An ink vehicle for intaglio plastic printing and a method for preparing the same

Abstract

The application discloses an ink binder for gravure plastic printing and a preparation method thereof, and relates to the field of gravure printing. The ink binder for gravure plastic printing comprises the following components: 45-55 parts of special acrylic resin, 40-50 parts of anhydrous ethanol and 1-3 parts of phosphate adhesion promoter. The special acrylic resin is a quaternary copolymer of IBOMA, 2-EHA, HPMA and IA, has a core-shell structure, and the sol part of the special acrylic resin has a Mw of 8000-12000. The preparation method comprises the following steps: construction of a soft core and hard shell structure, and gradient solvent replacement process. The application firstly constructs a soft core-hard shell partition structure through quaternary copolymerization of a 2-EHA / IA core layer and an IBOMA / HPMA shell layer, and the BOPP adhesion reaches 93.1%, and meanwhile, the hardness reaches 2H. Through a three-step method of low-temperature reduced pressure, normal-pressure azeotropy and normal-temperature liquid supplement, the water removal rate is greater than 99.6%, and the core-shell structure retention rate is greater than 95%.

Description

Technical Field

[0001] This invention relates to the field of gravure plastic printing technology, specifically to an ink binder for gravure plastic printing and its preparation method. Background Technology

[0002] Gravure printing is a mainstream process in food packaging, interior design, and other fields. The performance of its ink binders directly determines key indicators such as adhesion, abrasion resistance, and solvent residue of printed materials. With increasingly stringent global environmental regulations, traditional solvent-based ink binders face elimination due to benzene-based solvent residues, making alcohol-soluble systems an inevitable choice. However, existing alcohol-soluble ink binders face three major technical challenges.

[0003] First, there's the conflict between adhesion and abrasion resistance. Non-polar plastic substrates like BOPP and PET require low-Tg resins (Tg < 0℃) to ensure adhesion, but printed surfaces require high Tg (Tg > 50℃) to improve abrasion resistance. Traditional linear acrylic resins (such as styrene-acrylic / pure acrylic copolymers) cannot achieve this balance. This results in high-adhesion resins (Tg ≈ -10℃) having a pencil hardness ≤ HB, making them prone to scratching after printing; while high-hardness resins (Tg ≈ 60℃) have a cross-cut adhesion test result ≤ 3B, making the packaging bag seals easy to peel off.

[0004] Second, there is a conflict between ethanol solubility and structural stability. To meet the ethanol solubility requirement, existing technologies mainly employ two approaches: introducing carboxyl monomers and reducing molecular weight. However, when the carboxyl content is >5%, the molecular weight drops sharply (Mw < 5000), leading to deterioration in water resistance after film formation (water absorption > 8%). Resins with Mw = 6000~8000 are ethanol-soluble, but the printed film exhibits poor anti-blocking properties (adhesion occurs after 24 hours of pressing at 40℃). In particular, core-shell structure resins, due to their phase separation characteristics, are prone to aggregation in ethanol (particle size > 200 nm), resulting in deterioration of printing leveling properties (DOI value < 80).

[0005] Third, there is the risk of migration caused by residual emulsifiers. Although aqueous acrylic emulsions can be converted into alcohol-soluble systems through solvent displacement, the residual rate of traditional emulsifiers (such as OP-10 and SDS) is >0.3%, and their alkylphenol polyoxyethylene ethers (APEO) migrate to the food contact layer. Carboxyl self-emulsification (such as MAA) requires pH >8 to maintain solubility, but high pH catalyzes ester hydrolysis, broadening the molecular weight distribution (PDI > 3.0). Summary of the Invention

[0006] The purpose of this invention is to provide an ink binder for gravure plastic printing and its preparation method. By using core-shell partitioned polymerization design, gradient solvent replacement and reactive emulsifier bonding technology, the invention improves the problems of adhesion-abrasion resistance imbalance and poor ethanol dispersion stability of core-shell structure. For the first time, it achieves a balance of high hardness, high adhesion and low VOCs, providing a new environmentally friendly solution for gravure plastic printing.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] An ink binder for gravure plastic printing, comprising the following components by weight:

[0009] 45-55 parts of special acrylic resin, 40-50 parts of anhydrous ethanol, and 1-3 parts of phosphate ester adhesion promoter;

[0010] Among them, the special acrylic resin is a quaternary copolymer of IBOMA, 2-EHA, HPMA and IA, with a core-shell structure, and the sol portion of the special acrylic resin has a Mw of 8000~12000.

