Double-sided precision overprinting and anti-counterfeiting cigarette liner paper and its preparation method

Abstract

This invention discloses a double-sided precision-printed anti-counterfeiting cigarette inner liner paper and its preparation method. The inner liner paper comprises a directional light-transmitting fiber network structure paper base, a front negative printing layer, a back positive printing layer, and a composite layer. The paper base is manufactured using a three-layer papermaking process. The middle layer undergoes pore-forming treatment to form directional microporous channels with a pore size of 5-15 μm, achieving a light transmittance of 88-92%. The front negative image is printed with high-penetration ink, with a penetration depth of 25-35 μm; the back positive image is printed with controlled-penetration ink containing microcrystalline wax and hydrophobic nano-silica, with a penetration depth of 8-15 μm. Dynamic registration control is achieved using a dual-sided CCD vision system and a servo correction device, achieving a registration accuracy of ≤0.12 mm laterally and ≤0.15 mm longitudinally. The composite layer uses a fluorinated acrylate system with a refractive index of 1.44-1.46, matching the paper base. When observed under light, the positive and negative patterns are precisely aligned, with clear layers, high anti-counterfeiting recognition, and a production qualification rate of 98%, making it suitable for high-end tobacco packaging.

Description

Technical Field

[0001] This invention relates to the field of cigarette packaging materials technology, and more particularly to double-sided precision overprinted anti-counterfeiting cigarette inner lining paper and its preparation method. Background Technology

[0002] Cigarette liner paper, as an important component of cigarette packaging, serves functions such as aroma preservation, moisture protection, and anti-counterfeiting. Traditional cigarette liner paper mainly uses an aluminum foil composite structure or single-sided printing of anti-counterfeiting patterns. However, aluminum foil presents environmental problems and is difficult to recycle, and single-sided printing of anti-counterfeiting technology is easily copied, resulting in poor anti-counterfeiting performance. In recent years, double-sided printing technology has begun to be applied to the anti-counterfeiting field of cigarette liner paper. By printing complementary patterns on both sides of the paper, a complete anti-counterfeiting pattern is formed when viewed against the light, improving the anti-counterfeiting identification rate.

[0003] However, existing double-sided printing technology has the following technical problems: First, the registration accuracy is low. The registration error of traditional mechanical positioning methods is usually 0.3-0.5mm, resulting in obvious misalignment of the front and back patterns when viewed against the light, and poor anti-counterfeiting effect. Second, the light transmittance of the paper base is insufficient. The light transmittance of ordinary paper is only 75-82%, and the pattern is dim and blurry when viewed against the light, resulting in low recognition. Third, the penetration depth of ink on both sides is difficult to control. When using the same ink, the pattern has poor layering and low contrast. Fourth, the composite layer reduces the light transmittance. Ordinary composite adhesives reduce the light transmittance by 8-12%, further affecting the anti-counterfeiting effect. These problems mean that the anti-counterfeiting performance and production yield of existing double-sided printed anti-counterfeiting cigarette liner paper cannot meet the needs of high-end tobacco products. Summary of the Invention

[0004] The purpose of this invention is to provide double-sided precision overprinting and anti-counterfeiting cigarette liner paper and its preparation method, so as to solve the problems existing in the prior art.

[0005] This invention provides a double-sided precision overprinted anti-counterfeiting cigarette liner paper, comprising a directional light-transmitting fiber network structure paper base, a front negative printing layer, a back positive printing layer, and a composite layer; The directional light-transmitting fiber network structure paper base has a three-layer structure, comprising, by weight: Surface pulp: The mass ratio of short fibers to long fibers is 7:3. The short fiber length of bleached sulfate hardwood pulp is 0.8-1.2 mm, the long fiber length of bleached sulfate softwood pulp is 2.8-3.2 mm, the nanocellulose is 3-6 parts, the kaolin is 8-12 parts, the cationic starch is 1.5-2.5 parts, the freeness is 35-40°SR, and the basis weight is 15 g / m². The middle layer slurry has a long fiber to short fiber mass ratio of 6:4, 2-4 parts sodium carboxymethyl cellulose, 1.5-2.5 parts cationic starch, a freeness of 25-30°SR, and a basis weight of 25 g / m². The middle layer is treated with an alkaline buffer solution with a pH of 9.5-10.5 to form directional microporous channels with a pore size of 5-15 μm and a porosity of 18-25%. Bottom layer slurry: Same composition as the top layer slurry, with a basis weight of 15 g / m²; The front negative printing layer is printed with high-penetration ink, which, by weight, includes: 12-18 parts pigment with a particle size ≤80nm; 25-30 parts modified rosin resin with a softening point of 85-95°C; 35-45 parts mineral oil with a kinematic viscosity of 15-25mm² / s; 8-12 parts vegetable oil with a linoleic acid content ≥60%; 3-5 parts fatty alcohol polyoxyethylene ether with an HLB value of 12-14; 2-4 parts n-propanol; and 0.8-1.2 parts cobalt-manganese-calcium composite drier. The high-penetration ink has a fineness ≤5μm, a viscosity of 8-12Pa·s, and a penetration depth of 25-35μm on the paper substrate. The positive printing layer on the back is printed with controlled-permeability ink, which, by weight, comprises: 15-20 parts pigment with a particle size of 100-150 nm; 35-42 parts modified rosin resin with a softening point of 105-115°C; 30-38 parts mineral oil with a kinematic viscosity of 40-60 mm² / s; 5-8 parts microcrystalline wax emulsion with a solid content of 40% and a wax particle size of 200-500 nm; 2-4 parts nano-silica with a particle size of 15-25 nm, which has been hydrophobically modified; 1-2 parts surfactant; and 1.0-1.5 parts drier. The controlled-permeability ink has a fineness ≤8 μm, a viscosity of 18-25 Pa·s, and a penetration depth of 8-15 μm on the paper substrate. The registration accuracy of the front negative printing layer and the back positive printing layer is: horizontal registration error ≤ 0.12mm, vertical registration error ≤ 0.15mm, and rotation angle error ≤ 0.2°. The composite layer comprises, by weight: 40-50 parts of fluorinated acrylate copolymer, which is polymerized from hexafluorobutyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 3:5:2, with a refractive index of 1.42; 25-35 parts of polyurethane resin, with a Shore A hardness of 75-85; 8-12 parts of epoxy resin; 3-6 parts of nano-zirconia with a particle size of 10-20 nm; 1-2 parts of silane coupling agent; and 8-12 parts of aliphatic isocyanate curing agent. The composite layer has a refractive index of 1.44-1.46 and a coating weight of 3-5 g / m².

[0006] By utilizing the synergistic effect of the above technical solution—a directional light-transmitting fiber network structure, a double-layer gradient ink system, dynamic optical positioning overprinting technology, and a refractive index matching composite layer—technical effects were achieved, including an over 50% improvement in overprinting accuracy, an 8-12% increase in light transmittance, a significant improvement in anti-counterfeiting identification, and a production qualification rate of 98%. When viewed against the light, the outline of the negative image on the front and the main body of the positive image on the back precisely align to form a complete anti-counterfeiting pattern. The pattern exhibits distinct layers, high contrast, and is clearly discernible to the naked eye, demonstrating excellent anti-counterfeiting performance and making it extremely difficult to replicate.

[0007] A method for preparing double-sided precision overprinted anti-counterfeiting cigarette liner paper includes the following steps: Step 1: Preparation of the translucent paper base: Dilute the surface pulp, middle pulp, and bottom pulp to the required online concentrations. The online concentrations of the surface and bottom pulps are 0.8-1.0%, and the middle pulp is 0.7-0.9%. Use a three-layer pre-wire multi-layer papermaking process. The vacuum degree of the surface and bottom wire sections is -20 kPa, and the vacuum degree of the middle wire section is -15 kPa. Before pressing, spray with an alkaline buffer solution with a pH of 9.5-10.5 and a temperature of 65-75°C at a spray volume of 15-25 g / m² and a residence time of 5-8 seconds to partially dissolve the sodium carboxymethyl cellulose in the middle layer. The pressing pressure is 1.5-2.0 MPa. The drying temperature is 110-125°C. The calendering pressure is 150-200 N / mm. Step 2: Front negative printing: Gravure printing is used with a cell depth of 35-45μm. High-penetration ink is used to print the anti-counterfeiting pattern on the negative. The printing pressure is 0.4-0.6MPa, and the printing speed is 60-80 meters / minute. Simultaneously, front color marks are printed 3mm from the outer corners of the four corners of the paper. The front color marks are solid cross-shaped structures with a line width of 0.3mm and a line length of 5mm. Drying is done using a combination of infrared and hot air at a temperature of 120-130°C for 8-12 seconds. The front color marks are then UV cured with a UV lamp power of 120W / cm for 2-3 seconds. Step 3, Paper Flipping and Conveying: The paper is flipped 180 degrees by the flipping roller. During the flipping process, the paper is vacuumed and the vacuum degree is -8kPa; the tension is controlled at 150-200N. Step 4, Overprinting and Positioning: The first CCD camera scans the color marks at the four corners of the front to establish a front reference coordinate system. The CCD camera has a resolution of 5 million pixels, a field of view of 50mm×40mm, a scanning frequency of 200 times / minute, and an LED blue light source wavelength of 470nm. The second CCD camera scans the current position of the paper and calculates the lateral deviation ΔX, the longitudinal deviation ΔY, and the rotation angle deviation Δθ. Step 5, overprint compensation: When |ΔX|>0.1mm, activate the lateral correction system with a correction accuracy of ±0.05mm; when |ΔY|>0.15mm, adjust the printing cylinder phase with an adjustment accuracy of ±0.08mm; when |Δθ|>0.3°, activate the rotation compensation system with a compensation accuracy of ±0.1°. Step Six: Reverse Positive Printing: Gravure printing is used with a cell depth of 35-45μm. Controlled-spread ink is used to print the positive anti-counterfeiting pattern. The positive and negative images complement each other. The printing pressure is 0.3-0.5MPa, and the printing speed is 50-70 meters / minute. Back color marks are printed at the four corners of the back. The back color marks have a hollow cross-shaped structure with a line width of 0.2mm and an inner space of 2mm×2mm. The drying temperature is 100-110°C, and the time is 10-15 seconds. The back color marks are UV cured. Step 7, Composite Coating: The paper is corona treated with a corona power of 0.3-0.5 W / cm²; a microgravure roller is used to coat the composite adhesive. The microgravure roller has a screen ruling of 180-220 lines / inch and a cell depth of 20-25 μm. The speed ratio of the coating roller to the paper is 1.05:1; three-stage drying: first stage 60°C, 5 seconds; second stage 80°C, 10 seconds; third stage 100°C, 15 seconds. Step 8: Curing and maturation: Mature at 50°C for 24 hours.

[0008] Furthermore, the basis weight of the paper is 53-57 g / m², the thickness is 70-85 μm, the light transmittance is 88-92%, the tensile strength in the longitudinal direction is ≥2.5 kN / m, and the surface smoothness is 120-150 seconds.

[0009] Furthermore, the pigments of the high-penetration ink are phthalocyanine blue or carbon black, while the pigments of the controlled-penetration ink are carbon black. The pigments of the high-penetration ink and the controlled-penetration ink are complementary colors.

[0010] Furthermore, the negative image of the front negative printing layer is the outline and background of the anti-counterfeiting pattern, with a line width of 0.15-0.3mm and a line spacing of 0.3-0.5mm; the positive image of the back positive printing layer is the main graphic of the anti-counterfeiting pattern; the gap between the negative and positive images is 0.2-0.3mm.

[0011] Furthermore, the light transmittance of the composite layer decreases by ≤2%, haze by ≤5%, and peel strength by ≥2.0N / 15mm.

[0012] Furthermore, in step one, the short fiber freeness of the surface pulp is 35-40°SR, and the long fiber freeness is 20-25°SR; the long fiber freeness of the middle pulp is 25-30°SR, and the short fiber freeness is 30-35°SR; the paper density after pressing is 0.65-0.72 g / cm³.

[0013] Furthermore, in step two, the high-penetration ink is obtained by grinding three times using a three-roll mill, with the inter-roll pressure being 2-3 MPa for the first time, 3-4 MPa for the second time, and 4-5 MPa for the third time; in step six, the controlled-penetration ink is obtained by grinding three times using a three-roll mill.

[0014] Furthermore, the overprinting positioning system in step four includes a dual-sided CCD vision system and a servo correction device; the servo correction device includes a lateral correction linear motor, a printing plate cylinder servo motor, and a rotation compensation mechanism, with a response time ≤50ms.

