A bio-based copolyester material, its preparation method and application

Abstract

This invention relates to the field of polymer synthesis and processing technology, and discloses a bio-based copolyester material and its preparation method and application. The bio-based copolyester material is prepared by the following method: (1) Esterification: 2,5-furandicarboxylic acid, polyol and diol are mixed evenly and subjected to esterification reaction at 200-240℃ and 0-5kPa for 4-8 hours; after the reaction, the esterification product is mixed evenly with the catalyst and then put into a polycondensation reactor; (2) Polycondensation: the esterification product is subjected to polycondensation reaction at 250-270℃ and 0.01-10kPa vacuum; after the reaction, the bio-based copolyester material is obtained by filtration, underwater pelletizing and drying. This invention can better solve the delamination problem caused by the phase interface between bio-based copolyester and PETG copolyester and further improve flexibility while satisfying the film shrinkage performance and barrier performance.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis and processing technology, and more specifically, to a bio-based copolyester material, its preparation method, and its application. Background Technology

[0002] 2,5-Furandicarboxylic acid (FDCA) is a green, renewable chemical intermediate with strong chemical stability. It is soluble in water under alkaline conditions, while appearing as a white solid powder in acidic environments. FDCA is a crucial raw material in the chemical industry, playing a key role, particularly in the synthesis of corrosion-resistant plastics. It is also an important component of bio-based industrial products, listed as a biorefined carbohydrate derivative. Due to its unique properties, FDCA is widely used in the production of green, biodegradable polyester materials, especially in replacing traditional terephthalic acid (PTA).

[0003] In the polyester production process, 2,5-furandicarboxylic acid can effectively replace traditional terephthalic acid, becoming a green and renewable polyester monomer. Polyester materials synthesized based on 2,5-furandicarboxylic acid, when made into films, exhibit excellent barrier properties, heat resistance, and mechanical strength, significantly improving the overall performance of heat-shrinkable films. Especially in terms of environmental protection, polyester materials based on 2,5-furandicarboxylic acid have better biodegradability, meeting the current demand for environmentally friendly packaging materials.

[0004] However, despite the theoretically good performance of 2,5-furandicarboxylic acid and its contained polyester materials, current technologies still have some limitations. Polyesters produced by polymerizing 2,5-furandicarboxylic acid with glycols have high rigidity, making them prone to brittle fracture during film processing: 1. Difficulty in smoothly threading the film at the transverse stretching inlet; 2. Excessive brittleness during stretching, especially in low-temperature stretching applications like shrink films; 3. Excessive brittleness during winding, leading to breakage during traction and winding; 4. Due to its molecular structure, PEF cannot be directly used to prepare heat-shrinkable films and must be used in combination with PETG polyester. However, the resulting bio-based polyester heat-shrinkable films are prone to delamination. Summary of the Invention

[0005] The purpose of this invention is to provide a bio-based copolyester material, its preparation method, and its application, in order to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention provides the following solution: On the one hand, the present invention provides a method for preparing a bio-based copolyester material, comprising the following steps: (1) Esterification: The uniformly mixed 2,5-furandicarboxylic acid, polyol and diol are subjected to esterification reaction at 200-240℃ and 0-5kPa for 4-8 hours. After the reaction is complete, the esterification product is mixed evenly with the catalyst and then fed into the polycondensation reactor. (2) Polycondensation: The esterification product is subjected to polycondensation reaction at 250-270℃ and 0.01-10kPa vacuum for 4-10 hours; after the reaction is completed, the product is filtered, granulated underwater and dried to obtain the bio-based copolyester material.

[0007] Furthermore, the diol is one or more selected from ethylene glycol, propylene glycol, butanediol, neopentyl glycol, and 1,4-cyclohexanediethanol; The polyol is one or more of polyethylene glycol, polypropylene glycol, polybutylene glycol, and polyhexanediol.

[0008] Furthermore, the molar ratio of 2,5-furandicarboxylic acid, polyol and diol is 1:(0.1-1.9):(0.1-1.9), wherein the total molar ratio of acid to alcohol is 1:2; The catalyst is one or both of antimony-based or titanium-based catalysts, and the amount of catalyst used is 100-500 ppm.

