Nanocomposite ink for intaglio printing and method for preparing the same

Abstract

The application provides a kind of nano-composite ink for gravure printing and a preparation method thereof.The nano-composite ink comprises 25-45% of resin binder, 3-12% of composite nano-filler, 8-18% of coloring pigment, 20-40% of organic solvent and 1-5% of multifunctional additive.The nano-composite ink for gravure printing of the application realizes high uniform dispersion of nanoparticles and long-term storage stability, has the characteristics of fast drying speed, high ink layer hardness and excellent wear resistance, and is excellent in environmental protection, free of benzene and heavy metals, and has good comprehensive printing suitability.

Description

Technical Field

[0001] This invention belongs to the field of printing ink technology, specifically relating to a nanocomposite ink for gravure printing and its preparation method. Background Technology

[0002] Gravure printing, with its outstanding advantages such as thick and full ink layers, vibrant and pure colors, rich and delicate tones, and excellent printing durability, has become the mainstream printing method in fields such as food packaging, tobacco packaging, high-end publications, and decorative materials. As the printing industry develops towards higher speeds, greater precision, and greener practices, the market is placing increasingly stringent demands on the comprehensive performance of gravure printing inks. These inks not only need to possess excellent printability, drying performance, and physical and mechanical properties of the ink layer, but also need to meet stringent environmental standards such as being benzene-free, heavy metal-free, and low in VOCs, making them suitable for high-end packaging and food contact printing applications.

[0003] Nanomaterials, with their nanoscale effects, large specific surface area effects, and quantum size effects, offer significant advantages in improving ink rheological properties, enhancing film density, and strengthening the mechanical strength and weather resistance of ink layers, making them a core research and development direction for high-performance gravure printing inks. Introducing nanoparticles as functional fillers into ink systems can effectively optimize ink storage stability and improve ink layer hardness and abrasion resistance. However, nanoparticles have extremely high surface energy, making them prone to spontaneous aggregation in traditional ink systems, forming micron-sized aggregates. This not only fails to leverage the functional advantages of nanomaterials but also leads to abnormally high ink viscosity, decreased dispersion stability, storage sedimentation and stratification, printing plate clogging, and pinhole defects in the ink layer, severely limiting the large-scale application of nanotechnology in the field of gravure printing inks.

[0004] To address the dispersion challenges of nanofillers, existing technologies primarily employ two approaches: single-surface modification and simple compounding of multiple nanoparticles. The former involves physically coating or chemically grafting nanoparticles with silane coupling agents, titanate coupling agents, or fatty acid derivatives to reduce surface energy and improve compatibility. However, the interfacial bonding of a single modified layer is limited, and aggregation is still likely during long-term storage, resulting in insufficient improvement in ink layer performance. The latter involves directly compounding multiple nanoparticles, attempting to achieve complementary performance, but without structural design, heterogeneous aggregation of different nanoparticles is prone to occur, making it difficult to control dispersion uniformity and achieve a synergistic enhancement effect. This presents a significant bottleneck in improving the overall performance of the ink layer.

[0005] In recent years, core-shell structured nanofillers have provided a new approach to optimizing dispersibility. Related technologies use inorganic nanoparticles as the core layer, coated with a single organic layer to form a core-shell structure, representing an improvement over simply modifying nanoparticles. However, such core-shell structures are only two layers in number, with limited functionality, and cannot simultaneously meet multiple requirements such as dispersion stability, film density, enhanced wear resistance, and controlled drying speed. Furthermore, the uniformity of the shell coating and the interfacial bonding strength are insufficient, resulting in uneven dispersion and poor storage stability in high-solids ink systems.

[0006] Currently, gravure printing inks generally suffer from multiple performance challenges that are difficult to balance: benzene-free environmentally friendly systems require the addition of a large amount of fast-drying solvents to ensure drying speed, which leads to increased costs and increased difficulty in VOC control; high abrasion-resistant inks are prone to increased ink layer brittleness and decreased adhesion due to the introduction of a large amount of rigid fillers; and drying speed is difficult to optimize in a coordinated manner with ink layer flexibility, environmental friendliness and printability, and mechanical strength and dispersion stability.

[0007] In summary, existing gravure printing inks suffer from core problems such as limitations in nanofiller dispersion technology, simplistic structural design, difficulty in balancing environmental protection and high performance, and lack of systematic control over the preparation process. Developing a nanocomposite ink that is stable in dispersion, dries quickly, is highly hard and wear-resistant, environmentally friendly and benzene-free, and suitable for high-speed printing has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0008] Based on the technical problems described above, the purpose of this invention is to overcome the shortcomings of existing gravure printing inks, such as easy agglomeration of nanofillers, poor dispersion stability, limited performance improvement, and difficulty in balancing environmental protection and high performance, and to provide a nano-composite ink for gravure printing. By introducing a three-layer composite nanofiller (core-intermediate layer-outer layer), combined with resin binder, benzene-free solvent, and multifunctional additives, highly uniform dispersion and long-term storage stability of the nanofiller are achieved. This results in an ink that combines rapid drying, high hardness, high abrasion resistance, and excellent adhesion, and is free of benzene, heavy metals, and low VOCs, meeting the requirements of high-end environmentally friendly packaging printing.

[0009] Specifically, according to one aspect of the present invention, a nanocomposite ink for gravure printing is provided, wherein the nanocomposite ink comprises the following components by weight percentage: 25-45% resin binder; 3-12% composite nanofiller; 8-18% coloring pigment; 20-40% organic solvent; 1-5% of multifunctional adjuvants, including: The resin binder comprises one or more of waterborne polyurethane resin, waterborne acrylic resin, and waterborne chloroacetic acid resin. The composite nanofiller is a particle with a three-layer structure of core-intermediate layer-outer layer, wherein: the core is titanium dioxide nanoparticles, the intermediate layer is a silane coupling agent modified layer, and the outer layer is an acrylate oligomer grafted functional layer. The multifunctional additives include dispersants, defoamers, leveling agents, thixotropic agents, and drying agents.

[0010] According to certain preferred embodiments of the invention, the average particle size of the nucleus is in the range of 10-50 nm.

[0011] According to certain preferred embodiments of the present invention, the average thickness of the intermediate layer is in the range of 2-8 nm.

[0012] According to certain preferred embodiments of the invention, the average thickness of the outer layer is in the range of 3-10 nm.

[0013] According to certain preferred embodiments of the present invention, the composite nanofiller is prepared by the following steps: (1) Add titanium dioxide nanoparticles to a mixed solvent of ethanol and deionized water, ultrasonically disperse for 20-40 min, stir for 30-60 min, adjust the pH to 3.5-5.5, heat to 45-65℃, and keep warm and stir for 1-3 h to prepare a nanoparticle dispersion. (2) Mix the silane coupling agent and the mixed solvent of ethanol and deionized water, add dropwise to the nanoparticle dispersion prepared in step (1), heat to 55-75℃, and reflux for 2-5 hours to prepare the silane coupling agent modified nanoparticle dispersion. (3) Add acrylate macromonomers and initiators to the silane coupling agent modified nanoparticle dispersion prepared in step (2), and heat to 75-90℃ under nitrogen protection and keep the reaction at this temperature for 3-6 hours. (4) The reaction product of step (3) is cooled, centrifuged, dried and ground to obtain the composite nanofiller, wherein: The silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; The acrylate macromonomers are selected from one or more of polymethyl methacrylate macromonomers, polybutyl acrylate macromonomers, and polyhydroxy acrylate macromonomers with a weight average molecular weight in the range of 800-1200. The initiator is benzoyl peroxide or azobisisobutyronitrile; Based on the total weight of titanium dioxide nanoparticles, silane coupling agents, and acrylate macromonomers as 100%, titanium dioxide nanoparticles account for 60-70%, silane coupling agents account for 5-10%, and acrylate macromonomers account for 25-35%.

[0014] According to certain preferred embodiments of the present invention, the acrylate macromonomer is a mixture of polymethyl methacrylate macromonomer and polybutyl acrylate macromonomer in a weight ratio of 2:1 to 4:1.

