Paper product gradient color green printing process and printing and dyeing material thereof

Abstract

The invention relates to the technical field of paper product printing, and discloses a paper product gradient color green printing process and a printing and dyeing material thereof.The process comprises the steps that the paper product gradient color green printing and dyeing material is prepared, and the printing and dyeing material is added into an ink fountain of printing equipment; printing the printing and dyeing material on the surface of the paper product printing stock; drying and curing the printed paper product; the printing and dyeing material comprises: 2-10 parts of an inorganic pigment; 1-5 parts of a modified water-based binder; 1-5 parts of a high-performance adhesion enhancer; 0.5 to 5 parts of a hydrophilic and oleophylic balanced surfactant; 0.5 to 1 part of a defoaming agent; 0.5 to 1 part of a preservative; 0.6 to 1.6 parts of a high adhesive force accelerant; and 3-5 parts of a pH buffer regulator. The modified water-based binder, the chlorinated polypropylene and the high-adhesion promoter have a synergistic effect, so that the adhesion and durability of the ink to a paper product printing stock are enhanced, and the interface bonding strength is improved by the high-adhesion promoter.

Description

Technical Field

[0001] This application relates to the field of paper product printing technology, specifically to a gradient color green printing process for paper products and its printing and dyeing materials. Background Technology

[0002] As consumers increasingly demand higher standards for product appearance and environmental performance, paper printing is evolving from single-color printing to diversified, high-value-added methods. Gradient printing, with its unique visual aesthetics, has been widely used in various paper packaging, books, promotional materials, and decorative materials. The demand for gradient printing is particularly growing in product designs that emphasize natural and ecological concepts.

[0003] In existing applications of gradient color printing on paper products, traditional flexographic printing, offset printing, or screen printing techniques are mainly relied upon. These methods achieve color gradient effects by adjusting ink layer thickness, dot size, or pattern overlay. For example, in flexographic printing, the amount of ink transferred is usually controlled by changing the line count and dot density of the anilox roller in order to create a color transition from light to dark on the substrate.

[0004] However, existing gradient color printing technologies for paper products have shortcomings in the ink film performance of some printing and dyeing materials. For example, the adhesion, abrasion resistance, and water resistance of the ink film are unstable, and some printed materials are prone to ink film peeling, wear, or blurring upon contact with water during use. Furthermore, traditional printing and dyeing material formulations still contain high levels of volatile organic compounds, causing air pollution during production and posing a potential threat to the environment. Therefore, this invention provides a green gradient color printing process for paper products and its printing and dyeing materials to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a green printing process for gradient colors on paper products and its printing and dyeing materials. This solves the problems of inaccurate control of ink layer thickness and dot line count in existing gradient color printing processes, unstable properties of printing and dyeing materials such as rheology, adhesion, abrasion resistance and water resistance, and environmental pollution.

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

[0007] The first aspect of this invention provides a gradient green printing process for paper products, comprising the following steps:

[0008] S1. Prepare paper substrates for printing, ensuring that their surfaces are suitable for ink adhesion and pattern presentation;

[0009] S2, the paper product gradually changing color green printing and dyeing material of a specific composition is added to the ink tank of the printing equipment, and the composition and proportion of the printing and dyeing material are optimized to provide good rheological property, adhesion and color performance;

[0010] S3, the paper product gradually changing color green printing and dyeing material is printed on the surface of the paper product printing substrate by controlling the ink amount superposition of the multi-color unit or adjusting the dot size and density of the printing pattern, which can realize accurate change of ink layer thickness and smooth transition of color, so as to form a preset gradually changing color green pattern;

[0011] S4, the printed paper product is dried and solidified to form a stable and mechanically strong ink film, so as to ensure the durability of the pattern and the subsequent processing performance of the printing substrate.

[0012] Preferably, the printing process adopts a flexographic printing method. The flexographic printing method further improves the smoothness and detail performance of the gradually changing color pattern by accurately controlling the screen roll line number in the range of 200LPI-1000LPI and the dot line number of the printing pattern in the range of 80LPI-175LPI, and controlling the ink transfer amount and dot shape.

[0013] Preferably, the drying and solidification includes hot air drying, infrared drying or convection drying. When hot air drying is adopted, the temperature is controlled in the range of 50℃-80℃, which ensures rapid solidification of the ink film and avoids damage to the paper product printing substrate or influence on the performance of the ink.