[0015] Further, the preparation method of the composite adhesive in step seven is as follows: fluorinated acrylate copolymer, polyurethane resin, and epoxy resin are mixed to obtain component A; nano-zirconia, silane coupling agent, and defoamer are added to component A to obtain component B; aliphatic isocyanate curing agent is added before use to obtain component C; the fluorinated acrylate copolymer is prepared by solution polymerization of hexafluorobutyl acrylate, methyl methacrylate, and acrylic acid at 75-85°C for 3-6 hours, with a number average molecular weight of 25,000-35,000.

[0016] The beneficial effects of this invention are: I. This invention employs a dynamic optical positioning and overprinting system, which monitors overprinting deviation in real time through a dual-sided CCD vision system. The servo correction device has a response time of ≤50ms, achieving a horizontal overprinting error of ≤0.12mm, a vertical overprinting error of ≤0.15mm, and a rotation angle error of ≤0.2°. This represents an improvement of over 50% compared to the 0.3-0.5mm overprinting error of existing technologies. Combined with a dual-layer gradient ink system, the high-penetration ink on the front penetrates to a depth of 25-35μm, while the controlled-penetration ink on the back penetrates to a depth of 8-15μm, forming a controllable penetration gradient. When observed under light, the outline of the negative image precisely matches the main body of the positive image, resulting in rich pattern layers, high contrast, and extremely high anti-counterfeiting recognition. The replication difficulty is 8-10 times that of ordinary printing, and the production qualification rate is increased from 65% of existing technologies to 98%.

[0017] II. This invention utilizes a directional light-transmitting fiber network structure paper base, employing a three-layer papermaking process with a pore-forming agent added to the middle layer. After dissolution treatment with an alkaline buffer, directional microporous channels with a pore size of 5-15 μm and a porosity of 18-25% are formed, resulting in a paper base light transmittance of 88-92%, an increase of 13-17% compared to the 75% transmittance of ordinary homogeneous paper. The composite layer uses a fluorinated acrylate copolymer system, employing refractive index matching technology to ensure that the refractive index difference between the composite layer (1.44-1.46) and the paper base fiber is ≤0.02, minimizing interfacial light scattering. The light transmittance decreases by ≤2% after lamination, far superior to the 8-12% decrease achieved with ordinary composite adhesives. The final product exhibits a light transmittance ≥88% and a haze ≤5%, resulting in a bright, clear pattern with discernible details when observed under light.

[0018] Third, this invention uses aluminum-free fiber substrate, and all raw materials are biodegradable, aligning with the trend of green packaging development. The dynamic overprinting system achieves a 98% production qualification rate and reduces the scrap rate by 33%, minimizing raw material waste. In the double-layer gradient ink system, the front ink drying time is ≤8 minutes, and the back ink drying time is ≤15 minutes, with a printing speed of 60-80 meters per minute. Compared to technologies such as holographic hot stamping that require equipment identification, production costs are reduced by 30-40%, and the anti-counterfeiting effect is visually identifiable, making it easy for consumers to identify. It is suitable for large-scale promotion and application in high-end tobacco, alcohol, and pharmaceutical industries. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic cross-sectional view of the paper-based directional light-transmitting fiber network structure of the present invention; Figure 2 This is a schematic diagram of the double-sided precision overprinting and anti-counterfeiting structure of the present invention; Figure 3 This is a schematic diagram of the preparation method of the present invention; Figure 4 This is a schematic diagram of the dynamic optical positioning and overprinting system of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0022] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0023] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.

[0024] See Figures 1 to 4 As shown I. Preparation of paper base with directional light-transmitting fiber network structure Raw material preparation The fiber length of bleached sulfate softwood pulp is controlled at 2.8-3.2 mm, with a length uniformity coefficient greater than 0.85. The fiber length of bleached sulfate hardwood pulp is controlled at 0.8-1.2 mm. Nanocellulose has a diameter of 20-50 nm and a length of 500-2000 nm, and is prepared by high-pressure homogenization. Kaolin has a particle size of 1-3 μm, a whiteness greater than 90 degrees, and an oil absorption value of 45-55 g / 100 g. Cationic starch has a degree of substitution of 0.03-0.06 and a viscosity of 15-25 mPa·s. Sodium carboxymethyl cellulose has a degree of substitution of 0.6-0.9 and a viscosity of 50-100 mPa·s.

[0025] Preparation of surface slurry Short fibers and long fibers are mixed at a mass ratio of 7:3. The short fibers are beaten in a beater at a beating concentration of 4% for 35-45 minutes to achieve a freeness of 35-40°SR. The long fibers are lightly beaten in a beater at a beating concentration of 4% for 15-20 minutes to achieve a freeness of 20-25°SR.

[0026] The short-fiber and long-fiber pulps were mixed, and 5 parts of nanocellulose were added. The nanocellulose was pre-dispersed in water with a solid content of 2%, and dispersed in a high-speed disperser at 3000 rpm for 10 minutes. The dispersed nanocellulose suspension was added to the mixed pulp and stirred for 30 minutes to ensure uniform dispersion.

[0027] Add 10 parts of kaolin, which has been pre-dispersed in water with a solid content of 30%. Stir in a mixing tank at 500 rpm for 15 minutes. Slowly add the kaolin slurry to the mixed slurry and continue stirring for 20 minutes.

[0028] Add 2 parts of cationic starch, which has been pre-dissolved in warm water at 70-80°C and has a solid content of 5%. Add the starch solution after the slurry temperature has dropped to 50°C and stir for 15 minutes.

[0029] Dilute the slurry to a final concentration of 0.8-1.0%, maintaining continuous stirring during the dilution process. Adjust the pH of the slurry to 7.0-7.5.

[0030] Preparation of intermediate layer slurry Long fibers and short fibers are mixed at a mass ratio of 6:4. The long fibers are beaten in a beater at a beating concentration of 4% for 25-30 minutes to achieve a freeness (SR) of 25-30°. The short fibers are beaten in a beater at a beating concentration of 4% for 30-40 minutes to achieve a freeness (SR) of 30-35°.

[0031] Mix the long-fiber and short-fiber slurries after beating and stir until homogeneous. Add 2-4 parts of sodium carboxymethyl cellulose as a pore-forming agent. Dissolve the sodium carboxymethyl cellulose in room temperature water beforehand, with a solid content of 3%, and stir in a mixing tank at 800 rpm for 20 minutes until completely dissolved. Slowly add the sodium carboxymethyl cellulose solution to the mixed slurry and stir for 40 minutes to ensure thorough dispersion and bonding with the fibers.

[0032] Add 1.5 parts of cationic starch, and dissolve and add it using the same method as for the surface slurry.

[0033] Dilute the slurry to a concentration of 0.7-0.9% for online application and adjust the pH of the slurry to 6.5-7.0.

[0034] Preparation of the base slurry The preparation method of the bottom layer slurry is exactly the same as that of the top layer slurry, and the raw material ratio, pulping process, order of addition of additives and dosage are all the same.

[0035] Three-layer front-end multi-layer papermaking process The papermaking process is carried out using a three-layer front-wire paper machine. The paper machine is equipped with three headboxes, which supply the top layer, middle layer, and bottom layer of pulp respectively.

[0036] The first headbox ejects the surface slurry, forming the first layer of fiber web on the forming mesh. At this point, the vacuum level of the web is controlled at -20 kPa, allowing the fibers to dehydrate rapidly and form a dense structure. The target basis weight of the surface layer is 15 g / m².

[0037] After the first layer of fiber web has undergone initial dewatering, the second headbox sprays out the middle layer of slurry to form the second layer of fiber web. At this point, the vacuum level in the web section is reduced to -15 kPa, maintaining a relatively loose structure in the middle layer of fiber web. The target basis weight of the middle layer is 25 g / m².

[0038] After the second layer of fiber web has undergone initial dewatering, the third headbox sprays out the bottom layer of slurry to form the third layer of fiber web. At this point, the vacuum level in the web section returns to -20 kPa, allowing the bottom layer fibers to dewater rapidly and form a dense structure. The target basis weight of the bottom layer is 15 g / m².

[0039] The three-layer fiber web continues to be dehydrated on the forming web, and is further dehydrated through a vacuum dehydration box, achieving a dryness of 18-22%.

[0040] Pore-forming agent dissolution treatment Before entering the press section, the wet paper sheet is sprayed with a pH buffer solution on both sides of the sheet via a spraying device. The buffer solution is prepared with sodium carbonate and sodium bicarbonate, with a pH value of 9.5-10.5 and a temperature of 65-75°C. The spraying rate is controlled at 15-25 g / m².

[0041] In an alkaline environment, sodium carboxymethyl cellulose in the middle layer partially dissolves and swells, detaching from the fiber network. The sprayed paper sheet remains on the wire section for 5-8 seconds to allow the sodium carboxymethyl cellulose to fully dissolve. The dissolved sodium carboxymethyl cellulose is drained with the white water, leaving directional microporous channels in the middle layer fiber network.

[0042] Pressing and drying The wet paper sheet, after being treated with a pore-forming agent, enters the press section. The first press pressure is 1.2-1.5 MPa, and the second press pressure is 1.5-2.0 MPa. After pressing, the paper sheet achieves a dryness of 40-45%.

[0043] The paper enters the drying section, where the drying cylinder temperatures are set in a gradient: 110°C for the first group, 115°C for the second, 120°C for the third, and 125°C for the fourth. The drying speed is controlled at 80-120 meters per minute. After drying, the paper's moisture content is reduced to 5-7%.

[0044] By controlling the pressing pressure, the paper density is kept between 0.65-0.72 g / cm³. Too low a density will result in insufficient strength, while too high a density will reduce light transmittance.

[0045] Calendering After drying, the paper sheets enter a soft calender for calendering. The linear pressure of the calendering rollers is 150-200 N / mm, the calendering temperature is 80-90°C, and the machine speed is 100-150 m / min. The calendering process achieves a paper surface smoothness of 120-150 seconds and a gloss of 50-65%.

[0046] Paper base quality testing The basis weight of the paper substrate should be 53-57 g / m². The thickness of the paper substrate should be 70-85 μm. The light transmittance of the paper substrate, measured at a wavelength of 550 nm, should reach 88-92%. The tensile strength of the paper substrate should be greater than 2.5 kN / m in the longitudinal direction and greater than 1.2 kN / m in the transverse direction. The surface smoothness of the paper substrate should be tested, with both sides smoothness within 120-150 seconds.

[0047] Pore ​​formation effect inspection: The structure of the middle layer fibers is observed using a scanning electron microscope. The micropore diameter should be in the range of 5-15 μm, and the porosity should be in the range of 18-25%. The micropores should be oriented and parallel to the thickness direction of the paper.

[0048] II. Preparation of a Two-Layer Gradient Ink System Preparation of high-penetration front-side ink Pigment pretreatment Phthalocyanine blue pigment was selected and its particle size was pulverized to 100-150 nm using an air jet mill. The pulverized pigment was then further ground in a ball mill with 0.5 parts of ammonium polyacrylate dispersant added, and the grinding time was 4 hours to reduce the pigment particle size to below 80 nm.

[0049] Binder preparation Add 28 parts of modified rosin resin to a reaction vessel and heat to 90°C until completely melted. The softening point of the modified rosin resin is 85-95°C, and the acid value is 150-170 mgKOH / g.

[0050] Add 40 parts of mineral oil to the molten resin. The kinematic viscosity of the mineral oil is 15-25 mm² / s, measured at 40°C. The flash point of the mineral oil should be above 200°C, and the aromatic content should be below 20%.

[0051] Add 10 parts of vegetable oil. Flaxseed oil should be used, with a linoleic acid content of 60-65% and an iodine value of 170-190.

[0052] While stirring, lower the temperature to 60°C and keep stirring for 30 minutes to ensure the resin and oil are fully mixed.

[0053] Pigment dispersion Add 15 parts of the pretreated pigment to the binder and disperse in a high-speed disperser at 2000 rpm for 20 minutes. Then, the mixture is first ground in a three-roll mill with an inter-roll pressure of 2-3 MPa, reducing the fineness to below 15 μm.

[0054] The ground material is then passed through a three-roll mill for a second grinding, with an inter-roll pressure of 3-4 MPa, reducing the fineness to below 10 μm.

[0055] The ground material was then subjected to a third fine grinding process using a three-roll mill, with an inter-roll pressure of 4-5 MPa, reducing the fineness to below 5 μm. Fineness was measured using a scraper fineness meter, and particle size was observed under a microscope.

[0056] Functional additives Cool the ground ink to 40°C. Add 4 parts of a penetration enhancer, fatty alcohol polyoxyethylene ether. The fatty alcohol polyoxyethylene ether has an HLB value of 12-14 and a cloud point of 65-75°C.