[0009] On the other hand, the present invention also protects bio-based copolyester materials prepared by the above-described preparation method.

[0010] In another aspect, the present invention also provides a bio-based heat-shrinkable film, which is a three-layer composite structure, including two surface film layers and a core film layer sandwiched between the two surface film layers. The surface film layer and / or the core film layer contains the above-mentioned bio-based copolyester material, and the surface layer shedding ratio of the bio-based heat-shrinkable film is ≤5%.

[0011] Furthermore, the surface layer shedding ratio is obtained by the following method: (1) Select the 5cm of the bio-based heat-shrinkable film. Two 10cm cube samples were prepared. One of the samples was coated with tetrahydrofuran, with the coating thickness maintained at 0.5-1µm. Then the other sample was placed on top of the sample film coated with tetrahydrofuran solvent. (2) Select 3kg / piece 5cm A 10cm sample was subjected to compression for 5 minutes; (3) Use a tensile testing machine to stretch the two sample blocks after they are joined together until the two bio-based heat-shrinkable films are completely separated. (4) Place the bio-based heat-shrinkable film coated with tetrahydrofuran on graph paper and count the area of ​​the surface peeling location, and then calculate the average value; (5) Repeat the above calculation 50 times and sum up all the surface peeling areas; (6) Calculate the surface shedding ratio. The calculation formula is: Surface shedding ratio = Surface shedding area / 50.

[0012] Furthermore, the total thickness of the film is 20-80 μm, and the thickness of a single surface film layer is 6-40 μm; By weight, the surface film material comprises 72-84 parts of the bio-based copolyester material of claim 4, 10-15 parts of PETG polyester, 5-10 parts of PET polyester and 1-3 parts of opening agent; The core membrane material comprises 50-80 parts of PETG polyester material, 10-20 parts of PETG polyester material, and 10-30 parts of the bio-based copolyester material as described in claim 4.

[0013] Furthermore, the opening agent is silicon dioxide.

[0014] On the other hand, the present invention also provides a method for preparing the above-mentioned bio-based heat-shrinkable film, which is prepared by a three-layer co-extrusion biaxial stretching process, specifically including the following steps: The core film material and the surface film material are fed, mixed, melted, plasticized, filtered, and extruded, and then cast, stretched longitudinally, stretched laterally, trimmed, and wound to obtain the bio-based heat-shrinkable film. The core membrane layer filtration extrusion temperature is 250℃-270℃, and the surface membrane layer filtration extrusion temperature is 255℃-275℃.

[0015] Furthermore, the preheating temperature for longitudinal stretching is 95-105℃, the longitudinal stretching temperature is 85℃-95℃, the longitudinal stretching ratio is 1.0-3.0, the longitudinal stretching setting temperature is 75℃-90℃, and the total time for longitudinal preheating, stretching, and setting is 3-6 seconds. The preheating temperature for the lateral stretching is 105-125℃, the lateral stretching temperature is 85℃-100℃, the lateral stretching ratio is 4-5.5 times, the lateral stretching setting temperature is 85℃-90℃, the air volume power in the setting zone is 80-90%, and the lateral stretching setting time is 15-20 seconds.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention introduces polyols into the synthesis of bio-based polyesters to reduce the polar repulsion between rigid monomers, furanyl dicarboxylic acid, to prepare flexible polyesters. Simultaneously, during the preparation of the heat-shrinkable film containing this polyol, different proportions of bio-based flexible copolyester and PETG copolyester are added to the surface and core layers. This satisfies both film shrinkage and barrier properties while effectively addressing the delamination problem caused by the phase interface between the bio-based copolyester and PETG copolyester, and further improving flexibility. Furthermore, to better enhance the barrier properties of the polyester heat-shrinkable film, a gradient heat treatment process is employed during the transverse stretching stage. This fully promotes the crystallization of the polyester material in the bio-based copolyester heat-shrinkable film, reducing the permeation channels for water vapor, oxygen, and carbon dioxide, thereby improving barrier performance. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1

[0019] 1. Preparation of bio-based copolyester materials

[0020] (1) Esterification: Weigh 2,5-furandicarboxylic acid, polyethylene glycol (PEG-400), and ethylene glycol in a molar ratio of 1:1:1, where the molar ratio of acid to total alcohol is 1:2; after mixing the raw materials evenly, put them into the esterification kettle and carry out the esterification reaction at 220℃ and 3kPa for 6 hours. The reaction is stopped when the esterification water rate reaches 98.5%; mix the esterification product with the titanium catalyst (tetrabutyl titanate) evenly, with a catalyst dosage of 300ppm, and put it into the polycondensation kettle.

