraction, 45-55 parts of hydroxyl-functionalized water-based polysiloxane emulsion, 12-18 parts of double-shell hybrid perfume microcapsules, 6-10 parts of hydrophobically modified nano-SiO2, 3-6 parts of polyether-fluoroalkyl grafted modified epoxy silane coupling agent, 2-3 parts of water-based epoxy silane coupling agent, 3-6 parts of auxiliary agent, and an appropriate amount of deionized water, with a system solid content of 45-50% and a VOC content of <50 g / L; the present application also provides a preparation method of the coating material, which comprises the steps of double-shell hybrid perfume microcapsule preparation, coating liquid preparation, and frame paper coating and drying.

[0007] In some embodiments, the double-shell hybrid perfume microcapsules have an inner urea-formaldehyde resin wall and an outer polysiloxane hybrid layer structure, the outer polysiloxane hybrid layer is formed by in-situ hydrolysis and polycondensation of the polyether-fluoroalkyl grafted modified epoxy silane coupling agent and the hydroxyl-functionalized water-based polysiloxane prepolymer, and the core material is natural plant essential oil.

[0008] The inner urea-formaldehyde resin wall material has excellent mechanical strength and film-forming property, can effectively wrap the perfume core material, avoid its premature volatilization during preparation, and provide an initial slow-release channel for the perfume; the outer polysiloxane hybrid layer is formed by in-situ hydrolysis and polycondensation, the Si-OH groups of which form Si-O-C chemical bonds with the amino groups of the inner urea-formaldehyde resin wall, rather than the physical coating of the prior art, which can not only construct a dense waterproof barrier by the low surface energy property of polysiloxane to reduce the water vapor and oxygen permeation rate and significantly prolong the fragrance retention period, but also form a homogeneous fusion system with the polysiloxane emulsion of the coating matrix to reduce the microcapsule agglomeration rate and completely solve the compatibility defects of traditional physical compounding, which is a chemical synergy effect that cannot be achieved by the combination of single-shell microcapsules and polysiloxane matrix in the prior art.

[0009] In some embodiments, the hydroxyl-functionalized water-based polysiloxane prepolymer is prepared by concentrating the hydroxyl-functionalized water-based polysiloxane emulsion through reduced pressure distillation, with a solid content of 60-70% and a viscosity of 300-500 mPa·s at 25℃.

[0010] Concentrating polysiloxane emulsions into prepolymers can increase the concentration of their active ingredients. During in-situ hydrolysis and polycondensation on the surface of microcapsules, a dense and uniform polysiloxane hybrid outer layer can be formed rapidly, avoiding the looseness and insufficient barrier properties of the hybrid layer due to excessively low emulsion solid content. At the same time, the prepolymer and emulsion originate from the same substrate, ensuring the chemical compatibility of the hybrid layer with the coating substrate and further enhancing the overall stability of the coating.

[0011] In some embodiments, the polyether-fluoroalkyl grafted modified epoxy silane coupling agent uses KH-560 as the matrix, grafting polyether segments and fluoroalkyl segments, wherein the molecular weight of the polyether segments is 500-800 and the molecular weight of the fluoroalkyl segments is C6-C8, and the grafting rate is 15-25%.

[0012] The epoxy groups of the KH-560 matrix can react with the amino groups of urea-formaldehyde resin wall materials and the hydroxyl groups of polysiloxanes to achieve chemical bonding between the hybrid layer and the inner wall material and the coating matrix. The polyether segments are hydrophilic, which can improve the dispersibility of the coupling agent in the aqueous system and enhance the flexibility of the hybrid layer, preventing the microcapsules from breaking due to excessive rigidity. The fluoroalkyl segments have lower surface energy, which can further improve the waterproof and antifouling properties of the coating and form a synergistic waterproof effect with polysiloxanes. The specific molecular weight and grafting rate of the segments can balance hydrophilicity / hydrophobicity, flexibility and barrier properties, avoiding the decrease in the adhesion of the hybrid layer due to excessively long segments or the inability to achieve functional improvement due to excessively short segments.

[0013] In some embodiments, the hydrophobically modified nano-SiO2 is methyltrimethoxysilane modified nano-SiO2 with a particle size of 50-100 nm.