[0057] Add 3 parts of n-propanol as an auxiliary penetrant. n-Propanol can reduce the surface tension of the ink and promote its penetration into the paper.

[0058] Add 1 part of a cobalt-manganese-calcium composite drying agent. The drying agent contains 6% cobalt, 6% manganese, and 8% calcium, calculated as metals. The drying agent can accelerate the oxidative polymerization and drying of the ink.

[0059] Add the above-mentioned additives to the ink and stir in a mixing tank at 500 rpm for 15 minutes to ensure uniform dispersion of the additives.

[0060] Fine grinding and filtration The ink with added additives is then ground again using a three-roll mill with an inter-roll pressure of 3-4 MPa to ensure that the additives and ink are fully mixed, and the final fineness is controlled below 5 μm.

[0061] The ink is filtered through a 200-mesh stainless steel filter to remove impurities and undispersed particle agglomerates. The filtered ink is then stored in a sealed container, protected from light.

[0062] Ink performance testing To test the viscosity of the ink, use a rotational viscometer at 25°C. The viscosity should be within the range of 8-12 Pa·s.

[0063] To test the fineness of the ink, use a scraper fineness gauge; the fineness should be less than 5μm.

[0064] To test the ink penetration performance, the ink is applied to a prepared paper substrate, and the penetration depth is measured after 30 seconds. The penetration depth should be within the range of 25-35 μm. Penetration depth is measured by examining a cross-sectional section of the paper under a microscope to determine the depth to which the ink penetrates the paper.

[0065] To test the ink drying time, under infrared drying conditions at 120°C, the drying time should be less than 8 minutes. The drying time is determined by whether the ink surface is sticky to the touch or becomes tacky again.

[0066] Preparation of back-side controlled-stain ink Pigment pretreatment Carbon black pigment is selected, and the particle size is controlled to 100-150nm through airflow milling and classification technology. The specific surface area of ​​the carbon black is 80-100m² / g, and the DBP oil absorption value is 90-110ml / 100g.

[0067] Binder preparation Add 40 parts of modified rosin resin to a reaction vessel and heat to 110°C until it is completely melted. The softening point of the modified rosin resin is 105-115°C, and the acid value is 140-160 mgKOH / g.

[0068] 34 parts of mineral oil were added to the molten resin. The kinematic viscosity of the mineral oil was 40-60 mm² / s, measured at 40°C. The viscosity of the mineral oil was higher than that of the mineral oil used in the front-side ink, which is beneficial for forming a high-viscosity system.

[0069] While stirring, reduce the temperature to 80°C and keep stirring for 30 minutes.

[0070] Preparation of permeation barrier agent Preparation of microcrystalline wax emulsion: 20 parts of microcrystalline wax were heated to 95-105°C in a reaction vessel until completely melted. The melting point of microcrystalline wax is 80-90°C, and its penetration is 5-15. 2 parts of the emulsifier, dehydrated sorbitan fatty acid ester, were dissolved in 30 parts of hot water. The melted microcrystalline wax was slowly added to the emulsifier solution under high-speed stirring at 5000 rpm for 20 minutes to form an oil-in-water emulsion. The emulsion was homogenized twice under a pressure of 30-40 MPa using a high-pressure homogenizer to reduce the wax particle size to 200-500 nm. The emulsion was cooled to room temperature to obtain a microcrystalline wax emulsion with a solid content of 40%.

[0071] Hydrophobic modification of nano-silica: 3 parts of nano-silica were dispersed in 50 parts of anhydrous ethanol, and 0.3 parts of the silane coupling agent hexamethyldisilazane were added. The mixture was refluxed at 60°C for 3 hours. The resulting silica surface was grafted with trimethylsilyl groups, exhibiting hydrophobicity. The ethanol was removed by evaporation of the dispersion at 60°C to obtain hydrophobically modified nano-silica. The hydrophobically modified silica had a particle size of 15-25 nm and a specific surface area of ​​180-220 m² / g.

[0072] Pigment dispersing and penetration barrier agent addition Add 18 parts of carbon black pigment to the binder and disperse it in a high-speed disperser at 1800 rpm for 25 minutes. Then grind it three times using a three-roll mill, with the grinding process being the same as that for the front ink, and finally control the fineness to below 8 μm.

[0073] Cool the ink to 50°C, add 15 parts of microcrystalline wax emulsion (equivalent to 6 parts of solid microcrystalline wax), and add 3 parts of hydrophobically modified nano-silica, which is pre-dispersed in mineral oil to form a dispersion with a solid content of 20%.

[0074] Adding 1.5 parts of dehydrated sorbitan fatty acid ester as a surfactant with an HLB value of 4-6 helps stabilize the ink system.

[0075] Add 1.2 parts of cobalt-manganese-calcium composite drying agent. The amount of drying agent is higher than that of the front ink, which accelerates the surface drying of the ink.

[0076] Stir in the mixing tank at 600 rpm for 20 minutes to ensure that all components are evenly mixed.

[0077] Fine grinding and filtration The ink is then ground again using a three-roll mill to ensure uniform dispersion of the microcrystalline wax and nano-silica. Finally, it is filtered through a 200-mesh filter.

[0078] Ink performance testing The viscosity of the ink should be tested at 25°C. The viscosity should be in the range of 18-25 Pa·s, which is significantly higher than that of the front ink.

[0079] The fineness of the ink should be tested; it should be less than 8μm.

[0080] To test the ink penetration barrier properties, the ink is applied to the paper substrate, and the penetration depth is measured after 30 seconds. The penetration depth should be in the range of 8-15μm, which is significantly smaller than that of the ink on the front side.

[0081] The surface hydrophobicity of the ink after drying is tested by measuring the contact angle. The contact angle should be greater than 95 degrees, indicating that the microcrystalline wax and hydrophobic silica have successfully migrated to the surface.

[0082] III. Construction of a Dynamic Optical Positioning and Overlay System Design and preparation of special overprinting color marks Front color code design The color mark on the front is a solid cross shape, located 3mm from the outer corner of each of the four printing areas. The cross shape consists of a vertical line and a horizontal line, each line being 0.3mm wide and 5mm long. The intersection of the cross lines is located at the center of the color mark.

[0083] The color mark ink uses a specially formulated high-contrast black ink with the following formula: 25 parts carbon black, 50 parts fast-drying alcohol-soluble resin, 20 parts ethanol, 5 parts propanol, and 2 parts drying agent. This ink has a gloss density greater than 1.8 and a drying time of less than 3 minutes.

[0084] Back color mark design The color mark on the back is a hollow cross-shaped frame structure, corresponding to the color mark on the front. The hollow frame consists of four line segments, each 0.2mm wide, with a square inner area of ​​2mm on each side. The outer dimensions of the hollow frame coincide with the outer contour of the solid cross on the front.

[0085] The back color mark ink uses the same formula as the front color mark ink to ensure consistent optical contrast.

[0086] Color mark printing process The color bars on the front are printed using gravure printing. Specially made color bar printing plates are used, with a cell depth of 25-30μm and a cell density of 180 lines per inch. The printing pressure is 0.3MPa, and the printing speed is 40 meters per minute.

[0087] Immediately after printing, the ink is cured using a UV curing device. The UV lamp power is 120W / cm, and the curing speed is 30 meters / minute. UV curing instantly solidifies the color mark ink, ensuring dimensional stability and preventing shrinkage or deformation. The cured color mark has a thickness of 3-4μm and a dimensional accuracy of ±0.02mm.

[0088] The back color mark is printed simultaneously in the back printing process, and the printing process parameters are the same as those for the front color mark.

[0089] Configuration of dual-side CCD camera system Hardware configuration The CCD camera is a 5-megapixel industrial camera with a resolution of 2448×2048 pixels and a pixel size of 3.45μm×3.45μm. The lens is a telecentric lens with a focal length of 50mm, an aperture of F4, and distortion of less than 0.1%.

[0090] The field of view is set to 50mm × 40mm, which completely covers the color mark area. The camera's spatial resolution is 20μm / pixel, enabling precise identification of color mark lines as small as 0.3mm.

[0091] The LED ring light source uses 470nm blue LEDs with a power of 30W. Blue light effectively reduces interference from fluorescent whitening agents in paper, improving the accuracy of color identification. The light source employs diffused illumination to ensure uniform lighting and avoid glare.

[0092] The camera is mounted at the inspection station between printing press units and secured by a precision-adjustable bracket. The camera's optical axis is perpendicular to the paper surface to ensure distortion-free imaging.

[0093] Scan frequency and trigger control The CCD camera's scanning frequency is set to 200 scans per minute, synchronized with the printing press speed. When the paper passes through the inspection station, the leading edge of the paper is detected by a photoelectric sensor, triggering the camera to take a picture.

[0094] The trigger signal is issued by the PLC control system. The trigger delay time is automatically calculated based on the paper speed and camera position to ensure that the color mark is in the center of the camera's field of view during shooting.

[0095] Each sheet of paper was photographed four times, with the color marks at each of the four corners scanned. The captured images were transmitted to an image processing workstation via gigabit Ethernet.

[0096] Image processing algorithms After image acquisition, preprocessing is performed first. The color image is converted to a grayscale image, and then Gaussian filtering is applied for noise reduction with a filter kernel size of 5×5 pixels.

[0097] Color marker contours were extracted using an adaptive thresholding method. The Otsu algorithm was employed for threshold calculation to automatically determine the optimal segmentation threshold. The resulting binary image showed white color markers against a black background.

[0098] Morphological processing of binary images is performed, including erosion and dilation operations, noise removal, and connection of broken lines.

[0099] Extract the geometric center of the color mark. For a solid cross on the front, determine the center point coordinates by calculating the centroid of the outline. For a hollow frame color mark on the back, determine the center point coordinates by calculating the intersection of the four line segments.

[0100] The pixel coordinates of the color mark center point are calculated and then converted into actual physical coordinates based on the camera calibration parameters. The camera calibration uses a checkerboard calibration board with a calibration accuracy of ±0.01mm.

[0101] Configuration of servo correction device Lateral correction system Lateral alignment is achieved using a linear motor-driven alignment roller. The linear motor has a stroke of ±10mm, a resolution of 0.01mm, and a response time of 30ms. The alignment roller is an active roller, coated with polyurethane material with a hardness of Shore A80, and has a diameter of 100mm.

[0102] Lateral correction control algorithm: When a lateral deviation ΔX greater than 0.1mm is detected, lateral correction is initiated. The correction amount is equal to the negative of the deviation ΔX. The correction speed is adaptively adjusted according to the deviation magnitude; the correction speed is faster when the deviation is large and slower when the deviation is small to avoid overshoot.

[0103] The correction accuracy is ±0.05mm. After correction, it is verified again by a CCD camera to ensure that the correction is in place.

[0104] Vertical overprinting adjustment system Vertical registration adjustment is achieved by controlling the phase of the back plate cylinder. The plate cylinder is driven by a servo motor with a resolution of 262,144 pulses / revolution, corresponding to a circumferential resolution of 0.003 mm for the plate cylinder.

[0105] Vertical registration control algorithm: When a vertical deviation ΔY is detected to be greater than 0.15mm, vertical registration adjustment is initiated. The adjustment method is to change the phase angle of the printing cylinder. The phase adjustment amount θ = ΔY / R, where R is the radius of the printing cylinder.

[0106] The servo motor maintains synchronization with the main drive through an electronic cam following function, and adjusts the phase in real time during operation with an adjustment accuracy of ±0.08mm.

[0107] Rotational compensation system When the paper has a rotation angle deviation, it is corrected by a rotation compensation mechanism. The rotation compensation mechanism is located in front of the printing unit and consists of a pair of rotatable pinch rollers.

[0108] Calculation of rotation angle deviation Δθ: The actual rotation angle of the paper is calculated by using the color mark coordinates of the four corners, and the deviation Δθ is obtained by comparing it with the theoretical value.

[0109] When |Δθ| is greater than 0.3°, rotational compensation is activated. The compensation method is to rotate the pinch roller assembly, with the rotation angle equal to the negative of the deviation angle Δθ. The accuracy of rotational compensation is ±0.1°.

[0110] Real-time overprint control process Step 1: After the front side of the paper is printed, it enters the flipping and conveying unit. The flipping unit uses a flipping roller structure to flip the paper 180 degrees. During the flipping process, vacuum adsorption is used to keep the paper flat.

[0111] Step Two: The paper passes through the first CCD inspection station, where CCD-1 scans the color marks at the four corners of the front. The image processing workstation calculates the center coordinates of the four color marks, establishing a front reference coordinate system. The origin of the reference coordinate system is the geometric center of the four color mark centers, the X-axis is the horizontal axis of the paper, and the Y-axis is the vertical axis of the paper.

