High-flexibility cigarette packet uv offset ink

Abstract

The application discloses a high-flexibility cigarette packet UV offset printing ink, which comprises a modified polyurethane acrylate prepolymer, active dilution monomers, a photoinitiator, pigments, fillers, wax and auxiliaries; the modified polyurethane acrylate prepolymer is prepared by the following steps: firstly, polyether polyol is reacted with diisocyanate to generate a prepolymer; secondly, the prepolymer is chain-extended with a hydroxyl-terminated polybutadiene; and finally, the prepolymer is capped with a hydroxyl-containing acrylate to obtain the modified polyurethane acrylate prepolymer, which contains polyether flexible chain segments, polybutadiene elastic chain segments and photocurable acrylate groups in the molecular chain. After curing, a polyurethane-polybutadiene micro-phase separation structure is formed, which endows the ink layer with super-strong flexibility, low shrinkage and excellent adhesion. The ink realizes breakthrough performances of a folding number of more than 250,000 times, no cracks in 180-degree folding, and a 3M adhesive tape peeling rate of less than 2% in a UV curing system, and has the characteristics of fast curing and environmental protection and safety, and perfectly adapts to high-strength post-processing requirements such as cigarette packet embossing, die cutting and repeated cover turning.

Description

Technical Field

[0001] This invention relates to the field of UV offset printing ink technology, and in particular to a highly flexible UV offset printing ink for cigarette packaging. Background Technology

[0002] Cigarette packaging printing, as one of the most demanding branches of the packaging printing industry, requires multiple post-processing steps, including embossing, die-cutting, flap folding, and high-speed automated packaging. This places extremely high demands on the flexibility, adhesion, and folding resistance of the inks. Currently, offset printing inks for cigarette packaging mainly fall into two categories: oxidative film-forming drying systems and UV curing systems. While oxidative film-forming inks offer good ink layer flexibility, they suffer from slow drying speeds, low production efficiency, and insufficient adhesion to non-absorbent substrates such as aluminum foil composite paper and transfer laser paper. UV offset printing inks, on the other hand, are increasingly widely used in cigarette packaging printing due to their advantages such as fast curing speed, high production efficiency, good chemical resistance, and absence of volatile organic solvents.

[0003] However, existing UV offset printing inks generally use photo-initiated crosslinking systems of acrylate oligomers (such as epoxy acrylates and polyester acrylates) and multifunctional monomers. During curing, these systems exhibit large volume shrinkage and high crosslinking density, resulting in significant ink layer brittleness and even lower folding resistance than traditional anodizing inks. Cigarette packaging products must withstand over 200,000 repeated folding and repacking cycles during consumer use; under these extreme conditions, existing UV ink layers are highly susceptible to cracking and peeling. To improve flexibility, some technologies have attempted to add flexible monomers or plasticizers. However, flexible monomers often reduce curing speed and ink layer strength, while plasticizers pose risks of migration and performance degradation.

[0004] Furthermore, the substrates for cigarette packaging printing are mostly non-absorbent materials with dense surfaces and low surface energy, such as aluminum foil and laser paper. Existing UV inks generally have poor adhesion to these materials, and the ink layer peeling rate is relatively high in 3M tape tests. At the same time, as a food contact packaging material, cigarette packaging has extremely strict safety requirements for ink components, prohibiting the use of traditional plasticizers and small molecule migrants.

[0005] Therefore, there is an urgent need to develop a UV offset printing ink system that combines ultra-fast curing speed, ultra-high flexibility, strong substrate adhesion, and meets food contact safety standards to meet the high-end needs of cigarette packaging printing. Summary of the Invention

[0006] Therefore, it is necessary to provide a highly flexible UV offset printing ink for cigarette packaging to address the technical problems of insufficient flexibility and poor adhesion of existing UV offset printing inks for cigarette packaging.

[0007] A highly flexible UV offset printing ink for cigarette packaging comprises a modified polyurethane acrylate prepolymer, reactive diluent monomers, photoinitiators, pigments, fillers, waxes, and additives. The modified polyurethane acrylate prepolymer is prepared by the following method: reacting a polyether polyol with a diisocyanate to form an isocyanate-terminated prepolymer, then reacting it with a hydroxyl-containing acrylate monomer to introduce a photocurable double bond, and then carrying out a chain extension reaction with hydroxyl-terminated polybutadiene to obtain a modified polyurethane acrylate prepolymer whose molecular chain simultaneously contains polyether flexible segments, polybutadiene elastic segments, and acrylate photocurable groups.

