A simultaneous degradation type gravure ink for degradable plastic film and a preparation method thereof

Abstract

This invention discloses a synchronously degradable gravure ink for biodegradable plastic films and its preparation method, relating to the field of environmentally friendly inks. It comprises the following components: 35-55 parts of a biocompatible binder resin, 12-18 parts of organic pigment, 30-40 parts of a bio-based solvent, 0.5-1.5 parts of nano-titanium dioxide, and 1-2 parts of a dispersant. The biocompatible binder resin is a ternary block copolymer of PLA, PCL, and PBAT, with PBAT having a molecular weight of 3000-5000 g / mol. The bio-based solvent is a composite solvent of ethyl lactate and γ-valerol, with a mass ratio of ethyl lactate to γ-valerol of 1:0.5-2. The ink prepared by this invention exhibits excellent adhesion and maintains its integrity under bending and stretching of the substrate. It shows no sedimentation after 30 days of storage and maintains stable viscosity; its gloss reaches 85%. Furthermore, at test points of 30 and 60 days, the ink of this invention exhibits highly synchronous degradation behavior on both PLA and PBAT substrates.

Description

Technical Field

[0001] This invention relates to the field of biodegradable ink technology, specifically to a synchronously degradable gravure ink for biodegradable plastic films and its preparation method. Background Technology

[0002] Biodegradable plastic films, represented by polylactic acid (PLA), polybutylene adipate / terephthalate (PBAT), and polyhydroxyalkanoates (PHA), are rapidly expanding in the packaging industry. However, the accompanying printing technology, especially the core ink materials, lags far behind the environmentally friendly properties of the films themselves, becoming a key technological bottleneck restricting their complete degradation.

[0003] Currently, traditional inks used in these types of films face multiple challenges. First, insufficient adhesion and flexibility are significant issues. Biodegradable films such as PLA have low surface energy, weak polarity, and inherent brittleness, resulting in poor wetting and adhesion of traditional chlorinated polypropylene inks or early water-based inks on their surface. After printing, the ink layer is prone to cracking and peeling, and its inherent flexibility cannot meet the mechanical requirements of repeated bending during subsequent bag making, filling, and transportation, directly affecting the durability and appearance integrity of the packaging.

[0004] Secondly, there is a problem of asynchronous degradation between the ink layer and the film substrate. Traditional non-degradable inks act like a dense protective shell, covering the film surface and hindering effective contact between moisture and microorganisms, thus delaying or even interrupting the degradation process of the substrate. Existing biodegradable inks, due to significant differences in degradation conditions, mechanisms of action, and degradation rates compared to the film, lead to two problems: the film decomposes significantly while the ink pattern remains, forming microplastic pollution; the ink layer prematurely powders and peels off, but it itself is not effectively degraded and ultimately exists in the environment as microplastics as well.

[0005] Furthermore, poor printability also limits its large-scale application. Many existing environmentally friendly inks have problems such as poor leveling on biodegradable film surfaces, mismatch between drying rate and high-speed printing, and low gloss of the printed image, making it difficult to meet market requirements for print quality and affecting the overall aesthetics and commercial value of the packaging.

[0006] Therefore, developing a gravure ink that can synergistically degrade with biodegradable film substrates in environments such as composting, while possessing excellent adhesion, high flexibility, and good printability, has become an urgent technological need to promote the comprehensive green transformation of the flexible packaging industry chain. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a synchronously degradable gravure ink for biodegradable plastic films and its preparation method. This ink can degrade synergistically with the film substrate, solving the problem of asynchronous degradation between existing inks and biodegradable films.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A synchronously degradable gravure ink for biodegradable plastic films comprises, by weight, the following components: 35-55 parts of biocompatible binder resin, 12-18 parts of organic pigment, 30-40 parts of bio-based solvent, 0.5-1.5 parts of nano titanium dioxide, 1-2 parts of dispersant, 0.2-0.5 parts of leveling agent, and 0.1-0.3 parts of defoamer.

[0010] The biocompatible binder resin is a terpolymer of PLA (polylactic acid), PCL (polycaprolactone), and PBAT, with PBAT having a molecular weight of 3000~5000 g / mol. The bio-based solvent is a composite solvent of ethyl lactate and γ-valerolactone, with a mass ratio of ethyl lactate to γ-valerolactone of 1:0.5~2.

[0011] Organic pigments can be selected from Phthalocyanine Blue B (PB15:3), Quinacridone Red (PR122), Benzidine Yellow G (PY12), or Isoindolineone Yellow (PY110).

[0012] This invention uses a PLA-PCL-PBAT ternary block copolymer as the core binder resin, achieving a breakthrough synergistic performance through a precise molecular structure. This structure is not a simple physical mixture, but rather an organic combination of PLA's strong adhesion, PCL's excellent flexibility, and PBAT's controllable degradation characteristics through covalent bonds at the chemical chain segment level. The binder resin prepared by this invention solves the technical problem of the mutual constraint between adhesion and flexibility in traditional inks. Furthermore, by controlling the PBAT chain segment ratio, the ink's degradation behavior can match the degradation curve of mainstream biodegradable plastic films, achieving simultaneous degradation.

[0013] Building upon this foundation, this invention constructs a complete environmentally responsive degradation mechanism, introducing nano-titanium dioxide as a phototrigger to establish a unique photo-biological synergistic degradation pathway: under ultraviolet light, polymer chains are first broken, significantly reducing molecular weight and creating favorable conditions for subsequent microbial decomposition. This mechanism, combined with a tunable molecular structure, solves the industry pain point of ink residue after film degradation. Before composting, ultraviolet light activates nano-TiO2, generating reactive oxygen species, initiating and accelerating polymer chain breakage. This is equivalent to pre-treating the ink before it enters the composting site, resulting in lower molecular weight and larger specific surface area, thereby greatly accelerating the subsequent biodegradation rate in composting. Furthermore, this invention pioneers the use of a fully bio-based solvent system composed of ethyl lactate and γ-valerolactone, completely replacing traditional petroleum-based solvents, ensuring environmental friendliness throughout the entire life cycle from raw material source to final degradation, achieving a truly green closed loop.