[0112] Step 3: The paper continues to be fed into the back-side printing unit. Before printing, the paper passes through the second CCD detection station, where CCD-2 scans the paper's current position. The paper's current coordinates are determined by identifying the paper's edge or pre-printed positioning marks.

[0113] Step 4: The control system calculates the deviation between the current paper position and the ideal printing position. The lateral deviation ΔX = X2 - X1, the longitudinal deviation ΔY = Y2 - Y1, and the rotation angle deviation Δθ is calculated based on the positional differences of the four corners.

[0114] Step 5: Perform compensation control based on the deviation. If |ΔX|>0.1mm, activate the lateral correction system with a correction amount of -ΔX. If |ΔY|>0.15mm, activate the longitudinal registration adjustment system to adjust the printing cylinder phase. If |Δθ|>0.3°, activate the rotation compensation system with a compensation angle of -Δθ.

[0115] Step Six: After the compensation operation is completed, the CCD-2 scans again to verify the compensation effect. If the deviation still exceeds the allowable range, a second compensation is performed. If the deviation is within the allowable range, the paper is allowed to enter the printing area.

[0116] Step 7: The paper enters the back printing area, and the printing cylinder prints the back pattern onto the back of the paper. Maintain stable registration parameters during the printing process.

[0117] Step 8: After printing, the paper passes through the third CCD inspection station. The CCD-3 simultaneously scans the front and back color marks. By using transmitted light illumination, the front and back color marks are simultaneously seen in the same image, allowing for the measurement of actual registration accuracy.

[0118] Step Nine: The control system records the registration accuracy data for each sheet of paper, including lateral registration error, vertical registration error, and rotation angle error. This data is stored in a database for statistical analysis and process optimization.

[0119] Step 10: If misregistration occurs repeatedly, the system will automatically alarm and stop the machine. The operator should check the paper tension, printing plate wear, and servo system status, and resume production after troubleshooting.

[0120] Measures to ensure printing accuracy Paper tension control: Throughout the printing process, the paper tension remains constant, controlled between 150-200N. Tension sensors monitor tension changes in real time, and the tension control roller automatically adjusts accordingly. Tension fluctuations are controlled within ±5N.

[0121] Temperature and humidity control: The temperature in the printing workshop is controlled at 23±2°C, and the relative humidity is controlled at 50±5%. The paper is equilibrated in the workshop environment for 48 hours before printing to stabilize the paper moisture content at 5-7%.

[0122] Plate precision assurance: The printing plates are made using computer-to-plate (CTP) technology, with a precision of ±0.01mm. Precision testing is performed on the printing plates before mounting to ensure accurate image positioning. The plate cylinder uses high-precision bearings with radial runout less than 0.02mm.

[0123] System calibration: System calibration is performed before each shift's startup. A standard test pattern is printed, and the actual printing position is detected using the CCD system, compared with the theoretical position, and the system error is calculated. The system error is input into the control system as a compensation benchmark.

[0124] IV. Preparation of High Transmittance Composite Layer Synthesis of fluorinated acrylate copolymers Monomer ratio 30 parts hexafluorobutyl acrylate, 50 parts methyl methacrylate, and 20 parts acrylic acid, by weight.

[0125] Hexafluorobutyl acrylate has a refractive index of 1.37; introducing fluorinated segments can lower the refractive index of the copolymer. Methyl methacrylate has a refractive index of 1.49 and serves as the host monomer to provide film-forming properties. Acrylic acid provides carboxyl functional groups for subsequent crosslinking reactions.

[0126] Initiators and solvents Azobisisobutyronitrile (AIB) is used as an initiator at a rate of 0.8 parts of the total monomer content. Ethyl acetate is used as a solvent at a rate of 100 parts of the total monomer content.

[0127] Synthesis process Add ethyl acetate to a four-necked flask, purge with nitrogen for 30 minutes to remove oxygen. Heat to 75°C under nitrogen protection.

[0128] Hexafluorobutyl acrylate, methyl methacrylate, acrylic acid and azobisisobutyronitrile were mixed to prepare a monomer mixture.

[0129] The monomer mixture was slowly added dropwise to the reaction flask using a constant-pressure dropping funnel over a period of 3 hours. The reaction temperature was maintained at 75-80°C during the addition process.

[0130] After the addition is complete, continue the reaction at 75°C for 2 hours. Then raise the temperature to 85°C and react for 1 hour to ensure complete monomer conversion.

[0131] After the reaction is complete, the solution is cooled to room temperature to obtain a fluorinated acrylate copolymer solution with a solid content of 45-50%.

[0132] copolymer properties The molecular weight of the copolymer was determined by gel permeation chromatography. The number average molecular weight was 25,000-35,000, the weight average molecular weight was 60,000-80,000, and the dispersity was 2.0-2.5.

[0133] The refractive index of the copolymer was determined by Abbe refractometer at 25°C and 589 nm, and the refractive index was 1.42.

[0134] The glass transition temperature (Tg) was determined by differential scanning calorimetry, and the Tg was 15-25°C. The copolymer was in a viscous flow state at room temperature.

[0135] Formulation of composite adhesive Group A allocation system Add 100 parts of the fluorinated acrylate copolymer solution, which is equivalent to 45 parts of solids, to the mixing tank.

[0136] Add 70 parts of polyurethane resin solution, which is equivalent to 30 parts of solid content. The polyurethane resin has a hydroxyl value of 100-120 mgKOH / g, a molecular weight of 30,000-50,000, and a Shore A hardness of 80.

[0137] Add 10 parts of epoxy resin. The epoxy resin is E-51 type bisphenol A epoxy resin with an epoxy value of 0.48-0.54.

[0138] Stir in a mixing tank at 300 rpm for 60 minutes to ensure thorough mixing of all components.

[0139] Group B allocation system A nano-zirconia dispersion was prepared. Four parts of nano-zirconia powder were added to 20 parts of ethyl acetate, and one part of polyacrylic acid was added as a dispersant. The mixture was ground in a sand mill for 2 hours to stabilize the zirconia particle size at 10-20 nm, resulting in a dispersion with a solid content of 20%.

[0140] Add 20 parts of nano-zirconia dispersion to component A, which is equivalent to 4 parts of solid zirconia. The refractive index of nano-zirconia is 2.2, and the refractive index of the composite adhesive can be finely adjusted by adjusting its content.

[0141] Add 1.5 parts of silane coupling agent KH-560. Silane coupling agents can enhance the adhesion between the composite adhesive and the paper.

[0142] Add 0.4 parts of defoamer. The defoamer is a polyether-modified siloxane, which can eliminate bubbles generated during the mixing and coating processes.

[0143] Mix in a mixing bowl at 400 rpm for 30 minutes.

[0144] Solid content adjustment The solid content of the composite adhesive was adjusted to 35-40% using ethyl acetate. The solid content was determined by drying samples in an oven at 105°C for 2 hours.

[0145] Refractive index adjustment A composite adhesive sample was coated onto a glass plate and dried at 80°C for 30 minutes to form a composite adhesive film. The refractive index of the film was measured using an Abbe refractometer.

[0146] The refractive index of the composite adhesive can be adjusted to 1.44-1.46 by adjusting the ratio of fluorinated acrylate and nano-zirconia. If the refractive index is too high, increase the amount of fluorinated acrylate. If the refractive index is too low, increase the amount of nano-zirconia.

[0147] The refractive index of paper-based cellulose fiber is 1.46-1.48. The difference Δn between the refractive index of the composite adhesive and the refractive index of the fiber is controlled within 0.02, which can minimize the scattering and reflection of light at the interface.

[0148] Group C allocation system The aliphatic isocyanate curing agent uses HDI trimer with an NCO content of 21-23%. The amount of curing agent used is calculated based on the hydroxyl content in components A and B.

[0149] The hydroxyl groups mainly come from polyurethane resin and acrylic acid, with the total amount of hydroxyl groups being 2.5-3.0% of the mass of components A+B. The molar ratio of isocyanate to hydroxyl groups is set at 1.1:1, slightly in excess to ensure complete curing.

[0150] The curing agent dosage is 10 parts. Add the curing agent 30 minutes before use, stir thoroughly for 10 minutes after adding, and then use immediately. The pot life of the composite adhesive is 4-6 hours.

[0151] Composite adhesive performance testing Viscosity measurement: The viscosity should be measured at 25°C using a rotational viscometer and should be within the range of 50-80 mPa·s.

[0152] Solid content determination: should be within the range of 35-40%.

[0153] Refractive index determination: The refractive index of the thin film should be in the range of 1.44-1.46.

[0154] Curing performance test: The composite adhesive is applied to a glass plate and cured in a 50°C oven. Samples are taken every 4 hours to test the surface dryness and hard dryness. The surface dryness time should be less than 12 hours, and the hard dryness time should be less than 24 hours.

[0155] Composite layer coating process Preparation before coating The printed paper undergoes a dust removal process. An electrostatic dust removal device removes dust and paper scraps from the paper surface. After dust removal, a dust removal roller further removes any remaining particles.

[0156] The paper surface is subjected to corona treatment. The corona treatment power is 0.3-0.5 W / cm², and the treatment speed is 40 m / min. Corona treatment can increase the surface energy of the paper and enhance the wetting and adhesion of the composite adhesive. The surface tension of the paper after treatment should reach 38-42 mN / m.

[0157] Microgravure roller coating The coating method is microgravure roller coating. The microgravure roller has a screen count of 200 lines per inch, a cell depth of 20-25 μm, and a cell volume of 3.5-4.5 cm³ / m².

[0158] The coating roller speed is matched with the paper speed at a ratio of 1.05:1, meaning the coating roller linear speed is slightly higher than the paper speed by 5%. This ratio ensures that the composite adhesive is fully transferred to the paper surface, resulting in uniform coating.

[0159] The doctor blade is made of steel, with a doctor blade angle of 30 degrees and a doctor blade pressure of 0.15-0.25 MPa. The doctor blade removes excess composite adhesive from the surface of the microgravure roller, leaving only the composite adhesive in the cells.

[0160] The coating amount should be controlled at 3-5 g / m². The coating amount is controlled by adjusting the cell depth and coating speed. Too low a coating amount will result in insufficient composite strength, while too high a coating amount will reduce light transmittance.

[0161] Three-stage drying process First stage of pre-baking: temperature 60°C, time 5 seconds. Pre-baking allows the solvent to begin to evaporate, and the composite adhesive gradually thickens, but still maintains its fluidity, allowing for leveling.

[0162] Second stage of intermediate drying: temperature 80°C, time 10 seconds. Intermediate drying accelerates solvent evaporation, increases the composite solid content to 70-80%, and basically loses its fluidity.

[0163] The third stage, setting and drying, is conducted at 100°C for 15 seconds. This process ensures complete evaporation of residual solvents, achieving a solid content of over 98%. The curing reaction of the composite adhesive then begins.

[0164] The drying chamber uses hot air circulation with an air velocity of 5-8 m / s to ensure uniform drying. The drying chamber is equipped with a solvent recovery device; volatile ethyl acetate is recovered through condensation.

[0165] Hot pressing composite process If lamination with aluminum foil or other materials is required, hot pressing lamination should be performed after coating and drying.

[0166] The composite substrate is preheated to 65-70°C before lamination. Preheating removes moisture from the substrate and improves the lamination quality.

[0167] The temperature of the composite roller is 75-85°C, the composite pressure is 0.3-0.5MPa, and the composite speed is 30 meters / minute.

[0168] Hot pressing lamination causes the isocyanate in the composite adhesive to react with the hydroxyl groups on the paper surface and the hydroxyl groups on the composite substrate surface, forming chemical bonds.

[0169] Curing and ripening The composite product is wound up and sent to the curing chamber. The curing temperature is 50°C and the curing time is 24 hours.

[0170] During the curing process, the reaction between isocyanate and hydroxyl groups proceeds further, the crosslinking density increases, and the composite strength gradually improves.

[0171] After curing, the composite adhesive is fully cured, forming a stable composite layer.

[0172] Composite layer performance testing Composite strength determination: The peel strength test method is adopted, with a peel angle of 180 degrees and a peel speed of 300 mm / min. The peel strength should be greater than 2.0 N / 15 mm.

[0173] Transmittance measurement: Transmittance was measured using a spectrophotometer at a wavelength of 550 nm. The transmittance of the laminated paper should be greater than 88%. The decrease in transmittance should not exceed 2% of the original transmittance.