[0015] According to certain preferred embodiments of the present invention, in step (1), the content of titanium dioxide nanoparticles in the nanoparticle dispersion is in the range of 5-20% by weight.

[0016] According to certain preferred embodiments of the present invention, the average particle size of the titanium dioxide nanoparticles is in the range of 10-50 nm.

[0017] According to certain preferred embodiments of the present invention, the mixed solvent of ethanol and deionized water is a mixed solvent of ethanol and deionized water in a weight ratio of 8:1 to 10:1.

[0018] According to certain preferred embodiments of the present invention, the waterborne polyurethane resin is a hydroxyl-terminated waterborne polyester polyurethane resin; the waterborne acrylic resin is a hydroxyl-modified thermoplastic acrylic resin; and the waterborne chloroacetic acid resin is a ternary chloroacetic acid resin.

[0019] According to certain preferred embodiments of the present invention, the coloring pigment is selected from one or more of azo condensation pigments, phthalocyanine pigments, quinacridone pigments, and diketopyrrolopyrrole pigments.

[0020] According to certain preferred embodiments of the present invention, the organic solvent is selected from one or more of ester solvents, alcohol solvents, and ether alcohol solvents.

[0021] According to certain preferred embodiments of the present invention, the ester solvent is selected from one or more of ethyl acetate, n-propyl acetate, and butyl acetate; the alcohol solvent is selected from one or more of ethanol, isopropanol, and n-propanol; and the ether alcohol solvent is selected from one or more of propylene glycol methyl ether and dipropylene glycol methyl ether.

[0022] According to certain preferred embodiments of the present invention, based on 100% by weight of the nanocomposite ink for gravure printing, the dispersant accounts for 0.5-1.8%, the defoamer accounts for 0.1-0.5%, the leveling agent accounts for 0.2-0.6%, the thixotropic agent accounts for 0.3-0.8%, and the drying agent accounts for 0.4-1.3%.

[0023] According to certain preferred embodiments of the present invention, the dispersant is selected from one or more of polyacrylate dispersants, phosphate dispersants, and high molecular weight block copolymer dispersants; the defoamer is selected from one or more of polysiloxane defoamers and mineral oil defoamers; the leveling agent is selected from one or more of acrylate leveling agents and organically modified polysiloxane leveling agents; the thixotropic agent is selected from one or more of fumed silica and polyamide wax; and the drying agent is an environmentally friendly metal soap drying agent.

[0024] According to certain preferred embodiments of the present invention, the nanocomposite ink for gravure printing comprises: 32-35% resin binder; 8-12% composite nanofiller; 8-15% coloring pigment; 30-40% organic solvent; 2-5% multifunctional additives.

[0025] According to another aspect of the present invention, a method for preparing the above-described nanocomposite ink for gravure printing is provided, the method comprising mixing the various components.

[0026] According to certain preferred embodiments of the present invention, the method includes the following steps: (a) Add a portion of the organic solvent to a dispersion tank, add the coloring pigment, a portion of the composite nanofiller and a portion of the dispersant while stirring, stir for 20-40 min, and then grind to a fineness ≤ 15 μm to obtain a pre-dispersion of the coloring pigment. (b) Add the remaining organic solvent to another dispersion tank, add the remaining composite nanofiller and the remaining dispersant while stirring, ultrasonically disperse for 15-30 min, and continue stirring for 40-80 min to obtain a nanofiller dispersion. (c) The resin binder is slowly added to the nanofiller dispersion and stirred for 60-90 min. Then the coloring pigment pre-dispersion is added and stirred for another 40-70 min to form a mixed system. (d) Add defoamer, leveling agent, thixotropic agent and drying agent sequentially to the mixing system of step (c), stir and mix and filter to obtain the nano-composite ink for gravure printing.

[0027] According to certain preferred embodiments of the present invention, the stirring speed in step (a) is 300-500 r / min.

[0028] According to certain preferred embodiments of the present invention, the stirring speed in step (b) is 600-900 r / min.

[0029] According to certain preferred embodiments of the present invention, the resin binder is added in step (c) at a time of 30-60 minutes and the stirring speed is 800-1200 r / min.

[0030] According to another aspect of the present invention, a method for preparing a nanocomposite ink for gravure printing is provided, the nanocomposite ink for gravure printing comprising, by weight percentage: 25-45% resin binder; 3-12% composite nanofiller; 8-18% coloring pigment; 20-40% organic solvent; and 1-5% multifunctional additive, wherein: the resin binder comprises one or more of waterborne polyurethane resin, waterborne acrylic resin, and waterborne vinyl chloride resin; and the multifunctional additive comprises a dispersant, a defoamer, a leveling agent, a thixotropic agent, and a drying agent, the method comprising the following steps: (a) Add a portion of the organic solvent to a dispersion tank, add the coloring pigment, a portion of the composite nanofiller and a portion of the dispersant while stirring, stir for 20-40 min, and then grind to a fineness ≤ 15 μm to obtain a pre-dispersion of the coloring pigment. (b) Add the remaining organic solvent to another dispersion tank, add the remaining composite nanofiller and the remaining dispersant while stirring, ultrasonically disperse for 15-30 min, and continue stirring for 40-80 min to obtain a nanofiller dispersion. (c) The resin binder is slowly added to the nanofiller dispersion and stirred for 60-90 min. Then the coloring pigment pre-dispersion is added and stirred for another 40-70 min to form a mixed system. (d) Add the defoamer, leveling agent, thixotropic agent, and drying agent sequentially to the mixing system of step (c), stir and mix, and filter to obtain the nano-composite ink for gravure printing, wherein: The composite nanofiller is prepared by the following steps: (1) Add titanium dioxide nanoparticles to a mixed solvent of ethanol and deionized water, ultrasonically disperse for 20-40 min, stir for 30-60 min, adjust the pH to 3.5-5.5, heat to 45-65℃, and keep warm and stir for 1-3 h to prepare a nanoparticle dispersion. (2) Mix the silane coupling agent and the mixed solvent of ethanol and deionized water, add dropwise to the nanoparticle dispersion prepared in step (1), heat to 55-75℃, and reflux for 2-5 hours to prepare the silane coupling agent modified nanoparticle dispersion. (3) Add acrylate macromonomers and initiators to the silane coupling agent modified nanoparticle dispersion prepared in step (2), and heat to 75-90℃ under nitrogen protection and keep the reaction at this temperature for 3-6 hours. (4) The reaction product of step (3) is cooled, centrifuged, dried and ground to obtain the composite nanofiller, wherein: The silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; The acrylate macromonomers are selected from one or more of polymethyl methacrylate macromonomers, polybutyl acrylate macromonomers, and polyhydroxy acrylate macromonomers with a weight average molecular weight in the range of 800-1200. The initiator is benzoyl peroxide or azobisisobutyronitrile; Based on the total weight of titanium dioxide nanoparticles, silane coupling agents, and acrylate macromonomers as 100%, titanium dioxide nanoparticles account for 60-70%, silane coupling agents account for 5-10%, and acrylate macromonomers account for 25-35%.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The dispersion stability of the ink is significantly improved. By adopting a three-layer composite nanofiller (core-middle layer-outer layer), the problem of nanoparticle aggregation is solved, and the ink can achieve long-term storage of more than 6 months without sedimentation or stratification, with a viscosity change rate of ≤5%.

[0032] 2. The key properties of the ink are synergistically enhanced. Specifically, the ink of the present invention has a surface drying time of ≤ 15s, a hard drying time of ≤ 80s, a pencil hardness of ≥ 3H, abrasion resistance loss of ≤ 0.012 g / 1000 cycles without exposing the substrate, and an adhesion to the substrate of ≤ Grade 1. Hardness, abrasion resistance, drying and flexibility are simultaneously optimized.

[0033] 3. Significantly superior environmental performance. The inks according to this invention are completely free of benzene, ketones, and heavy metals, and VOC emissions are reduced by more than 40% compared to traditional inks. They meet EU and domestic environmental standards for food packaging and can be used in high-end safety scenarios such as food and baby products.