[0021] (2) Polycondensation: The polycondensation kettle is heated to 260°C and vacuumed to 1 kPa to carry out the polycondensation reaction for 7 hours. After the reaction, the product is filtered, granulated underwater, and vacuum dried at 80°C for 12 hours to obtain bio-based copolyester chips.

[0022] 2. Preparation of bio-based heat-shrinkable films

[0023] The film was prepared using a three-layer co-extrusion biaxial stretching process, with a total film thickness of 50 μm. The thickness of each of the top and bottom surface layers is 10 μm, and the thickness of the core layer is 30 μm. By weight, the surface layer formulation consists of 78 parts of the above-mentioned bio-based copolyester chips, 12 parts of PETG polyester, 8 parts of PET polyester, and 2 parts of silica opening agent. The core layer formulation consists of 65 parts of PETG polyester material, 15 parts of PETG polyester material, and 20 parts of the above-mentioned bio-based copolyester chips.

[0024] The raw materials for the surface film layer and the core film layer are mixed evenly according to the formula and fed into the corresponding twin-screw extruder for melt plasticization, filtration and extrusion. The extrusion temperature of the core film layer is 260℃ and the extrusion temperature of the surface film layer is 265℃. The extruded melt is co-extruded through a T-die and cast into a sheet. The cast sheet is then subjected to longitudinal stretching and transverse stretching in sequence: longitudinal stretching preheating temperature 100℃, stretching temperature 90℃, stretching ratio 2.0 times, setting temperature 80℃, and total time for longitudinal preheating, stretching and setting is 4s; transverse stretching preheating temperature 115℃, stretching temperature 90℃, stretching ratio 4.5 times, setting temperature 88℃, setting zone air volume power 85%, and transverse stretching setting time is 18s. After stretching, the film is trimmed and wound up to obtain a bio-based heat shrinkable film.

[0025] Example 2

[0026] 1. Preparation of bio-based copolyester materials

[0027] (1) Esterification: Weigh 2,5-furandicarboxylic acid, polypropylene glycol (PPG-400), and 1,4-cyclohexanediethanol in a molar ratio of 1:0.3:1.7, where the molar ratio of acid to total alcohol is 1:2; After the raw materials are mixed evenly, they are put into the esterification kettle and the esterification reaction is carried out at 200℃ and 5kPa for 8 hours. The reaction is stopped when the esterification water rate reaches 98.2%; The esterification product is mixed evenly with antimony catalyst (antimony trioxide) with a catalyst dosage of 100ppm and then put into the polycondensation kettle.

[0028] (2) Polycondensation: The polycondensation kettle is heated to 250°C and vacuumed to 10 kPa to carry out the polycondensation reaction for 10 h. After the reaction, the product is filtered, granulated underwater and dried under vacuum at 80°C for 12 h to obtain bio-based copolyester chips.

[0029] 2. Preparation of bio-based heat-shrinkable films

[0030] The film was prepared using a three-layer co-extrusion biaxial stretching process, with a total film thickness of 20 μm. The thickness of each of the top and bottom surface layers is 6 μm, and the thickness of the core layer is 8 μm. By weight, the surface layer formulation consists of 72 parts of the above-mentioned bio-based copolyester chips, 15 parts of PETG polyester, 10 parts of PET polyester, and 3 parts of silica opening agent. The core layer formulation consists of 50 parts of PETG polyester material, 20 parts of PETG polyester material, and 30 parts of the above-mentioned bio-based copolyester chips.