[0174] Haze Measurement: Use a haze meter for measurement. The haze should be less than 5%. Excessive haze indicates scattering in the composite layer, affecting the clarity of the yin-yang pattern.

[0175] Visual inspection: The surface of the composite layer should be visually inspected for bubbles, streaks, and color differences. When inspected using a light transmission stage, the composite layer should be uniformly transparent, without any cloudy areas.

[0176] V. Complete Preparation Method Flow Step 1: Preparation of translucent base paper The oriented light-transmitting fiber network structure paper base is prepared according to the method in Section 1 of the specific implementation method. The prepared base paper is cut into the required printing specifications, with a width of 787mm or 889mm and a length determined according to the circumference of the printing press cylinder.

[0177] The cut base paper was equilibrated in a temperature and humidity controlled chamber for 48 hours at a temperature of 23±2°C and a relative humidity of 50±5%. After equilibration, the moisture content of the base paper stabilized at 5-7%, and the dimensions were stable, making it suitable for printing.

[0178] Conduct quality inspections on the base paper. Randomly check the basis weight; the deviation should be within ±2 g / m². Randomly check the light transmittance; the transmittance should be within the range of 88-92%. Inspect the paper surface; there should be no paper defects, dust, or spots.

[0179] Step Two: Design of the Anti-counterfeiting Pattern The negative portion of the anti-counterfeiting design is printed on the front of the paper. The negative portion includes the outline, background, and auxiliary patterns of the anti-counterfeiting design. The line width of the negative portion is 0.15-0.3mm, and the line spacing is 0.3-0.5mm.

[0180] Allow for overprinting margin when designing negative images. Considering the overprinting accuracy of ±0.15mm, a gap of 0.2-0.3mm should be left between the negative and positive lines to avoid overlap due to overprinting deviation.

[0181] After the negative design is completed, the printing plate is made. Laser engraving is used to create the gravure plate with an engraving precision of ±0.01mm. The gravure cell depth is 35-45μm, the cell shape is inverted cone, and the cell density is 180 lines / inch.

[0182] Step 3: Front-side high-penetration ink printing Add the prepared high-penetration front-side ink to the ink tank of the printing press. Before printing, test the ink's properties; the viscosity should be 8-12 Pa·s, and the fineness should be less than 5 μm. If the viscosity is too high, add an appropriate amount of mineral oil to dilute it. If the viscosity is too low, add an appropriate amount of resin to thicken it.

[0183] Install the printing plate onto the printing plate cylinder. The printing plate is positioned using a pin positioning method with a positioning accuracy of ±0.02mm. After installation, check the printing plate tension; the tension should be uniform, without slack or excessive tightness.

[0184] Adjust the printing pressure. The doctor blade pressure should be 0.4-0.6 MPa, and the doctor blade angle should be 55-65 degrees. The impression roller pressure should be 0.4-0.6 MPa, and the impression line width should be 3-5 mm.

[0185] Set the printing speed to 60-80 meters per minute. After starting the printing press, first perform paper calibration, adjust the paper tension to 150-200N, and adjust the paper position to center the paper.

[0186] Printing begins. During the printing process, printing pressure, ink viscosity, and registration are monitored in real time. A random inspection is conducted every 100 meters printed to check printing quality, including pattern clarity, color density, and registration accuracy.

[0187] The printed negative pattern includes the outline of the main pattern and the background texture. The main pattern can be traditional Chinese elements such as dragons, phoenixes, auspicious clouds, and landscapes. The background texture uses fine lines, with a line width of 0.15mm and a line spacing of 0.3mm, forming a grid or wavy texture.

[0188] Immediately after printing, the ink enters the drying unit. The drying unit employs a combination of infrared drying and hot air drying. The infrared lamp has a power of 8kW / m and an infrared wavelength of 2-4μm, primarily heating the ink layer. The hot air temperature is 120-130°C, and the air velocity is 6 m / s, removing solvents and moisture from the ink.

[0189] The drying time is 8-12 seconds. The dried ink surface should not be sticky to the touch and should not become tacky again. Solvent residue testing should show residual solvent levels of less than 5 mg / m².

[0190] Step 4: Printing the front color swatches While printing the negative image, a front color mark is printed 3mm from the outer corner of each of the four corners of the paper. The color mark ink is a specially formulated high-contrast black ink with a glossy density greater than 1.8.

[0191] After printing, the color mark is cured using a UV curing device. The UV lamp has a power of 120W / cm, a wavelength of 365nm, a curing speed of 30m / min, and a curing time of 2-3 seconds. UV curing instantly cures the color mark ink, resulting in a surface hardness greater than 3H, good wear resistance, and dimensional stability.

[0192] Step 5: Front Printing Quality Inspection One sheet is randomly selected from every 100 meters printed for front-side printing quality inspection.

[0193] Pattern clarity check: Use a 10x magnifying glass to observe the printed pattern. The edges of the lines should be clear, without burrs or broken lines.

[0194] Color density testing: Use a densitometer to measure the color density of the printed pattern. The color density should be within the range of 1.2-1.5, and the color density deviation should be less than 0.05.

[0195] Ink penetration depth test: Tear the paper open, observe the cross-section, and measure the ink penetration depth. The penetration depth should be within the range of 25-35μm, and the penetration should be uniform, without insufficient or excessive penetration.

[0196] Color mark size accuracy inspection: Use a tool microscope to measure the color mark size. The line width should be 0.3±0.02mm, the line length should be 5±0.03mm, and the perpendicularity of the crosshairs should be less than 0.5 degrees.

[0197] If the test fails, adjust the printing parameters, including ink viscosity, printing pressure, and drying temperature, until the quality requirements are met.

[0198] Step Six: Paper Flipping and Conveying The printed paper enters the flipping conveyor unit. The flipping unit uses a flipping roller with a diameter of 200mm, a rubber-coated surface, and a Shore A60 hardness.

[0199] As the paper passes through the flipping roller, the roller rotates 180 degrees, flipping the paper over. During the flipping process, the paper is held in place by vacuum suction holes to prevent it from drifting or wrinkling. The vacuum level is -8 kPa.

[0200] The flipped paper enters the conveyor belt for transport. The conveyor belt is made of anti-static material with a surface resistance of 10^6-10^9 ohms to prevent the paper from attracting dust due to static electricity.

[0201] During the conveying process, the paper tension is maintained at 150-200N, which is monitored in real time by a tension sensor and automatically adjusted by a tension control roller. Tension fluctuations are controlled within ±5N.

[0202] The conveying speed is synchronized with the printing speed, at 60-80 meters per minute. During the conveying process, guide rollers maintain the stability of the paper's running direction, and the lateral deviation of the paper is controlled within ±1mm.

[0203] Step 7: Registration and positioning before back printing After the paper is flipped over, it first passes through the first CCD inspection station. The CCD-1 scans the color marks at the four corners of the front side to establish a reference coordinate system for the front side.

[0204] The CCD-1 captures images of the color stops on the front side, and the images are transmitted to an image processing workstation. The workstation processes the images, extracts the outlines of the color stops, and calculates the coordinates of the center of each color stop. The center coordinates of the four color stops are points A, B, C, and D.

[0205] Calculate the geometric center O of the four points, and use it as the origin of the coordinate system. Calculate vectors AB and DC, and take their average value as the X-axis direction. The Y-axis is perpendicular to the X-axis. Establish a frontal reference coordinate system XOY.

[0206] The paper continues to be fed to the second CCD inspection station before the back printing unit. The CCD-2 scans the current position of the paper and determines the center position of the paper by identifying the paper's edges.

[0207] Calculate the deviation between the current center position O' of the paper and the ideal printing position O. The lateral deviation ΔX = Xo' - Xo, and the longitudinal deviation ΔY = Yo' - Yo.

[0208] The rotation angle deviation is calculated by considering the positional differences at the four corners. Ideally, the front reference coordinate system and the back printed coordinate system should coincide. If a rotational deviation exists, the positions of the four corners will deviate from the ideal positions. The rotation angle deviation Δθ is calculated using the least squares method.

[0209] Step 8: Automatic Compensation for Registration Deviation The control system automatically compensates for the detected deviation.

[0210] Lateral Deviation Compensation: If the lateral deviation |ΔX| is greater than 0.1mm, the lateral correction system is activated. The lateral correction motor drives the correction roller to move by -ΔX. The movement time is 50ms. During the movement, the paper continues to move. The correction system uses feedforward control to calculate the correction amount in advance.

[0211] Longitudinal Deviation Compensation: If the longitudinal deviation |ΔY| is greater than 0.15mm, the longitudinal registration adjustment system is activated. The plate cylinder servo motor is controlled to adjust the plate cylinder phase. The phase adjustment amount Δφ = ΔY / (π×D), where D is the plate cylinder diameter. The servo motor follows the main drive via an electronic cam, adjusting the phase in real time during operation.

[0212] Rotational Deviation Compensation: If the rotational deviation |Δθ| is greater than 0.3 degrees, the rotational compensation system is activated. The rotational compensation mechanism rotates by an angle of -Δθ and takes 80ms. Located in front of the printing unit, the rotational compensation mechanism holds and rotates the paper using a pair of rotatable gripper rollers.

[0213] After compensation, the CCD-2 scanner scans again to verify the compensation effect. If the deviation still exceeds the allowable range (lateral deviation greater than 0.15mm, longitudinal deviation greater than 0.20mm, or rotational deviation greater than 0.4 degrees), a second compensation is performed. If the paper still fails to meet the requirements after two compensations, it is marked as waste and will not be printed.

[0214] If the deviations are within the allowable range, with a lateral deviation of less than 0.15 mm, a longitudinal deviation of less than 0.20 mm, and a rotational deviation of less than 0.4 degrees, the paper is allowed to enter the printing area and back-side printing is performed.

[0215] Step Nine: Design of Positive Anti-counterfeiting Pattern The positive image portion of the security design is printed on the back of the paper. The positive image is the main design element of the security design, including the main graphic, text, and decorative elements.

[0216] The positive and negative images complement each other. When the front and back are superimposed and viewed under transmitted light, the outline of the negative image and the main graphic of the positive image are precisely matched to form a complete anti-counterfeiting pattern.

[0217] When designing the positive image, the position and shape of the negative image should be fully considered. A gap of 0.2-0.3mm should be reserved between the positive and negative images to ensure the integrity of the pattern after assembly and to avoid overlap of patterns due to registration errors.

[0218] Positive plate making uses the same process as negative plate making, with laser engraving of the intaglio plate, engraving accuracy of ±0.01mm, and cell depth of 35-45μm.

[0219] Step 10: Backside ink control printing Add the prepared back-side controlled-spread ink to the ink tank of the printing press. Check the ink viscosity; it should be within the range of 18-25 Pa·s. Check the ink fineness; it should be less than 8 μm.

[0220] The printing plate is installed onto the printing plate cylinder, and the positioning method is the same as that for the front printing plate.

[0221] Adjust the printing pressure. Due to the higher viscosity of the ink on the back side, reduce the doctor blade pressure appropriately to 0.3-0.5 MPa. The impression roller pressure should be 0.3-0.5 MPa, lower than the front printing pressure, to prevent excessive pressure from causing bleed-through.

[0222] Set the printing speed to 50-70 meters per minute, lower than the front-side printing speed. Lowering the speed improves registration accuracy and facilitates the transfer of high-viscosity inks.

[0223] Printing begins. During the printing process, the dynamic registration system works continuously, monitoring the position of each sheet of paper in real time and adjusting the registration parameters accordingly.

[0224] The printed positive design includes the main image and decorative elements. The main image can be the body of a dragon, the feathers of a phoenix, or the shape of auspicious clouds. Decorative elements include text, borders, and embellishments.

[0225] After printing, the ink enters the drying unit. The drying temperature is 100-110°C, lower than the front drying temperature, to avoid ink backflow caused by high temperature. The drying time is 10-15 seconds to ensure that the ink on the back is fully dried and a microcrystalline wax barrier layer is formed on the surface.

[0226] Step 11: Printing the color bar on the back While printing the positive image, back color marks are printed on the back of the four corners of the paper. The positions of the color marks correspond to the front color marks and are precisely controlled by an overprinting positioning system.

[0227] The color mark on the back is a hollow cross-shaped frame with a line width of 0.2mm and an inner space of 2mm × 2mm. The color mark ink is the same as that on the front, with a light density greater than 1.8.

[0228] After printing, the color marks are cured by UV, and the curing process is the same as that for the front color marks.

[0229] Step 12: Real-time detection of printing accuracy After the back printing is completed, the paper passes through the third CCD inspection station. The CCD-3 uses a light-transmitting illumination method, with the light source located below the paper and the camera located above it.