[0008] In one embodiment, the polyether polyol is polytetrahydrofuran ether diol with a number average molecular weight of 1000-2000; the diisocyanate is isophorone diisocyanate; the hydroxyl-containing acrylate monomer is hydroxyethyl acrylate or hydroxyethyl methacrylate; and the hydroxyl-terminated polybutadiene has a number average molecular weight of 2000-3000 and a hydroxyl value of 0.5-1.0 mmol / g.

[0009] In one embodiment, the modified polyurethane acrylate prepolymer is prepared by: dehydrating polytetrahydrofuran ether diol at 100-120°C under negative pressure, cooling to 60-80°C, adding isophorone diisocyanate and catalyst dibutyltin dilaurate, and reacting for 2-4 hours to obtain an isocyanate-terminated prepolymer; adding hydroxyl-terminated polybutadiene and reacting at 70-90°C for 1-2 hours; then adding hydroxyethyl acrylate and polymerization inhibitor p-hydroxyanisole and reacting at 60-80°C until the infrared absorption peak of the isocyanate group completely disappears, thus obtaining the prepolymer.

[0010] In one embodiment, the high-flexibility UV offset printing ink for cigarette packaging contains, by weight, 35-55 parts of modified polyurethane acrylate prepolymer, 15-30 parts of reactive diluent monomer, 3-8 parts of photoinitiator, 15-25 parts of pigment, 3-8 parts of filler, 1-3 parts of wax, and 0.5-3 parts of additives.

[0011] In one embodiment, the reactive diluent monomer is at least two combinations of ethoxylated trimethylolpropane triacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, and isobornyl acrylate.

[0012] In one embodiment, the photoinitiator is a combination of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 1:0.5 to 1:0.5 to 1.

[0013] In one embodiment, the filler is surface-modified nano-silica or nano-barium sulfate with a particle size ≤100nm; the wax is polytetrafluoroethylene modified polyethylene wax; and the additives include leveling agents, defoamers, and dispersants.

[0014] In one embodiment, the ink has a fineness of ≤10μm, a viscosity of 8~15Pa·s at 25℃ and a shear rate of 2.5Pa·s, and the cured ink layer shows no cracks in a 180° folding test, with an MIT (Mean Integrity Test) of ≥250,000 folds.

[0015] This invention also discloses a method for preparing the high-flexibility UV offset printing ink for cigarette packaging, comprising the following steps: S1. The modified polyurethane acrylate prepolymer, reactive diluent monomer, photoinitiator and additives are heated and mixed evenly under light-protected conditions to obtain a mixed base material; S2. Add pigments, fillers and some active diluent monomers to the mixed base material and disperse at high speed to obtain a pre-dispersed slurry; S3. Grind the pre-dispersed slurry to a fineness of ≤10μm using a three-roll mill or a bead mill; S4. Add wax and the remaining active diluent monomer to the ground slurry, mix evenly under light protection and stirring, degas under vacuum, adjust the viscosity, filter, and obtain the high-flexibility cigarette packaging UV offset printing ink.

[0016] In one embodiment, the heating temperature in step S1 is 40~60℃ and the mixing time is 15~30 minutes; the high-speed dispersion speed in step S2 is 1000~2000 rpm and the dispersion time is 20~40 minutes; and the grinding temperature in step S3 is controlled at ≤40℃.

[0017] In one embodiment, in step S4, the viscosity is adjusted to 8~15 Pa·s at a shear rate of 2.5 Pa·s at 25°C.

[0018] The aforementioned high-flexibility UV offset printing ink for cigarette packaging chemically links polyether segments (providing low-temperature flexibility and folding resistance) and polybutadiene elastic segments (providing high elasticity, low-temperature performance, and hydrophobicity) through polyurethane bonds, and introduces acrylate photocurable groups. During curing, a polyurethane-polybutadiene microphase separation structure is formed. The soft segments (polyether and polybutadiene) provide excellent elastic deformation capability, while the hard segments (urethane) provide cohesive strength. This structure avoids the high brittleness of the traditional all-acrylate crosslinked network in UV inks, allowing the ink layer to effectively dissipate stress through soft segment deformation during repeated folding. Simultaneously, the low glass transition temperature of the polybutadiene segments (approximately -80°C) ensures flexibility in low-temperature environments, while the acrylate groups guarantee rapid photocuring, meeting the demands of high-speed printing. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention is provided below in conjunction with the following description. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown below, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0022] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0024] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation. Example 1