[0031] The raw materials for the surface film layer and the core film layer are mixed evenly according to the formula and fed into the corresponding twin-screw extruder for melt plasticization, filtration and extrusion. The extrusion temperature of the core film layer is 250℃ and the extrusion temperature of the surface film layer is 255℃. The extruded melt is co-extruded through a T-die and cast into a sheet. The cast sheet is then subjected to longitudinal stretching and transverse stretching in sequence: longitudinal stretching preheating temperature 95℃, stretching temperature 85℃, stretching ratio 1.0, setting temperature 75℃, and total time for longitudinal preheating, stretching and setting is 3s; transverse stretching preheating temperature 105℃, stretching temperature 85℃, stretching ratio 4.0, setting temperature 85℃, setting zone airflow power 80%, and transverse stretching setting time is 15s. After stretching, the film is trimmed and wound up to obtain a bio-based heat shrink film.

[0032] Example 3

[0033] 1. Preparation of bio-based copolyester materials

[0034] (1) Esterification: Weigh 2,5-furandicarboxylic acid, polybutanediol (PBG-400), and 1,4-butanediol in a molar ratio of 1:1.7:0.3, where the molar ratio of acid to total alcohol is 1:2; After the raw materials are mixed evenly, they are put into the esterification kettle and the esterification reaction is carried out at 240℃ and atmospheric pressure for 4 hours. The reaction is stopped when the esterification water rate reaches 98.8%; The esterification product is mixed evenly with a titanium-antimony composite catalyst (tetrabutyl titanate: antimony trioxide = 1:1), with a catalyst dosage of 500 ppm, and then put into the polycondensation kettle; (2) Polycondensation: The polycondensation kettle is heated to 270°C and vacuumed to 0.01 kPa to carry out the polycondensation reaction for 4 hours. After the reaction, the product is filtered, granulated underwater, and vacuum dried at 80°C for 12 hours to obtain bio-based copolyester chips.

[0035] 2. Preparation of bio-based heat-shrinkable films

[0036] The film was prepared using a three-layer co-extrusion biaxial stretching process, with a total film thickness of 80 μm. The thickness of each of the top and bottom surface layers is 20 μm, and the thickness of the core layer is 40 μm. By weight, the surface layer formulation consists of 84 parts of the above-mentioned bio-based copolyester chips, 10 parts of PETG polyester, 5 parts of PET polyester, and 1 part of silica opening agent. The core layer formulation consists of 80 parts of PETG polyester material, 10 parts of PETG polyester material, and 10 parts of the above-mentioned bio-based copolyester chips.

[0037] The raw materials for the surface film layer and the core film layer are mixed evenly according to the formula and fed into the corresponding twin-screw extruder for melt plasticization, filtration and extrusion. The extrusion temperature of the core film layer is 270℃ and the extrusion temperature of the surface film layer is 275℃. The extruded melt is co-extruded through a T-die and cast into a sheet. The cast sheet is then subjected to longitudinal stretching and transverse stretching in sequence: longitudinal stretching preheating temperature 105℃, stretching temperature 95℃, stretching ratio 3.0 times, setting temperature 90℃, and total time for longitudinal preheating, stretching and setting is 6s; transverse stretching preheating temperature 125℃, stretching temperature 100℃, stretching ratio 5.5 times, setting temperature 90℃, setting zone air volume power 90%, and transverse stretching setting time 20s. After stretching, the film is trimmed and wound up to obtain a bio-based heat shrinkable film.

[0038] Example 4

[0039] 1. Preparation of bio-based copolyester materials

[0040] (1) Esterification: Weigh 2,5-furandicarboxylic acid, polyethylene glycol (PEG-600), and ethylene glycol in a molar ratio of 1:0.5:1.5, where the molar ratio of acid to total alcohol is 1:2; After mixing the raw materials evenly, put them into the esterification kettle and carry out the esterification reaction at 230℃ and 2kPa for 5 hours. The reaction is stopped when the esterification water rate reaches 99.0%; Mix the esterification product with the titanium catalyst (isopropyl titanate) evenly, with a catalyst dosage of 200ppm, and put it into the polycondensation kettle; (2) Polycondensation: Heat the polycondensation kettle to 265℃, evacuate to a vacuum degree of 0.5kPa, and carry out the polycondensation reaction for 6 hours; After the reaction is completed, the product is filtered, granulated underwater, and vacuum dried at 80℃ for 12 hours to obtain bio-based copolyester chips.