[0014] Methyltrimethoxysilane modification can endow nano-SiO2 with excellent hydrophobicity, forming a synergistic hydrophobic system with polysiloxane alkyl bodies and microcapsule hybrid outer layers; the 50-100nm particle size can fill the micropores of the polysiloxane coating, reduce water vapor permeation channels, and at the same time improve the mechanical strength and density of the coating, avoiding the decrease in water resistance due to insufficient coating thickness, thus achieving the effect of "thin coating, high water resistance" while taking into account the requirement of maintaining the stiffness of the frame paper.

[0015] In some embodiments, the additives include 1-2 parts of polyether-modified polysiloxane dispersant, 0.5-1 part of silicone defoamer, 1-2 parts of acrylate leveling agent, and 0.5-1 part of wetting agent.

[0016] Polyether-modified polysiloxane dispersants can further improve the dispersion stability of bishelled hybrid microcapsules and nano-SiO2 in aqueous systems, forming a synergistic dispersion effect with modified coupling agents; organosilicon defoamers can eliminate bubbles generated during the preparation of coating solutions, avoiding defects such as pinholes and pitting on the coating surface; acrylate leveling agents can improve the leveling properties of coating solutions, ensuring uniform spreading of the coating on the frame paper surface and avoiding local coatings that are too thick or too thin; wetting agents can improve the wettability of coating solutions and frame paper substrates, enhance the adhesion between the coating and the substrate, and prevent coating peeling.

[0017] In some embodiments, the preparation method of the coating material includes: first preparing urea-formaldehyde resin inner wall fragrance microcapsules using the complex coagulation method, then adding a modified coupling agent and polysiloxane prepolymer to prepare double-shell hybrid microcapsules, and finally mixing with the remaining components to prepare a coating liquid and coating it on the back of the frame paper.

[0018] The complex coagulation method for preparing urea-formaldehyde resin inner wall microcapsules is a mature and cost-controllable process that can achieve efficient encapsulation of fragrance core materials. The in-situ hydrolysis-condensation method for preparing bi-shell hybrid microcapsules does not require complex equipment and can be achieved simply by adjusting pH and temperature, making it suitable for industrial production. Coating the back of the frame paper can avoid conflict between the coating and the front printing ink, while reducing the impact of the coating on the stiffness of the front of the frame paper and taking into account the needs of subsequent packaging printing.

[0019] In some embodiments, the process conditions for preparing urea-formaldehyde resin inner wall fragrance microcapsules by complex coagulation are pH 3.5-4.5, temperature 40-50℃, and stirring time 1-2h; the process conditions for preparing polysiloxane hybrid outer layer are pH 4-6, temperature 50-60℃, and stirring time 2-4h.

[0020] The complex coagulation method can achieve uniform coagulation of urea-formaldehyde resin into a wall under pH 3.5-4.5 and 40-50℃ conditions, avoiding the reaction being too fast and the wall material being loose due to excessively low pH, or the reaction being incomplete due to excessively high pH. The in-situ hydrolysis and condensation of polysiloxane under pH 4-6 and 50-60℃ conditions can control the hydrolysis and condensation rate, ensuring that the hybrid layer grows slowly and is firmly bonded to the inner wall material, avoiding the hybrid layer cracking due to excessively fast reaction, or low production efficiency due to excessively slow reaction.

[0021] In some embodiments, the hydroxyl-functionalized aqueous polysiloxane emulsion has a solid content of 50%, a viscosity of 100-200 mPa·s at 25°C, and a hydroxyl content of 0.5-1.0 mmol / g; the double-shelled hybrid fragrance microcapsules have a particle size of 2-6 μm and an outer polysiloxane hybrid layer thickness of 1-3 μm.

[0022] Limiting the emulsion's solid content, viscosity, and hydroxyl content ensures good film-forming properties and cross-linking activity. If the hydroxyl content is too low, it cannot fully react with the coupling agent and microcapsule hybrid layer; if it is too high, the coating will be over-crosslinked and its flexibility will decrease. The microcapsule particle size of 2-6 μm can be matched with the coating thickness (8-12 μm), avoiding the problem of the coating surface being rough due to the particle size being too large, or the fragrance encapsulation being insufficient due to the particle size being too small. The hybrid layer thickness of 1-3 μm can balance barrier properties and flexibility. If it is too thick, the microcapsules will be too rigid and easily break; if it is too thin, it will not achieve effective barrier properties.

[0023] In some implementations, the coating process parameters are: feed rate 8-12 g / m³ 2 (Dry weight), drying temperature 100-110℃, time 20s, forming a coating thickness of 8-12μm.