[0034] 4. Superior printability of the ink. The ink of this invention has stable rheological and thixotropic properties, does not clog the printing plate or cause ink splatter during high-speed printing, has a gloss level of ≥85°, and produces clear and full patterns. It is compatible with high-speed gravure printing machines of 50-200 m / min, and its overall printing performance is significantly better than commercially available environmentally friendly gravure inks. Attached Figure Description

[0035] The accompanying drawings are provided in this specification to more clearly explain the technical solutions of the present invention; however, the art is not limited thereto.

[0036] Figure 1 A transmission electron microscope (TEM) image of the composite nanofiller prepared in Preparation Example 1 is shown. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It will be understood that other embodiments may be implemented without departing from the scope or spirit of the invention. Therefore, the following detailed description is non-limiting.

[0038] Unless otherwise specified, all figures used in this specification to represent characteristic dimensions, quantities, and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters listed in the foregoing specification are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired properties using the teachings disclosed herein.

[0039] As mentioned above, existing gravure printing inks suffer from the following technical problems: First, nanofillers are prone to agglomeration and poor dispersion; single modification or simple compounding cannot achieve long-term stable dispersion, resulting in easy sedimentation and large viscosity fluctuations. Second, the nanofiller structure is singular, making it difficult to synergistically improve drying, hardness, and abrasion resistance, with limited enhancing effects. Third, it is difficult to balance environmental friendliness and high performance; benzene-free systems often result in decreased printability, and high abrasion-resistant formulations easily lead to brittle ink layers and poor adhesion. Fourth, the solvent, resin, and additive systems are poorly matched, making it difficult to simultaneously achieve drying speed and flexibility, as well as environmental friendliness and printability, thus failing to meet the demands of high-speed, environmentally friendly, and highly durable high-end packaging printing. This invention aims to solve one or more of the above technical problems.

[0040] Specifically, according to one aspect of the present invention, a nanocomposite ink for gravure printing is provided, comprising, by weight percentage: 25-45% resin binder; 3-12% composite nanofiller; 8-18% coloring pigment; 20-40% organic solvent; and 1-5% multifunctional additive, wherein: the resin binder comprises one or more of waterborne polyurethane resin, waterborne acrylic resin, and waterborne chloroacetic acid resin; the composite nanofiller is a particle with a three-layer structure of core-intermediate-outer layer, wherein the core is titanium dioxide nanoparticles, the intermediate layer is a silane coupling agent modified layer, and the outer layer is an acrylate oligomer grafted functional layer; and the multifunctional additive comprises a dispersant, an antifoaming agent, a leveling agent, a thixotropic agent, and a drying agent.

[0041] This invention fundamentally solves the technical problems of traditional gravure printing inks, such as the easy agglomeration of nanofillers, poor dispersion stability, difficulty in balancing drying speed and ink layer performance, and the inability to simultaneously achieve environmental protection and printability, through the compounding and structural innovation of the ink components. The proposed nanocomposite ink for gravure printing uses a three-layer composite nanofiller as its core functional component, combined with environmentally friendly water-based resin binders, benzene-free organic solvents, highly weather-resistant pigments, and multifunctional additives. This achieves highly uniform dispersion and long-term storage stability of nanoparticles in the ink system, while simultaneously endowing the ink with comprehensive advantages such as rapid drying, high hardness, high abrasion resistance, excellent adhesion, and low VOC emissions. It is perfectly suited for high-speed, environmentally friendly, and high-durability gravure printing scenarios such as food packaging, tobacco packaging, and high-end publications.

[0042] I. Resin binder The resin binder, serving as the film-forming matrix and dispersion carrier of the ink, accounts for 25-45% of the total weight of the ink, preferably 30-40%. The resin binder determines the film-forming properties, adhesion, drying speed, ink layer flexibility, and mechanical strength of the ink. This invention uses one or more of waterborne polyurethane resin, waterborne acrylic resin, and waterborne vinyl chloride resin.

[0043] According to certain preferred embodiments of the present invention, the waterborne polyurethane resin is a hydroxyl-terminated waterborne polyester polyurethane resin with a viscosity of 100-800 mPa•s (25℃), such as HL-320, LD320 series (Shanghai Linde Chemical), and JLY-1035 (Hunan Jinliyuan New Material Technology Co., Ltd.). This type of resin contains hydroxyl active groups in its molecular chain, which can form hydrogen bonds and partial crosslinks with the acrylate oligomers on the outer layer of the composite nanofiller, improving the binding force and dispersion stability of the nanofiller in the resin system. Simultaneously, the polyester-type soft segment structure imparts good flexibility to the ink layer, avoiding the problems of ink layer brittleness and peeling caused by the addition of high-rigidity nanofillers. The hydroxyl-terminated structure can also accelerate the solvent evaporation rate and improve the ink drying speed.

[0044] The waterborne acrylic resin is preferably a hydroxyl-modified thermoplastic acrylic resin with a viscosity of 1000-2000 mPa•s (25℃), an acid value of 5-12 mgKOH / g, and a glass transition temperature T. g The optimal temperature range is 45-65℃, for example, PJ60126-50 (Jiangmen Paint Factory Co., Ltd.) and RAGH (Derui Chemical Co., Ltd.). This resin exhibits excellent weather resistance, gloss, and pigment wetting properties. The hydroxyl-modified groups enhance its compatibility with nanofillers and polyurethane resins, and the moderate temperature range... g It can balance the hardness and flexibility of the ink layer, and its high gloss properties can enhance the visual effect of printed materials. At the same time, its thermoplastic properties are suitable for the rapid film formation requirements of high-speed printing, and it has no cross-linking residue, ensuring food contact safety.

[0045] The waterborne vinyl chloride resin is preferably a ternary vinyl chloride resin with a vinyl chloride content of 70-85% by weight and a hydroxyl content of 1-3% by weight, such as TP-500S (Hanwha Chemical Co., Ltd.). The ternary structure introduces hydroxyl functional groups, which improves the compatibility of the resin with water-based systems and nanofillers. The high vinyl chloride content endows the ink layer with excellent water resistance, oil resistance, and abrasion resistance, meeting the media resistance requirements of packaging printing. The hydroxyl groups can form an interfacial bond with the composite nanofillers, further improving the density and mechanical strength of the ink layer.

[0046] The resin binder of this invention can be used alone or in combination with two or three of the aforementioned resins. When the resin binder content is less than 25%, the ink film-forming properties are insufficient, the ink layer is prone to powdering and peeling, and the dispersion stability decreases; when the content is higher than 45%, the ink viscosity is too high, the drying speed is slowed down, and problems such as plate clogging and ink splattering are prone to occur, affecting the suitability for high-speed printing.

[0047] II. Composite Nanofillers The composite nanofiller is the core functional enhancing component of the ink, accounting for 3-12% of the total weight of the ink, preferably 5-10%. This invention breaks through the technical limitations of traditional single modification of nanofillers and core-shell two-layer structures, and innovatively designs a composite nanoparticle with a core-middle-outer three-layer structure. It upgrades the performance of nanofillers from three dimensions: interface structure, dispersibility, and functionality, solves the problem of nanoparticle agglomeration, and simultaneously improves the ink layer hardness, wear resistance, drying speed, and film density.

[0048] The core of the composite nanofiller is titanium dioxide nanoparticles with an average particle size in the range of 10-50 nm, preferably 20-40 nm, and more preferably 30 nm. Nano-titanium dioxide possesses high hardness, high refractive index, UV shielding, and chemical stability. As a core layer, it provides rigid support for the ink layer, improving wear resistance and hardness, while also enhancing ink layer coverage and gloss.

[0049] The intermediate layer is a silane coupling agent modified layer with an average thickness in the range of 2-8 nm, preferably 4-6 nm. The silane coupling agent acts as a bridge between the inorganic core and the organic outer layer, binding to the surface of titanium dioxide nanoparticles through a hydrolysis-condensation reaction. This reduces the surface energy of the nanoparticles, inhibits aggregation, and simultaneously provides grafting sites for the outer layer of acrylate oligomers, achieving a strong bond at the inorganic-organic interface.