[0041] 2. Preparation of bio-based heat-shrinkable films

[0042] The film was prepared using a three-layer co-extrusion biaxial stretching process, with a total film thickness of 40 μm. The thickness of each of the top and bottom surface layers is 8 μm, and the thickness of the core layer is 24 μm. By weight, the surface layer formulation consists of 80 parts of the above-mentioned bio-based copolyester chips, 12 parts of PETG polyester, 7 parts of PET polyester, and 1 part of silica opening agent. The core layer formulation consists of 70 parts of PETG polyester material, 15 parts of PETG polyester material, and 15 parts of the above-mentioned bio-based copolyester chips.

[0043] The raw materials for the surface film layer and the core film layer are mixed evenly according to the formula and fed into the corresponding twin-screw extruder for melt plasticization, filtration and extrusion. The extrusion temperature of the core film layer is 265℃ and the extrusion temperature of the surface film layer is 270℃. The extruded melt is co-extruded through a T-die and cast into a sheet. The cast sheet is then subjected to longitudinal stretching and transverse stretching in sequence: longitudinal stretching preheating temperature 100℃, stretching temperature 88℃, stretching ratio 2.5 times, setting temperature 85℃, and total time for longitudinal preheating, stretching and setting is 5s; transverse stretching preheating temperature 120℃, stretching temperature 95℃, stretching ratio 5.0 times, setting temperature 88℃, setting zone air volume power 85%, and transverse stretching setting time is 18s. After stretching, the film is trimmed and wound up to obtain a bio-based heat shrink film.

[0044] Comparative Example 1

[0045] This comparative example is pure PEF polyester without polyol modification.

[0046] 1. Comparison of the preparation of polyester materials

[0047] (1) Esterification: Weigh 2,5-furandicarboxylic acid and ethylene glycol in a molar ratio of 1:2. After mixing the raw materials evenly, put them into the esterification kettle and carry out the esterification reaction at 220℃ and 3kPa for 6 hours. The reaction is stopped when the esterification water rate reaches 98.5%. Mix the esterification product with tetrabutyl titanate evenly and add 300ppm of catalyst into the polycondensation kettle. (2) Polycondensation: The polycondensation kettle was heated to 260°C and vacuumed to 1 kPa to carry out the polycondensation reaction for 7 hours. After the reaction, the product was filtered, granulated underwater, and vacuum dried at 80°C for 12 hours to obtain pure PEF contrast polyester chips.

[0048] 2. Thin Film Preparation

[0049] Using the same three-layer co-extrusion structure, formulation ratio, extrusion and stretching process as in Example 1, except that the bio-based copolyester chips were replaced with the above-mentioned pure PEF chips, a comparative heat-shrinkable film was prepared.

[0050] Comparative Example 2

[0051] This comparative example uses a polyester modification method, but it is a single-layer blend structure.

[0052] 1. Preparation of polyester materials

[0053] Bio-based copolyester chips were prepared using the same synthesis process and parameters as in Example 1.

[0054] 2. Preparation of comparative thin films

[0055] A single-layer biaxial stretching process was used to produce a film with a total thickness of 50 μm. The formulation consisted of 78 parts of the above-mentioned bio-based copolyester chips, 12 parts of PETG polyester, 8 parts of PET polyester, and 2 parts of silica opening agent. The extrusion temperature and stretching process parameters were exactly the same as in Example 1, resulting in a comparative heat-shrinkable film.

[0056] Comparative Example 3

[0057] 1. Preparation of polyester materials

[0058] Bio-based copolyester chips were prepared using the same synthesis process and parameters as in Example 1.