[0230] Under transmitted light, both the front and back color marks are displayed in the image. The front color mark is a solid cross, and the back color mark is a hollow frame. Ideally, the solid cross should be precisely centered in the hollow frame.

[0231] The image processing workstation measures the relative positions of the centers of the front and back color marks and calculates the actual registration accuracy. The lateral registration error is ΔXreal, the longitudinal registration error is ΔYreal, and the rotation angle error is Δθreal.

[0232] Acceptance criteria: Lateral overprinting error |ΔXreal|≤0.12mm, longitudinal overprinting error |ΔYreal|≤0.15mm, rotation angle error |Δθreal|≤0.2 degrees.

[0233] If the registration accuracy is acceptable, the paper is marked as a qualified product. If the registration accuracy is out of tolerance, the paper is marked as a defective product and will be rejected in the subsequent slitting process.

[0234] The system records the registration accuracy data for each sheet of paper and stores it in the database. It performs hourly statistics to calculate the average registration accuracy and the registration accuracy pass rate.

[0235] Step Thirteen: Verification of Anti-counterfeiting Effect Randomly inspect the printed paper to verify its anti-counterfeiting effect.

[0236] Observe the paper against the light source, which can be natural light or an LED light source. The observation angle should be along the normal direction of the paper, and the observation distance should be 30-50cm.

[0237] When viewed against the light, the outline of the negative image on the front and the main body of the positive image on the back precisely match to form a complete anti-counterfeiting pattern. The lines of the negative image are dark, while the main body of the positive image is light, creating a sharp contrast and making the pattern clearly discernible.

[0238] Check the alignment accuracy. The alignment accuracy between the negative image lines and the positive image edges should be within 0.2mm. If the registration accuracy is out of tolerance, misalignment will occur, with the negative image lines deviating from the positive image edges, thus reducing the anti-counterfeiting effect.

[0239] Examine the pattern's layers. Due to the high penetration of the ink on the front and the controlled penetration of the ink on the back, a penetration gradient is formed, resulting in a rich sense of layering in the pattern. The central area is where the inks from both sides overlap, appearing darker. Individual penetration areas on the front exhibit a medium tone. Individual areas on the back appear lighter. This multi-layered tone variation enhances the anti-counterfeiting identification.

[0240] Step Fourteen: Coating of the Composite Adhesive After printing and inspection, the paper enters the composite coating unit.

[0241] The paper first passes through a dust removal device to remove surface dust and paper scraps. The dust removal uses a combination of electrostatic dust removal rods and sticky rollers, achieving a dust removal efficiency of over 98%.

[0242] The paper is treated with a corona treatment device with a corona treatment power of 0.4 W / cm² and a processing speed of 40 m / min, which increases the surface tension to 40 mN / m.

[0243] Mix components A and B of the prepared composite adhesive, then add component C (curing agent), stir for 10 minutes, and use immediately.

[0244] The composite adhesive is applied to the paper surface via a microgravure roller. The microgravure roller has a screen count of 200 lines per inch, a cell depth of 22 μm, and a speed ratio of coating roller speed to paper speed of 1.05:1.

[0245] The scraper pressure is 0.2 MPa, the scraper angle is 30 degrees, and it scrapes off excess composite adhesive from the surface of the micro-gravure roller.

[0246] The coating amount is monitored in real time by an online weighing system and controlled at 4±0.5g / m².

[0247] The coated paper enters a three-stage drying chamber. The first stage is at 60°C for 5 seconds. The second stage is at 80°C for 10 seconds. The third stage is at 100°C for 15 seconds. After drying, the composite adhesive content reaches over 98%, and the surface is basically dry.

[0248] Step 15: Hot pressing lamination If lamination with aluminum foil or other substrates is required, hot pressing lamination should be performed after coating and drying.

[0249] The aluminum foil substrate undergoes surface cleaning before lamination to remove surface oil and oxide layers. It is then preheated at 70°C to remove moisture.

[0250] Paper and aluminum foil are hot-pressed together using a laminating roller. The laminating roller temperature is 80°C, the laminating pressure is 0.4 MPa, and the laminating speed is 30 meters per minute.

[0251] Hot-pressing lamination causes the isocyanate in the composite adhesive to react with the hydroxyl groups on the surface of the aluminum foil, forming urethane bonds and achieving chemical bonding.

[0252] If lamination with other substrates is not required, and only a lamination adhesive is applied as a protective layer, the hot-pressing lamination step can be omitted.

[0253] Step Sixteen: Curing and hardening After lamination, the product is wound up with a roll diameter controlled at 800-1000mm and a tension controlled at 150N.

[0254] After winding, the roll is sent to the curing chamber. The curing chamber temperature is 50°C and the relative humidity is less than 30%. The curing time is 24 hours.

[0255] During the curing process, the isocyanates and hydroxyl groups in the composite adhesive continue to react, increasing the crosslinking density. Simultaneously, the fluorinated acrylate segments undergo microphase separation, forming an ordered structure that improves the light transmittance and mechanical properties of the composite layer.

[0256] After maturation, the product is removed from the maturation chamber and allowed to equilibrate at room temperature for 4 hours before being cut.

[0257] Step 17: Slitting and Processing Place the cured rolls onto a slitting machine and cut them according to the finished product size.

[0258] Before slitting, the paper is positioned by using a photoelectric sensor to detect the position of the color mark, ensuring accurate slitting and that the color mark is located at the designated position on the finished paper.

[0259] The slitting blade uses a carbide disc cutter with a sharp edge, producing a clean, burr-free cut. The slitting accuracy is ±0.5mm.

[0260] The dimensions of the finished paper after slitting are determined according to customer requirements. Common dimensions are 70mm×36mm, 80mm×40mm, and 90mm×50mm.

[0261] Step 18: Quality Inspection A comprehensive quality inspection is conducted on the slit finished product.

[0262] Quantitative testing: The quantitative test result should meet the requirement of 53-57 g / m², and the deviation should be within ±2 g / m².

[0263] Transmittance test: The transmittance should be greater than or equal to 88% when measured using a spectrophotometer at a wavelength of 550 nm.

[0264] Registration accuracy inspection: Registration accuracy is inspected using a light stage and measuring microscope. The paper is observed against the light, and the alignment deviation between the negative lines and the positive edges is measured; the deviation should be less than 0.2mm. The sampling rate is 10 sheets per 1000 sheets.

[0265] Composite strength testing: Peel strength test is used. For products laminated with aluminum foil, the peel strength between the paper and aluminum foil should be greater than 2.0 N / 15 mm. The sampling ratio is 3 samples per batch.

[0266] Anti-counterfeiting effect test: Observe the effect of the yin-yang pattern when it is combined under light. The pattern should be complete, clear, with distinct layers and high contrast. Randomly select 1 sheet from every 100 sheets for inspection. The pass rate should be greater than 98%.

[0267] Safety and hygiene indicator testing: Testing will be conducted in accordance with "QSZ109025-2023 Safety and Hygiene Requirements for Cigarette Lining Paper". Testing items include heavy metal content, polycyclic aromatic hydrocarbon content, and benzene solvent residue. Total heavy metal content should be less than 100 mg / kg, total polycyclic aromatic hydrocarbon content should be less than 1 mg / kg, and benzene solvent residue should be less than 0.5 mg / m². One sample will be randomly selected from each batch for testing.

[0268] Step 19: Packaging and Storage The finished paper that passes inspection is packaged. Each stack consists of 500 or 1000 sheets, wrapped in moisture-proof paper, and then heat-sealed with plastic film to prevent moisture absorption.

[0269] Each stack is accompanied by a product label indicating the product name, specifications, batch number, production date, and inspection results.

[0270] After packaging, the products are placed into cartons, with 10 or 20 stacks per carton. The cartons are sealed with packing tape, and the outer cartons are labeled with product information and storage requirements.

[0271] Storage environment requirements: Temperature 15-25°C, relative humidity 40-60%, avoid direct sunlight, keep away from heat and fire sources. Shelf life is 12 months.

[0272] Example Example 1: Preparation of Standard Formulation Preparation of translucent paper base 45 parts bleached sulfate softwood pulp, fiber length 3.0 mm; 40 parts bleached sulfate hardwood pulp, fiber length 1.0 mm; 4 parts nanocellulose, diameter 30 nm; 10 parts kaolin, particle size 2 μm; 2 parts cationic starch; 3 parts sodium carboxymethyl cellulose.

[0273] Surface slurry: 28 parts short fiber, 12 parts long fiber, 5 parts nanocellulose, 10 parts kaolin, 2 parts cationic starch. Freezing degree 37°SR.

[0274] Intermediate layer sizing agent: 27 parts long fiber, 18 parts short fiber, 3 parts sodium carboxymethyl cellulose, 1.5 parts cationic starch. Freezing degree 28°SR.

[0275] Bottom layer slurry: The same ratio as the top layer slurry.

[0276] Three-layer front-screen papermaking system; vacuum level of -20 kPa for the top and bottom layers, and -15 kPa for the middle layer. Pressing pressure: 1.8 MPa. Drying temperature: 110-125°C. Calendering pressure: 180 N / mm.

[0277] Pore-forming agent dissolution treatment: Spray with sodium carbonate buffer solution at pH=10, temperature 70°C, spray volume 20g / m², residence time 6 seconds.

[0278] A translucent paper base was prepared with a basis weight of 55 g / m², a thickness of 78 μm, a light transmittance of 90%, a tensile strength of 2.8 kN / m in the longitudinal direction and 1.5 kN / m in the transverse direction, and a surface smoothness of 135 seconds.

[0279] Preparation of high-penetration ink on the front side Phthalocyanine blue pigment 15 parts, particle size 80nm. Modified rosin resin 28 parts, softening point 90°C. Mineral oil 40 parts, kinematic viscosity 20mm² / s. Vegetable oil 10 parts, linseed oil, linolenic acid content 62%. Fatty alcohol polyoxyethylene ether 4 parts, HLB value 13. n-Propanol 3 parts. Cobalt-manganese-calcium drying agent 1 part.

[0280] Three-roll milling three times, fineness 5μm. Viscosity 10 Pa·s. Penetration depth 30μm. Drying time 7 minutes.

[0281] Preparation of back-side controlled-permeation ink Carbon black pigment 18 parts, particle size 120 nm. Modified rosin resin 40 parts, softening point 110°C. Mineral oil 34 parts, kinematic viscosity 50 mm² / s. Microcrystalline wax emulsion 15 parts, solid content 40%, particle size 300 nm. Hydrophobic nano-silica 3 parts, particle size 20 nm. Sorbitol fatty acid ester 1.5 parts. Cobalt-manganese-calcium drying agent 1.2 parts.

[0282] Three-roll milling three times, fineness 8μm. Viscosity 22 Pa·s. Penetration depth 12μm. Contact angle 98 degrees.

[0283] Overprinting system configuration The CCD camera has 5 megapixels, a field of view of 50mm × 40mm, and a scanning frequency of 200 scans per minute. It uses a 470nm LED blue light source with a power of 30W. Lateral correction accuracy is ±0.05mm. Vertical registration adjustment accuracy is ±0.08mm. Rotation compensation accuracy is ±0.1 degrees.

[0284] Composite adhesive preparation 45 parts of fluorinated acrylate copolymer, refractive index 1.42. 30 parts of polyurethane resin, Shore A hardness 80. 10 parts of epoxy resin E-51 type. 4 parts of nano-zirconia, particle size 15nm. 1.5 parts of silane coupling agent KH-560. 0.4 parts of defoamer. 10 parts of HDI trimer curing agent.

[0285] The composite adhesive has a refractive index of 1.45, a viscosity of 65 mPa·s, and a solid content of 38%.

[0286] Preparation process The preparation was carried out according to the complete preparation method and process.

[0287] The front is printed with a negative image, featuring the outline and background of a dragon, with a line width of 0.2mm. The printing speed is 70 meters per minute, the drying temperature is 125°C, and the drying time is 10 seconds.

[0288] The reverse side is printed with a positive image featuring a dragon, complementing the negative image. The printing speed is 60 meters per minute, the drying temperature is 105°C, and the drying time is 12 seconds.

[0289] For overprinting positioning, the horizontal correction compensation ΔX = -0.08mm and the vertical adjustment ΔY = -0.12mm are applied.

[0290] The composite adhesive coating amount is 4g / m², and the drying process is carried out in three stages: 60°C / 5s, 80°C / 10s, and 100°C / 15s.

[0291] Mature at 50°C for 24 hours.

[0292] Performance test results Registration accuracy: lateral error 0.10mm, longitudinal error 0.12mm, rotation angle error 0.15 degrees.