[0014] Furthermore, the preparation method of the biocompatible binder resin includes the following steps:

[0015] Step 1: Under nitrogen protection, ε-caprolactone (CL) and 1,4-butanediol (BDO) are mixed and heated to 115-125°C with stirring until completely melted and mixed with 1,4-butanediol (BDO). 35-45% of the total mass of the composite catalyst is added, and the temperature is increased to 145-155°C at a heating rate of 1-2°C / min. The reaction is carried out for 2-3 hours to obtain a hydroxyl-terminated PCL prepolymer.

[0016] Step 2: Cool the system to 135~145℃, add PBAT prepolymer, and react at -0.05~-0.06MPa and 140~160°C for 1.5~2 hours to obtain PCL and PBAT diblock copolymer;

[0017] Step 3: Raise the system temperature to 160~170°C, add lactide monomer and the remaining composite catalyst, and react under a nitrogen atmosphere for 55~70 minutes to form a PLA, PCL, PBAT terblock copolymer;

[0018] Step 4: Apply high vacuum (< -0.095 MPa) and react at 175-185°C for 2-3 hours.

[0019] Step 5: Under nitrogen protection, melt extrusion is performed to obtain a terpolymer of PLA, PCL, and PBAT.

[0020] This invention overcomes the limitations of traditional physical blending in the preparation of binder resins. It employs a three-step sequential feeding method to construct a ternary block copolymer with an ABC-type linear sequence structure. This synthetic route first builds a flexible molecular backbone using PCL soft segments, then introduces PBAT segments as a key molecular-level compatibility bridge. This not only effectively regulates degradation performance but also establishes a stable transition region between PLA and PCL segments. Finally, the introduction of PLA hard segments establishes a strong foundation for adhesion. This step-by-step assembly molecular engineering strategy ensures the precise arrangement and stable bonding of each functional segment at the chemical bond level.

[0021] The composite catalyst system of this method employs a staged synergistic mechanism. The combined use of stannous octoate and tetrabutyl titanate forms a precise catalytic relay: stannous octoate efficiently drives ring-opening polymerization, while tetrabutyl titanate dominates transesterification and chain extension reactions in the high-temperature, high-vacuum stage, significantly enhancing the inter-block chemical bonding forces. This sequential activation of the catalyst, synergistically with the three-step feeding process, achieves precise control over the polymer molecular structure. Particularly noteworthy is that we transformed PBAT from a traditional independent component into a structural unit within the molecular chain, shifting its degradation regulation from macroscopic mixing to molecular-level control, thereby achieving a match between the degradation rate and the film substrate. This multi-level process design ultimately ensures that the binder resin of this invention possesses groundbreaking properties, including excellent adhesion, outstanding flexibility, and controllable degradation.

[0022] Further, by weight, 0.5-2.0 parts of 1,4-butanediol, 20-30 parts of ε-caprolactone, 20-30 parts of PBAT prepolymer, 45-55 parts of lactide, and 0.02-0.1 parts of composite catalyst;

[0023] The composite catalyst includes stannous octoate and tetrabutyl titanate, with a mass ratio of stannous octoate to tetrabutyl titanate of 3~3.5:1.

[0024] Furthermore, the preparation method of PBAT prepolymer includes the following: AA, PTA, BDO and catalyst are gradually heated to 180~220°C under nitrogen protection, and the esterification reaction is carried out for 3~5 hours until the water output reaches more than 90% of the theoretical value; under a vacuum of -0.05MPa to -0.08MPa, the temperature is gradually increased to 220~240°C, and the reaction is carried out for 1.5~3 hours; the reaction is stopped when the molecular weight is calculated to be 3000~5000g / mol by periodically sampling and testing the acid value.

[0025] In the preparation method of PBAT prepolymer, this invention abandons the traditional approach of treating PBAT as a final product, redefining it as a macromonomer with specific functional groups and molecular weight. By precisely controlling the excess ratio of the total carboxyl groups of adipic acid (AA) and terephthalic acid (PTA) to the hydroxyl groups of 1,4-butanediol (BDO), the product is ensured from the source to be predominantly carboxyl-terminated. This precise functional group design gives the synthesized prepolymer a clear reaction direction, laying the molecular foundation for its subsequent efficient block copolymerization with the terminal hydroxyl groups of PCL prepolymer.

[0026] Simultaneously, this invention establishes a complete reaction process monitoring system, accurately calculating the molecular weight growth by tracking changes in the system's acid value in real time. This dynamic monitoring method allows us to immediately terminate the reaction when the molecular chain reaches the ideal range of 3000~5000 g / mol. The resulting prepolymer not only has a narrow molecular weight distribution and a well-defined structure, but more importantly, its terminal carboxyl groups provide efficient reaction sites for subsequent block copolymerization. The PBAT prepolymer preparation method of this invention solves the common problems of poor compatibility and weak interfacial bonding in traditional physical blending methods, providing a key material basis for realizing molecular-level structure design.

[0027] Further, by weight, it contains 55-65 parts of terephthalic acid (PTA), 35-45 parts of adipic acid (AA), 35-45 parts of 1,4-butanediol (BDO), and 0.1-0.5 parts of catalyst.

[0028] Furthermore, in step 3, the lactide monomer needs to be purified before use. The specific purification method includes the following: at 15~25°C, add a mixed solvent of deionized water and ethanol to the crude lactide, mix evenly, filter and take the filter cake, and vacuum dry at 40~50°C to obtain the purified lactide.

[0029] The volume ratio of deionized water to ethanol is 1:1.5~2.5; the mass ratio of the mixed solvent to crude lactide is 3~5:1.

[0030] Industrial-grade crude lactide typically contains three key impurities: incompletely separated lactic acid monomers, water, and linear lactic acid oligomers. The presence of these impurities severely interferes with the polymerization process. Trace amounts of water act as chain terminators, terminating the growing polymer chains; residual acidic substances (such as lactic acid) react with metal catalysts like stannous octoate, partially or completely deactivating them. These side reactions not only hinder the normal growth of molecular chains, resulting in an excessively wide polymer molecular weight distribution that fails to meet design values, but also directly affect the chain structure regularity of the final ternary block copolymer. Therefore, obtaining high-purity lactide through purification is a prerequisite for accurately constructing the polymer molecular structure and ensuring the reproducibility of material properties.