[0025] This invention discloses a highly flexible UV offset printing ink for cigarette packaging, comprising a modified polyurethane acrylate prepolymer, a reactive diluent monomer, a photoinitiator, pigments, fillers, waxes, and additives; The modified polyurethane acrylate prepolymer is prepared by the following method: reacting a polyether polyol with a diisocyanate to form an isocyanate-terminated prepolymer, then reacting it with a hydroxyl-containing acrylate monomer to introduce a photocurable double bond, and then carrying out a chain extension reaction with hydroxyl-terminated polybutadiene to obtain a modified polyurethane acrylate prepolymer whose molecular chain simultaneously contains polyether flexible segments, polybutadiene elastic segments, and acrylate photocurable groups.

[0026] This invention chemically links polyether segments (providing low-temperature flexibility and folding resistance) and polybutadiene elastic segments (providing high elasticity, low-temperature performance, and hydrophobicity) through polyurethane bonds, and introduces acrylate photocurable groups. During curing, a polyurethane-polybutadiene microphase separation structure is formed. The soft segments (polyether and polybutadiene) provide excellent elastic deformation capability, while the hard segments (urethane) provide cohesive strength. This structure avoids the high brittleness of traditional UV ink's all-acrylate crosslinked network, allowing the ink layer to effectively dissipate stress through soft segment deformation during repeated folding. Simultaneously, the low glass transition temperature of the polybutadiene segments (approximately -80°C) ensures flexibility in low-temperature environments, while the acrylate groups guarantee rapid photocuring, meeting the demands of high-speed printing.

[0027] Furthermore, the polyether polyol is polytetrahydrofuran ether diol with a number average molecular weight of 1000-2000; the diisocyanate is isophorone diisocyanate; the hydroxyl-containing acrylate monomer is hydroxyethyl acrylate or hydroxyethyl methacrylate; and the hydroxyl-terminated polybutadiene has a number average molecular weight of 2000-3000 and a hydroxyl value of 0.5-1.0 mmol / g. In the above preferred raw materials, the asymmetric structure of isophorone diisocyanate imparts good solubility and flexibility to the prepolymer; the regular segments of polytetrahydrofuran ether diol provide high resilience; and the hydrophobic segments of hydroxyl-terminated polybutadiene enhance wetting and adhesion to low surface energy substrates (such as laser paper).

[0028] Furthermore, the preparation method of the modified polyurethane acrylate prepolymer is as follows: polytetrahydrofuran ether diol is dehydrated at 100-120°C under negative pressure, cooled to 60-80°C, isophorone diisocyanate and dibutyltin dilaurate catalyst are added, and the reaction is carried out for 2-4 hours to obtain an isocyanate-terminated prepolymer; hydroxyl-terminated polybutadiene is added, and the reaction is carried out at 70-90°C for 1-2 hours; then hydroxyethyl acrylate and p-hydroxyanisole polymerization inhibitor are added, and the reaction is carried out at 60-80°C until the isocyanate group infrared absorption peak is reached. Complete disappearance yields the product. This stepwise synthesis method ensures that the polyether and polybutadiene segments are orderly linked by urethane bonds to form a block structure, which facilitates subsequent microphase separation. The polymerization inhibitor prevents the acrylate groups from thermally polymerizing during synthesis, ensuring the storage stability and photocurability of the prepolymer.

[0029] Furthermore, the high-flexibility UV offset printing ink for cigarette packaging, by weight, comprises 35-55 parts of modified polyurethane acrylate prepolymer, 15-30 parts of reactive diluent monomer, 3-8 parts of photoinitiator, 15-25 parts of pigment, 3-8 parts of filler, 1-3 parts of wax, and 0.5-3 parts of additives. When the prepolymer content is less than 35 parts, the flexibility improvement is insufficient; when it is more than 55 parts, the viscosity is too high, affecting print transfer and leveling properties. Within this range, the reactive diluent monomer can effectively adjust the viscosity and participate in crosslinking without affecting the ink layer elasticity.

[0030] Furthermore, the reactive diluent monomer is at least two combinations selected from ethoxylated trimethylolpropane triacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, and isobornyl acrylate. The ethoxylated monomer has a flexible ether chain, which reduces the crosslinking density; the bifunctional monomer (such as tripropylene glycol diacrylate and 1,6-hexanediol diacrylate) provides appropriate crosslinking points; and the isobornyl acrylate imparts ink layer hardness and adhesion. Through this multifunctional combination, an optimal balance between crosslinking density and flexibility can be achieved.