[0059] 2. Preparation of comparative thin films

[0060] The three-layer co-extrusion structure, extrusion and stretching process are exactly the same as in Example 1, with only the formulation range adjusted: Surface film formulation: 60 parts of the above-mentioned bio-based copolyester chips, 25 parts of PETG polyester, 12 parts of PET polyester, and 3 parts of silica opening agent; Core membrane formulation: 30 parts PETG polyester material, 10 parts PETG polyester material, and 60 parts of the above-mentioned bio-based copolyester chips; A contrast heat-shrinkable film was prepared.

[0061] Comparative Example 4

[0062] 1. Preparation of polyester materials

[0063] Bio-based copolyester chips were prepared using the same synthesis process and parameters as in Example 1.

[0064] 2. Preparation of comparative thin films

[0065] Using the same three-layer co-extrusion structure, formulation, and extrusion temperature as in Example 1, only the stretching process range was adjusted: longitudinal stretching preheating temperature 80℃, stretching temperature 75℃, stretching ratio 3.5 times, setting temperature 70℃, total time 2s; transverse stretching preheating temperature 95℃, stretching temperature 75℃, stretching ratio 3.5 times, setting temperature 75℃, setting zone airflow power 70%, setting time 10s; a comparative heat shrink film was obtained.

[0066] Detection content and testing methods

[0067] All tests were performed in parallel five times, and the average value was taken. The test environment was 23℃ and 50% relative humidity.

[0068] (a) Mechanical property testing

[0069] Tested according to GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", the sample was dumbbell-shaped, the tensile speed was 50 mm / min, and the test indicators were: Longitudinal and transverse tensile strength (MPa); Longitudinal and transverse elongation at break (%): The higher the value, the better the material flexibility and the lower the risk of brittle fracture.

[0070] (II) Evaluation of processing performance

[0071] Simulated operating conditions of an industrial biaxial stretching production line; evaluation indicators: Success rate of membrane penetration at the horizontal pull entrance: The percentage of successful membrane penetrations out of 10 consecutive membrane penetration operations, corresponding to the problem of "unable to successfully penetrate membrane at the horizontal pull entrance"; Number of film breaks during continuous stretching: The number of times the film breaks during stretching in 1 hour of continuous production, corresponding to the problem of "brittle fracture during stretching"; Number of film breaks during winding: The number of times the film breaks during the continuous winding of 1000m film corresponds to the problem of "breakage due to excessive brittleness during winding".

[0072] (III) Interface bonding (anti-delamination) performance testing

[0073] Select 5 bio-based heat shrink film A 10cm sample block was coated with tetrahydrofuran, and then coated with another bio-based heat-shrinkable film of the same size. A 3kg sample plate was used to press the film, and after 5 minutes, the two films were separated using a tensile testing machine. The percentage of the surface layer of the tetrahydrofuran-coated film that peeled off after separation was counted and was less than 5%. (1) Select two small square samples of 5cm x 10cm. Apply tetrahydrofuran to one of the samples quickly and evenly, keeping the coating thickness at 0.5-1µm. Then quickly cover the sample film coated with tetrahydrofuran solvent with the other film.

[0074] (2) Select 3kg / piece 5cm A 10cm sample was subjected to compression for 5 minutes; (3) Use a tensile testing machine to stretch the two sample blocks after they are joined together until the film is completely separated. (4) Place the sample film on graph paper and count the area of ​​the surface peeling location, then calculate the average value; (5) Repeat the above calculation 50 times and sum up all the surface peeling areas; (6) Calculate the surface shedding ratio. The calculation formula is: Surface shedding ratio = Surface shedding area / 50.

[0075] (iv) Core performance testing

[0076] Heat shrinkage performance: According to GB / T13519-2016 "Polyester heat shrinkable film", a 100mm×100mm sample was immersed in a 90℃ constant temperature water bath for 10s. After cooling, the dimensional change was measured, and the longitudinal and transverse heat shrinkage rates (%) were calculated.

[0077] High barrier performance: Oxygen permeability (OTR): Tested according to GB / T31354-2014, under conditions of 23℃ and 50%RH, unit: cm. 3 / (m 2 24h 0.1MPa); Water vapor transmission rate (WVTR): Tested according to GB / T31034-2014, conditions 38℃, 90%RH, unit g / (m 2 24h).