[0011] Phosphate ester adhesion promoters can specifically include VISIOMER® HEMA-P 100.

[0012] Traditional alcohol-soluble acrylic resins employ linear random copolymerization, failing to simultaneously achieve low Tg (adhesion strength) and high Tg (abrasion resistance). This invention constructs a "soft core-hard shell" partitioned structure: the core layer consists of the flexible monomer 2-EHA and the polar monomer IA, directly contacting the substrate and providing 93.1% adhesion; the shell layer consists of the rigid monomer IBOMA and the crosslinking monomer HPMA, forming a dense network on the surface (pencil hardness ≥2H). For the first time, through quaternary copolymerization of the "2-EHA / IA core layer and IBOMA / HPMA shell layer," a single resin simultaneously achieves high adhesion and high hardness performance. The sol portion of the special acrylic resin has a Mw of 8000~12000, and the sol molecular chain ensures ethanol solubility, with a viscosity ≤200 cP at 25℃.

[0013] Furthermore, the core layer of the core-shell structure has a Tg of -15 to -5°C and a shell layer Tg of 50 to 60°C. The heating rate, as determined by DSC, is 9.5 to 10.5°C / min.

[0014] A preparation method, applicable to the preparation of the ink binder for gravure plastic printing, includes the following steps:

[0015] Under S100 and inert gas protection, in a mixed solution of deionized water and sodium methyl propylene sulfonate, after heating, a mixed monomer of 2-EHA and IA is added dropwise, and ammonium persulfate is added dropwise simultaneously. The reaction is kept at the temperature to form a flexible core layer with a core-shell structure.

[0016] After cooling to S200, a mixture of monomers including IBOMA, HPMA, and ethylene glycol dimethacrylate is added dropwise, along with potassium persulfate. The reaction is maintained at this temperature to form a rigid shell, resulting in an aqueous core-shell emulsion.

[0017] S300. After cooling the above aqueous core-shell emulsion, slowly add anhydrous ethanol dropwise, and simultaneously remove water by vacuum distillation until the water content of the system is ≤8%;

[0018] S400: Heat the system from step S300, add anhydrous ethanol, distill under normal pressure until the water content is <0.5%, cool down, add phosphate ester adhesion promoter, and continue stirring to react.

[0019] S500: Cool the system from step S400, stir at low speed, add the remaining anhydrous ethanol until the solid content of the solution reaches 45-49%, mix evenly, and obtain the target ink binder.

[0020] Simultaneous addition of 2-EHA / IA mixed monomers and ammonium persulfate to S100 ensures uniform distribution of carboxyl groups (core layer Tg = -10±2℃), avoiding "island structure". Sodium methacrylate (containing double bonds) is used in copolymerization, and its sulfonic acid groups are chemically anchored to the polymer chain (residual rate <0.01%), completely avoiding APEO migration risk. Compared with traditional physically adsorbed emulsifiers, this invention meets food contact safety standards. The protective gas can be an inert gas, such as argon, or nitrogen.

[0021] After premixing IBOMA, HPMA, and EGDMA in S200, KPS is added dropwise simultaneously to ensure uniform dispersion of the crosslinking agent EGDMA (gel fraction ≤ 5%). The shell layer Tg = 55±5℃, overcoming the defect of "polar-nonpolar phase separation" in traditional random copolymerization. The addition of EGDMA to the shell layer forms a gel network; the sol portion Mw = 8000~12000; the sol molecular chains ensure ethanol solubility; the viscosity at 25℃ is ≤ 200 cP; the gel network provides solvent resistance; and it does not show the bottom layer after being wiped with methyl ethyl ketone (MEK) more than 50 times.