[0031] Furthermore, the photoinitiator is a combination of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and 1-hydroxycyclohexylphenyl ketone, in a mass ratio of 1:0.5~1:0.5~1. Acylphosphine oxide initiators possess deep curing capabilities and photobleaching effects, amino ketones provide high photosensitivity, and hydroxy ketones provide surface curing. This ternary composite initiation system exhibits high initiation efficiency under both UV-LED and conventional mercury lamps, ensuring complete curing of thick ink layers (solid ink with smoke coating) with minimal yellowing.

[0032] Furthermore, the filler is surface-modified nano-silica or nano-barium sulfate with a particle size ≤100nm; the wax is polytetrafluoroethylene modified polyethylene wax; the additives include leveling agents, defoamers, and dispersants. The nanofiller not only enhances the mechanical strength of the ink layer, but its surface-modified groups can also form chemical bonds with the resin, strengthening cohesion; the PTFE-modified wax forms a low-friction coefficient slip layer on the ink layer surface, reducing damage during die-cutting and folding; the dispersant ensures stable dispersion of pigments and fillers, preventing agglomeration that affects fineness and gloss.

[0033] Furthermore, the ink has a fineness ≤10μm, a viscosity of 8~15Pa·s at 25℃ and a shear rate of 2.5Pa·s, and the cured ink layer shows no cracks in a 180° folding test, with an MIT (Mean Intact Size) of ≥250,000 folds. The fineness ensures high-precision dot reproduction and solid uniformity; the viscosity window matches the ink roller transfer requirements of high-speed offset printing presses; and the folding resistance meets the stringent standards of the cigarette packaging industry. Example 2

[0034] A method for preparing the highly flexible UV offset printing ink for cigarette packaging includes the following steps: S1. The modified polyurethane acrylate prepolymer, reactive diluent monomer, photoinitiator and additives are heated and mixed evenly under light-protected conditions to obtain a mixed base material; S2. Add pigments, fillers and some active diluent monomers to the mixed base material and disperse at high speed to obtain a pre-dispersed slurry; S3. Grind the pre-dispersed slurry to a fineness of ≤10μm using a three-roll mill or a bead mill; S4. Add wax and the remaining active diluent monomer to the ground slurry, mix evenly under light protection and stirring, degas under vacuum, adjust the viscosity, filter, and obtain the high-flexibility cigarette packaging UV offset printing ink.

[0035] This method employs a "premix-dispersion-grinding-adjustment" process, with all operations conducted in the dark to prevent premature decomposition of the photoinitiator. First, the resin, monomer, and initiator are fully dissolved to form a homogeneous phase before the pigment is added, ensuring complete wetting. After grinding, wax and remaining monomers are added to adjust the final viscosity and smoothness. Vacuum degassing removes microbubbles, preventing pinhole defects in printing. The process has a wide processing window, making it suitable for industrial-scale mass production.

[0036] Furthermore, in step S1, the heating temperature is 40~60℃, and the mixing time is 15~30 minutes; in step S2, the high-speed dispersion speed is 1000~2000 rpm, and the dispersion time is 20~40 minutes; in step S3, the grinding temperature is controlled at ≤40℃. Low-temperature grinding avoids frictional heat from inducing local polymerization or causing thermal decomposition of the photoinitiator, ensuring the storage stability and curing activity of the ink.

[0037] Furthermore, in step S4, the viscosity is adjusted to 8~15 Pa·s at 25°C and a shear rate of 2.5 Pa·s. This viscosity range ensures excellent ink-water balance and transferability on the offset printing press, while also taking into account the smoothness of the cured ink layer. Example 3

[0038] In this embodiment, the high-flexibility UV offset printing ink for cigarette packaging comprises the following components by weight: 45 parts of modified polyurethane acrylate prepolymer (self-made, PTMEG molecular weight 1500, HTPB molecular weight 2500), 12 parts of ethoxylated trimethylolpropane triacrylate, 8 parts of tripropylene glycol diacrylate, 5 parts of isoborneol acrylate, 3 parts of TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide), 2 parts of 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone), 2 parts of 184 (1-hydroxycyclohexylphenyl ketone), and benzidine yellow G. 20 parts, 5 parts nano silica (surface treated with γ-methacryloxypropyltrimethoxysilane, particle size 50nm), 2 parts PTFE modified polyethylene wax, 1 part dispersant (BYK-168), 0.3 parts leveling agent (BYK-333), and 0.2 parts defoamer (BYK-055).