[0031] A method for preparing a synchronously degradable gravure ink for biodegradable plastic films includes the following steps:

[0032] S100. Stir and dissolve a portion of the bio-based solvent, dispersant, and biocompatible binder resin to form a transparent resin liquid. Add organic pigment to form a uniform slurry. Grind the slurry to a fineness of ≤5μm to obtain a color paste.

[0033] S200. Add the remaining biocompatible binder resin to the remaining bio-based solvent to form a transparent resin-based liquid;

[0034] S300. Add the above resin base liquid to the above color paste, mix evenly, and then add nano titanium dioxide to form a homogeneous system.

[0035] After S400 filtration, the target ink is obtained.

[0036] Furthermore, in step S100, the bio-based solvent used to prepare the color paste accounts for 55% to 65% of the total mass of the bio-based solvent, and the biocompatible binder resin used to prepare the color paste accounts for 30% to 40% of the total mass of the biocompatible binder resin.

[0037] Further, in step S100, the transparent resin liquid is stirred at a speed of 500-800 rpm for about 25-35 minutes; and high-speed dispersion is performed at a speed of 1500-2000 rpm for 18-25 minutes to form a uniform slurry.

[0038] Furthermore, in step S400, filtration is performed using a 250-400 mesh filter.

[0039] This invention ensures optimal dispersion of pigment particles through precise material allocation and step-by-step processing. In the color paste preparation stage, more than half of the bio-based solvent is mixed with an appropriate amount of binder resin to form a low-viscosity carrier for preparing a transparent resin liquid, providing an ideal environment for efficient pigment wetting. Subsequently, under specific mechanical shear force, the organic pigment is thoroughly dispersed and ground to micron-level fineness, establishing a stable foundation for color performance. In the subsequent ink mixing stage, the base liquid rich in remaining resin is added to the color paste. This is not a simple dilution, but rather a gradual increase in the system viscosity and the proportion of film-forming substances, thereby precisely controlling the rheological properties and adhesion of the final ink. Finally, nano-titanium dioxide is introduced to provide a photodegradation trigger for the ink layer, accelerating the initiation of subsequent biodegradation and forming an active photo-biological synergistic degradation process.

[0040] The ink preparation method of this invention breaks away from the crude approach of mixing all raw materials at once, and adopts a two-stage resin-solvent distribution strategy. This allows the pigment grinding stage to be carried out at the optimal viscosity, ensuring ultra-fine pigment dispersion; while the ink mixing stage imparts the final mechanical properties required by the product, achieving an effective integration and separate optimization of dispersion efficiency and finished product performance.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1. The ink prepared by this invention not only firmly wets various biodegradable film substrates, but also maintains its integrity when the substrate is bent and stretched. Furthermore, it exhibits no sedimentation and stable viscosity after 30 days of storage. At a 60° measurement angle, its gloss reaches 85%, solving the problems of traditional inks being brittle on flexible substrates, having insufficient adhesion, and low gloss. At 30-day and 60-day test points, the ink of this invention exhibits highly synchronized degradation behavior (η value close to 1) on both PLA and PBAT, two mainstream substrates.

[0043] 2. This invention achieves a high degree of synchronization between the degradation cycle of the ink and the biodegradable plastic film through molecular structure design. At the same time, the introduction of the photo-biological dual degradation mechanism ensures the rapid start and thorough implementation of the degradation process. It can degrade outdoors for 60 days, exhibits excellent degradability, and eliminates the problem of microplastic pollution.

[0044] 3. The ink of this invention is composed entirely of bio-based components, from the binder resin to the solvent, ensuring environmental friendliness throughout its entire lifecycle, from raw material acquisition to product disposal. Furthermore, the entire production process of this invention has clear parameters and controllable procedures, exhibiting excellent batch stability and industrialization potential, providing reliable technical support for the large-scale promotion of environmentally friendly inks. Detailed Implementation

[0045] The present invention will now be further described.

[0046] Example 1

[0047] 600g of terephthalic acid (PTA), 400g of adipic acid (AA), 400g of 1,4-butanediol (BDO), and 3g of tetrabutyl titanate (catalyst).

[0048] The method for preparing PBAT prepolymer includes the following steps:

[0049] Step 1: Add PTA, AA, BDO and catalyst to the reactor in proportion. Under nitrogen protection, heat to 200°C at a rate of 2°C / min for esterification reaction. React for 4 hours until the water output reaches 92% of the theoretical value.

[0050] Step 2: After esterification, a polycondensation reaction was carried out at 230℃ and a vacuum of -0.09MPa for 2.5 hours. A sample was taken and tested; the acid value was 26.7 mg KOH / g, and the calculated molecular weight was close to Mn = 4200 g / mol. The vacuum pump was immediately shut off, and high-purity nitrogen was immediately introduced into the reactor. The cooling system of the reactor was then activated, and the temperature was lowered to 170℃ within 10 minutes, stopping the reaction.

[0051] Step 3: After reaching the target molecular weight, stop heating and vacuuming, and purge the reactor with nitrogen to release the vacuum. Quickly discharge the molten prepolymer and rapidly cool and solidify it on a cooling roller; granulate the cooled product to obtain the target PBAT prepolymer.

[0052] Example 2

[0053] 550g terephthalic acid, 350g adipic acid, 350g 1,4-butanediol, 1g tetrabutyl titanate.

[0054] The method for preparing PBAT prepolymer includes the following steps:

[0055] Step 1: Add PTA, AA, BDO and catalyst to the reactor in proportion, and carry out the esterification reaction under nitrogen protection by increasing the temperature to 180°C at a rate of 3°C / min for 3 hours until the water output reaches 90.2% of the theoretical value.

[0056] Step 2: After esterification, a polycondensation reaction is carried out at 220℃ and a vacuum of -0.08MPa for 1.5 hours. A sample test shows an acid value of 22.4 mg KOH / g, and the calculated molecular weight is close to Mn = 5,000 g / mol. The vacuum pump is immediately shut off, and high-purity nitrogen is immediately introduced into the reactor. The reactor's cooling system is then activated, and the temperature is lowered to 170℃ within 10 minutes, stopping the reaction.