[0022] Traditional solvent replacement processes involve a single addition of ethanol followed by high-temperature dehydration, resulting in damage to the core-shell structure (shell peeling rate >40%). This invention employs a three-stage ethanol addition-temperature-pressure synergistic process: In stage S300, ethanol is added dropwise at low temperature (to prevent aggregation), while simultaneously undergoing vacuum distillation to remove moisture to ≤8%, preserving the core-shell integrity; in stage S400, the temperature is increased under atmospheric pressure distillation (to prevent bumping), and ethanol is added for azeotropic dehydration to <0.5%; in stage S500, the remaining ethanol is added at room temperature, and the solid content is adjusted to 45-49% by low-speed stirring. For the first time, this three-step method—low-temperature vacuum distillation, atmospheric pressure azeotropic distillation, and room-temperature replenishment—achieves a moisture removal rate >99.6% and a core-shell structure retention rate >95%.

[0023] In S400, the temperature is first lowered to below 40°C, and then phosphate ester adhesion promoters are added to avoid the risk of high-temperature hydrolysis (the hydrolysis rate of phosphate ester bonds is >15% at 70°C); the phosphate ester forms ionic bonds with the IA carboxyl groups of the core layer, improving the adhesion of BOPP to 93.1%.

[0024] Furthermore, in steps S300, S400, and S500, the volume of anhydrous ethanol added accounts for 30-35% and 40-45% of the total ethanol volume, respectively.

[0025] Furthermore, the mass ratio of IBOMA, 2-EHA, HPMA and IA is 18~22:22~28:2~2.5:1.

[0026] Further, in step S100, the amount of deionized water added is 35-40% of the total system mass; the mass ratio of sodium methacrylate sulfonate, ammonium persulfate and IA is 0.5-0.8:0.1-0.2:1; the temperature is raised to 82-87℃ and the reaction time is maintained for 1.5-2 hours.

[0027] Further, in step S200, the mass ratio of IBOMA, ethylene glycol dimethacrylate and potassium persulfate is 1:0.015~0.02:0.006~0.01; the temperature is lowered to 68~72℃, and the reaction time is kept at this temperature for 1.5~2h; the solid content of the aqueous core-shell emulsion is 38~42%.

[0028] Furthermore, in step S300, the temperature is lowered to 36~42℃, and the dropping rate of anhydrous ethanol is ≤1mL / min; the pressure of vacuum distillation is -0.08~-0.07MPa, and the temperature is 38~42℃.

[0029] Further, in step S400, the temperature is raised to 63~68℃; then lowered to 35~40℃, and the stirring reaction time is 0.5~1.0h.

[0030] Further, in step S500, the temperature is lowered to 20~25℃, the stirring speed is 280~320rpm, and the time is 25~35min.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention, for the first time, constructs a soft-core-hard-shell partitioned structure through quaternary copolymerization of a 2-EHA / IA core layer and an IBOMA / HPMA shell layer, achieving a BOPP adhesion of 93.1% and a hardness of 2H, thus enabling a single resin to simultaneously meet high adhesion and high hardness performance requirements. The preparation method of this invention employs a triple-set approach: core-shell functional partitioning design, sol-gel synergistic regulation, and gradient solvent replacement process. This solves three long-standing problems in the field of alcohol-soluble ink binders: mutual incompatibility between adhesion and abrasion resistance, insolubility of high molecular weight molecules in ethanol, and core-shell structure breakage. Furthermore, for the first time, a three-step method—low-temperature decompression, atmospheric pressure azeotropic distillation, and room-temperature replenishment—achieves a moisture removal rate >99.6% and a core-shell structure retention rate >95%.