[0039] Preparation of the modified polyurethane acrylate prepolymer: 150g of 1500 molecular weight PTMEG was dehydrated at 110℃ and -0.095MPa for 1 hour, then cooled to 70℃. 111g of IPDI (NCO / OH molar ratio 1.6) and 0.15g of DBTDL were added, and the reaction was carried out at 80℃ for 3 hours until the NCO value decreased to the theoretical value. 125g of 2500 molecular weight HTPB was added, and the reaction was carried out at 80℃ for 1.5 hours. 23.2g of HEA (containing 0.05g of MEHQ) was added, and the reaction was carried out at 70℃ until the NCO infrared peak disappeared. The product was then discharged.

[0040] Following the method in Example 2, the prepolymer, monomer, photoinitiator, and additives were mixed at 50°C in the dark for 20 minutes; pigment, nano-silica, and part of the monomer (tripropylene glycol diacrylate) were added and dispersed at 1500 rpm for 30 minutes; the mixture was then milled three times with a roller temperature ≤35°C until a fineness of 8 μm was achieved; wax and the remaining monomer were added, stirred in the dark, degassed under vacuum, and the viscosity was adjusted to 12 Pa·s. Example 4

[0041] In this embodiment, the high-flexibility UV offset printing ink for cigarette packaging comprises the following components by weight: 50 parts of modified polyurethane acrylate prepolymer (PTMEG molecular weight 1000, HTPB molecular weight 2000), 10 parts of 1,6-hexanediol diacrylate, 10 parts of tripropylene glycol diacrylate, 5 parts of isobornyl acrylate, 2.5 parts of TPO, 2.5 parts of 907, 2 parts of 184, 18 parts of phthalocyanine blue BGS, 6 parts of nano-barium sulfate (surface treated with stearic acid, particle size 80nm), 2.5 parts of PTFE-modified polyethylene wax, 1.2 parts of dispersant, 0.3 parts of leveling agent, and 0.2 parts of defoamer. The preparation method is the same as in Example 3, grinding to a fineness of 9μm and adjusting the viscosity to 10 Pa·s. Example 5

[0042] In this embodiment, the high-flexibility UV offset printing ink for cigarette packaging comprises the following components by weight: 40 parts of modified polyurethane acrylate prepolymer (PTMEG molecular weight 2000, HTPB molecular weight 3000), 15 parts of ethoxylated trimethylolpropane triacrylate, 8 parts of 1,6-hexanediol diacrylate, 5 parts of tripropylene glycol diacrylate, 3.5 parts of TPO, 1.5 parts of 907, 2 parts of 184, 22 parts of Golden Red C, 4 parts of nano-silica, 2 parts of PTFE-modified polyethylene wax, 0.8 parts of dispersant, 0.2 parts of leveling agent, and 0.1 parts of defoamer. The preparation method is the same as in Example 3, with the viscosity adjusted to 13 Pa·s.

[0043] In summary, the high-flexibility UV offset printing ink for cigarette packaging disclosed in this invention introduces both polyether flexible segments and polybutadiene elastic segments into a polyurethane acrylate prepolymer to form a chemically bonded microphase separation structure. After curing, the ink layer exhibits high elasticity, low shrinkage, and excellent adhesion. Compared with the prior art, the beneficial effects are as follows: (1) The polyether segments provide an extremely low glass transition temperature (approximately -75°C), and the polybutadiene segments further impart high elasticity and hydrophobicity, so that the ink layer does not crack even after repeated folding at room temperature or even low temperature; (2) The polybutadiene segments have good wettability on low surface energy substrates, and combined with the hydrogen bond adsorption of urethane bonds, the adhesion of the ink to aluminum foil paper and laser paper is significantly improved, and the 3M tape peeling rate is less than 2%; (3) By optimizing the monomer functionality ratio and initiator combination, the unity of high flexibility and rapid curing is achieved, and the curing speed meets the requirements of high-speed offset printing; (4) The system does not contain migratory plasticizers and small molecule residues, which meets the food contact safety standards for cigarette packaging. This invention fundamentally solves the industry pain points of existing UV cigarette packaging inks, such as creases, cracking, and poor adhesion, and has broad application prospects.