[0024] The feed rate and coating thickness ensure that the coating has sufficient waterproof barrier properties, while avoiding excessive coating thickness that would reduce the stiffness of the frame paper and increase costs. The drying conditions of 100-110℃ and 20s can quickly remove moisture from the coating liquid, while avoiding excessively high temperatures that would cause premature evaporation of fragrance and rupture of microcapsules, or excessively low temperatures that would result in insufficient drying and reduced coating adhesion, thus meeting the needs of continuous production in the frame paper industry.

[0025] The present invention has the following advantages over the prior art: This invention overcomes the technical bottleneck of simple physical composites of microcapsules and polysiloxane coatings in existing technologies by designing a hybrid double-shell structure of inner urea-formaldehyde resin and outer polysiloxane. It solves core pain points of traditional solutions such as poor compatibility, easy microcapsule breakage, short fragrance retention period, and conflicts between waterproofing and stiffness. Compared with existing technologies, this invention uses polysiloxane as both the coating matrix and, through in-situ hydrolysis and polycondensation, forms the outer hybrid layer of the microcapsule, achieving a chemical association between the polysiloxane and the microcapsule, rather than a conventional physical superposition. The inner and outer layers of the double-shell microcapsule form a functional synergy, retaining the mechanical strength and initial sustained-release advantages of urea-formaldehyde resin while leveraging the waterproof barrier and long-term stability properties of polysiloxane. Furthermore, the amphiphilic segment design of the modified coupling agent further strengthens the adhesion between the microcapsule and the coating matrix and substrate. Furthermore, this invention, through hydrophobically modified nano-SiO2 filling and precise process parameter control, effectively preserves the stiffness of the frame paper while ensuring excellent waterproof, moisture-proof, and long-lasting aroma retention functions. The coating is also water-based and low in VOCs, aligning with environmental protection industry trends. This invention requires no additional complex production equipment, is compatible with existing frame paper coating production lines, and has strong industrial feasibility. Compared to existing technologies, it possesses outstanding substantive features and significant technological advancements, greatly expanding the application scenarios of frame paper in the high-end packaging field. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 1. Formula composition (parts by weight) Hydroxyl-functionalized waterborne polysiloxane emulsion (solid content 50%, viscosity at 25℃ 150 mPa·s, hydroxyl content 0.8 mmol / g): 50 parts; Double-shelled hybrid fragrance microcapsules (particle size 4μm, outer polysiloxane hybrid layer thickness 2μm, core material is lavender essential oil): 15 parts; Methyltrimethoxysilane modified nano-SiO2 (particle size 80nm): 8 parts; Polyether-fluoroalkyl grafted modified epoxy silane coupling agent (based on KH-560, with a polyether segment molecular weight of 600, a fluoroalkyl segment of C7, and a grafting rate of 20%): 4.5 parts; Waterborne epoxy silane coupling agent (KH-560): 2.5 parts; Additives: 1.5 parts of polyether-modified polysiloxane dispersant (BYK-348), 0.8 parts of silicone defoamer, 1.5 parts of acrylate leveling agent, and 0.7 parts of wetting agent; Deionized water: 64 parts, with the solid content of the system adjusted to 48% and the VOC content to 42g / L.