[0014] The second aspect of the present application provides a paper product gradually changing color green printing and dyeing material, which comprises the following components in mass fraction:

[0015] 2-10 parts of inorganic pigment as the source of color, which has environmental protection characteristics meeting the requirements of green printing;

[0016] 1-5 parts of modified water-based binder as the basic resin binder, which can optimize the rheological property, printing suitability and drying property of the ink after modification, and synergistically enhance the water resistance, chemical resistance and film strength with chlorinated polypropylene;

[0017] 1-5 parts of chlorinated polypropylene as a key resin component, which provides good film forming property, excellent adhesion to non-polar substrate and excellent water resistance barrier;

[0018] 0.5-5 parts of hydrophilic-lipophilic balance surfactant as a non-ionic surfactant, which balances the hydrophilic and hydrophobic properties of the ink to effectively inhibit the emulsification tendency of the ink in the printing process or in the water environment while optimizing the leveling property and wetting property of the ink on the printing substrate;

[0019] Defoaming agent 0.5-1 part, used to eliminate or inhibit the generation of foam during the preparation and printing of ink, to ensure the uniformity of ink texture and printing quality;

[0020] Preservative 0.5-1 part, used to prevent the deterioration of ink due to the growth of microorganisms during storage;

[0021] High adhesion promoter 0.6-1.6 parts, which is a silane coupling agent, can significantly improve the adhesion strength and friction resistance of ink to various substrates, including treated or untreated plastics, metals, glass, etc.

[0022] pH buffer 3-5 parts, used to maintain the stability of the acidity and alkalinity of the ink system, usually weakly alkaline, which is crucial for the storage stability, drying speed, printing suitability and water resistance of the ink. At the same time, stable pH value helps to maintain the surface activity of surfactants and the effectiveness of defoaming agent and preservative.

[0023] Preferably, the modified water-based binder is preferably a water-based polyurethane dispersion or a high-solid water-based acrylic emulsion, which is selected for its excellent film-forming properties and environmental protection characteristics.

[0024] Preferably, the water-based polyurethane dispersion is prepared by pre-polymerizing polyether polyol and polyester polyol, diisocyanate, chain extender and hydrophilic chain extender, and then dispersing in water, which ensures uniform dispersion of polyurethane molecules and stable performance.

[0025] The third aspect of the present application provides a preparation method of a paper product gradual color green printing and dyeing material, which is used to prepare the paper product gradual color green printing and dyeing material, comprising the following steps:

[0026] Pigment pre-dispersion: add the environmentally friendly inorganic pigment, part of the modified water-based binder and the hydrophilic-lipophilic balance surfactant into a high-speed stirring tank, stir at a speed of 800 rpm-1500 rpm for 15-30 minutes, to fully wet the pigment particles and prevent their agglomeration, thereby forming a uniform pigment paste.

[0027] Fine grinding: transfer the obtained pigment paste to a sand mill, select grinding media with a diameter of 0.8-1.5 mm, and grind at a linear speed of 2000-3000 rpm until the fineness of pigment particles is less than 10 microns. This fine grinding process ensures uniform particle size distribution of pigment particles, improves the tinting power, gloss and printing stability of ink, and obtains the ground pigment paste.

[0028] Final mixing and preparation: Transfer the obtained ground pigment paste into a mixing tank, sequentially add the remaining modified water-based binder, the chlorinated polypropylene, the environmentally friendly defoamer, the environmentally friendly preservative, the high adhesion promoter, and the pH buffer regulator. Stir at a speed of 300 rpm-600 rpm for 45 minutes-90 minutes. This mixing and preparation process ensures that all components are thoroughly mixed and uniform, forming an ink system with stable rheological properties and printing suitability, i.e., a uniformly mixed ink system.

[0029] Filtering and quality testing: Filter the formed ink system to remove coarse particles and impurities, obtaining the paper product gradual color green printing and dyeing material.

[0030] Preferably, the filtering uses a polyester filter screen or a stainless steel filter screen with a mesh size of 50-100 mesh. The selection of this specific mesh size effectively traps coarse particles while ensuring smooth passage of the ink, ensuring that the ink system is free of coarse particles and impurities, thereby ensuring the leveling and uniformity of the printed pattern.