[0050] The outer layer is an acrylate oligomer grafted functional layer, preferably with an average thickness in the range of 3-10 nm, more preferably 5-7 nm. The acrylate oligomer has a similar molecular structure to the ink resin binder, which can improve the compatibility and dispersion uniformity of the nanofiller in the resin system, preventing the agglomeration and sedimentation of nanoparticles. Simultaneously, the oligomer segments can participate in the ink film-forming process, filling the voids in the ink layer, improving film density, and further enhancing abrasion resistance, flexibility, and adhesion.

[0051] According to certain preferred embodiments of the present invention, the composite nanofiller is prepared by the following steps: (1) Add titanium dioxide nanoparticles to a mixed solvent of ethanol and deionized water, ultrasonically disperse for 20-40 min, stir for 30-60 min, adjust the pH to 3.5-5.5, heat to 45-65℃, and keep warm and stir for 1-3 h to prepare a nanoparticle dispersion. (2) Mix the silane coupling agent and the mixed solvent of ethanol and deionized water, add dropwise to the nanoparticle dispersion prepared in step (1), heat to 55-75℃, and reflux for 2-5 hours to prepare the silane coupling agent modified nanoparticle dispersion. (3) Add acrylate macromonomers and initiators to the silane coupling agent modified nanoparticle dispersion prepared in step (2), and heat to 75-90℃ under nitrogen protection and keep the reaction at this temperature for 3-6 h. (4) The reaction product of step (3) is cooled, centrifuged, dried and ground to obtain the composite nanofiller.

[0052] In step (1), the weight ratio of the mixed solvent of ethanol and deionized water is 8:1-10:1, preferably 9:1. This ratio ensures sufficient wetting and dispersion of the nano-titanium dioxide and avoids the decrease in coupling agent hydrolysis efficiency caused by excessive organic solvent. Preferably, the titanium dioxide content in the nanoparticle dispersion is 5-20% by weight, preferably 8-12% by weight.

[0053] In step (2), the silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane, preferably γ-methacryloxypropyltrimethoxysilane, which contains carbon-carbon double bonds that can undergo grafting reactions with acrylate macromonomers to strengthen interfacial bonding.

[0054] In step (3), the weight-average molecular weight of the acrylate macromonomers is 800-1200, preferably 1000, which ensures the flexibility and compatibility of the grafted layer. Preferably, the acrylate macromonomers are selected from one or more of polymethyl methacrylate (PMMA), polybutyl acrylate (PBMA), and polyhydroxyacrylate (PHA) macromonomers, more preferably a mixture of PMMA and PBMA macromonomers in a weight ratio of 2:1-4:1. PMMA provides rigidity, while PBMA provides flexibility; the blend balances the hardness and toughness of the ink layer. Preferably, the initiator is benzoyl peroxide or azobisisobutyronitrile (AIBN), preferably AIBN.

[0055] Based on the total weight of titanium dioxide nanoparticles, silane coupling agents, and acrylate macromonomers as 100%, titanium dioxide nanoparticles account for 60-70%, silane coupling agents account for 5-10%, and acrylate macromonomers account for 25-35%. This ratio ensures the enhanced rigidity of the core layer, the interfacial bridging of the intermediate layer, and the compatibility and dispersion of the outer layer.

[0056] When the content of composite nanofiller is less than 3%, the improvement in hardness and wear resistance is not significant; when it is higher than 12%, the nanoparticles are prone to local agglomeration, resulting in excessively high ink viscosity, slow drying speed, and decreased printability.

[0057] III. Coloring Pigments The coloring pigment accounts for 8-18% of the total weight of the ink, preferably 10-15%, and is used to provide the color and opacity required for printing.

[0058] According to certain preferred embodiments of the present invention, the coloring pigment is selected from one or more of azo condensation pigments, phthalocyanine pigments, quinacridone pigments, and diketopyrrolopyrrole pigments. Azo condensation pigments have high tinting strength and bright colors, suitable for warm tones such as red and yellow; phthalocyanine pigments have excellent lightfastness, weather resistance, and solvent resistance, and high saturation of blue-green tones; quinacridone and diketopyrrolopyrrole pigments are high-grade organic pigments, resistant to migration and high temperatures, and have pure colors, suitable for the high-fidelity color requirements of high-end printing.

[0059] All the pigments mentioned above are environmentally friendly organic pigments, free of heavy metals such as lead, cadmium, and chromium, and free of benzene derivatives. They comply with EU RoHS and Chinese safety standards for food packaging inks and can be used for direct contact printing on food, baby products, and other packaging. When the pigment content is below 8%, the hiding power is insufficient and the color saturation is low; when it is above 18%, the pigment dispersion becomes more difficult, and flocculation and color spots are more likely to occur. The ink viscosity also increases, the drying speed slows down, and the printing clarity is affected.

[0060] IV. Organic Solvents The organic solvent accounts for 20-40% of the total weight of the ink, preferably 30-40%, and serves as a dispersion medium and volatile component, controlling the ink viscosity, drying speed, and printing leveling properties. This invention employs a benzene-free and ketone-free environmentally friendly solvent system, avoiding the toxicity and VOC exceeding problems of traditional benzene-based solvents, while ensuring that the solvent evaporation rate matches the printing speed.

[0061] According to certain preferred embodiments of the present invention, the organic solvent is selected from one or more of ester solvents, alcohol solvents, and ether alcohol solvents. Ester solvents are selected from one or more of ethyl acetate, n-propyl acetate, and butyl acetate, which have a fast evaporation rate, improving the surface drying speed of the ink and exhibiting excellent wetting properties for resins and pigments. Alcohol solvents are selected from one or more of ethanol, isopropanol, and n-propanol, which have a moderate evaporation rate, adjusting ink viscosity, reducing surface tension, and improving leveling properties. Ether alcohol solvents are selected from one or more of propylene glycol methyl ether and dipropylene glycol methyl ether, which have a slower evaporation rate, preventing the ink from drying too quickly and causing clogging, while simultaneously improving the smoothness and gloss of the ink layer.

[0062] This invention enables gradient control of evaporation rates by combining ester, alcohol, and ether alcohol solvents.

[0063] When the organic solvent content is below 20%, the ink viscosity is too high and cannot be transferred properly during printing; when it is above 40%, VOC emissions increase, the ink layer becomes thinner, the covering power is insufficient, and problems such as ink splatter and missing printing are prone to occur.

[0064] V. Multifunctional Additives The multifunctional additive accounts for 1-5% of the total weight of the ink, preferably 2-4%, and includes dispersants, defoamers, leveling agents, thixotropic agents, and drying agents. The additives work synergistically to optimize the rheological properties, printability, and film-forming performance of the ink.

[0065] According to certain preferred embodiments of the present invention, based on 100% of the total ink weight, the dispersant accounts for 0.5-1.8%, the defoamer accounts for 0.1-0.5%, the leveling agent accounts for 0.2-0.6%, the thixotropic agent accounts for 0.3-0.8%, and the drier accounts for 0.4-1.3%. This ratio ensures that the additives achieve the best effect, without excessive residue, and does not affect the ink layer performance or environmental friendliness.

[0066] The dispersant is preferably one or more of polyacrylate dispersants, phosphate dispersants, and high molecular weight block copolymer dispersants. The preferred dispersant is a polyacrylate dispersant, which exhibits excellent compatibility with the acrylate oligomers and resin binders on the outer layer of the composite nanofiller. Through the combined effects of steric hindrance and electrostatic repulsion, it further stabilizes the nanofiller and coloring pigments, preventing agglomeration and sedimentation, and improving dispersion uniformity.

[0067] The defoamer is preferably one or more of polysiloxane defoamers and mineral oil defoamers, with polysiloxane defoamers being preferred. Polysiloxane defoamers have a fast defoaming speed, long-lasting foam suppression, and do not affect the gloss of the ink layer. They can eliminate bubbles generated during ink preparation and printing, and prevent pinholes and shrinkage defects in the ink layer.