[0028] 2. Preparation steps (1) Preparation of urea-formaldehyde resin inner wall fragrance microcapsules by complex coagulation method: urea-formaldehyde resin prepolymer and lavender essential oil are mixed at a mass ratio of 3:1, deionized water is added and stirred evenly, the pH of the system is adjusted to 4.0, the temperature is raised to 45℃, and the mixture is stirred at a constant temperature for 1.5h to form urea-formaldehyde resin inner wall microcapsules and obtain microcapsule slurry. (2) Preparation of bi-shell hybrid fragrance microcapsules: 2.0 parts of polyether-fluoroalkyl graft modified epoxy silane coupling agent and hydroxyl-functionalized waterborne polysiloxane prepolymer (obtained by vacuum distillation and concentration of the hydroxyl-functionalized waterborne polysiloxane emulsion, with a solid content of 65% and a viscosity of 400 mPa·s at 25°C) were added to the above microcapsule slurry. The pH of the system was adjusted to 5.0, the temperature was raised to 55°C, and the mixture was stirred at a constant temperature for 3 hours to allow the modified coupling agent and the polysiloxane prepolymer to undergo in-situ hydrolysis and condensation, forming a polysiloxane hybrid outer layer on the surface of the urea-formaldehyde resin microcapsules. After filtration and washing, bi-shell hybrid fragrance microcapsules were obtained. (3) Preparation of coating solution: Mix the remaining hydroxyl-functionalized waterborne polysiloxane emulsion with 50% of deionized water, polyether-modified polysiloxane dispersant and wetting agent, and stir at 900 r / min for 30 min; then add the bishell hybrid fragrance microcapsules and methyltrimethoxysilane-modified nano-SiO2 prepared in step (2), and disperse at 1800 r / min for 20 min, and grind to fineness ≤12 μm; then add the remaining 2.5 parts of polyether-fluoroalkyl grafted modified epoxy silane coupling agent, waterborne epoxy silane coupling agent, organosilicon defoamer, acrylate leveling agent and remaining deionized water, stir at 900 r / min for 30 min, and filter through a 100 mesh filter to obtain the coating solution; (4) Coating and molding: Using frame paper as the substrate, the above coating liquid is applied to the back of the frame paper by gravure coating, with a loading amount of 10g / m. 2 (Dry weight), dry at 105℃ for 20s to form a coating with a thickness of 10μm, and obtain the finished frame paper.

[0029] Example 2 1. Formula composition (parts by weight) Hydroxyl-functionalized waterborne polysiloxane emulsion (solid content 50%, viscosity at 25℃ 100 mPa·s, hydroxyl content 0.5 mmol / g): 45 parts; Bi-shell hybrid fragrance microcapsules (particle size 2μm, outer polysiloxane hybrid layer thickness 1μm, core material is lavender essential oil): 12 parts; Methyltrimethoxysilane modified nano-SiO2 (particle size 50nm): 6 parts; Polyether-fluoroalkyl grafted modified epoxy silane coupling agent (parameters same as in Example 1): 3.0 parts; Waterborne epoxy silane coupling agent (KH-560): 2.0 parts; Additives: 1.0 part of polyether-modified polysiloxane dispersant (BYK-348), 0.5 part of silicone defoamer, 1.0 part of acrylate leveling agent, and 0.5 part of wetting agent; Deionized water: 59 parts, with the solid content of the system adjusted to 45% and the VOC content to 45g / L.

[0030] 2. Preparation steps (1) Preparation of urea-formaldehyde resin inner wall fragrance microcapsules by complex coagulation method: adjust the pH of the system to 3.5, raise the temperature to 40°C, stir at constant temperature for 1 h, and the remaining steps are the same as in Example 1; (2) Preparation of double-shell hybrid fragrance microcapsules: Add 1.0 part of polyether-fluoroalkyl graft modified epoxy silane coupling agent, adjust the pH of the system to 4.0, heat to 50°C, stir at constant temperature for 2 hours, the solid content of polysiloxane prepolymer is 60% and the viscosity is 300 mPa·s, and the remaining steps are the same as in Example 1. (3) Preparation of coating liquid: The stirring rate is 800 r / min, the high-speed shear rate is 1500 r / min, and the remaining steps are the same as in Example 1; (4) Coating and molding: The material feeding amount is 8g / m 2 (Dry weight), drying temperature 100℃, coating thickness 8μm, the remaining steps are the same as in Example 1.

[0031] Example 3 1. Formula composition (parts by weight) Hydroxyl-functionalized waterborne polysiloxane emulsion (solid content 50%, viscosity at 25℃ 200 mPa·s, hydroxyl content 1.0 mmol / g): 55 parts; Double-shelled hybrid fragrance microcapsules (particle size 6μm, outer polysiloxane hybrid layer thickness 3μm, core material is lavender essential oil): 18 parts; Methyltrimethoxysilane modified nano-SiO2 (particle size 100nm): 10 parts; Polyether-fluoroalkyl grafted modified epoxy silane coupling agent (parameters same as in Example 1): 6.0 parts; Waterborne epoxy silane coupling agent (KH-560): 3.0 parts; Additives: 2.0 parts of polyether-modified polysiloxane dispersant (BYK-348), 1.0 part of silicone defoamer, 2.0 parts of acrylate leveling agent, and 1.0 part of wetting agent; Deionized water: 71 parts, with the solid content of the system adjusted to 50% and the VOC content to 48g / L.