[0078] Based on the testing content and methods, the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0079] Table 1

[0080] The following section describes a univariate parallel controlled experiment using the method for testing the surface peeling ratio of the bio-based composite heat-shrinkable film of this invention. A conventional, industry-standard test method of the same type was used as a control. All tests employed a uniform sample system. The test samples are shown in Table 2.

[0081] Table 2

[0082] Note: All samples were conditioned for 24 hours at 23℃ and 50% relative humidity. Each test group was sampled in parallel, and the basic size of the samples was uniformly 5cm×10cm.

[0083] All comparative examples used test samples that were completely identical to the method of the invention, except that the test method was replaced with the industry-standard interlayer bonding strength / delamination resistance test method, and the specific settings are shown in Table 3.

[0084] Table 3

[0085] The results of the parallel tests are shown in Table 4.

[0086] Table 4

[0087] As shown in the table, the dry peel strength of the comparative example 1 of the critical defect sample is 2.2 N / 15 mm, which meets the industry standard of ≥1.5 N / 15 mm and would be judged as a qualified product by conventional factory inspection. However, the surface peeling ratio measured by the method of this invention is 9%, which is close to the qualified threshold of ≤10% set by this invention. This can provide an early warning of the risk of delamination when the sample is printed and closed at the client's site. All conventional testing methods cannot identify this potential defect.

[0088] The method of this invention calculates the average value by accumulating 50 repeated tests, eliminating the single test error caused by uneven film thickness, solvent coating deviation, and local defects in the sample. The data repeatability is far superior to conventional tests, and it is fully adapted to the needs of industrial batch quality control.

[0089] Comparative verification: The single test result of the qualified reference sample in Comparative Example 2 was 4%, which deviated significantly from the 7% of the method of the invention. The coefficient of variation (CV value) of a single test reached 35%, which made it very easy for qualified samples to be misjudged as unqualified and unqualified samples to be misjudged as qualified. In contrast, the coefficient of variation of the test results of the method of the invention was only 4.2%, and the data stability was improved by more than 8 times, which can be used as a stable standard for factory quality inspection.

[0090] The method of this invention utilizes the synergistic effects of selective swelling of tetrahydrofuran through thin coating, compression bonding, and stretching separation to precisely target the interlayer interface between bio-based polyester and PETG. This effectively amplifies weak interfacial bonding defects, resulting in a detection sensitivity far exceeding that of conventional tests.

[0091] Comparative verification: The solvent immersion test of the failed control sample in Comparative Example 3 only measured 5% of the delamination area, and the 100-grid test in Comparative Example 4 only showed a level 3. Conventional methods could not accurately determine its severe delamination defect. However, the method of this invention measured a surface peeling rate of 28%, which far exceeded the 10% pass line. It can directly and accurately detect unqualified products and prevent defective products from flowing downstream.

[0092] The surface peeling ratio of the method of this invention has a direct linear correlation with the failure rate of the sealing process and the ink smudging rate of the core process of heat shrink film, and can be directly used as the product qualification standard. Industry test verification: when the surface peeling ratio measured by this method is ≤10%, the failure rate of the sealing process is ≤0.1%; when the peeling ratio is >10%, the failure rate of the sealing process soars to over 5%.

[0093] The peel strength of Comparative Example 1 and the 100-grid grade of Comparative Example 4 are both indirect mechanical indicators, which have no direct linear correlation with the actual production defect rate. They cannot be used to define a precise pass line through a single value, and can only be used as auxiliary reference indicators. They cannot meet the batch quality inspection requirements of the products of this invention.

[0094] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a bio-based copolyester material, characterized in that, Includes the following steps: (1) Esterification: The uniformly mixed 2,5-furandicarboxylic acid, polyol and diol are subjected to esterification reaction at 200-240℃ and 0-5kPa for 4-8 hours. After the reaction is complete, the esterification product is mixed evenly with the catalyst and then fed into the polycondensation reactor. (2) Polycondensation: The esterification product is subjected to polycondensation reaction at 250-270℃ and 0.01-10kPa vacuum for 4-10 hours; after the reaction is completed, the product is filtered, granulated underwater and dried to obtain the bio-based copolyester material.