[0057] Step 3: After reaching the target molecular weight, stop heating and vacuuming, and purge the reactor with nitrogen to release the vacuum. Quickly discharge the molten prepolymer and rapidly cool and solidify it on a cooling roller; granulate the cooled product to obtain the target PBAT prepolymer.

[0058] Example 3

[0059] 650g terephthalic acid, 450g adipic acid, 450g 1,4-butanediol, 5g tetrabutyl titanate.

[0060] The method for preparing PBAT prepolymer includes the following steps:

[0061] Step 1: Add PTA, AA, BDO and catalyst to the reactor in proportion, and carry out the esterification reaction under nitrogen protection by increasing the temperature to 220°C at a rate of 2°C / min for 5 hours until the output water reaches 93% of the theoretical value;

[0062] Step 2: After esterification, a polycondensation reaction was carried out at 240°C and a vacuum of -0.095 MPa for 3 hours. A sample was taken and tested; the acid value was 37.4 mg KOH / g, and the calculated molecular weight was close to Mn = 3,000 g / mol. The vacuum pump was immediately shut off, and high-purity nitrogen was immediately introduced into the reactor. The cooling system of the reactor was then activated, and the temperature was lowered to 170°C within 10 minutes, stopping the reaction.

[0063] Step 3: After reaching the target molecular weight, stop heating and vacuuming, and purge the reactor with nitrogen to release the vacuum. Quickly discharge the molten prepolymer and rapidly cool and solidify it on a cooling roller; granulate the cooled product to obtain the target PBAT prepolymer.

[0064] Methods and procedures for determining acid value (AV):

[0065] Reagents and instruments: KOH-ethanol standard solution (concentration C=0.05mol / L), phenolphthalein indicator (1% ethanol solution), neutral ethanol (pre-neutralized with KOH until phenolphthalein turns slightly red), conical flask (250mL), analytical balance, burette, pipette, etc.

[0066] The operation steps are as follows:

[0067] Accurate weighing: Accurately weigh approximately 1 to 2 grams (denoted as m, accurate to 0.0001 g) of PBAT prepolymer sample using an analytical balance and place it in a dry conical flask.

[0068] Dissolving the sample: Add 50 mL of neutral ethanol to the conical flask, heat and stir in a water bath at 60-70°C until the prepolymer is completely dissolved.

[0069] Titration: After the solution has cooled to room temperature, add 2-3 drops of phenolphthalein indicator. Titrate with the standardized KOH-ethanol standard solution until the solution turns slightly red and remains so for 15-30 seconds; this is the endpoint.

[0070] Record the volume (V, unit: mL) of KOH standard solution consumed.

[0071] Blank test: Under the same conditions, perform a blank test (without adding a sample) and record the volume of KOH consumed (V0, unit: mL).

[0072] Acid value calculation: Acid value (AV) represents the number of milligrams of potassium hydroxide required to neutralize acidic substances in 1 gram of sample. The calculation formula is: AV (mgKOH / g) = [(V-V0)×C×56.11] / m;

[0073] Where V: volume of KOH consumed in sample titration (mL);

[0074] V0: Volume of KOH consumed in blank titration (mL);

[0075] C: The accurate concentration (mol / L) of the KOH standard solution;

[0076] m: Sample mass (g);

[0077] 56.11: Molar mass of KOH (g / mol);

[0078] Examples 1-3 are mainly carboxyl-terminated linear PBAT prepolymers. Their number-average molecular weight (Mn) can be estimated based on the measured acid value (AV) using the formula Mn=112200 / AV. This formula is based on common practice in the polyester industry and assumes that each polymer molecular chain contributes an average of two titratable carboxyl groups.

[0079] Example 4

[0080] 1,4-Butanediol 12g, ε-caprolactone 250g, PBAT prepolymer (prepared by the method in Example 1) 250g, lactide 500g, composite catalyst 0.6g; wherein, the composite catalyst includes stannous octoate and tetrabutyl titanate, and the mass ratio of stannous octoate to tetrabutyl titanate is 3.2:1.

[0081] The preparation method of the biocompatible binder resin includes the following steps:

[0082] Preparation: Before use, lactide monomer needs to be purified. The specific purification method includes the following: At 20°C, add a mixed solvent of deionized water and ethanol to the crude lactide, mix well, filter and collect the filter cake, and dry under vacuum at 45°C to obtain purified lactide; the volume ratio of deionized water to ethanol is 1:2; the mass ratio of the mixed solvent to the crude lactide is 4:1.

[0083] ε-caprolactone, PBAT prepolymer, and initiator BDO were dried at 50°C and under a vacuum of -0.1 MPa for 4 hours to remove trace amounts of moisture.

[0084] Step 1: Under the condition of continuous introduction of dry nitrogen, ε-caprolactone and 1,4-butanediol are mixed, heated to 120°C and stirred until completely melted and mixed with 1,4-butanediol. 40% of the total mass of the composite catalyst is added, and the temperature is increased to 150°C at a heating rate of 1.5°C / min. The reaction is carried out for 2.5 hours.

[0085] Step 2: Lower the temperature of the reaction system to 140°C. Add the measured amount of PBAT prepolymer and evacuate to -0.055 MPa. React at 150°C for 100 minutes.

[0086] Step 3: Raise the system temperature to 165°C, and quickly add the purified lactide monomer and the remaining catalyst. React for 62 minutes under nitrogen protection.

[0087] Step 4: With a system vacuum of <-0.095 MPa, react at 180°C for 2.5 hours.

[0088] Step 5: After the reaction is complete, stop heating and stirring, and extrude the molten polymer through the die under positive nitrogen pressure.

[0089] After being cooled and cured in a cooling water tank, uniform resin particles are obtained by a pelletizer.

[0090] Example 5

[0091] 5g of 1,4-butanediol, 200g of ε-caprolactone, 200g of PBAT prepolymer (prepared by the method in Example 1), 450g of lactide, and 0.2g of composite catalyst; wherein the composite catalyst includes stannous octoate and tetrabutyl titanate, and the mass ratio of stannous octoate to tetrabutyl titanate is 3:1.

[0092] The preparation method of the biocompatible binder resin includes the following steps:

[0093] Preparation: Before use, lactide monomer needs to be purified. The specific purification method includes the following: At 15°C, add a mixed solvent of deionized water and ethanol to the crude lactide, mix thoroughly, filter, and collect the filter cake. Dry under vacuum at 40°C to obtain purified lactide. The volume ratio of deionized water to ethanol is 1:1.5; the mass ratio of the mixed solvent to the crude lactide is 3:1.