[0032] 2. Preparation steps (1) Preparation of urea-formaldehyde resin inner wall fragrance microcapsules by complex coagulation method: adjust the pH of the system to 4.5, raise the temperature to 50°C, stir at constant temperature for 2 hours, and the remaining steps are the same as in Example 1; (2) Preparation of double-shell hybrid fragrance microcapsules: Add 3.0 parts of polyether-fluoroalkyl graft modified epoxy silane coupling agent, adjust the pH of the system to 6.0, heat to 60℃, stir at constant temperature for 4h, the solid content of polysiloxane prepolymer is 70%, the viscosity is 500mPa·s, and the remaining steps are the same as in Example 1. (3) Preparation of coating liquid: The stirring rate is 1000 r / min, the high-speed shear rate is 2000 r / min, and the remaining steps are the same as in Example 1; (4) Coating and molding: The material feeding amount is 12g / m 2 (Dry weight), drying temperature 110℃, coating thickness 12μm, the remaining steps are the same as in Example 1.

[0033] Example 4 1. Formula composition (parts by weight) Hydroxyl-functionalized waterborne polysiloxane emulsion (50% solids content, viscosity 140 mPa at 25°C) 48 parts of the following: s, hydroxyl content 0.7 mmol / g; double-shelled hybrid fragrance microcapsules (particle size 3 μm, outer polysiloxane hybrid layer thickness 1.8 μm, core material is rose essential oil): 16 parts; methyltrimethoxysilane modified nano-SiO2 (particle size 70 nm): 7 parts; polyether-fluoroalkyl grafted modified epoxy silane coupling agent (based on KH-560, polyether segment molecular weight 550, fluoroalkyl segment C6, grafting rate 18%): 4.0 parts; waterborne epoxy silane coupling agent (KH-560): 2.2 parts; additives: polyether modified polysiloxane dispersant (BYK-348) 1.3 parts, silicone defoamer 0.7 parts, acrylate leveling agent 1.2 parts, wetting agent 0.6 parts; deionized water: 64 parts, adjusting the system solid content to 47% and VOC content to 44 g / L.

[0034] 2. Preparation steps (1) Preparation of urea-formaldehyde resin inner wall fragrance microcapsules by complex coagulation method: Adjust the pH of the system to 3.8, raise the temperature to 43°C, and stir at a constant temperature for 1.3 h. The remaining steps are the same as in Example 1. (2) Preparation of double-shell hybrid fragrance microcapsules: Add 1.8 parts of polyether-fluoroalkyl graft-modified epoxy silane coupling agent, adjust the pH of the system to 4.8, raise the temperature to 53°C, and stir at a constant temperature for 2.8 h. The solid content of the polysiloxane prepolymer is 63%, and the viscosity is 380 mPa. s, the remaining steps are the same as in Example 1; (3) Preparation of coating liquid: the stirring rate is 850 r / min, the high-speed shear rate is 1700 r / min, the remaining steps are the same as in Example 1; (4) Coating and molding: the feeding amount is 9 g / m 2 (Dry weight), drying temperature 103℃, coating thickness 9μm, the remaining steps are the same as in Example 1.

[0035] Example 5 1. Formula composition (parts by weight) Hydroxyl-functionalized waterborne polysiloxane emulsion (50% solids content, viscosity 180 mPa at 25°C) 52 parts of the following: s, hydroxyl content 0.9 mmol / g; double-shelled hybrid fragrance microcapsules (particle size 5 μm, outer polysiloxane hybrid layer thickness 2.5 μm, core material citrus essential oil): 14 parts; methyltrimethoxysilane modified nano-SiO2 (particle size 90 nm): 9 parts; polyether-fluoroalkyl grafted modified epoxy silane coupling agent (based on KH-560, polyether segment molecular weight 700, fluoroalkyl segment C8, grafting rate 22%): 5.0 parts; waterborne epoxy silane coupling agent (KH-560): 2.7 parts; additives: polyether modified polysiloxane dispersant (BYK-348) 1.8 parts, silicone defoamer 0.9 parts, acrylate leveling agent 1.8 parts, wetting agent 0.9 parts; deionized water: 65 parts, adjusting the system solid content to 49% and VOC content to 46 g / L.