[0031] In summary, the present application includes at least one of the following beneficial technical effects:

[0032] 1. The present application uses modified water-based binder, chlorinated polypropylene, and high adhesion promoter to enhance the adhesion and durability of the ink to the paper product printing substrate. The modified water-based binder optimizes the rheological properties and film-forming properties of the ink, the chlorinated polypropylene provides excellent film-forming properties and adhesion to the printing substrate, and the high adhesion promoter further enhances the interfacial bonding strength. The combination of these components results in a printed pattern with excellent resistance to rubbing, water resistance, and chemical resistance.

[0033] 2. The present application can realize the presentation of gradual color patterns and smooth transition of colors on the surface of paper products by controlling the ink amount superposition of multi-color units or adjusting the dot size and density of the printed pattern, combined with specific flexographic printing parameters. This process control method ensures the fineness and visual uniformity of the gradual color effect, effectively avoiding the color discontinuity or graininess that may occur in traditional printing, and improving the printing quality and aesthetic appearance of the final product.

[0034] 3. The present application improves the processing performance of the material through an optimized extrusion process and composite material formulation. The use of precise temperature control extrusion process enables the material to flow uniformly during extrusion, avoiding uneven surface or uneven flow of the material. This optimization technology not only improves the flame retardant performance of the final product, but also makes the processing process more efficient, avoiding the production instability and waste problems caused by uneven dispersion of materials in traditional processes. DETAILED DESCRIPTION

[0035] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically specified are commercially available analytical pure or higher grade products.

[0036] Environment-friendly inorganic pigment: phthalocyanine green (CAS: 1328-53-6).

[0037] Modified water-based binder includes:

[0038] High solid content water-based acrylic emulsion: styrene-acrylic emulsion (CAS: 25085-34-1);

[0039] Aliphatic polyether type water-based polyurethane dispersion (CAS: 9017-09-8 based on its main polymer skeleton).

[0040] Chlorinated polypropylene (CAS: 68442-33-1).

[0041] Hydrophilic-lipophilic balance surfactant: dimethylsiloxane (CAS: 67762-85-0).

[0042] High adhesion promoter: γ-aminopropyl triethoxysilane (CAS: 919-30-2).

[0043] Polar monomer: maleic anhydride (CAS: 108-31-6).

[0044] Polypropylene wax (CAS: 9003-07-0).

[0045] Example 1:

[0046] Raw material components (by mass fraction):

[0047] Inorganic pigment (phthalocyanine green) 5 parts, modified water-based binder (water-based polyurethane dispersion) 3 parts, hydrophilic-lipophilic balance surfactant 1.5 parts, modified water-based binder (high solid content water-based acrylic emulsion) 2 parts, chlorinated polypropylene 3 parts, environment-friendly defoamer 0.8 parts, environment-friendly preservative 0.6 parts, high adhesion promoter 1.0 parts and pH buffer regulator 4 parts.

[0048] Preparation steps:

[0049] Pigment pre-dispersion: 5 parts of environment-friendly inorganic pigment (phthalocyanine green), 3 parts of modified water-based binder (water-based polyurethane dispersion) and 1.5 parts of hydrophilic-lipophilic balance surfactant are added to a high-speed stirring tank with model number FD-2000, stirred at a speed of 1200 rpm for 20 minutes to form a pigment slurry.

[0050] Fine grinding: The pigment paste was transferred to a sand mill, and zirconium oxide grinding media with a diameter of 1.0 mm was selected to grind at a linear speed of 2500 rpm until the pigment particle size was less than 5 microns (measured by a doctor blade fineness gauge). The ground pigment paste was obtained.

[0051] Final mixing and formulation: The ground pigment paste was transferred to a mixing tank, and the remaining 2 parts of modified water-based binder (high solid content water-based acrylic emulsion), 3 parts of chlorinated polypropylene, 0.8 parts of environmentally friendly defoamer, 0.6 parts of environmentally friendly preservative, 1.0 parts of high adhesion promoter, and 4 parts of pH buffer regulator were added in sequence. Stirring was carried out at a speed of 450 rpm for 60 minutes to form a uniformly mixed ink system.

[0052] Filtration and quality testing: The ink system was filtered using a polyester filter with a mesh size of 80 mesh to remove coarse particles and impurities. A paper product with a gradual color green printing and dyeing material was obtained.

[0053] Example 2:

[0054] Raw material components (by mass fraction):

[0055] Inorganic pigment (phthalocyanine green) 5 parts, modified water-based binder (water-based polyurethane dispersion) 3 parts, hydrophilic-lipophilic balance surfactant 1.5 parts, modified water-based binder (high solid content water-based acrylic emulsion) 2 parts, environmentally friendly defoamer 0.8 parts, environmentally friendly preservative 0.6 parts, high adhesion promoter 1.0 parts, pH buffer regulator 4 parts, and functionalized polyolefin wax 3.5 parts.