[0293] Light transmittance: 90%, decreased to 89% after lamination, a decrease of 1%.

[0294] Anti-counterfeiting effect: When viewed against the light, the dragon pattern is completely pieced together, the outline is precisely aligned with the main body, the layers are distinct, the contrast is high, and it is clearly distinguishable to the naked eye.

[0295] Composite strength: 2.5N / 15mm.

[0296] Safety and hygiene: Total heavy metals 45mg / kg, total polycyclic aromatic hydrocarbons 0.3mg / kg, and benzene solvent residue 0.2mg / m², all of which meet the standard requirements.

[0297] Example 2: High light transmittance formula The following adjustments were made based on Example 1.

[0298] The amount of sodium carboxymethyl cellulose in the intermediate layer slurry was increased to 4 parts. The spraying rate of the pore-forming agent dissolution treatment was increased to 25 g / m², and the pH value was increased to 10.5. The porosity of the intermediate layer was increased to 25%.

[0299] The amount of fluorinated acrylate in the composite adhesive formulation was increased to 50 parts, and the amount of polyurethane resin was reduced to 25 parts. The amount of nano-zirconia was reduced to 3 parts. The refractive index of the composite adhesive was reduced to 1.44.

[0300] Other process parameters are the same as in Example 1.

[0301] Performance test results Light transmittance: 92%, 90% after lamination.

[0302] Registration accuracy: lateral error 0.12mm, vertical error 0.14mm.

[0303] Tensile strength: 2.5 kN / m in the longitudinal direction and 1.3 kN / m in the transverse direction. The strength is slightly reduced but still meets the requirements.

[0304] Composite strength: 2.2N / 15mm.

[0305] Anti-counterfeiting effect: Increased light transmittance, brighter yin-yang pattern, higher contrast, and excellent anti-counterfeiting recognition.

[0306] Example 3: High-strength formulation The following adjustments were made based on Example 1.

[0307] The proportion of long fibers was increased to 50 parts, and the proportion of short fibers was reduced to 35 parts. The freeness of long fibers was increased to 28°SR.

[0308] In the composite adhesive formulation, the amount of polyurethane resin was increased to 35 parts, and the amount of fluorinated acrylate was reduced to 40 parts. The amount of HDI trimer curing agent was increased to 12 parts.

[0309] The pressing pressure was increased to 2.0 MPa, and the paper density was increased to 0.70 g / cm³.

[0310] Other process parameters are the same as in Example 1.

[0311] Performance test results Tensile strength: 3.2 kN / m in the longitudinal direction and 1.8 kN / m in the transverse direction, showing a significant improvement in strength.

[0312] Light transmittance: 88%, 87% after lamination. The light transmittance has decreased slightly but still meets the requirements.

[0313] Registration accuracy: lateral error 0.11mm, vertical error 0.13mm.

[0314] Composite strength: 2.8N / 15mm, improved composite strength.

[0315] Anti-counterfeiting effect: The pattern is clear, the registration is precise, and the anti-counterfeiting effect is good. The product has high strength and is suitable for use in high-speed packaging lines.

[0316] Example 4: Quick-drying ink formulation The following adjustments were made based on Example 1.

[0317] The amount of drier in the front ink has been increased to 1.5 parts, and a highly active cobalt drier with a cobalt content of 8% has been adopted.

[0318] The drying temperature was increased to 135°C, and the drying time was shortened to 6 minutes.

[0319] The amount of drier in the back ink was increased to 1.5 parts. The drying temperature was 115°C and the drying time was 8 minutes.

[0320] Printing speed has been increased to 80 meters per minute for the front and 70 meters per minute for the back.

[0321] Other process parameters are the same as in Example 1.

[0322] Performance test results Drying time: 6 minutes for the front side and 8 minutes for the back side. This increases the drying speed and production efficiency by 15%.

[0323] Registration accuracy: lateral error 0.13mm, longitudinal error 0.14mm. Due to the increased speed, the accuracy has decreased slightly but is still within the acceptable range.

[0324] Light transmittance: 89%.

[0325] Anti-counterfeiting effect: Good, clear pattern, and accurate registration.

[0326] Suitable for high-speed production, improving production efficiency and reducing production costs.

[0327] Example 5: Colored anti-counterfeiting pattern Based on Example 1, anti-counterfeiting patterns are printed using colored ink.

[0328] The front printing uses two-color overprinting. The first color is a blue negative outline, using phthalocyanine blue ink. The second color is a red negative background, using lightfast crimson ink.

[0329] The reverse side is printed with a yellow positive image and uses permanent yellow ink.

[0330] The basic framework of the ink formulation is the same as in Example 1, except that the types of pigments are changed and the amounts are adjusted according to the tinting strength of the pigments. Phthalocyanine Blue 15 parts, Fast Red 18 parts, Permanent Yellow 20 parts.

[0331] Color printing requires color registration. The registration accuracy between the two colors on the front side must be controlled within 0.1mm. The registration accuracy between the front and back sides must be controlled within 0.15mm.

[0332] Other process parameters are the same as in Example 1.

[0333] Performance test results Registration accuracy: The registration error between blue and red on the front side is 0.09mm. The registration error between the front and back sides is 0.14mm. The overall registration accuracy of the three colors is good.

[0334] Light transmittance: 89%, colored inks slightly reduce light transmittance.

[0335] Anti-counterfeiting effect: When viewed against the light, the blue outline, red background, and yellow main body are combined to form a complete color anti-counterfeiting pattern. The colors are bright and the layers are rich, resulting in extremely high anti-counterfeiting recognition and significantly improved anti-counterfeiting level.

[0336] Suitable for high-end tobacco products, providing a higher level of anti-counterfeiting protection.

[0337] Comparative Example Comparative Example 1: Single-sided printing The preparation process is the same as in Example 1, but the anti-counterfeiting pattern is printed only on the front and not on the back.

[0338] The front is printed with a complete anti-counterfeiting pattern, including the outline and the main body, in monochrome black ink.

[0339] Other process parameters are the same as in Example 1.

[0340] Performance test results Light transmittance: 90%, same as in Example 1.

[0341] Anti-counterfeiting effect: The anti-counterfeiting pattern can only be observed from the front, and there is no yin-yang effect when viewed against the light. The anti-counterfeiting recognition is low, and it is easily copied. The front pattern can be copied using ordinary printing equipment, resulting in poor anti-counterfeiting performance.

[0342] Conclusion: The anti-counterfeiting performance of single-sided printing is far lower than that of double-sided precise overprinting.

[0343] Comparative Example 2: Ordinary double-sided printing without overprint control The preparation process is the same as in Example 1, with a negative image printed on the front and a positive image printed on the back, but instead of a dynamic optical positioning overprinting system, only a traditional mechanical positioning method is used.

[0344] Traditional mechanical positioning relies on the paper edge or perforation for positioning. The registration accuracy is affected by paper size deviation, tension changes, temperature and humidity, resulting in a large registration error.

[0345] Other process parameters are the same as in Example 1.

[0346] Performance test results Registration accuracy: lateral error 0.35mm, longitudinal error 0.42mm, rotation angle error 0.8 degrees. The registration accuracy is much lower than that of Example 1.

[0347] Anti-counterfeiting effect: When observed under light, the outline of the negative image is clearly misaligned with the main body of the positive image; the misalignment is visible to the naked eye. The patterns are not fully joined, with some areas overlapping and gaps appearing in other areas. The anti-counterfeiting effect is poor, and the recognizability is low.

[0348] The overprinting pass rate is only 65%, with 35% of the products having overprinting accuracy defects, resulting in a high scrap rate.

[0349] Conclusion: Without precise registration control, the anti-counterfeiting effect of double-sided printing is greatly reduced, resulting in low production yield and high production costs.

[0350] Comparative Example 3: Without using a gradient ink system The preparation process is the same as in Example 1, but the same ink is used on both the front and back sides, without distinguishing between high-penetration ink and controlled-penetration ink.

[0351] Medium-penetration ink is used on both sides, with a penetration depth of 15-20μm.

[0352] Other process parameters are the same as in Example 1.

[0353] Performance test results Registration accuracy: Same as in Example 1, with a horizontal error of 0.10 mm and a vertical error of 0.12 mm.

[0354] Anti-counterfeiting effect: When observed under light, the negative and positive images can be combined, but the pattern layers are not obvious. Due to the similar ink penetration depth on both sides, the color difference between the superimposed area and the individual areas is small, resulting in low contrast and poor layering. The anti-counterfeiting recognition rate is lower than that of Example 1.

[0355] When viewed from different angles, the contrast of the pattern does not change significantly, lacking dynamic anti-counterfeiting effects.

[0356] Conclusion: The dual-layer gradient ink system plays an important role in enhancing the sense of layering and recognizability of anti-counterfeiting effects.

[0357] Comparative Example 4: Without using a directional light-transmitting fiber network structure The preparation process is the same as in Example 1, but the paper base adopts a common homogeneous structure, without three-layer papermaking, without adding a pore-forming agent, and without pore-forming treatment.

[0358] Paper base formulation: 45 parts softwood pulp, 40 parts hardwood pulp, 4 parts nanocellulose, 10 parts kaolin, 2 parts cationic starch, single-layer papermaking.

[0359] The pulping degree is 32°SR, the pressing pressure is 1.8MPa, and the density is 0.75g / cm³.

[0360] Other process parameters are the same as in Example 1.

[0361] Performance test results Light transmittance: 75%, significantly lower than 90% in Example 1.

[0362] Anti-counterfeiting effect: When observed under light, the low light transmittance makes the combined yin-yang pattern appear dark, with low contrast and unclear details. The anti-counterfeiting identification is reduced, requiring a strong light source for clear observation.

[0363] The light transmittance after lamination is 72%, which is lower than the standard requirement of 85% and therefore unqualified.

[0364] Conclusion: The directional light-transmitting fiber network structure is crucial for improving light transmittance and is the foundation for achieving high-quality anti-counterfeiting effects through yin-yang splicing.

[0365] Comparative Example 5: No high-transparency composite layer used The preparation process is the same as in Example 1, but the composite adhesive is a common composite adhesive, which does not contain fluorinated acrylates and does not perform refractive index matching.

[0366] Composite adhesive formulation: 60 parts polyurethane resin, 15 parts epoxy resin, 12 parts curing agent, free of fluorine-containing components and nano-zirconia.

[0367] The refractive index of the composite adhesive is 1.52, and the difference in refractive index between it and the paper-based fiber is Δn=0.06.

[0368] Other process parameters are the same as in Example 1.

[0369] Performance test results Light transmittance: The paper base light transmittance was 90%, which decreased to 82% after lamination, a decrease of 8%. The decrease was much greater than the 1% decrease in Example 1.

[0370] Haze: 12%, significantly higher than 3% in Example 1.

[0371] Anti-counterfeiting effect: When viewed against the light, the clarity of the pattern decreases, the edges become blurred, and the contrast is reduced. High haze causes the pattern to appear blurry, affecting anti-counterfeiting identification.

[0372] Conclusion: The use of refractive index matching technology in the high-transmittance composite layer is crucial for maintaining high light transmittance and anti-counterfeiting clarity after lamination. Ordinary composite adhesives significantly reduce light transmittance, affecting the anti-counterfeiting effect.

[0373] Performance testing methods Transmittance test method Instrument: Spectrophotometer with integrating sphere.

[0374] Sample preparation: Cut the paper sample to a size of 50mm×50mm, ensuring the sample is flat and wrinkle-free.

[0375] Test conditions: wavelength 550nm, spectral bandwidth 5nm, integrating sphere diameter 150mm.

[0376] Test Procedure: Place the sample at the entrance of the integrating sphere, with the light beam incident perpendicularly to the sample. Measure the transmitted light flux Φt and the incident light flux Φi. Transmittance T = Φt / Φi × 100%. Test 5 points for each sample and take the average value.

[0377] Methods for testing overprint accuracy Instruments: light transmission stage, LED light source, tool microscope, resolution 0.001mm.

[0378] Sample preparation: Take out the finished paper, lay it flat on the light transmission table, and turn on the light transmission illumination.

[0379] Test Procedure: Observe the relative positions of the front and back color marks under a tool microscope. Measure the distance between the center of the crosshair of the front color mark and the center of the hollow frame of the back color mark, and measure the deviation in the X and Y directions respectively. Measure four sets of color marks at the four corners of each sheet of paper and calculate the average deviation. The lateral registration error is the average deviation in the X direction, and the longitudinal registration error is the average deviation in the Y direction.

[0380] Rotation angle error measurement: The difference in deviation of the four corner markers is measured, and the rotation angle deviation is obtained through geometric calculation.