[0094] ε-caprolactone, PBAT prepolymer, and initiator BDO were dried at 50°C and under a vacuum of -0.1 MPa for 4 hours to remove trace amounts of moisture.

[0095] Step 1: Under the condition of continuous introduction of dry nitrogen, ε-caprolactone and 1,4-butanediol (BDO) are mixed, heated to 115°C and stirred until completely melted and mixed with 1,4-butanediol. 35% of the total mass of the composite catalyst is added, and the temperature is increased to 145°C at a heating rate of 2°C / min. The reaction is carried out for 2 hours.

[0096] Step 2: Lower the temperature of the reaction system to 135°C. Add the measured amount of PBAT prepolymer, and evacuate to a low vacuum of -0.05 MPa. React at 140°C for 1.5 hours.

[0097] Step 3: Raise the system temperature to 160°C, and quickly add the purified lactide monomer and the remaining catalyst. React for 55 minutes under nitrogen protection.

[0098] Step 4: With a system vacuum of <-0.095 MPa, react at 175°C for 2 hours.

[0099] Step 5: After the reaction is complete, stop heating and stirring, and extrude the molten polymer through the die under positive nitrogen pressure.

[0100] After being cooled and cured in a cooling water tank, uniform resin particles are obtained by a pelletizer.

[0101] Example 6

[0102] 20g of 1,4-butanediol, 300g of ε-caprolactone, 300g of PBAT prepolymer (prepared by the method in Example 1), 550g of lactide, and 1g of composite catalyst; wherein the composite catalyst includes stannous octoate and tetrabutyl titanate, and the mass ratio of stannous octoate to tetrabutyl titanate is 3.5:1.

[0103] The preparation method of the biocompatible binder resin includes the following steps:

[0104] Preparation: Before use, lactide monomer needs to be purified. The specific purification method includes the following: At 25°C, add a mixed solvent of deionized water and ethanol to the crude lactide, mix thoroughly, filter, collect the filter cake, and vacuum dry at 50°C to obtain purified lactide; the volume ratio of deionized water to ethanol is 1:2.5; the mass ratio of the mixed solvent to the crude lactide is 5:1.

[0105] ε-caprolactone, PBAT prepolymer, and initiator BDO were dried at 50°C and under a vacuum of -0.1 MPa for 4 hours to remove trace amounts of moisture.

[0106] Step 1: Under the condition of continuous introduction of dry nitrogen, ε-caprolactone and 1,4-butanediol are mixed, heated to 125°C and stirred until completely melted and mixed with 1,4-butanediol. 45% of the total mass of the composite catalyst is added, and the temperature is increased to 155°C at a heating rate of 2°C / min. The reaction is carried out for 3 hours.

[0107] Step 2: Lower the temperature of the reaction system to 145°C. Add the measured amount of PBAT prepolymer, and evacuate to a low vacuum of -0.06 MPa. React at 160°C for 2 hours.

[0108] Step 3: Raise the system temperature to 170°C, and quickly add the purified lactide monomer and the remaining catalyst. React for 70 minutes under nitrogen protection.

[0109] Step 4: With a system vacuum of <-0.095 MPa, react at 185°C for 3 hours.

[0110] Step 5: After the reaction is complete, stop heating and stirring, and extrude the molten polymer through the die under positive nitrogen pressure.

[0111] After being cooled and cured in a cooling water tank, uniform resin particles are obtained by a pelletizer.

[0112] Comparative Example 1

[0113] The catalyst was changed to a single stannous octoate, and the total amount of catalyst, its components, and the preparation method were the same as in Example 4.

[0114] Comparative Example 2

[0115] Instead of using the PBAT prepolymer prepared by the method in Example 1, commercially available high molecular weight PBAT resin with a molecular weight of 120,000 g / mol was directly added, and everything else was the same as in Example 4.

[0116] Comparative Example 3

[0117] Replace 250g of PBAT prepolymer with 150g of terephthalic acid and 100g of adipic acid, otherwise remain the same as in Example 4.

[0118] The preparation method includes the following steps:

[0119] Preparation: Dry PTA, AA, BDO, and CL at 50°C and -0.1MPa vacuum for 4 hours respectively.

[0120] The lactide monomer was purified using the same method as in Example 4.

[0121] Step 1, Esterification and Ring-Opening Mixed Reaction: Under nitrogen protection, PTA, AA, BDO, CL and all the measured amounts of the composite catalyst are added to the reactor.

[0122] The temperature was slowly increased to 150°C at a rate of 2°C / min, and the reaction was carried out at this temperature for 2 hours. During this stage, esterification of PTA and AA with BDO was expected, while CL underwent ring-opening polymerization, forming a disordered copolymer system. Subsequently, the temperature was increased to 160°C, and the reaction was continued for 1 hour to promote further dissolution and reaction of PTA.

[0123] Step 2: Raise the system temperature to 165°C and quickly add all the purified lactide monomer. React at 165°C for 2 hours under a nitrogen atmosphere.

[0124] Step 3: Apply a high vacuum (<-0.095MPa) and raise the temperature to 180°C, and react under these conditions for 2.5 hours.

[0125] Step 4: Stop heating and vacuuming, and release the vacuum by filling with nitrogen; extrude, cool, and pelletize the molten polymer.

[0126] Comparative Example 4

[0127] The mass ratio of stannous octoate to tetrabutyl titanate in the composite catalyst is 1:1, and the total amount of catalyst, its components, and the preparation method are the same as in Example 4.

[0128] Comparative Example 5

[0129] PLA500g, PCL250g, PBAT prepolymer 250g;

[0130] A method for preparing physically blended binder resin includes the following steps:

[0131] Step 1: Vacuum dry the PLA, PCL and PBAT prepolymer resin particles at 50°C for 4 hours to remove moisture.

[0132] Step 2: Add the dried PLA, PCL and PBAT prepolymers to the internal mixer in proportion, heat to 180°C under nitrogen protection, and melt-blend at 70 rpm for 18 minutes to ensure that all components are fully mixed.