[0033] In the 2-EHA / IA core layer and the IBOMA / HPMA shell, " / " represents "and";

[0034] IBOMA: Isobornyl methacrylate;

[0035] 2-EHA: 2-Ethylhexyl acrylate;

[0036] HPMA: Hydroxypropyl methacrylate;

[0037] IA: itaconic acid;

[0038] BOPP: Biaxially oriented polypropylene film;

[0039] PET: Polyethylene terephthalate;

[0040] KPS: Potassium persulfate;

[0041] EGDMA: Ethylene glycol dimethacrylate;

[0042] Tg: Glass transition temperature. Detailed Implementation

[0043] Example 1

[0044] An ink binder for gravure plastic printing comprises the following components:

[0045] Special acrylic resin 500g, anhydrous ethanol 450g, phosphate ester adhesion promoter 20g;

[0046] Among them, the special acrylic resin is a quaternary copolymer of IBOMA, 2-EHA, HPMA and IA, with a core-shell structure, and the sol portion of the special acrylic resin has Mw=10000.

[0047] The core-shell structure has a core layer Tg of -10℃ and a shell layer Tg of 55℃, with a heating rate of 10℃ / min.

[0048] A preparation method, applicable to the preparation of the ink binder for gravure plastic printing, includes the following steps:

[0049] The mass ratio of IBOMA, 2-EHA, HPMA and IA is 20:25:2.2:1.

[0050] Under S100 and inert gas protection, in a mixed solution of deionized water and sodium methacrylate sulfonate, the temperature was raised to 85°C, and a mixture of monomers of 2-EHA and IA was added dropwise, while ammonium persulfate was added dropwise simultaneously. The reaction was maintained at this temperature for 1.8 h to form a flexible core layer with a core-shell structure. The amount of deionized water added was 37% of the total system mass. The mass ratio of sodium methacrylate sulfonate, ammonium persulfate and IA was 0.6:0.15:1.

[0051] S200, cool to 70℃, add dropwise a mixture of monomers IBOMA, HPMA, and ethylene glycol dimethacrylate, and simultaneously add potassium persulfate, keep the reaction at this temperature for 1.8h to form a rigid shell, and obtain an aqueous core-shell emulsion with a solid content of 40%; the mass ratio of IBOMA, ethylene glycol dimethacrylate, and potassium persulfate is 1:0.018:0.008.

[0052] S300. After cooling the above aqueous core-shell emulsion to 39°C, slowly add anhydrous ethanol (32% of the total ethanol volume) dropwise at a rate ≤1 mL / min. Simultaneously, distill under reduced pressure at -0.075 MPa and 40°C to remove water until the water content of the system is 7%.

[0053] S400: Heat the system from step S300 to 65°C, add anhydrous ethanol accounting for 43% of the total ethanol volume, distill under normal pressure until the water content is 0.35%, cool down to 37°C, add phosphate ester adhesion promoter, and continue stirring the reaction for 0.8h.

[0054] S500: Cool the system from step S400 to 22°C, stir at low speed (300 rpm) for 30 minutes, add the remaining anhydrous ethanol until the solid content of the solution reaches 47%, mix evenly, and obtain the target ink binder.

[0055] Example 2

[0056] An ink binder for gravure plastic printing comprises the following components:

[0057] Special acrylic resin 450g, anhydrous ethanol 400g, phosphate ester adhesion promoter 10g;

[0058] Among them, the special acrylic resin is a quaternary copolymer of IBOMA, 2-EHA, HPMA and IA, with a core-shell structure, and the sol portion of the special acrylic resin has a Mw=8000.

[0059] The core-shell structure has a core layer Tg of -15℃ and a shell layer Tg of 50℃, with a heating rate of 9.5℃ / min.

[0060] A preparation method, applicable to the preparation of the ink binder for gravure plastic printing, includes the following steps:

[0061] The mass ratio of IBOMA, 2-EHA, HPMA and IA is 18:22:2:1.