[0036] 2. Preparation steps (1) Preparation of urea-formaldehyde resin inner wall fragrance microcapsules by complex coagulation method: Adjust the pH of the system to 4.2, raise the temperature to 47°C, and stir at a constant temperature for 1.7 h. The remaining steps are the same as in Example 1. (2) Preparation of double-shell hybrid fragrance microcapsules: Add 2.5 parts of polyether-fluoroalkyl graft-modified epoxy silane coupling agent, adjust the pH of the system to 5.5, raise the temperature to 57°C, and stir at a constant temperature for 3.5 h. The polysiloxane prepolymer has a solid content of 68% and a viscosity of 450 mPa. s, the remaining steps are the same as in Example 1; (3) Preparation of coating liquid: the stirring rate is 950 r / min, the high-speed shear rate is 1900 r / min, the remaining steps are the same as in Example 1; (4) Coating and molding: the feeding amount is 11 g / m 2 (Dry weight), drying temperature 108℃, coating thickness 11μm, the remaining steps are the same as in Example 1.

[0037] Comparative Example 1 1. Formula differences The double-shelled hybrid fragrance microcapsules in Example 1 were replaced with single-shelled urea-formaldehyde resin fragrance microcapsules (without polysiloxane hybrid outer layer, particle size 4μm, core material lavender essential oil), and the rest of the formulation was completely consistent with that in Example 1.

[0038] 2. Differences in preparation steps The preparation process of the double-shell hybrid microcapsules in step (2) is omitted. After the single-shell microcapsules are prepared in step (1), they are directly used in step (3). All 4.5 parts of polyether-fluoroalkyl graft modified epoxy silane coupling agent are used for the coating crosslinking in step (3). The remaining preparation steps are completely consistent with those in Example 1.

[0039] Comparative Example 2 1. Formula differences The bishelled hybrid fragrance microcapsules in Example 1 were removed, and the remaining formulation composition was completely consistent with that in Example 1.

[0040] 2. Differences in preparation steps The microcapsule preparation process in steps (1) and (2) is omitted. In step (3), the remaining components are added directly. The remaining preparation steps are completely consistent with those in Example 1.

[0041] Comparative Example 3 1. Formula differences The polyether-fluoroalkyl grafted modified epoxy silane coupling agent in Example 1 was replaced with a common waterborne epoxy silane coupling agent (KH-560), with the amount remaining at 4.5 parts. The rest of the formulation composition was completely consistent with that in Example 1.

[0042] 2. Preparation steps Completely identical to Example 1 (only the coupling agent type was changed).

[0043] Comparative Example 4 1. Formula differences The methyltrimethoxysilane-modified nano-SiO2 in Example 1 was removed, and the rest of the formulation was completely consistent with that in Example 1.

[0044] 2. Differences in preparation steps The addition of nano-SiO2 and related operations after sand milling are omitted in step (3), and the remaining preparation steps are completely consistent with those in Example 1.

[0045] Comparative Example 5 1. Formula differences The hybrid layer of the double-shell hybrid microcapsule is prepared only with hydroxyl-functionalized aqueous polysiloxane prepolymer (without polyether-fluoroalkyl graft-modified epoxy silane coupling agent). No graft coupling agent is added in step (2), and the rest of the formulation is completely consistent with that in Example 1.

[0046] 2. Differences in preparation steps In step (2), only hydroxyl-functionalized waterborne polysiloxane prepolymer was added, the pH was adjusted to 5.0, and the temperature was 55°C and stirred for 3 hours. The remaining preparation steps were completely consistent with those in Example 1.

[0047] Performance verification 1. Water contact angle test Referring to GB / T30693-2014 "Determination of Contact Angle of Plastic Films and Sheets", the finished frame paper of each example and comparative example was taken and cut into 50mm×50mm samples. Using a contact angle measuring instrument, under the conditions of 25℃ and 50% relative humidity, deionized water was dropped onto the coating surface. Five different points were tested for each sample, and the contact angle values ​​were recorded. The average value was taken as the final result.

[0048] 2. Cobb 60s water absorption value test Referring to GB / T1540-2002 "Determination of Water Absorption of Paper and Paperboard - Cobb Method", each sample was cut into 125mm × 125mm pieces, and the initial mass of the sample (m0) was measured. The sample was fixed in the Cobb absorbent apparatus, and deionized water was added to the specified height. After standing for 60 seconds, the surface moisture of the sample was quickly wiped off, and the mass after water absorption (m1) was measured. The Cobb 60s water absorption value (unit: g / m) was calculated according to the formula (m1-m0) × 10. 2 Each sample was tested in 3 groups, and the average value was taken.