[0044] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A highly flexible UV offset printing ink for cigarette packaging, characterized in that, It contains modified polyurethane acrylate prepolymer, reactive diluent monomer, photoinitiator, pigment, filler, wax and additives; The modified polyurethane acrylate prepolymer is prepared by the following method: reacting a polyether polyol with a diisocyanate to form an isocyanate-terminated prepolymer, then reacting it with a hydroxyl-containing acrylate monomer to introduce a photocurable double bond, and then carrying out a chain extension reaction with hydroxyl-terminated polybutadiene to obtain a modified polyurethane acrylate prepolymer whose molecular chain simultaneously contains polyether flexible segments, polybutadiene elastic segments, and acrylate photocurable groups.

2. The high-flexibility UV offset printing ink for cigarette packaging according to claim 1, characterized in that, The polyether polyol is polytetrahydrofuran ether diol with a number average molecular weight of 1000-2000; the diisocyanate is isophorone diisocyanate; the hydroxyl-containing acrylate monomer is hydroxyethyl acrylate or hydroxyethyl methacrylate; the hydroxyl-terminated polybutadiene has a number average molecular weight of 2000-3000 and a hydroxyl value of 0.5-1.0 mmol / g.

3. The high-flexibility UV offset printing ink for cigarette packaging according to claim 2, characterized in that, The modified polyurethane acrylate prepolymer is prepared as follows: polytetrahydrofuran ether diol is dehydrated at 100-120°C under negative pressure, cooled to 60-80°C, isophorone diisocyanate and dibutyltin dilaurate catalyst are added, and the reaction is carried out for 2-4 hours to obtain isocyanate-terminated prepolymer; hydroxyl-terminated polybutadiene is added, and the reaction is carried out at 70-90°C for 1-2 hours; then hydroxyethyl acrylate and polymerization inhibitor p-hydroxyanisole are added, and the reaction is carried out at 60-80°C until the infrared absorption peak of the isocyanate group completely disappears, thus obtaining the prepolymer.

4. The high-flexibility UV offset printing ink for cigarette packaging according to claim 3, characterized in that, The high-flexibility UV offset printing ink for cigarette packaging, by weight, comprises 35-55 parts of modified polyurethane acrylate prepolymer, 15-30 parts of reactive diluent monomer, 3-8 parts of photoinitiator, 15-25 parts of pigment, 3-8 parts of filler, 1-3 parts of wax, and 0.5-3 parts of additives.

5. The high-flexibility UV offset printing ink for cigarette packaging according to claim 4, characterized in that, The reactive diluent monomer is at least two combinations selected from ethoxylated trimethylolpropane triacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, and isobornyl acrylate.

6. The high-flexibility UV offset printing ink for cigarette packaging according to claim 5, characterized in that, The photoinitiator is a combination of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone and 1-hydroxycyclohexylphenyl ketone, in a mass ratio of 1:0.5~1:0.5~1.

7. The high-flexibility UV offset printing ink for cigarette packaging according to claim 6, characterized in that, The filler is surface-modified nano-silica or nano-barium sulfate with a particle size ≤100nm; the wax is polytetrafluoroethylene modified polyethylene wax; the additives include leveling agents, defoamers and dispersants.

8. The high-flexibility UV offset printing ink for cigarette packaging according to claim 7, characterized in that, The ink has a fineness of ≤10μm, a viscosity of 8~15Pa·s at 25℃ and a shear rate of 2.5Pa·s, and the cured ink layer shows no cracks in a 180° folding test, with an MIT (Mean Ink) folding resistance of ≥250,000 cycles.

9. A method for preparing the high-flexibility UV offset printing ink for cigarette packaging according to any one of claims 1 to 8, comprising the following steps: S1. The modified polyurethane acrylate prepolymer, reactive diluent monomer, photoinitiator and additives are heated and mixed evenly under light-protected conditions to obtain a mixed base material; S2. Add pigments, fillers and some active diluent monomers to the mixed base material and disperse at high speed to obtain a pre-dispersed slurry; S3. Grind the pre-dispersed slurry to a fineness of ≤10μm using a three-roll mill or a bead mill; S4. Add wax and the remaining active diluent monomer to the ground slurry, mix evenly under light protection and stirring, degas under vacuum, adjust the viscosity, filter, and obtain the high-flexibility cigarette packaging UV offset printing ink.

10. The high-flexibility UV offset printing ink for cigarette packaging according to claim 9, characterized in that, In step S1, the heating temperature is 40~60℃ and the mixing time is 15~30 minutes; in step S2, the high-speed dispersion speed is 1000~2000rpm and the dispersion time is 20~40 minutes; in step S3, the grinding temperature is controlled at ≤40℃.