[0056] Preparation steps:

[0057] Preparation of functionalized polyolefin wax:

[0058] 100 parts of polypropylene wax and 5 parts of maleic anhydride were added to a reaction kettle with stirring and heating devices. 1 part of benzoyl peroxide initiator was added, and the grafting polymerization reaction was carried out at 180°C for 4 hours. After cooling, the functionalized polyolefin wax was obtained.

[0059] Preparation of printing and dyeing materials:

[0060] Pigment pre-dispersion: 5 parts of environmentally friendly inorganic pigment (phthalocyanine green pigment), 3 parts of modified water-based binder (water-based polyurethane dispersion), and 1.5 parts of hydrophilic-lipophilic balance surfactant were added to a high-speed stirring tank with a model of FD-2000. Stirring was carried out at a speed of 1200 rpm for 20 minutes to form a pigment paste.

[0061] Fine grinding: The pigment slurry was transferred to a sand mill. Zirconia grinding media with a diameter of 1.0 mm was selected, and the grinding was carried out at a linear speed of 2500 rpm. The grinding was carried out until the fineness of the pigment particles was less than 5 microns, and the ground pigment slurry was obtained.

[0062] Final mixing and formulation: The ground pigment slurry was transferred to a mixing tank. The remaining 2 parts of the modified water-based binder (high solid content water-based acrylic emulsion), 3.5 parts of the functionalized polyolefin wax, 0.8 parts of the environmentally friendly defoamer, 0.6 parts of the environmentally friendly preservative, 1.0 parts of the high adhesion promoter, and 4 parts of the pH buffer regulator were sequentially added. After stirring at a speed of 450 rpm for 60 minutes, a uniformly mixed ink system was formed.

[0063] Filtration and quality detection: The above ink system was filtered using a polyester filter screen with a mesh size of 80 mesh to remove coarse particles and impurities. A paper product gradient green printing material was obtained.

[0064] Example 3:

[0065] Raw material components (by mass fraction):

[0066] Inorganic pigment (phthalocyanine green) 5 parts, modified water-based binder (water-based polyurethane dispersion) 3 parts, hydrophilic-lipophilic balance surfactant 1.5 parts, modified water-based binder (high solid content water-based acrylic emulsion) 2 parts, high-performance chlorine-free polymer 4 parts, environmentally friendly defoamer 0.8 parts, environmentally friendly preservative 0.6 parts, high adhesion promoter 1.0 parts, and pH buffer regulator 4 parts.

[0067] Preparation steps:

[0068] Pigment pre-dispersion: 5 parts of environmentally friendly inorganic pigment (phthalocyanine green pigment), 3 parts of modified water-based binder (water-based polyurethane dispersion), and 1.5 parts of hydrophilic-lipophilic balance surfactant were added to a high-speed stirring tank with a model of FD-2000. After stirring at a speed of 1200 rpm for 20 minutes, a pigment slurry was formed.

[0069] Fine grinding: The pigment slurry was transferred to a sand mill. Zirconia grinding media with a diameter of 1.0 mm was selected, and the grinding was carried out at a linear speed of 2500 rpm. The grinding was carried out until the fineness of the pigment particles was less than 5 microns, and the ground pigment slurry was obtained.

[0070] Final mixing and formulation: The ground pigment slurry was transferred to a mixing tank. The remaining 2 parts of the modified water-based binder (high solid content water-based acrylic emulsion), 3.5 parts of the functionalized polyolefin wax, 0.8 parts of the environmentally friendly defoamer, 0.6 parts of the environmentally friendly preservative, 1.0 parts of the high adhesion promoter, and 4 parts of the pH buffer regulator were sequentially added. After stirring at a speed of 450 rpm for 60 minutes, a uniformly mixed ink system was formed.

[0071] Filtration and quality detection: The ink system described above was filtered using a polyester filter with a mesh size of 80 mesh to remove coarse particles and impurities. A paper product gradient color green printing material was obtained.

[0072] Example 4:

[0073] Process steps:

[0074] Preparation of the printing substrate: A white paper product printing substrate with a thickness of 250 pm was prepared.