[0068] The leveling agent is preferably one or more of acrylate leveling agents and organic modified polysiloxane leveling agents, which can reduce the surface tension of ink, improve leveling and wetting properties, make the ink layer uniform and smooth, eliminate brush marks and orange peel texture, and improve gloss and printing visual effect.

[0069] The thixotropic agent is preferably one or more of fumed silica and polyamide wax, with fumed silica being preferred. It can impart shear-thinning properties to the ink, resulting in high viscosity at rest to prevent sedimentation, and reduced viscosity during printing to facilitate transfer. It also prevents ink splatter and plate clogging during high-speed printing.

[0070] The drying agent is preferably an environmentally friendly metal soap-based drying agent that does not contain toxic metals such as lead and cobalt. It can accelerate solvent evaporation and ink layer curing, shorten the drying time, and improve printing efficiency, while not affecting the flexibility and adhesion of the ink layer.

[0071] When the total content of additives is less than 1%, the function is insufficient, and the ink is prone to problems such as agglomeration, bubbling, poor leveling, and slow drying; when it is more than 5%, the additive residue will reduce the adhesion and abrasion resistance of the ink layer, and increase the cost and VOC emissions, which violates the concept of environmental protection.

[0072] VI. Optimal Formula According to certain preferred embodiments of the present invention, the nanocomposite ink for gravure printing comprises: 32-35% resin binder; 8-12% composite nanofiller; 8-15% coloring pigment; 30-40% organic solvent; and 2-5% multifunctional additives. This preferred formulation achieves an optimized balance in terms of dispersion stability, drying speed, mechanical properties, environmental friendliness, and printability, fully meeting the requirements of high-end environmentally friendly gravure printing.

[0073] VII. Preparation Method According to another aspect of the present invention, a method for preparing the above-described nanocomposite ink for gravure printing is provided, the method comprising mixing the various components and using a stepwise dispersion and precise control process to ensure uniform mixing of nanofillers, pigments and resins, avoid agglomeration of nanoparticles, and ensure stable ink performance.

[0074] According to certain preferred embodiments of the present invention, the method includes the following steps: (a) Pre-dispersion of coloring pigment: Add a portion of organic solvent to a dispersion tank, add coloring pigment, a portion of composite nanofiller and a portion of dispersant while stirring, stir for 20-40 min, and then grind to a fineness ≤ 15 μm to obtain a pre-dispersion of coloring pigment; (b) Nanofiller dispersion: Add the remaining organic solvent to another dispersion tank, add the remaining composite nanofiller and remaining dispersant while stirring, ultrasonically disperse for 15-30 min, and continue stirring for 40-80 min to obtain nanofiller dispersion; (c) Main mixing: Slowly add the resin binder to the nanofiller dispersion and stir for 60-90 min. Then add the coloring pigment pre-dispersion and continue stirring for 40-70 min to form a mixed system. (d) Additive formulation and finished product: Defoamer, leveling agent, thixotropic agent and drying agent are added to the mixing system in sequence, stirred and mixed and filtered to obtain the nano-composite ink for gravure printing.

[0075] In step (a), preferably, the amount of organic solvent used is 60-80% of the total solvent, and the stirring speed is 300-500 r / min.

[0076] In step (b), preferably, ultrasonic dispersion for 15-30 min can completely depolymerize the nanofiller and prevent agglomeration, and stirring at a speed of 600-900 r / min for 40-80 min can make the nanofiller uniformly dispersed in the solvent to form a stable system.

[0077] In step (c), preferably, the resin binder should be added slowly and continuously over 30-60 minutes, with a stirring speed of 800-1200 r / min, to prevent excessive local concentration from causing flocculation. Mixing the resin and nanofiller first, and then adding the pigment pre-dispersion liquid, can prevent the pigment from encapsulating the nanoparticles and ensure uniform dispersion.

[0078] In step (d), preferably, various additives are added sequentially, and each additive is stirred for 10-20 minutes. Finally, the mixture is filtered through a 100-200 mesh screen to remove mechanical impurities and agglomerated particles, thus ensuring the quality of the ink.

[0079] The preparation method of this invention is simple, highly controllable, and suitable for industrial production. It solves the dispersion problem of nanofillers and pigments through stepwise dispersion, eliminating the need for complex equipment, reducing production costs, and ensuring batch-to-batch stability of inks.

[0080] In summary, the nanocomposite ink for gravure printing of this invention achieves a synergistic improvement in dispersion stability, drying speed, mechanical properties, environmental friendliness, and printability through the innovative compounding of a three-layer composite nanofiller, environmentally friendly resin, benzene-free solvent, high-performance pigment, and multifunctional additives, combined with a stepwise dispersion preparation process. This overcomes many shortcomings of existing technologies and has broad market application prospects and industrial value.

[0081] The present invention will now be described in more detail with reference to embodiments. It should be noted that these descriptions and embodiments are intended to facilitate understanding of the present invention and are not intended to limit the invention.

[0082] Example In this invention, unless otherwise specified, all reagents used are commercially available products and are used directly without further purification. Furthermore, "%" refers to "weight %" and "parts" refers to "parts by weight".

[0083] Table 1 below lists specific information about the raw materials used in the embodiments and comparative examples of the present invention.

[0084]

[0085] Table 2 below lists specific information about the experimental equipment used in the embodiments and comparative examples of the present invention.

[0086]

[0087] Performance testing methods 1. Storage stability test method (QB 567-1983 "Test method for storage stability of inks") The test was conducted in a constant temperature and humidity environment, with an ambient temperature of 25°C and a relative humidity controlled at 50% ± 5%. Ink samples prepared in the following examples or comparative examples were filled into sealed brown glass bottles, filling the bottles to 4 / 5 of their total volume. After sealing, the bottles were placed on a constant temperature rack and left to stand for 6 months. The test consisted of two parts: appearance evaluation and viscosity change rate measurement. First, after 6 months, the samples were removed, the bottle caps were opened, and the ink was visually observed for phenomena such as sedimentation, stratification, clumping, flocculation, and floating, and the appearance was recorded. Then, using an NDJ-5S rotational viscometer, the initial viscosity η1 and the viscosity η2 after 6 months of storage were measured under constant temperature conditions of 25°C. The viscosity fluctuation range was calculated using the following formula: Viscosity change rate = (η2-η1) / η1×100%.

[0088] The criteria for evaluation are as follows: excellent: no sedimentation, no stratification, no clumping, and viscosity change rate ≤ 5% after 6 months; qualified: viscosity change rate 5%-10%; unqualified: viscosity change rate greater than 10%.

[0089] 2. Drying speed test method (GB / T 13217.4-2008 Determination of drying speed of gravure plastic inks) The testing environment was 25℃ and 50%±5% relative humidity. Biaxially oriented polypropylene film was used as the substrate. The ink samples prepared in the following examples or comparative examples were uniformly coated onto the film surface using a bar coater, with a coating thickness of 24 μm. Surface drying time was determined using the finger-touch method: starting from the completion of coating, the ink layer surface was lightly touched with a finger every 2 seconds. The shortest time after the finger touches the surface without ink sticking, fingerprint residue, or ink layer adhesion was taken as the surface drying time. Complete drying time was determined using the filter paper pressing method: after coating, quantitative filter paper was placed on the ink layer every 2 seconds, and a 500g standard pressure roller was used to roll it once at a uniform speed. The filter paper was then quickly lifted. The shortest time after the filter paper shows no ink transfer and the ink layer is completely cured without damage was taken as the complete drying time. Each sample was tested in parallel 5 times, and the average value was taken as the final result. The unit of measurement was seconds (s).