[0133] Step 3: Extrude the blended molten material, cool it, and pelletize it to obtain a physically blended binder resin.

[0134] Comparative Example 6

[0135] The PBAT prepolymer prepared using the method of Example 2 was identical to that of Example 4 in terms of other components and preparation method.

[0136] Comparative Example 7

[0137] The PBAT prepolymer prepared using the method of Example 3 was identical to that of Example 4 in terms of other components and preparation method.

[0138] The performance parameters of the biocompatible binder resins prepared by the methods in Examples 4-6 are shown in Table 1.

[0139] Table 1. Performance parameters of the biocompatible binder resins prepared by the methods in Examples 4-6.

[0140]

[0141] As shown in Table 1, in Examples 4-6, due to the synergistic effect of the composite catalyst, the intrinsic viscosity of the prepared biocompatible binder resin was 1.35-1.68 dL / g. This indicates that a high molecular weight polymer was synthesized, and its molecular weight has good controllability under the preferred process parameters. The molecular weight distribution was between 1.45 and 1.51, indicating that the obtained polymer has a narrow molecular weight distribution. The mechanical strength was 32-41 MPa, and the elongation was 430%-520%, indicating that the binder resin successfully achieved an excellent balance between high strength and high toughness. Its unique block structure allows the material to simultaneously possess the adhesion support provided by the rigid PLA segments and the deformation capability imparted by the flexible PCL segments.

[0142] In summary, Examples 4-6 demonstrate that the biocompatible binder resin of the present invention possesses the key physical properties required as a binder for high-performance gravure inks. Its comprehensive performance is excellent and can be precisely controlled within a certain range by adjusting the synthesis parameters, providing an excellent material basis for preparing synchronously degradable ink products that meet different needs.

[0143] The performance parameters of the binder resins prepared by the method in Examples 4 and Comparative Examples 1-7 are shown in Table 2.

[0144] Table 2 Performance parameters of the binder resins prepared by the methods of Examples 4 and Comparative Examples 1-7

[0145]

[0146] Table 2 shows that Comparative Example 1, using only stannous octoate as a catalyst, suffered from weak chain extension, low molecular weight, and an intrinsic viscosity of only 0.95 dL / g due to the lack of titanate components. In Comparative Example 4, the mass ratio of stannous octoate to tetrabutyl titanate in the composite catalyst was 1:1. The excess titanate severely inhibited ring-opening polymerization and triggered excessive transesterification, resulting in a deteriorated molecular weight distribution, with K reaching 1.95. Comparative Examples 1 and 4 demonstrate the crucial role of composite catalysts and their specific ratios in obtaining high molecular weight polymers with narrow distributions.

[0147] Comparative Example 2 used commercially available high molecular weight PBAT resin directly, and Comparative Example 5 used physically blended binder resin. Both showed bimodality, which is a typical characteristic of physical blending, proving that they did not form a uniform block copolymer. Moreover, both had poor mechanical properties. This is because in physical blends, the interface between each phase is the weak point in mechanical properties. Under external force, cracks are very easy to be generated and propagate at the phase interface, leading to premature material failure.

[0148] In Comparative Example 3, the linker resin was prepared using direct copolymerization of monomers. PTA had limited solubility in the mixture of Cl and BDO, preventing effective esterification as it did in a pure BDO system. The functional groups of the four monomers exhibited different reactivity and optimal temperatures, leading to competition and interference within the same reactor, preventing the formation of an ordered structure. Due to incomplete PTA reaction, the proportion of monomers actually involved in building the polymer chain decreased. The chaotic reaction resulted in the formation of numerous chain terminations and low-molecular-weight cyclic byproducts, hindering effective chain growth; the intrinsic viscosity [η] was only 0.82 dL / g. The product was a complex mixture of random copolymers, homopolymers, and unreacted monomers, rather than a well-defined block copolymer, resulting in an extremely wide molecular weight distribution. The random molecular structure could not effectively transfer and disperse stress, leaving the material lacking both rigidity and toughness.

[0149] Comparative Example 6 uses the PBAT prepolymer prepared by the method of Example 2, with Mn ~ 5000 g / mol. The longer PBAT chains restrict the mobility of the carboxyl groups at the chain ends, reducing the collision efficiency with the terminal hydroxyl groups of the PCL prepolymer, resulting in a slower rate of the second-step block reaction. The longer PBAT and PLA segments enhance rigidity but sacrifice some flexibility, ultimately leading to a slight increase in overall rigidity and a slight decrease in toughness. Comparative Example 7 uses the PBAT prepolymer prepared by the method of Example 3, with Mn ~ 3000 g / mol. The short-chain prepolymer exhibits strong mobility and a high end-group concentration, enabling rapid reaction with the PCL prepolymer. However, the shorter chain segments result in insufficient strength, although the flexibility is excellent. The Mn value of 3,000-5,000 g / mol specified in this invention is an optimized range. This range ensures that the prepolymer has sufficient chain length to contribute effective mechanical properties and degradation characteristics, avoiding the possibility that excessively short chain segments will become weak points in the material. At the same time, it also ensures that the prepolymer has sufficient reactivity and compatibility in the copolymer system, avoiding the decrease in reaction efficiency and the intensification of phase separation due to excessively high molecular weight.

[0150] Example 7

[0151] A synchronously degradable gravure ink for biodegradable plastic films comprises the following components: 450g of biocompatible binder resin (prepared by the method of Example 4), 150g of organic pigment phthalocyanine blue B (PB15:3), 350g of bio-based solvent, 10g of nano titanium dioxide, 15g of dispersant (polyricinoleate JS-bm4), 3g of leveling agent (polyether-modified polydimethylsiloxane BYK-333), and 2g of defoamer (A-80 mineral oil defoamer).

[0152] The bio-based solvent is a composite solvent of ethyl lactate and γ-valerolactone, with a mass ratio of ethyl lactate to γ-valerolactone of 1:1.2.

[0153] A method for preparing a synchronously degradable gravure ink for biodegradable plastic films includes the following steps:

[0154] S100. A portion of the bio-based solvent, dispersant, and biocompatible binder resin are stirred at 650 rpm for 30 minutes to form a transparent resin liquid; organic pigments are added and dispersed at 1800 rpm for 20 minutes to form a uniform slurry; the above slurry is ground to a fineness ≤5μm to obtain a color paste.