[0075] Ink addition to the ink tank: The prepared paper product gradient color green printing material was added to the ink tank of the flexographic printing equipment.

[0076] Printing: The flexographic printing used a screen roller line number of 600 LPI, and the screen dot line number of the printed pattern was 120 LPI.

[0077] By controlling the ink amount superposition of the multi-color unit of the flexographic printing equipment and adjusting the screen dot size and density of the printed pattern, the printing material was printed onto the surface of the paper product printing substrate to form a gradient color green pattern.

[0078] Drying and curing: The printed paper product was dried and cured using a hot air drying method at a temperature of 70°C to form an ink film.

[0079] Comparative Example 1:

[0080] Compared with Example 1, the difference is that no chlorinated polypropylene is added, and the rest is the same.

[0081] Comparative Example 2:

[0082] Compared with Example 1, the difference is that in the pigment fine grinding step, the pigment particle fineness only reaches 15 microns, and the rest is the same.

[0083] Comparative Example 3:

[0084] Compared with Example 1, the difference is that the addition amount of the high adhesion promoter is 0.3 parts, and the rest is the same.

[0085] Comparative Example 4:

[0086] Compared with Example 1, the difference is that the modified water-based binder only uses a high solid content water-based acrylic emulsion, does not contain a water-based polyurethane dispersion, and the total mass fraction is 3 parts, and the rest is the same.

[0087] Comparative Example 5:

[0088] Compared with Example 4, the difference is that traditional flexographic printing parameters are used, and the rest is the same.

[0089] Comparative Example 6:

[0090] The difference compared with Example 1 is that the amount of pH buffer regulator added is 1 part, and the rest is the same.

[0091] Experiment 1:

[0092] Purpose of the experiment: to evaluate the rheological properties, pH stability, storage performance, and pigment dispersion uniformity of the prepared printing and dyeing materials.

[0093] Experimental steps:

[0094] Viscosity test:

[0095] Take 200 mL of the printing and dyeing material sample to be tested and place it in a 250 mL beaker.

[0096] Place the beaker on the sample stage of the viscometer and adjust the rotor immersion depth to the mark line below the sample surface.

[0097] Set the test temperature to 25°C, start the constant temperature water bath circulation system, and after the sample temperature stabilizes, set the viscometer speed to 50 rpm.

[0098] Start the viscometer, and after the reading stabilizes, record the viscosity value (unit: mPa·s). Test each sample 3 times and take the average value.

[0099] pH value test:

[0100] Take 50 mL of the printing and dyeing material sample to be tested and place it in a 100 mL beaker.

[0101] Immerse the pH meter electrode into the sample, ensuring that the electrode tip is completely submerged.

[0102] After the pH reading stabilizes, record the pH value. Test each sample 3 times and take the average value.

[0103] Storage stability test:

[0104] Place 100 mL of each printing and dyeing material sample to be tested in a sealed glass bottle.

[0105] Place the sealed glass bottle in a constant temperature oven set to 50°C and continue for 7 days. After 7 days, remove the sample and cool it to 25°C at room temperature.

[0106] Visually observe whether the sample has layering, precipitation, caking, or surface skinning phenomena, and record the observation results.

[0107] Pigment particle fineness test:

[0108] Take a small amount of the printing and dyeing material sample to be tested and add it to the deep groove end of the doctor blade fineness meter. Use the spatula to evenly spread the sample from the deep groove end to the shallow groove end at a uniform speed and pressure.

[0109] The scale value (unit: microns) at which the first continuous pigment particle or defect appeared was observed and recorded on the surface of the ink film scraped by the doctor blade. Each sample was tested 3 times, and the average value was taken.

[0110] The experimental results are shown in Table 1.

[0111] Table 1: Test results of printing and dyeing material performance

[0112]

[0113] As shown in Table 1, by introducing modified water-based binder, chlorinated polypropylene (or its alternative polymer) and pH buffer regulator, etc., the printing and dyeing material exhibits stable physical and chemical properties. Specifically, the printing and dyeing materials prepared in Examples 1-3 all maintain a suitable viscosity range and weak alkaline pH value, which indicates that the synergistic effect between the components can effectively balance the rheological property and storage stability of the ink system. The addition of the pH buffer regulator allows the pH value of the ink system to remain stable during storage, which helps to maintain the wetting and leveling effect of the surfactant, as well as the functions of the defoamer and preservative.