[0062] Under S100 and inert gas protection, in a mixed solution of deionized water and sodium methallyl sulfonate, the temperature was raised to 82°C, and a mixture of monomers of 2-EHA and IA was added dropwise, while ammonium persulfate was added dropwise simultaneously. The reaction was maintained at this temperature for 1.5 hours to form a flexible core layer with a core-shell structure. The amount of deionized water added was 35% of the total mass of the system. The mass ratio of sodium methallyl sulfonate, ammonium persulfate and IA was 0.5:0.1:1.

[0063] S200, cooling to 68℃, add dropwise a mixture of monomers IBOMA, HPMA, and ethylene glycol dimethacrylate, and simultaneously add potassium persulfate. Keep the reaction at this temperature for 1.5h to form a rigid shell, thus obtaining an aqueous core-shell emulsion with a solid content of 38%. The mass ratio of IBOMA, ethylene glycol dimethacrylate, and potassium persulfate is 1:0.015:0.006.

[0064] S300. After cooling the above aqueous core-shell emulsion to 36°C, slowly add anhydrous ethanol (30% of the total ethanol volume) dropwise at a rate ≤1 mL / min. Simultaneously, distill under reduced pressure at -0.08 MPa and 38°C to remove water until the water content of the system is 0.8%.

[0065] S400: Heat the system from step S300 to 63°C, add anhydrous ethanol accounting for 40% of the total ethanol volume, distill under normal pressure until the water content is 0.4%, cool down to 35°C, add phosphate ester adhesion promoter, and continue stirring the reaction for 0.5 h.

[0066] S500: Cool the system from step S400 to 20°C, stir at low speed (280 rpm) for 25 minutes, add the remaining anhydrous ethanol until the solid content of the solution reaches 45%, mix evenly, and obtain the target ink binder.

[0067] Example 3

[0068] An ink binder for gravure plastic printing comprises the following components:

[0069] Special acrylic resin 550g, anhydrous ethanol 500g, phosphate ester adhesion promoter 30g;

[0070] Among them, the special acrylic resin is a quaternary copolymer of IBOMA, 2-EHA, HPMA and IA, with a core-shell structure, and the sol portion of the special acrylic resin has a Mw=12000.

[0071] The core-shell structure has a core layer Tg of -5℃ and a shell layer Tg of 60℃, with a heating rate of 10.5℃ / min.

[0072] A preparation method, applicable to the preparation of the ink binder for gravure plastic printing, includes the following steps:

[0073] The mass ratio of IBOMA, 2-EHA, HPMA and IA is 22:28:2.5:1.

[0074] Under S100 and inert gas protection, in a mixed solution of deionized water and sodium methacrylate sulfonate, the temperature was raised to 87°C, and a mixture of monomers of 2-EHA and IA was added dropwise, while ammonium persulfate was added dropwise simultaneously. The reaction was maintained at this temperature for 2 hours to form a flexible core layer with a core-shell structure. The amount of deionized water added was 40% of the total mass of the system. The mass ratio of sodium methacrylate sulfonate, ammonium persulfate and IA was 0.8:0.2:1.

[0075] S200, cool down to 72℃, add dropwise a mixture of monomers IBOMA, HPMA, and ethylene glycol dimethacrylate, and simultaneously add potassium persulfate, keep the reaction at this temperature for 2 hours to form a rigid shell, and obtain an aqueous core-shell emulsion with a solid content of 42%; the mass ratio of IBOMA, ethylene glycol dimethacrylate, and potassium persulfate is 1:0.02:0.01.

[0076] S300. After cooling the above aqueous core-shell emulsion to 42°C, slowly add anhydrous ethanol (35% of the total ethanol volume) dropwise at a rate ≤1 mL / min. Simultaneously, distill under reduced pressure at -0.07 MPa and 42°C to remove water until the water content of the system is 6%.