[0049] 3. Flavor Retention Rate Test Gas chromatography (GC) was used to test the initial content (W0) of lavender essential oil in the coating of each sample. Then, the samples were stored under two different environments: ① at room temperature (25℃, RH 50%) for 12 months; ② in a damp heat accelerated aging chamber at 85℃ and 85%RH for 12 months. After storage, the residual content (W1) of essential oil was tested under the same gas chromatography conditions. The fragrance retention rate was calculated by formula (W1 / W0)×100%. Three groups were tested for each sample, and the average value was taken.

[0050] 4. Microcapsule aggregation rate test Take the coating of each sample and observe the cross section and surface of the coating using a scanning electron microscope (SEM). Select 5 fields of view (magnification 1000x), count 100 microcapsules in each field of view, record the number of aggregated microcapsules (aggregated microcapsules of 3 or more), calculate the aggregation rate according to the formula (number of aggregated microcapsules / total number of microcapsules) × 100%, and take the average value of the 5 fields of view.

[0051] 5. Stiffness retention rate test of frame paper Referring to GB / T22364-2008 "Determination of bending stiffness of paper and paperboard", the transverse stiffness (S0) of uncoated frame paper was tested first; then the initial transverse stiffness (S1) and the transverse stiffness (S2) after 12 months of storage at room temperature were tested for each finished frame paper. The initial stiffness retention rate was calculated by formula (S1 / S0)×100%, and the long-term stiffness retention rate was calculated by formula (S2 / S0)×100%. Three sets of tests were conducted for each sample, and the average value was taken.

[0052] 6. Coating adhesion test Referring to GB / T9286-1998 "Cross-cut test for paint and varnish film", a cross-cut tester was used to cut a grid on the surface of each sample coating (grid size 1mm×1mm, grid depth to the frame paper substrate). Transparent tape was used to stick the grid area and then quickly peeled off. The coating peeling was observed and rated according to the standard (0 for no peeling, 1 for a small amount of peeling, and 2 for a large amount of peeling). Three areas were tested for each sample, and the worst rating was taken as the final result.

[0053] Performance test results

[0054] As can be seen from the performance test results of the above embodiments and comparative examples, the water-based polysiloxane-based environmentally friendly functional coating material and its preparation method for frame paper provided by the present invention, through the synergistic design of double-shell hybrid fragrance microcapsules, polyether-fluoroalkyl grafted modified epoxy silane coupling agents, and hydrophobically modified nano-SiO2, can stably achieve a balance between waterproofing, moisture resistance, long-lasting fragrance retention, and frame paper stiffness retention. Examples 1-3 cover the parameter range defined in the claims and all exhibit excellent performance, with a water contact angle of 135-140°, a fragrance retention rate of over 95% after 12 months at room temperature, and a stiffness retention rate of over 96%, proving that the parameter limits of the present invention are scientifically reasonable and have reliable industrialization feasibility.

[0055] Comparisons of Examples 1-5 show that when the polysiloxane hybrid outer layer, double-shell hybrid microcapsules, and hydrophobically modified nano-SiO2 are missing, or when conventional coupling agents are used instead, or when no grafting coupling agent is involved in the hybrid layer, the coating's waterproofness, fragrance retention, compatibility, and stiffness all deteriorate significantly. This indicates that the core innovative features of this invention are irreplaceable and are not a simple combination of existing technologies; rather, they overcome the technical bottlenecks of traditional physical composites through chemical synergy.

[0056] In summary, this invention effectively solves the technical pain points of existing frame paper coatings, and its technical effect is significantly better than that of existing single-component or simple composite solutions, possessing outstanding substantive features and significant technological progress.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-based polysiloxane-based environmentally friendly functional coating material suitable for frame paper, characterized in that, By mass parts, it includes the following components: 45-55 parts of hydroxyl-functionalized waterborne polysiloxane emulsion; 12-18 parts of double-shelled hybrid fragrance microcapsules, wherein the microcapsules have an inner urea-formaldehyde resin wall and an outer polysiloxane hybrid layer structure. The outer polysiloxane hybrid layer is formed by in-situ hydrolysis and condensation of a hydroxyl-functionalized waterborne polysiloxane prepolymer with a polyether-fluoroalkyl graft-modified epoxy silane coupling agent. The hydroxyl-functionalized waterborne polysiloxane prepolymer is obtained by vacuum distillation and concentration of the hydroxyl-functionalized waterborne polysiloxane emulsion, with a solid content of 60-70% and a viscosity of 300-500 mPa·s at 25°C. The core material is natural plant essential oil. Hydrophobically modified nano-SiO2 6-10 parts; 3-6 parts of polyether-fluoroalkyl grafted modified epoxy silane coupling agent, wherein the modified coupling agent is based on KH-560 and grafted with polyether segments and fluoroalkyl segments; 2-3 parts of water-based epoxy silane coupling agent; Additives 3-6 parts, including dispersants, defoamers, leveling agents and wetting agents; Use an appropriate amount of deionized water to make the solid content of the system 45-50% and the VOC content <50g / L.