[0114] Comparative Example 1 does not add chlorinated polypropylene, resulting in a relatively low viscosity and a slight precipitation after high-temperature storage, which indicates that chlorinated polypropylene, as a key resin component, plays a role in maintaining the stable dispersion state of the ink system and providing suitable rheological properties. The pigment particle fineness of Comparative Example 2 is significantly higher than that of other samples, indicating that the fine grinding process is not sufficient, which usually leads to a decrease in the tinting strength of the ink and a damage to the printing smoothness.

[0115] The selection and proportion control of the components of the printing and dyeing material help to ensure the performance consistency and stability of the ink during preparation, storage and use. In particular, the selection of high molecular materials (such as modified water-based binder, chlorinated polypropylene and its environmentally friendly alternatives) provides support and functional protection for the printing and dyeing material.

[0116] Experiment 2:

[0117] Purpose of the experiment: To evaluate the adhesion strength, mechanical abrasion resistance, water erosion resistance, color uniformity and continuity, and drying rate of the printed ink film.

[0118] Experimental steps:

[0119] Adhesion test:

[0120] Take the paper product sample printed with the ink film and place it on a flat test table.

[0121] Use a cross-cut tool to cut two sets of parallel lines perpendicularly across the surface of the ink film, 6 lines per set, with a 1 mm spacing, forming 25 small squares. The depth of the cuts should penetrate the ink film to the surface of the substrate.

[0122] Apply a transparent pressure sensitive adhesive tape (25 mm wide) to the grid area, ensuring that the tape is in full contact with the ink film.

[0123] After 2 minutes of tape application, quickly peel the tape off at a 60 degree angle.

[0124] Visually assess the ink film residue in the peeled area and record the adhesion rating according to the ASTM D3359 standard (0B to 5B, with 5B being the best).

[0125] Rub-off resistance test:

[0126] Fix the paper product sample printed with the ink film on the workbench of the rubbing tester.

[0127] Select standard cotton cloth as the rubbing medium and fix it to the rubbing head.

[0128] Set the rubbing pressure to 1 kgf and the rubbing stroke to 50 mm.

[0129] Start the rubbing tester and perform 50 reciprocating rubs on the surface of the ink film.

[0130] After the rubbing is complete, visually observe the degree of wear and color change on the surface of the ink film and record the results.

[0131] Water resistance test:

[0132] Take three samples of the paper product printed with the ink film, each with a size of 5 cm x 5 cm.

[0133] Completely immerse the first sample in deionized water for 30 minutes.

[0134] Add 5 drops of deionized water to the surface of the second sample and let it stand for 15 minutes.

[0135] The third sample serves as a blank control and is not subjected to water contact.

[0136] After the immersion and water drop treatments are complete, remove the samples and gently blot the surface moisture with soft absorbent paper.

[0137] Visually observe whether there are any phenomena such as blistering, softening, peeling, or color penetration into the interior of the substrate, and record the results.

[0138] Color uniformity and gradient effect test:

[0139] Take the paper product sample printed with the gradient color ink film and place it under a standard light source.

[0140] Using a colorimeter, measure the Lab color values of one point every 1 cm along the gradient direction.

[0141] Record the Lab values of each point and plot the color change curve.

[0142] Visually assess whether there are visible defects in the printed surface, such as uneven ink dots or color breaks.

[0143] Dryness speed test:

[0144] Place the paper product sample printed with the ink film in a test environment with an ambient temperature of 23±2°C and a relative humidity of 50±5%.

[0145] Every 10 seconds, gently touch the ink film surface with a fingertip to determine whether it is dry to the touch (no ink stains the fingertip). Record the dry-to-the-touch time.

[0146] Every 30 seconds, press the ink film surface with a fingertip to determine whether it is dry to the touch (no fingerprint marks, the ink film is completely cured). Record the time.

[0147] The experimental results are shown in Table 2.

[0148] Table 2: Performance test results of printed ink films

[0149]

[0150]

[0151] As shown in Table 2, the ink films formed by the printing of the dyeing materials prepared in Examples 1-3 all exhibit high adhesion strength in the adhesion test, especially Example 1 reaches a 5B grade, which is consistent with the synergistic effect of the modified water-based binder, chlorinated polypropylene (or its environmentally friendly substitute), and high adhesion promoter in the dyeing material. These high molecular components enhance the bonding strength between the ink film and the surface of the paper product substrate during film formation through intermolecular forces or chemical bonding, thereby improving the anti-peeling and wear resistance of the ink film.