[0077] S400: Heat the system from step S300 to 68°C, add anhydrous ethanol accounting for 45% of the total ethanol volume, distill under normal pressure until the water content is 0.3%, cool to 40°C, add phosphate ester adhesion promoter, and continue stirring the reaction for 1.0 h.

[0078] S500: Cool the system from step S400 to 25°C, stir at low speed (320 rpm) for 35 minutes, add the remaining anhydrous ethanol until the solid content of the solution reaches 49%, mix evenly, and obtain the target ink binder.

[0079] Comparative Example 1

[0080] A printing ink binder comprises the following components:

[0081] 500g acrylic resin, 450g anhydrous ethanol, 20g phosphate ester adhesion promoter;

[0082] The acrylic resin is a random copolymer (non-core-shell) of IBOMA, 2-EHA, HPMA and IA, and the acrylic resin Mw=10000.

[0083] A preparation method, applicable to the preparation of the printing ink binder, includes the following steps:

[0084] Synthesis of S100 random copolymer emulsion: Under N2 protection, 37% of the total system mass of deionized water was added to the reactor, followed by sodium methacrylate sulfonate. The temperature was raised to 85℃, and mixed monomers: IBOMA, 2-EHA 25, HPMA 2.2, IA 1, and ammonium persulfate were added dropwise at a rate of 2 mL / min. The reaction was maintained at this temperature for 1.8 h to obtain a random copolymer emulsion (solid content 40%, Tg≈35℃).

[0085] The mass ratio of IBOMA, 2-EHA, HPMA, and IA is 20:25:2.2:1. The mass ratio of sodium methacrylate sulfonate, ammonium persulfate, and IA is 0.6:0.15:1; the mass ratio of IBOMA, ethylene glycol dimethacrylate, and potassium persulfate is 1:0.018:0.008.

[0086] S200, Solvent Replacement: Cool the emulsion to 70°C, add all anhydrous ethanol at once, and stir vigorously at 500 rpm. Distill and dehydrate under reduced pressure of -0.075 MPa at 70°C until the water content is ≤0.4%.

[0087] S300, Additives and Adjustments: Maintain 65℃, add phosphate ester adhesion promoter, and stir for 0.5 h. Cool to 25℃, add deionized water to adjust the solid content to 47%, mix evenly, and obtain the target ink binder.

[0088] Comparative Example 2

[0089] The formula is the same as in Example 1.

[0090] In the preparation method, steps S100 and S200 are the same as in Example 1.

[0091] Replace steps S300, S400, and S500 of the ethanol replacement process with the following steps:

[0092] After cooling the above aqueous core-shell emulsion to 39°C, anhydrous ethanol was added, and the system was kept at -0.075 MPa and 40°C to remove water until the water content of the system was 3.5%. Phosphate ester adhesion promoters were added, and the reaction was continued with stirring for 0.8 h. The system was then cooled to 22°C and stirred at a low speed of 300 rpm for 30 min to obtain the target ink binder.

[0093] Comparative Example 3

[0094] The formula is the same as in Example 1.

[0095] In the preparation method, steps S100-S300 and S500 are the same as in Example 1.

[0096] In step S400, the phosphate ester adhesion promoter is added directly without cooling.

[0097] Comparative Example 4

[0098] The formula is the same as in Example 1.

[0099] In the preparation method, steps S100 and S300-S500 are the same as in Example 1.

[0100] In step S200, ethylene glycol dimethacrylate is not added.

[0101] The performance parameters of the gravure plastic printing ink binder prepared using the formulations and preparation methods of Examples 1-3 are shown in Table 1.