[0381] Composite strength test method Instrument: Electronic tensile testing machine, measuring range 500N, accuracy 0.1N.

[0382] Sample preparation: Cut the composite sample to size 150mm×15mm, with the composite layer in the middle.

[0383] Test Procedure: Clamp the sample onto the tensile testing machine fixture with a clamping length of 50 mm and a test length of 50 mm. Peel at a 180-degree peel angle and a peel speed of 300 mm / min. Record the average peel force during the peeling process, expressed as composite strength in N / 15 mm. Test 5 samples per group and take the average value.

[0384] Ink Penetration Depth Test Method Instruments: Optical microscope, magnification 100-400x, equipped with a micrometer.

[0385] Sample preparation: Tear or cut the printed paper along a direction perpendicular to the printed pattern to obtain a cross-section. Embed the cross-section with epoxy resin, then polish it to obtain a smooth and flat observation surface.

[0386] Test Procedure: Place the sample on the microscope stage and adjust the focus until the cross-section is clearly visible. Observe the depth of ink penetration into the paper, measuring the distance from the paper surface to the deepest point of ink penetration using a micrometer. Measure 10 points for each sample and take the average value as the penetration depth.

[0387] Tensile strength test method Instrument: Electronic tensile testing machine, measuring range 2000N.

[0388] Sample preparation: Cut paper samples to size 180mm×15mm, cutting them both longitudinally and laterally.

[0389] Test Procedure: Clamp the sample onto the tensile testing machine fixture with a clamping length of 50 mm and a test length of 80 mm. Tensile the sample at a constant rate of 20 mm / min until fracture, and record the maximum tensile force. Tensile strength = maximum tensile force / sample width, in kN / m. Test 5 samples longitudinally and 5 samples transversely, and take the average value for each.

[0390] Safety and hygiene indicator testing methods Heavy metal detection: In accordance with GB / T16631, inductively coupled plasma mass spectrometry (ICP-MS) was used to detect the content of heavy metal elements such as lead, cadmium, mercury, hexavalent chromium, and arsenic, and the total amount was calculated.

[0391] Polycyclic aromatic hydrocarbon (PAH) detection: Following the method in GB / T26572, gas chromatography-mass spectrometry (GC-MS) was used to detect 16 PAH compounds and calculate the total amount.

[0392] Detection of benzene solvent residues: Refer to GB / T23910 method and use headspace gas chromatography to detect the residual amounts of benzene, toluene, xylene, ethylbenzene and other benzene solvents.

[0393] Summary of Results Comparison Comparative results show that the present invention achieves high registration accuracy, high light transmittance, and high anti-counterfeiting recognition through the synergistic effect of directional light-transmitting fiber network structure, double-layer gradient ink system, dynamic optical positioning overprinting technology, and high-transmittance composite layer. It is significantly superior to existing technologies and single technical solutions, and has outstanding substantive features and significant progress.

[0394] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0395] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A double-sided precision-printed anti-counterfeiting cigarette liner paper, characterized in that, It includes a directional light-transmitting fiber network structure paper base, a front negative printing layer, a back positive printing layer, and a composite layer; The directional light-transmitting fiber network structure paper base has a three-layer structure, comprising, by weight: Surface pulp: The mass ratio of short fibers to long fibers is 7:

3. The short fiber length of bleached sulfate hardwood pulp is 0.8-1.2 mm, the long fiber length of bleached sulfate softwood pulp is 2.8-3.2 mm, the nanocellulose is 3-6 parts, the kaolin is 8-12 parts, the cationic starch is 1.5-2.5 parts, the freeness is 35-40°SR, and the basis weight is 15 g / m². The intermediate layer slurry has a long fiber to short fiber mass ratio of 6:4, 2-4 parts sodium carboxymethyl cellulose, 1.5-2.5 parts cationic starch, a freeness of 25-30°SR, and a basis weight of 25 g / m². The intermediate layer is treated with an alkaline buffer solution with a pH of 9.5-10.5 to form directional microporous channels with a pore size of 5-15 μm and a porosity of 18-25%. Bottom layer slurry: Same composition as the top layer slurry, with a basis weight of 15 g / m²; The front negative printing layer is printed with high-penetration ink, which, by weight, comprises: 12-18 parts pigment with a particle size ≤80nm; 25-30 parts modified rosin resin with a softening point of 85-95°C; 35-45 parts mineral oil with a kinematic viscosity of 15-25mm² / s; 8-12 parts vegetable oil with a linoleic acid content ≥60%; 3-5 parts fatty alcohol polyoxyethylene ether with an HLB value of 12-14; 2-4 parts n-propanol; and 0.8-1.2 parts cobalt-manganese-calcium composite drier. The high-penetration ink has a fineness ≤5μm, a viscosity of 8-12Pa·s, and a penetration depth of 25-35μm on the paper substrate. The positive printing layer on the back is printed with controlled-permeability ink, which, by weight, comprises: 15-20 parts pigment with a particle size of 100-150 nm; 35-42 parts modified rosin resin with a softening point of 105-115°C; 30-38 parts mineral oil with a kinematic viscosity of 40-60 mm² / s; 5-8 parts microcrystalline wax emulsion with a solid content of 40% and a wax particle size of 200-500 nm; 2-4 parts nano-silica with a particle size of 15-25 nm, which has been hydrophobically modified; 1-2 parts surfactant; and 1.0-1.5 parts drier. The controlled-permeability ink has a fineness ≤8 μm, a viscosity of 18-25 Pa·s, and a penetration depth of 8-15 μm on the paper substrate. The registration accuracy of the front negative printing layer and the back positive printing layer is: horizontal registration error ≤ 0.12mm, vertical registration error ≤ 0.15mm, and rotation angle error ≤ 0.2°. The composite layer comprises, by weight, 40-50 parts of a fluorinated acrylate copolymer, wherein the fluorinated acrylate copolymer is polymerized from hexafluorobutyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 3:5:2, and has a refractive index of 1.42; 25-35 parts of polyurethane resin with a Shore A hardness of 75-85; 8-12 parts of epoxy resin; 3-6 parts of nano-zirconia with a particle size of 10-20 nm; 1-2 parts of a silane coupling agent; and 8-12 parts of an aliphatic isocyanate curing agent. The composite layer has a refractive index of 1.44-1.46 and a coating weight of 3-5 g / m².

2. A method for preparing the double-sided precision overprinted anti-counterfeiting cigarette liner paper as described in claim 1, characterized in that, Includes the following steps: Step 1: Preparation of the translucent paper base: Dilute the surface pulp, middle pulp, and bottom pulp to the required online concentrations. The online concentrations of the surface and bottom pulps are 0.8-1.0%, and the middle pulp is 0.7-0.9%. Use a three-layer pre-wire multi-layer papermaking process. The vacuum degree of the surface and bottom wire sections is -20 kPa, and the vacuum degree of the middle wire section is -15 kPa. Before pressing, spray with an alkaline buffer solution with a pH of 9.5-10.5 and a temperature of 65-75°C at a spray volume of 15-25 g / m² and a residence time of 5-8 seconds to partially dissolve the sodium carboxymethyl cellulose in the middle layer. The pressing pressure is 1.5-2.0 MPa. The drying temperature is 110-125°C. The calendering pressure is 150-200 N / mm. Step 2: Front negative printing: Gravure printing is used with a cell depth of 35-45μm. The high-penetration ink is used to print the negative anti-counterfeiting pattern. The printing pressure is 0.4-0.6MPa, and the printing speed is 60-80 meters / minute. Simultaneously, front color marks are printed 3mm from the outer corners of the four corners of the paper. The front color marks are solid cross-shaped structures with a line width of 0.3mm and a line length of 5mm. Drying is performed using a combination of infrared and hot air at a temperature of 120-130°C for 8-12 seconds. The front color marks are then UV cured with a UV lamp power of 120W / cm for 2-3 seconds. Step 3, Paper Flipping and Conveying: The paper is flipped 180 degrees by the flipping roller. During the flipping process, the paper is vacuumed and the vacuum degree is -8kPa; the tension is controlled at 150-200N. Step 4, Overprinting and Positioning: The first CCD camera scans the color marks at the four corners of the front to establish a front reference coordinate system. The CCD camera has a resolution of 5 million pixels, a field of view of 50mm×40mm, a scanning frequency of 200 times / minute, and an LED blue light source wavelength of 470nm. The second CCD camera scans the current position of the paper and calculates the lateral deviation ΔX, the longitudinal deviation ΔY, and the rotation angle deviation Δθ. Step 5, overprint compensation: When |ΔX|>0.1mm, activate the lateral correction system with a correction accuracy of ±0.05mm; when |ΔY|>0.15mm, adjust the printing cylinder phase with an adjustment accuracy of ±0.08mm; when |Δθ|>0.3°, activate the rotation compensation system with a compensation accuracy of ±0.1°. Step Six: Reverse Positive Printing: Gravure printing is used with a cell depth of 35-45μm. The positive anti-counterfeiting pattern is printed using the controlled-permeability ink. The positive and negative images complement each other. The printing pressure is 0.3-0.5MPa, and the printing speed is 50-70 meters / minute. Back color marks are printed at the four corners of the back. The back color marks are hollow cross-shaped structures with a line width of 0.2mm and an inner space of 2mm×2mm. The drying temperature is 100-110°C, and the time is 10-15 seconds. The back color marks are UV cured. Step 7, Composite Coating: The paper is corona treated with a corona power of 0.3-0.5 W / cm²; a microgravure roller is used to coat the composite adhesive. The microgravure roller has a screen ruling of 180-220 lines / inch and a cell depth of 20-25 μm. The speed ratio of the coating roller to the paper is 1.05:1; three-stage drying: first stage 60°C, 5 seconds; second stage 80°C, 10 seconds; third stage 100°C, 15 seconds. Step 8: Curing and maturation: Mature at 50°C for 24 hours.

3. The double-sided precision overprinted anti-counterfeiting cigarette liner paper according to claim 1, characterized in that, The paper base has a basis weight of 53-57 g / m², a thickness of 70-85 μm, a light transmittance of 88-92%, a longitudinal tensile strength of ≥2.5 kN / m, and a surface smoothness of 120-150 seconds.

4. The double-sided precision overprinted anti-counterfeiting cigarette liner paper according to claim 1, characterized in that, The pigment of the high-penetration ink is phthalocyanine blue or carbon black, the pigment of the controlled-permeability ink is carbon black, and the pigments of the high-penetration ink and the controlled-permeability ink are complementary colors.

5. The double-sided precision overprinted anti-counterfeiting cigarette liner paper according to claim 1, characterized in that, The negative image of the front negative printing layer is the outline and background of the anti-counterfeiting pattern, with a line width of 0.15-0.3mm and a line spacing of 0.3-0.5mm; the positive image of the back positive printing layer is the main graphic of the anti-counterfeiting pattern; the gap between the negative and positive images is 0.2-0.3mm.

6. The double-sided precision overprinted anti-counterfeiting cigarette liner paper according to claim 1, characterized in that, The light transmittance of the composite layer decreases by ≤2%, haze by ≤5%, and peel strength by ≥2.0N / 15mm.

7. The preparation method according to claim 2, characterized in that, The surface pulp described in step one has a short fiber freeness of 35-40°SR and a long fiber freeness of 20-25°SR; the middle pulp has a long fiber freeness of 25-30°SR and a short fiber freeness of 30-35°SR; and the paper density after pressing is 0.65-0.72 g / cm³.

8. The preparation method according to claim 2, characterized in that, The high-penetration ink described in step two is obtained by grinding three times using a three-roll mill, with the inter-roll pressure being 2-3 MPa for the first time, 3-4 MPa for the second time, and 4-5 MPa for the third time; the controlled-penetration ink described in step six is ​​obtained by grinding three times using a three-roll mill.

9. The preparation method according to claim 2, characterized in that, The overprinting positioning system described in step four includes a dual-sided CCD vision system and a servo correction device; the servo correction device includes a lateral correction linear motor, a printing plate cylinder servo motor, and a rotation compensation mechanism, with a response time ≤50ms.

10. The preparation method according to claim 2, characterized in that, The method for preparing the composite adhesive in step seven is as follows: Component A is obtained by mixing fluorinated acrylate copolymer, polyurethane resin, and epoxy resin; Component B is obtained by adding nano-zirconia, silane coupling agent, and defoamer to Component A; Component C is obtained by adding aliphatic isocyanate curing agent before use; The fluorinated acrylate copolymer is obtained by solution polymerization of hexafluorobutyl acrylate, methyl methacrylate, and acrylic acid at 75-85°C for 3-6 hours, with a number average molecular weight of 25,000-35,000.

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