[0152] In the abrasion resistance and water resistance tests, the ink films of the examples exhibit good durability and water resistance. This indicates that the formulation of the dyeing material, especially the excellent film-forming property and hydrophobic barrier provided by chlorinated polypropylene (or functionalized polyolefin wax, high-performance chlorine-free polymer), effectively resists mechanical wear and water erosion. In contrast, Comparative Example 1, which lacks chlorinated polypropylene, has significantly decreased adhesion and abrasion resistance of its ink film, and softening and peeling occur in the water resistance test, further verifying the important role of this key component in providing strength and protection performance of the ink film. Comparative Example 4, which only uses an acrylic emulsion as a binder, is also affected in terms of water resistance and adhesion, which is consistent with the mechanism of polyurethane dispersion in providing excellent flexibility and adhesion.

[0153] In terms of color uniformity and gradient effect, the gradient color ink film printed in Example 4 presents smooth and continuous color transition through precise control of ink amount superposition and dot parameters in the printing process. This indicates that the printing process of the present application realizes visual continuous gradient through adjustment of ink layer thickness variation and dot distribution, ensuring the visual quality of the pattern.

[0154] Experiment 3:

[0155] Purpose of the experiment: To evaluate the content of volatile organic compounds (VOCs) in printing and dyeing materials.

[0156] Experimental steps:

[0157] Prepare 5 clean sample bottles, and weigh about 10 g of the sample of the printing and dyeing material to be tested in each sample bottle, accurate to 0.01 g.

[0158] Put the sample bottle into the headspace sampler, and set the headspace sampling conditions: equilibrium temperature 120°C, equilibrium time 30 minutes.

[0159] After headspace sampling, separate and identify the VOCs present in the sample by gas chromatography-mass spectrometry (GC-MS).

[0160] According to the peak area of each VOC and the standard curve, calculate the content of each VOC and sum up to get the total VOC content (unit: g / L).

[0161] Repeat the test for each sample 3 times and take the average value.

[0162] The experimental results are shown in Table 3.

[0163] Table 3: Test results of VOC content in printing and dyeing materials

[0164] Sample No. Total VOCs content (g / L) Example 1 18.5 Example 2 15.2 Example 3 14.8 Comparative Example 1 17.1 Comparative Example 2 18.9 Comparative Example 3 21.3 Comparative Example 4 20.8 Comparative Example 6 17.5

[0165] From Table 3, it can be seen that the total VOC content of the printing and dyeing materials prepared in Examples 1-3 is at a low level. This is directly related to the selection of environmentally friendly inorganic pigments, environmentally friendly defoamers, environmentally friendly preservatives and the components of the water-based binder system in the present application. In particular, by using water as the main solvent, the use of high content of organic solvents in traditional solvent-based inks is significantly reduced, which reduces the emission of VOCs from the source.

[0166] The environmentally friendly alternatives to chlorinated polypropylene provided in the present application, such as the functionalized polyolefin wax and high-performance chlorine-free polymers employed in Examples 2 and 3, also exhibit technical effects in terms of VOC content. The data show that the VOC content of Examples 2 and 3 is lower than that of Example 1. This indicates that the introduction of these environmentally friendly alternative polymers further optimizes the environmental friendliness of the formulation while maintaining the performance of the printing material.

[0167] Experiment 4:

[0168] Purpose of the experiment: To evaluate the effects of different printing process parameters on the gradient color printing effect and the uniformity of the ink film.

[0169] Experimental steps:

[0170] Prepare the paper product samples printed in Example 4 and Comparative Example 5, and ensure that the ink film has completely dried, then place the samples in a standard observation environment.

[0171] Visually assess the gradient continuity: observe whether the color transition in the gradient color area of the sample is smooth and continuous, and whether there are visible color jumps, discontinuities or uneven color blocks.

[0172] Visually assess the ink film leveling: observe whether there are defects such as streaks, shrinkage, orange peel, etc. on the surface of the printed ink film, and whether the ink layer thickness is uniform.

[0173] Record all the measured data, and the experimental results are shown in Table 4.

[0174] Table 4: Comparison test results of printing process effects

[0175] Sample No. Gradation continuity Ink film levelness Example 4 Extremely smooth No apparent defects Comparative Example 5 Slight fault present Occasional streaks

[0176] As can be seen from Table 4, Example 4 employs specific anilox roll line numbers and printing pattern dot line numbers, and emphasizes the realization of gradient by controlling the ink amount superposition of multi-color units and adjusting the dot size and density of the printing pattern. The test results show that the ink film printed in Example 4 exhibits extremely smooth gradient continuity, and no color jumps or discontinuities are observed by naked eye, and the ink film leveling is good with no obvious leveling defects.