[0090] 3. Pencil Hardness Test Method (GB / T 6739-2006 "Determination of Hardness of Paints and Varnishes by Pencil Method") Before testing, the ink samples prepared in the following examples or comparative examples were coated onto a biaxially oriented polypropylene film substrate and cured completely for 24 hours at 25°C and 50% RH. Zhonghua drawing pencils were used, with hardness grades ranging from 6B to HB to 6H from softest to hardest. Before testing, the pencils were sharpened to a cylindrical shape using a special pencil sharpener, with approximately 3 mm of lead exposed. The sample coated with the ink film was horizontally fixed on the hardness tester platform. The QHQ-A type pencil hardness tester was adjusted so that the pencil and the ink film surface formed a 45° angle, and a constant load of 750 g was applied. Testing began with a low-hardness pencil, and the hardness tester was pushed forward at a uniform speed across the ink film surface, advancing approximately 10 mm. Scratches, indentations, and peeling were observed on the ink film surface. Each hardness pencil was tested in parallel three times, and the highest pencil hardness that did not scratch the ink film in all three tests was taken as the pencil hardness result for that sample.

[0091] 4. Abrasion resistance test method (GB / T 1768-2006 "Determination of abrasion resistance of paints and varnishes - Rotating rubber grinding wheel method") The ink samples prepared in the following examples or comparative examples were coated onto a standard test paperboard with an ink layer thickness of 24 μm. After curing at 25°C for 24 h, a standard template measuring 100 mm × 100 mm was prepared. The initial mass m1 of the template was weighed using an analytical balance. The template was fixed on the turntable of a 5751 Taber abrasion tester. A CS-10 standard rubber abrasive wheel was selected, with a load of 500 g applied to the wheel. The tester was set to rotate 1000 times, and the abrasion test was performed. After 1000 rotations, the template was removed, and its mass m2 was weighed again using an analytical balance. The abrasion mass of the ink layer was calculated using the formula (abrasion loss = m1 - m2), in grams (g). The smaller the abrasion loss value, the better the abrasion resistance of the ink layer.

[0092] 5. Adhesion test method (GB / T 9286-1998 "Paints and Varnishes Cross-cut Test") The ink samples prepared in the following examples or comparative examples were coated onto a biaxially oriented polypropylene film and cured completely for 24 hours at 25°C and 50% RH. The sample was fixed flat on a rigid platform, and six parallel horizontal and six vertical cuts were made vertically on the ink layer surface using a 1 mm pitch multi-blade cutter to form a 1 mm × 1 mm square grid. 3M 600 standard pressure-sensitive tape was applied to the grid area, and air bubbles were removed by pressing with a finger. After standing for 90 seconds, the tape was quickly peeled off perpendicular to the sample surface at a 90° angle. The area and state of ink layer detachment within the grid were rated according to a 0-5 standard: Grade 0: completely smooth cuts, no detachment; Grade 1: minor detachment at the cut intersections; Grade 2: partial detachment along the cuts; Grade 3: large area detachment; Grade 4: entire sheet detachment; Grade 5: complete detachment. Grade 0 is the best, and Grade 5 is the worst.

[0093] 6. Gloss Test Method (GB / T 13217.2-1991 "Test Method for Gloss of Gravure Plastic Inks") Before testing, the ink samples prepared in the following examples or comparative examples were uniformly coated onto a biaxially oriented polypropylene film substrate using a 24 μm wire bar coater and cured at 25°C and 50% RH for 24 hours. A KGZ-1 type 60° angle gloss meter was used, with the measuring window attached to the ink layer surface. Five test points were selected at different locations on the sample, and the 60° gloss value of each test point was read. The arithmetic mean of the five test points was calculated as the final result, expressed in gloss units (°). A higher gloss value indicates a smoother ink layer surface, better flatness, and superior printing visual effect.

[0094] 7. VOC content test method (GB 38507-2020 "Limits for Volatile Organic Compounds (VOCs) Content in Inks") Before testing, ink samples prepared in the following examples or comparative examples were placed in headspace vials, sealed, and then inserted into a headspace sampler. Headspace conditions were set as follows: equilibrium temperature 80°C, equilibrium time 30 min, allowing VOCs in the ink to evaporate into the headspace gas phase. An Agilent 7890B GC-MS analyzer was used, employing an HP-5 capillary column, high-purity nitrogen as the carrier gas, a flow rate of 1.0 mL / min, an injection port temperature of 200°C, and a detector temperature of 250°C. Separation efficiency was controlled by programmed temperature ramping. A standard curve was plotted using the external standard method, and the total VOC content (benzene compounds, esters, alcohols, ethers, etc.) in the samples was quantitatively determined in g / L. Simultaneously, the VOC content of traditional benzene-based gravure inks was tested as a control, and the reduction rate was calculated using the following formula: VOC reduction rate = (VOC content of traditional ink - VOC content of ink of this invention) / VOC content of traditional ink × 100%.

[0095] Preparation Example 1 (Core-Intermediate-Outer Three-Layer TiO2 Composite Nanofiller 1) Titanium dioxide nanoparticles with an average particle size of approximately 30 nm were weighed and added to a mixed solvent of ethanol and deionized water at a weight ratio of 9:1. The mixture was then ultrasonically dispersed in an ultrasonic disperser for 30 min, followed by mechanical stirring for 45 min to ensure thorough pre-dispersion of the nanoparticles. The pH of the system was adjusted to 4.5 with glacial acetic acid, and the temperature was raised to 55 °C and stirred for 2 h to obtain a uniform and stable TiO2 nanoparticle dispersion. The content of titanium dioxide nanoparticles in the nanoparticle dispersion was approximately 8% by weight. γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) was mixed evenly with an ethanol-water mixed solvent (weight ratio of 9:1) and slowly added dropwise to the above dispersion. The temperature was raised to 65 °C and refluxed for 3.5 h to complete the modification of the silane coupling agent intermediate layer. Polymethyl methacrylate (PMMA) macromonomers with a weight-average molecular weight of 1000 and benzoyl peroxide initiator were added to the system. Under nitrogen protection, the temperature was raised to 80°C and maintained for 4.5 h to achieve grafting of the acrylate oligomer outer layer. Based on the total weight of titanium dioxide nanoparticles, silane coupling agent, and acrylate macromonomers as 100%, titanium dioxide nanoparticles accounted for 65%, silane coupling agent for 8%, and acrylate macromonomers for 27%. After the reaction, the mixture was cooled to room temperature, centrifuged at 8000 r / min for 15 min, washed three times with deionized water, vacuum dried at 80°C for 12 h, and ground through a 200-mesh sieve to obtain the TiO2 composite nanofiller.

[0096] The TiO2 composite nanofiller prepared in Preparation Example 1 was diluted to 0.1-0.5 mg / mL with an ethanol-water mixed solvent and ultrasonically dispersed for 20 min to prepare a monodisperse. The diluted solution was dropped onto a 300-mesh carbon support film copper mesh. After drying at room temperature, it was stained with ruthenium tetroxide (RuO4) in the vapor phase for 8-12 min. The contrast was enhanced by the different staining selectivity of ruthenium tetroxide (RuO4) for the PMMA layer and the silane layer. The morphology and dispersibility were observed at low magnification using a JEM-2100F transmission electron microscope at 200 kV, and the sizes of 50 particles were counted at high magnification. Figure 1 A transmission electron microscope (TEM) image of the TiO2 composite nanofiller prepared in Preparation Example 1 is shown. Figure 1 As shown, the particles are spherical, uniformly dispersed, and without agglomeration. Figure 1 The inset is a magnified view of a single TiO2 composite nanofiller particle, showing the three-layer contrast after staining: the TiO2 core is dark black (as indicated by label "1"), the silane coupling agent modified intermediate layer is dark gray (as indicated by label "2"), and the PMMA outer layer is light gray (as indicated by label "3"). The average core particle size was statistically measured to be approximately 30 nm, the intermediate layer thickness approximately 8 nm, and the outer layer thickness approximately 5 nm.

[0097] Preparation Example 2 (Core-Intermediate Layer-Outer Layer Three-Layer TiO2 Composite Nanofiller 2) TiO2 composite nanofillers were prepared in a manner similar to that of Preparation Example 1, except that γ-glycidoxypropyltrimethoxysilane (KH-570) was replaced with γ-methacryloyloxypropyltrimethoxysilane. TEM testing was performed in a manner similar to that of Preparation Example 1. The morphology of the composite nanofillers obtained in Preparation Example 2 was similar to that of the composite nanofillers obtained in Preparation Example 1, both exhibiting a three-layer structure. The measured average core diameter was approximately 30 nm, the thickness of the middle layer was approximately 5.5 nm, and the thickness of the outer layer was approximately 8 nm.