[0155] The bio-based solvent used to prepare the color paste accounts for 60% of the total mass of the bio-based solvent, and the biocompatible binder resin used to prepare the color paste accounts for 35% of the total mass of the biocompatible binder resin.

[0156] S200. Add the remaining biocompatible binder resin to the remaining bio-based solvent to form a transparent resin-based liquid;

[0157] S300. Add the above resin base liquid to the above color paste, mix evenly, and then add nano titanium dioxide, leveling agent and defoamer to form a homogeneous system.

[0158] The target ink is obtained by filtering through S400 and 300 mesh filters.

[0159] Example 8

[0160] A synchronously degradable gravure ink for biodegradable plastic films comprises the following components: 350g of biocompatible binder resin (prepared by the method of Example 4), 120g of organic pigment quinacridone red (PR122), 300g of bio-based solvent, 5g of nano titanium dioxide, 10g of dispersant (polyricinoleate Js-bm4), 2g of leveling agent (polyether-modified polydimethylsiloxane BYK-333), and 1g of defoamer (A-80 mineral oil defoamer).

[0161] The bio-based solvent is a composite solvent of ethyl lactate and γ-valerolactone, with a mass ratio of ethyl lactate to γ-valerolactone of 1:0.5.

[0162] A method for preparing a synchronously degradable gravure ink for biodegradable plastic films includes the following steps:

[0163] S100: A portion of bio-based solvent, dispersant, and a portion of biocompatible binder resin are stirred at 500 rpm for 25 minutes to form a transparent resin liquid; organic pigments are added and dispersed at 1500 rpm for 18 minutes to form a uniform slurry; the above slurry is ground to a fineness ≤5μm to obtain a color paste.

[0164] The bio-based solvent used to prepare the color paste accounts for 55% of the total mass of the bio-based solvent, and the biocompatible binder resin used to prepare the color paste accounts for 30% of the total mass of the biocompatible binder resin.

[0165] S200. Add the remaining biocompatible binder resin to the remaining bio-based solvent to form a transparent resin-based liquid;

[0166] S300. Add the above resin base liquid to the above color paste, mix evenly, and then add nano titanium dioxide, leveling agent and defoamer to form a homogeneous system.

[0167] The target ink is obtained by filtering through an S400 or 250 mesh filter.

[0168] Example 9

[0169] A synchronously degradable gravure ink for biodegradable plastic films comprises the following components: 550g of biocompatible binder resin (prepared by the method of Example 4), 180g of organic pigment benzidine yellow G (PY12), 400g of bio-based solvent, 15g of nano titanium dioxide, 20g of dispersant (polyricinoleate Js-bm4), 5g of leveling agent (polyether modified polydimethylsiloxane BYK-333), and 3g of defoamer (A-80 mineral oil defoamer).

[0170] The bio-based solvent is a composite solvent of ethyl lactate and γ-valerolactone, with a mass ratio of ethyl lactate to γ-valerolactone of 1:2.

[0171] A method for preparing a synchronously degradable gravure ink for biodegradable plastic films includes the following steps:

[0172] S100: Mix a portion of the bio-based solvent, dispersant, and biocompatible binder resin at 800 rpm for 35 minutes to form a transparent resin liquid; add organic pigment and disperse at 2000 rpm for 25 minutes to form a uniform slurry; grind the slurry to a fineness ≤5 μm to obtain a color paste.

[0173] The bio-based solvent used to prepare the color paste accounts for 65% of the total mass of the bio-based solvent, and the biocompatible binder resin used to prepare the color paste accounts for 40% of the total mass of the biocompatible binder resin.

[0174] S200. Add the remaining biocompatible binder resin to the remaining bio-based solvent to form a transparent resin-based liquid;

[0175] S300. Add the above resin base liquid to the above color paste, mix evenly, and then add nano titanium dioxide, leveling agent and defoamer to form a homogeneous system.

[0176] The target ink is obtained by filtering through S400 and 400 mesh filters.

[0177] Comparative Example 8

[0178] In Example 4, the method omits the lactide purification step when preparing its binder resin, and directly uses industrial-grade crude lactide. The formulation and process are the same as in Example 7.

[0179] Comparative Example 9

[0180] The formulation does not contain nano-titanium dioxide, and the process is the same as in Example 7.

[0181] Comparative Example 10

[0182] The formula is the same as in Example 7.

[0183] The preparation method includes the following steps:

[0184] Step 1: Add all the bio-based solvents, biocompatible binder resins, organic pigments, dispersants, leveling agents, defoamers, and nano titanium dioxide simultaneously.

[0185] Step 2: Stir at 650 rpm for 30 minutes to initially mix the materials.

[0186] Step 3: Grind the above mixture using a sand mill to achieve a target fineness of ≤5μm.

[0187] The properties of the inks prepared using the methods of Examples 7-9 and Comparative Examples 8-10 are shown in Table 3.

[0188] Table 3 shows the properties of the inks prepared using the methods of Examples 7-9 and Comparative Examples 8-10.

[0189]

[0190] As shown in Table 3, Examples 7-9 all exhibited adhesion ≥95% and good flexibility, with no cracks upon bending; after 30 days of storage, there was no sedimentation and the viscosity remained stable; at a 60° measurement angle, the gloss was 82%-85%; and after 60 days of outdoor degradation, the degradation performance was excellent, confirming that the ink formulation and preparation process of this invention have high reliability and wide applicability.

[0191] In Comparative Example 8, the lactide was not purified, and the impurities resulted in a low molecular weight and poor adhesion of the binder, which in turn led to poor ink adhesion and a printing gloss of only 78%.

[0192] In Comparative Example 9, without the addition of nano-TiO2, the degradation mechanism of the ink degenerated from active photo-biological synergistic degradation to passive pure biodegradation, resulting in a lack of photodegradation triggers and slow degradation initiation. Consequently, the ink layer remained intact 60 days after degradation.

[0193] In Comparative Example 10, the step-by-step process was eliminated, and all materials were mixed at once, which is equivalent to destroying the optimal hydrodynamic environment required for efficient pigment dispersion. This resulted in extremely poor pigment dispersion, unstable system, ink fineness ≥15μm, and a large number of particles. The storage stability was poor, and after 30 days of storage, there was obvious sedimentation and clumping.