[0177] Comparative Example 5 does not use the specific printing process parameters of the present application, and its gradient continuity exhibits slight discontinuity, and there are occasional streaks on the surface of the ink film, which reflects the insufficient control of the uniformity of the ink layer distribution. This result shows that the anilox roll line number of the printing equipment, the dot line number of the printing pattern, and the parameters such as ink amount superposition and dot size density adjustment play a key role in realizing high-quality gradient color printing. Precise control of these parameters helps to ensure the accurate transfer and uniform spreading of the ink on the surface of the substrate, and thus form a smooth color transition and a uniform ink film layer.

Claims

1. A paper product gradient color green printing process characterized by, The method comprises the following steps: S1. Preparing a paper product printing substrate and preparing a paper product gradient color green printing and dyeing material; S2. Adding the prepared paper product gradient color green printing and dyeing material to an ink tank of a printing device; S3. Printing the paper product gradient color green printing and dyeing material to the surface of the paper product printing substrate by controlling the ink amount superposition of the multi-color unit or adjusting the dot size and density of the printing pattern to form a gradient color green pattern; S4. Drying and curing the printed paper product to form an ink film.

2. A paper product gradient color green printing process according to claim 1, characterized in that, In step S3, the printing is flexographic printing, and the screen roller line number used in the flexographic printing is 200LPI-1000LPI, and the dot line number of the printing pattern is 80LPI-175LPI.

3. A paper product gradient color green printing process according to claim 1, characterized in that, In step S4, the drying and curing comprises hot air drying, infrared drying or convection drying, and the hot air drying temperature is 50-80℃.

4. A paper product gradient color green printing material applied to the paper product gradient color green printing process according to any one of claims 1-3, characterized in that, The method comprises the following components in mass fraction: Inorganic pigment: 2-10 parts; Modified water-based binder: 1-5 parts; High-performance adhesion enhancer: 1-5 parts; Hydrophilic-lipophilic balance surfactant: 0.5-5 parts; Defoaming agent: 0.5-1 part; Preservative: 0.5-1 part; High adhesion promoter: 0.6-1.6 parts; pH buffer regulator: 3-5 parts.

5. A paper product gradient color green printing material according to claim 4, wherein The modified water-based binder is a water-based polyurethane dispersion or a high solid content water-based acrylic emulsion.

6. A paper product gradient color green printing material according to claim 4, wherein The water-based polyurethane dispersion is prepared by pre-polymerizing polyether polyol or polyester polyol, diisocyanate, chain extender and hydrophilic chain extender, and dispersing in water.

7. A paper product gradient color green printing material according to claim 4, wherein The high-performance adhesion enhancer is a functionalized polyolefin wax or a high-performance chlorine-free polymer.

8. A paper product gradient color green printing material according to claim 7, characterized by, The functionalized polyolefin wax is prepared by graft polymerization of polypropylene wax and unsaturated polar monomer.

9. A method for preparing a paper product gradient green printing material for preparing a paper product gradient green printing material according to any one of claims 4 to 8, characterized in that, The method comprises the following steps: The inorganic pigment, modified water-based binder and hydrophilic-lipophilic balance surfactant are added to a high-speed stirring tank, stirred at a speed of 800-1500 rpm for 15-30 minutes to form a pigment paste; The pigment paste is transferred to a sand mill, and grinding media with a diameter of 0.8-1.5 mm is selected, and the grinding is carried out at a linear speed of 2000-3000 rpm until the pigment particle fineness is less than 10 microns to obtain the ground pigment paste; The ground pigment paste is transferred to a mixing tank, and the remaining modified water-based binder, high-performance adhesion enhancer, defoaming agent, preservative, high adhesion promoter and pH buffer regulator are sequentially added, and stirred at a speed of 300-600 rpm for 45-90 minutes to form a uniformly mixed ink; The formed ink is filtered to remove impurities to obtain a paper product gradient color green printing and dyeing material.

10. The method for preparing a gradient green printing material for paper products according to claim 9, characterized in that, The filtering uses a polyester filter screen or a stainless steel filter screen with a mesh number of 50-100.

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