[0098] Preparation Example 3 (Core-Intermediate Layer-Outer Layer Three-Layer TiO2 Composite Nanofiller 3) TiO2 composite nanofillers were prepared in a manner similar to that of Preparation Example 1, except that the polymethyl methacrylate (PMMA) macromonomer with a weight average molecular weight of 1000 was replaced with a mixture of PMMA macromonomer and polybutyl acrylate macromonomer in an equal weight ratio of 3:1. TEM testing was performed in a manner similar to that of Preparation Example 1. The morphology of the composite nanofiller obtained in Preparation Example 3 was similar to that of the composite nanofiller obtained in Preparation Example 1, both exhibiting a three-layer structure. The core average particle size was measured to be approximately 30 nm, the middle layer thickness to be approximately 5 nm, and the outer layer thickness to be approximately 5.5 nm.

[0099] Preparation Example 4 (Core-Intermediate Layer-Outer Layer Three-Layer SiO2 Composite Nanofiller 4) The composite nanofiller was prepared in a similar manner to Preparation Example 1, except that the titanium dioxide nanoparticles with an average particle size of approximately 30 nm were replaced with SiO2 nanoparticles with an average particle size of approximately 30 nm. TEM testing was performed in a similar manner to Preparation Example 1. The morphology of the composite nanofiller obtained in Preparation Example 4 was similar to that of the composite nanofiller obtained in Preparation Example 1, both exhibiting a three-layer structure. The core average particle size was measured to be approximately 30 nm, the middle layer thickness to be approximately 6 nm, and the outer layer thickness to be approximately 6.7 nm.

[0100] Preparation Example 5 (Three-layer Al2O3 composite nanofiller: core-intermediate layer-outer layer 5) The composite nanofiller was prepared in a similar manner to Preparation Example 1, except that the titanium dioxide nanoparticles with an average particle size of approximately 30 nm were replaced with Al₂O₃ nanoparticles with an average particle size of approximately 30 nm. TEM testing was performed in a similar manner to Preparation Example 1. The morphology of the composite nanofiller obtained in Preparation Example 5 was similar to that of the composite nanofiller obtained in Preparation Example 1, both exhibiting a three-layer structure. The core average particle size was measured to be approximately 30 nm, the middle layer thickness to be approximately 4 nm, and the outer layer thickness to be approximately 5.5 nm.

[0101] Preparation Example 6 (Core-Outer Layer TiO2 Composite Nanofiller 6) The composite nanofiller was prepared in a similar manner to Preparation Example 1, except that the acrylate macromonomer grafting step was omitted. After modification, it was directly cooled, centrifuged at 8000 r / min for 15 min, washed three times with deionized water, vacuum dried at 80 ℃ for 12 h, and then ground and sieved. TEM testing was performed in a similar manner to Preparation Example 1. The composite nanofiller obtained in Preparation Example 6 has a bilayer structure. The core average particle size was measured to be approximately 30 nm, and the outer layer thickness was approximately 5.5 nm.

[0102] Example 1 (E1) The composite nanofiller used in Example 1 is the TiO2-based composite nanofiller 1 with a core-intermediate-outer three-layer structure obtained in Preparation Example 1. By weight percentage, the formulation of the nanocomposite ink for gravure printing prepared in Example 1 is as follows: resin binder (hydroxyl-terminated waterborne polyester polyurethane resin) 32%, composite nanofiller from Preparation Example 1 8%, coloring pigment (phthalocyanine blue pigment) 15%, organic solvent (ethyl acetate:isopropanol = 7:3) 40%, and multifunctional additives 5%, including dispersant 1.8%, defoamer 0.5%, leveling agent 0.6%, thixotropic agent 0.8%, and drying agent 1.3%, with a total weight percentage of 100%.

[0103] The preparation process is divided into four stages: pigment pre-dispersion, nanofiller dispersion, resin mixing, additive formulation, and filtration of the finished product.

[0104] The first step is the preparation of pre-dispersion of the coloring pigment: 70% of the total organic solvent mass is added to a dispersion tank, a high-speed disperser is turned on, and the speed is set to 300 r / min. While stirring, the coloring pigment, 50% of the composite nanofiller, and the dispersant are added sequentially, and stirring is maintained for 30 min to allow the pigment and filler to be initially wetted and dispersed. Then the mixture is transferred to a horizontal sand mill and ground at 1500 r / min until the ink fineness is ≤ 15 μm. The resulting uniform pre-dispersion of the coloring pigment is then ready for use.

[0105] The second step is the preparation of the composite nanofiller dispersion: the remaining 30% of the organic solvent is added to another dispersion tank, the speed of the high-speed disperser is adjusted to 600 r / min, the remaining 50% of the composite nanofiller is added, and the ultrasonic disperser is turned on for 20 min. After ultrasonication, stirring is continued for 60 min to obtain the nanofiller dispersion.

[0106] The third step is the main mixing process: While maintaining the stirring state of the nanofiller dispersion, increase the rotation speed to 800 r / min, and slowly and continuously add the resin binder into the dispersion tank over 30 minutes. After the resin binder is added, continue stirring for 60 minutes. Then, add all the prepared pre-dispersion of the coloring pigment, maintaining the same rotation speed and continuing to stir for 50 minutes to ensure uniform mixing of the pigment, composite nanofiller, and resin binder, forming the basic ink system.

[0107] The fourth step is the preparation of additives and filtration of the finished product: Defoamer, leveling agent, thixotropic agent, and drying agent are added sequentially to the mixture. After each additive is added, the mixture is stirred for 10 minutes until completely homogeneous. After all additives have been added, stirring continues for 40 minutes. Finally, the mixture is pressure filtered through a 100-mesh stainless steel filter to remove mechanical impurities and undispersed agglomerated particles, yielding nano-composite ink 1 for gravure printing.

[0108] The nanocomposite ink 1 for gravure printing was characterized according to the test methods described in detail above.

[0109] Examples 2-12 (E2-E12) and Comparative Examples 1-3 (CE1-CE3) Examples 2-12 (E2-E12) and Comparative Examples 1-3 (CE1-CE3) were prepared in a manner similar to that of Example 1 to prepare nanocomposite inks 2-12 and 1-3 for gravure printing, respectively, except that the component types and ratios were changed as shown in Table 3 below.

[0110] The nanocomposite inks 2-12 for gravure printing and the comparative nanocomposite inks 1-3 for gravure printing were characterized according to the test methods described in detail above, and the results are shown in Table 4 below together with the corresponding results of Example 1.

[0111]

[0112]

[0113] As can be seen from the performance test results in Table 4, the nanocomposite inks for gravure printing prepared in Examples 1-12 of this invention are significantly better than those in Comparative Examples 1-3 in terms of storage stability, drying speed, ink layer hardness, abrasion resistance, adhesion, gloss and environmental friendliness. This verifies the synergistic effect of the three-layer TiO2 composite nanofiller (core-middle layer-outer layer) on the comprehensive performance of the ink.

[0114] Specifically, regarding storage stability, the inks prepared in Examples 1-12 showed no sedimentation, stratification, or agglomeration after 6 months of standing, with viscosity changes ranging from only 2.1% to 4.6%. This indicates that the three-layer nanofiller can fundamentally inhibit nanoparticle aggregation and significantly improve the long-term storage stability of the ink. In contrast, Comparative Example 1, using SiO2-based three-layer fillers, and Comparative Example 2, using Al2O3-based three-layer fillers, both exhibited significant sedimentation, with viscosity changes reaching 12.5% ​​and 15.8%, respectively. Comparative Example 3, using a traditional core-shell two-layer TiO2 filler, showed agglomeration and a viscosity change rate as high as 22.3%.