[0102] Table 1 Performance parameters of gravure plastic printing ink binders prepared using the formulations and preparation methods of Examples 1-3

[0103]

[0104] As shown in Table 1, the gravure plastic printing ink binder prepared by the formulation and preparation method of Examples 1-3 of this invention constructs a soft core-hard shell partitioned structure through quaternary copolymerization of 2-EHA / IA core layer and IBOMA / HPMA shell layer. The soft core (Tg=-10℃~-5℃) provides adhesion, and the hard shell (IBOMA crosslinked network, Tg=55~60℃) provides hardness. The BOPP adhesion reaches 93.1%, and the hardness reaches 2H, realizing that a single resin can simultaneously meet the requirements of high adhesion and high hardness performance.

[0105] It can withstand more than 50 methyl ethyl ketone (MEK) wiping cycles; using a three-step method of low-temperature decompression, atmospheric pressure azeotropic distillation, and room-temperature replenishment, it achieves a water removal rate of >99.6% and a core-shell integrity rate (TEM) of 97%, with a dehydration time of <4.5 hours. The emulsion particle size is stable at 82~88 nm, and it shows no gelation after 30 days of storage at 40℃, achieving high molecular weight miscibility with ethanol. VOCs residue ≤2.1 mg / m³ 2 It meets environmental protection requirements.

[0106] The performance parameters of the printing ink binders prepared using the formulations and preparation methods of Examples 1 and Comparative Examples 1-4 are shown in Table 2.

[0107] Table 2 shows the performance parameters of the printing ink binders prepared using the formulations and preparation methods of Examples 1 and Comparative Examples 1-4.

[0108]

[0109] Note: "-" indicates that it is not present or does not exist.

[0110] As shown in Table 2, in Comparative Example 1, the random copolymers of IBOMA, 2-EHA, HPMA, and IA lacked a core-shell structure and lost their functional partitions. The addition of phosphate ester adhesion promoters at 65℃ led to hydrolytic deactivation, resulting in a BOPP adhesion of only 80.3% and a shell hardness of only H. The lack of a cross-linked shell protection reduced the number of methyl ethyl ketone (MEK) wiping cycles to 15. Phase separation in the random copolymers triggered self-polymerization, leading to gelation after only 7 days of storage at 40℃. A single addition of ethanol increased the particle size to 120 nm.

[0111] In Comparative Example 2, the addition of ethanol in a single step caused a sharp increase in the ethanol concentration in the aqueous phase, resulting in a decrease in solvent polarity and a surge in core-shell swelling stress. Simultaneously, the zeta potential on the particle surface decreased, leading to double-layer compression and cracking of the core-shell interface. Exposed carboxyl groups then self-polymerized to form a gel. This ethanol-induced self-polymerization resulted in gel formation within 7 days of storage at 40°C. The aggregation of the core-shell structure increased the particle size to 250 nm, resulting in a core-shell integrity rate (TEM) of only 58%, leading to a decrease in shell protection and a reduction in the number of methyl ethyl ketone (MEK) wiping cycles to 20. This demonstrates that the ethanol gradient replacement process of this invention can effectively control the emulsion particle size and ensure a core-shell integrity rate (TEM) of over 95%. The chain reaction of solvent shock, structural damage, and self-polymerization triggered by a single ethanol addition conversely proves that the gradient replacement process of this invention ensures the stability of the core-shell structure through a triple protection mechanism of controlling the gradual change in solvent polarity, maintaining the zeta potential, and suppressing swelling stress.

[0112] In Comparative Example 3, the direct addition of phosphate ester adhesion promoters at 65℃ led to hydrolysis, resulting in reduced activity and adhesion dropping to 82.1%. Furthermore, the hydrolysis products were difficult to remove, causing VOC residues to rise to 6.9 mg / m³. 2 .

[0113] In Comparative Example 4, ethylene glycol dimethacrylate (EGDMA) was not added during shell preparation, resulting in a lack of cross-linking in the shell. This led to the uncross-linked shell swelling and dissolving in ethanol due to the free sliding of molecular chains, causing the resin to rapidly peel off the matrix. The shell's resistance to methyl ethyl ketone (MEK) wiping was only 8 times. The shell's Tg decreased, lowering the molecular chain forging energy barrier, resulting in a soft and sticky surface and a shell hardness reduced to HB. The uncross-linked shell could not coat the core layer, and the IA carboxyl groups in the core layer initiated self-polymerization, leading to gelation after 15 days of storage at 40°C. EGDMA not only provides double bonds for polymerization and covalently links the molecular chains but also enhances the hydrogen bonds between the HPMA hydroxyl groups and IBOMA ester groups. The absence of EGDMA causes the shell to lose its rigidity and robust core function.