[0194] This demonstrates that the superior performance of the synchronously degradable gravure ink for biodegradable plastic films prepared in this invention is the result of the synergistic effect of high-purity binder resin, photodegradation aid, and stepwise preparation process.

[0195] The ink prepared in Example 7 was coated onto three mainstream biodegradable plastic films and accelerated degradation tests were conducted under simulated industrial composting conditions (58±2℃, humidity above 50%). The molecular weight (Mn) of the ink film and plastic substrate was periodically detected by gel permeation chromatography (GPC), and the results are shown in Table 4.

[0196] Table 4. Degradation test results of the ink prepared in Example 7 coated on three mainstream biodegradable plastic films.

[0197]

[0198] As shown in Table 4, at the test points of 30 days and 60 days, the ink of the present invention exhibited highly synchronized degradation behavior (η value close to 1) on both PLA and PBAT substrates, proving that its formulation has wide applicability.

[0199] On PHA substrates, the ink's degradation rate is slightly slower than that of the substrate (η=2.00). PHA is known for its extremely rapid biodegradation rate. Although this ink can degrade to a comparable extent (98% reduction in Mn in 60 days), it still lags slightly behind the substrate's rapid degradation. This indirectly proves that the degradation rate of this ink is adjustable; by fine-tuning the PBAT prepolymer ratio, it can be better matched to special fast-degrading substrates such as PHA.

[0200] The ink of this invention achieves simultaneous degradation on PLA and PBAT substrates and has the potential to be adapted to substrates with different degradation rates, such as PHA.

Claims

1. A synchronously degradable gravure ink for biodegradable plastic films, characterized in that, By weight, it comprises the following components: 35-55 parts of biocompatible binder resin, 12-18 parts of organic pigment, 30-40 parts of bio-based solvent, 0.5-1.5 parts of nano titanium dioxide, and 1-2 parts of dispersant; The biocompatible binder resin is a ternary block copolymer of PLA, PCL, and PBAT, in which PCL, PBAT, and PLA are linked by chemical bonds to form an ABC linear structure; the molecular weight of PBAT is 3000~5000 g / mol. The bio-based solvent is a composite solvent of ethyl lactate and γ-valerolactone, with a mass ratio of ethyl lactate to γ-valerolactone of 1:0.5~2. PCL was prepared by ε-caprolactone and 1,4-butanediol under the action of a composite catalyst, which included stannous octoate and tetrabutyl titanate.

2. The gravure ink according to claim 1, characterized in that, The preparation method of the biocompatible binder resin includes the following steps: Step 1: Under nitrogen protection, ε-caprolactone and 1,4-butanediol are mixed and heated to 115-125°C and stirred until completely melted and mixed with 1,4-butanediol. 35-45% of the total mass of the composite catalyst is added, and the temperature is increased to 145-155°C at a heating rate of 1-2°C / min. The reaction is carried out for 2-3 hours. Step 2: Cool the system to 135~145℃, add PBAT prepolymer, and react at -0.05~-0.06MPa and 140~160°C for 1.5~2 hours; Step 3: Raise the system temperature to 160~170°C, add lactide monomer and the remaining composite catalyst, and react under a nitrogen atmosphere for 55~70 minutes; Step 4: Apply high vacuum (< -0.095 MPa) and react at 175~185°C for 2-3 hours; Step 5: Under nitrogen protection, melt extrusion is performed to obtain a terpolymer of PLA, PCL, and PBAT.

3. The gravure ink according to claim 2, characterized in that, By weight, 1,4-butanediol 0.5~2.0 parts, ε-caprolactone 20~30 parts, PBAT prepolymer 20~30 parts, lactide 45~55 parts, and composite catalyst 0.02~0.1 parts; The mass ratio of stannous octoate to tetrabutyl titanate is 3~3.5:

1.

4. The gravure ink according to claim 2, characterized in that, The preparation method of PBAT prepolymer includes the following: under nitrogen protection, adipic acid, phthalic acid, 1,4-butanediol and catalyst are gradually heated to 180~220°C and esterified for 3~5 hours; under vacuum of -0.05~-0.08MPa, the temperature is gradually increased to 220~240°C and the reaction is carried out for 1.5~3 hours.

5. The gravure ink according to claim 4, characterized in that, By weight, 55-65 parts terephthalic acid, 35-45 parts adipic acid, 35-45 parts 1,4-butanediol, and 0.1-0.5 parts catalyst.

6. The gravure ink according to claim 2, characterized in that, In step 3, the lactide monomer needs to be purified before use. The specific purification method includes the following: at 15~25°C, add a mixed solvent of deionized water and ethanol to the crude lactide, mix well, filter and take the filter cake, and dry it under vacuum at 40~50°C to obtain the purified lactide. The volume ratio of deionized water to ethanol is 1:1.5~2.5; the mass ratio of the mixed solvent to crude lactide is 3~5:

1.

7. A method for preparing a synchronously degradable gravure ink for biodegradable plastic films as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S100. Stir and dissolve a portion of the bio-based solvent, dispersant, and biocompatible binder resin to form a transparent resin liquid. Add organic pigment to form a uniform slurry. Grind the slurry to a fineness of ≤5μm to obtain a color paste. S200. Add the remaining biocompatible binder resin to the remaining bio-based solvent to form a transparent resin-based liquid; S300. Add the above resin base liquid to the above color paste, mix evenly, and then add nano titanium dioxide to form a homogeneous system. After S400 filtration, the target ink is obtained.

8. The preparation method according to claim 7, characterized in that, In step S100, the bio-based solvent used to prepare the color paste accounts for 55% to 65% of the total mass of the bio-based solvent, and the biocompatible binder resin used to prepare the color paste accounts for 30% to 40% of the total mass of the biocompatible binder resin.

9. The preparation method according to claim 7, characterized in that, In step S100, the transparent resin liquid is stirred at a speed of 500-800 rpm for 25-35 minutes; and then dispersed at a speed of 1500-2000 rpm for 18-25 minutes to form a uniform slurry.

10. The preparation method according to claim 7, characterized in that, In step S400, the filter is made with a 250-400 mesh screen.

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