[0115] Regarding drying performance, the inks of Examples 1-12 have a surface drying time of 10-15s and a complete drying time of 65-80s, meeting the rapid drying requirements of high-speed gravure printing. The inks of Comparative Examples 1-3 have a surface drying time of 22-30s and a complete drying time of 95-120s, indicating a lower drying rate that is unsuitable for high-speed printing scenarios. In terms of ink layer mechanical properties, the inks of Examples 1-12 have a pencil hardness of 3H-4H, a low abrasion resistance weight loss of 0.006-0.012g / 1000 cycles, and an adhesion grade of 0-1. The inks of Comparative Examples 1-3 have a hardness of only H-2H, abrasion resistance weight loss of 0.025-0.035g / 1000 cycles, and an adhesion grade reduced to 2-3.

[0116] In terms of gloss and environmental friendliness, the inks in Examples 1-12 have a 60° gloss of 85°-92°, with a full and bright ink layer; the VOC reduction rate is 40%-52%, and they are free of benzene and heavy metals, meeting food packaging safety standards. The inks in Comparative Examples 1-3 have a gloss of only 70°-78° and a VOC reduction rate of only 20%-28%, showing a significant difference in environmental friendliness and printing appearance.

[0117] Among them, Examples 11 and 12 used the filler with PMMA and PBA compound outer layer prepared in Example 3, which had the best performance in all aspects, with a viscosity change rate as low as 2.1%-2.3%, a surface drying time of 10-11s, a hard drying time of 65-66s, a hardness of 4H, a wear resistance loss of 0.006-0.007g / 1000 cycles, an adhesion grade of 0, a gloss of 91°-92°, and a VOC reduction rate of 51%-52%, thus further proving that the compounding of acrylate macromonomers can optimize interfacial bonding and film-forming performance.

[0118] In summary, this invention, through the scientific compounding of TiO2 nanofillers with a specific three-layer structure with water-based resins, benzene-free solvents, and multifunctional additives, successfully balances the ink dispersion stability, drying properties, mechanical strength, and environmental friendliness. It solves the problems of traditional nano-inks, such as easy agglomeration, limited performance, and poor environmental performance, and meets the stringent requirements of high-end food packaging and high-speed gravure printing.

[0119] Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the spirit and scope of this disclosure. Therefore, if such modifications and variations fall within the scope of this invention, this disclosure is also intended to include such modifications and variations.

Claims

1. A nano-composite ink for gravure printing, characterized in that, By weight percentage, it contains the following components: 25-45% resin binder; 3-12% composite nanofiller; 8-18% coloring pigment; 20-40% organic solvent; 1-5% of multifunctional adjuvants, including: The resin binder comprises one or more of waterborne polyurethane resin, waterborne acrylic resin, and waterborne chloroacetic acid resin. The composite nanofiller is a particle with a three-layer structure of core-intermediate layer-outer layer, wherein: the core is titanium dioxide nanoparticles, the intermediate layer is a silane coupling agent modified layer, and the outer layer is an acrylate oligomer grafted functional layer. The multifunctional additives include dispersants, defoamers, leveling agents, thixotropic agents, and drying agents.

2. The nano-composite ink for gravure printing according to claim 1, characterized in that, The average particle size of the nuclei is in the range of 10-50 nm; The average thickness of the intermediate layer is in the range of 2-8 nm; The average thickness of the outer layer is in the range of 3-10 nm.

3. The nano-composite ink for gravure printing according to claim 1, characterized in that, The composite nanofiller is prepared by the following steps: (1) Add titanium dioxide nanoparticles to a mixed solvent of ethanol and deionized water, ultrasonically disperse for 20-40 min, stir for 30-60 min, adjust the pH to 3.5-5.5, heat to 45-65℃, and keep warm and stir for 1-3 h to prepare a nanoparticle dispersion. (2) Mix the silane coupling agent and the mixed solvent of ethanol and deionized water, add dropwise to the nanoparticle dispersion prepared in step (1), heat to 55-75℃, and reflux for 2-5 hours to prepare the silane coupling agent modified nanoparticle dispersion. (3) Add acrylate macromonomers and initiators to the silane coupling agent modified nanoparticle dispersion prepared in step (2), and heat to 75-90℃ under nitrogen protection and keep the reaction at this temperature for 3-6 h. (4) The reaction product from step (3) is cooled, centrifuged, dried, and ground to obtain the composite nanofiller, wherein: The silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; The acrylate macromonomers are selected from one or more of polymethyl methacrylate macromonomers, polybutyl acrylate macromonomers, and polyhydroxy acrylate macromonomers with a weight average molecular weight in the range of 800-1200. The initiator is benzoyl peroxide or azobisisobutyronitrile; Based on the total weight of titanium dioxide nanoparticles, silane coupling agents, and acrylate macromonomers as 100%, titanium dioxide nanoparticles account for 60-70%, silane coupling agents account for 5-10%, and acrylate macromonomers account for 25-35%.

4. The nano-composite ink for gravure printing according to claim 3, characterized in that, The acrylate macromonomers are a mixture of polymethyl methacrylate macromonomers and polybutyl acrylate macromonomers in a weight ratio of 2:1 to 4:

1.

5. The nanocomposite ink for gravure printing according to claim 1, characterized in that, The average particle size of the titanium dioxide nanoparticles is in the range of 10-50 nm.

6. The nano-composite ink for gravure printing according to claim 1, characterized in that, The waterborne polyurethane resin is a hydroxyl-terminated waterborne polyester polyurethane resin; the waterborne acrylic resin is a hydroxyl-modified thermoplastic acrylic resin; the waterborne chloroacetic acid resin is a ternary chloroacetic acid resin; the coloring pigment is selected from one or more of azo condensation pigments, phthalocyanine pigments, quinacridone pigments, and diketopyrrolopyrrole pigments; the organic solvent is selected from one or more of ester solvents, alcohol solvents, and ether alcohol solvents.

7. The nanocomposite ink for gravure printing according to claim 6, characterized in that, The ester solvent is selected from one or more of ethyl acetate, n-propyl acetate, and butyl acetate; the alcohol solvent is selected from one or more of ethanol, isopropanol, and n-propanol; and the ether alcohol solvent is selected from one or more of propylene glycol methyl ether and dipropylene glycol methyl ether.

8. The nanocomposite ink for gravure printing according to claim 1, characterized in that, Based on the weight of the aforementioned nano-composite ink for gravure printing (100%), the dispersant accounts for 0.5-1.8%, the defoamer for 0.1-0.5%, the leveling agent for 0.2-0.6%, the thixotropic agent for 0.3-0.8%, and the drier for 0.4-1.3%; or The dispersant is selected from one or more of polyacrylate dispersants, phosphate ester dispersants, and high molecular weight block copolymer dispersants; the defoamer is selected from one or more of polysiloxane defoamers and mineral oil defoamers; the leveling agent is selected from one or more of acrylate leveling agents and organically modified polysiloxane leveling agents; the thixotropic agent is selected from one or more of fumed silica and polyamide wax; and the drying agent is an environmentally friendly metal soap drying agent.

9. A method for preparing nanocomposite ink for gravure printing according to any one of claims 1-8, characterized in that, The method includes mixing the various components.

10. The method according to claim 9, characterized in that, The method includes the following steps: (a) Add a portion of the organic solvent to a dispersion tank, add the coloring pigment, a portion of the composite nanofiller and a portion of the dispersant while stirring, stir for 20-40 min, and then grind to a fineness ≤ 15 μm to obtain a pre-dispersion of the coloring pigment. (b) Add the remaining organic solvent to another dispersion tank, add the remaining composite nanofiller and the remaining dispersant while stirring, ultrasonically disperse for 15-30 min, and continue stirring for 40-80 min to obtain a nanofiller dispersion. (c) The resin binder is slowly added to the nanofiller dispersion and stirred for 60-90 min. Then the coloring pigment pre-dispersion is added and stirred for another 40-70 min to form a mixed system. (d) Add defoamer, leveling agent, thixotropic agent and drying agent sequentially to the mixing system of step (c), stir and mix and filter to obtain the nano-composite ink for gravure printing.

Images