2. The coating material according to claim 1, characterized in that, The hydroxyl-functionalized aqueous polysiloxane emulsion has a solid content of 50%, a viscosity of 100-200 mPa·s at 25°C, and a hydroxyl content of 0.5-1.0 mmol / g; the double-shelled hybrid fragrance microcapsules have a particle size of 2-6 μm and an outer polysiloxane hybrid layer thickness of 1-3 μm.

3. The coating material according to claim 1, characterized in that, The polyether-fluoroalkyl grafted modified epoxy silane coupling agent has a polyether segment molecular weight of 500-800, a fluoroalkyl segment of C6-C8, and a grafting rate of 15-25%.

4. The coating material according to claim 1, characterized in that, The hydrophobically modified nano-SiO2 is methyltrimethoxysilane modified nano-SiO2 with a particle size of 50-100 nm.

5. The coating material according to claim 1, characterized in that, The additives include 1-2 parts of polyether-modified polysiloxane dispersant, 0.5-1 part of organosilicon defoamer, 1-2 parts of acrylate leveling agent, and 0.5-1 part of wetting agent.

6. The coating material according to claim 1, characterized in that, The natural plant essential oil is one or more of lavender essential oil, rose essential oil, or citrus essential oil.

7. A method for preparing a coating material according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Urea-formaldehyde resin inner wall fragrance microcapsules were prepared by complex coagulation method to obtain microcapsule slurry; (2) Add 1-3 parts of polyether-fluoroalkyl grafted modified epoxy silane coupling agent and hydroxyl-functionalized waterborne polysiloxane emulsion prepolymer to the microcapsule slurry, adjust the pH of the system to 4-6, stir at 50-60℃ for 2-4h to allow it to hydrolyze and condense in situ, forming a polysiloxane hybrid outer layer on the surface of urea-formaldehyde resin microcapsules, and obtain double-shell hybrid fragrance microcapsules; (3) Mix the remaining hydroxyl-functionalized waterborne polysiloxane emulsion with 50% of deionized water, dispersant and wetting agent, and stir at 800-1000 r / min for 30 min; (4) Add the double-shelled hybrid fragrance microcapsules and hydrophobically modified nano-SiO2 obtained in step (2), disperse them at high speed of 1500-2000r / min for 20min, and grind them to a fineness of ≤12μm; (5) Add the remaining 2-3 parts of polyether-fluoroalkyl graft modified epoxy silane coupling agent, waterborne epoxy silane coupling agent, remaining additives and remaining deionized water, stir at 800-1000 r / min for 25-35 min, filter through a 100 mesh screen to obtain the coating liquid. (6) Using frame paper as the substrate, the coating liquid is applied to the back of the frame paper by gravure or roller coating, with a feed rate of 8-12 g / m. 2 (Dry weight), dry at 100-110℃ for 20s to form a coating with a thickness of 8-12μm.

8. The preparation method according to claim 7, characterized in that, The process conditions for the complex coagulation method in step (1) are pH 3.5-4.5, temperature 40-50℃, and stirring time 1-2h.

9. The coating material according to any one of claims 1-6, characterized in that, After being coated onto frame paper, the water contact angle was tested at 135-140° according to GB / T30693-2014, and the water absorption value of Cobb 60s was tested at 10-12 g / m³ according to GB / T1540-2002. 2 .

10. The coating material according to any one of claims 1-6, characterized in that, After being coated onto frame paper, the fragrance retention rate was greater than 95% after 12 months at room temperature; under accelerated aging conditions of 85℃ / 85%RH for 12 months, the fragrance retention rate was more than 30% higher than that of the control coating, which had the same components and processes except that the microcapsules were made of single-shell urea-formaldehyde resin.

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