Claims

1. A method for preparing an ink binder for gravure plastic printing, characterized in that, Includes the following steps: Under S100 and inert gas protection, in a mixed solution of deionized water and sodium methyl propylene sulfonate, after heating, a mixed monomer of 2-EHA and IA is added dropwise, and ammonium persulfate is added dropwise simultaneously. The reaction is kept at the temperature to form a flexible core layer with a core-shell structure. After cooling to S200, a mixture of monomers including IBOMA, HPMA, and ethylene glycol dimethacrylate is added dropwise, along with potassium persulfate. The reaction is maintained at this temperature to form a rigid shell, resulting in an aqueous core-shell emulsion. S300. After cooling the above aqueous core-shell emulsion, slowly add anhydrous ethanol dropwise, and simultaneously remove water by vacuum distillation until the water content of the system is ≤8%; S400: Heat the system from step S300, add anhydrous ethanol, distill under normal pressure until the water content is <0.5%, cool down, add phosphate ester adhesion promoter, and continue stirring to react. S500: Cool down the system from step S400, stir at low speed, add the remaining anhydrous ethanol until the solid content of the solution reaches 45-49%, mix evenly, and obtain the target ink binder. The mass ratio of IBOMA, 2-EHA, HPMA, and IA is 18~22:22~28:2~2.5:1; In step S100, the amount of deionized water added is 35-40% of the total system mass; the mass ratio of sodium methyl propylene sulfonate, ammonium persulfate and IA is 0.5-0.8:0.1-0.2:1; the temperature is raised to 82-87℃ and the reaction time is maintained for 1.5-2 hours. In step S200, the mass ratio of IBOMA, ethylene glycol dimethacrylate and potassium persulfate is 1:0.015~0.02:0.006~0.01; the temperature is lowered to 68~72℃ and the reaction time is kept at this temperature for 1.5~2h; the solid content of the aqueous core-shell emulsion is 38~42%.

2. The preparation method according to claim 1, characterized in that, In steps S300 and S400, the volume of anhydrous ethanol added accounts for 30-35% and 40-45% of the total ethanol volume, respectively.

3. The preparation method according to claim 1, characterized in that, In step S300, the temperature is lowered to 36~42℃, and the dropping rate of anhydrous ethanol is ≤1mL / min; the pressure of vacuum distillation is -0.08~-0.07MPa, and the temperature is 38~42℃.

4. The preparation method according to claim 1, characterized in that, In step S400, the temperature is raised to 63~68℃; then lowered to 35~40℃, and the reaction is stirred for 0.5~1.0h.

5. The preparation method according to claim 1, characterized in that, In step S500, the temperature is lowered to 20~25℃, and the stirring speed is 280~320rpm for 25~35min.

6. An ink binder for gravure plastic printing, characterized in that, Prepared using the preparation method according to any one of claims 1 to 5, and comprising, by weight, the following components: 45-55 parts of special acrylic resin, 40-50 parts of anhydrous ethanol, and 1-3 parts of phosphate ester adhesion promoter; Among them, the special acrylic resin is a quaternary copolymer of IBOMA, 2-EHA, HPMA and IA, with a core-shell structure, and the sol portion of the special acrylic resin has a Mw of 8000~12000.

7. The ink binder for gravure plastic printing according to claim 6, characterized in that, The core-shell structure has a core layer Tg of -15 to -5°C, a shell layer Tg of 50 to 60°C, and a heating rate of 9.5 to 10.5°C / min.

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