2. The method for preparing the bio-based copolyester material according to claim 1, characterized in that, The diol is one or more selected from ethylene glycol, propylene glycol, butanediol, neopentyl glycol, and 1,4-cyclohexanediethanol. The polyol is one or more of polyethylene glycol, polypropylene glycol, polybutylene glycol, and polyhexanediol.

3. The method for preparing the bio-based copolyester material according to claim 1, characterized in that, The molar ratio of 2,5-furandicarboxylic acid, polyol and diol is 1:(0.1-1.9):(0.1-1.9), wherein the total molar ratio of acid to alcohol is 1:2; The catalyst is one or both of antimony-based or titanium-based catalysts, and the amount of catalyst used is 100-500 ppm.

4. A bio-based copolyester material, characterized in that, It is prepared by any one of claims 1-3.

5. A bio-based heat-shrinkable film, characterized in that, It is a three-layer composite structure, including two surface film layers and a core film layer sandwiched between the two surface film layers. The surface film layer and / or the core film layer contains the bio-based copolyester material as described in claim 3, and the surface shedding rate of the bio-based heat shrink film is ≤5%.

6. The bio-based heat-shrinkable film according to claim 5, characterized in that, The surface layer shedding ratio was obtained using the following method: (1) Select the 5cm of the bio-based heat-shrinkable film. Two 10cm cube samples were prepared. One of the samples was coated with tetrahydrofuran, with the coating thickness maintained at 0.5-1µm. Then the other sample was placed on top of the sample film coated with tetrahydrofuran solvent. (2) Select 3kg / piece 5cm A 10cm sample was subjected to compression for 5 minutes; (3) Use a tensile testing machine to stretch the two sample blocks after they are joined together until the two bio-based heat-shrinkable films are completely separated. (4) Place the bio-based heat-shrinkable film coated with tetrahydrofuran on graph paper and count the area of ​​the surface peeling location, and then calculate the average value; (5) Repeat the above calculation 50 times and sum up all the surface peeling areas; (6) Calculate the surface shedding ratio. The calculation formula is: Surface shedding ratio = Surface shedding area / 50.

7. The bio-based heat-shrinkable film according to claim 5, characterized in that, The total thickness of the film is 20-80 μm, and the thickness of a single surface film layer is 6-40 μm. By weight, the surface film material comprises 72-84 parts of the bio-based copolyester material of claim 4, 10-15 parts of PETG polyester, 5-10 parts of PET polyester and 1-3 parts of opening agent; The core membrane material comprises 50-80 parts of PETG polyester material, 10-20 parts of PETG polyester material, and 10-30 parts of the bio-based copolyester material as described in claim 4.

8. The bio-based heat-shrinkable film according to claim 7, characterized in that, The opening agent is silicon dioxide.

9. A method for preparing a bio-based heat-shrinkable film according to any one of claims 5-8, characterized in that, It is prepared using a three-layer co-extrusion biaxial stretching process, specifically including the following steps: The core film material and the surface film material are fed, mixed, melted, plasticized, filtered, and extruded, and then cast, stretched longitudinally, stretched laterally, trimmed, and wound to obtain the bio-based heat-shrinkable film. The core membrane layer filtration extrusion temperature is 250℃-270℃, and the surface membrane layer filtration extrusion temperature is 255℃-275℃.

10. The method for preparing the bio-based heat-shrinkable film according to claim 8, characterized in that, The preheating temperature for longitudinal stretching is 95-105℃, the longitudinal stretching temperature is 85℃-95℃, the longitudinal stretching ratio is 1.0-3.0, the longitudinal stretching setting temperature is 75℃-90℃, and the total time for longitudinal preheating, stretching, and setting is 3-6 seconds. The preheating temperature for the lateral stretching is 105-125℃, the lateral stretching temperature is 85℃-100℃, the lateral stretching ratio is 4-5.5 times, the lateral stretching setting temperature is 85℃-90℃, the air volume power in the setting zone is 80-90%, and the lateral stretching setting time is 15-20 seconds.

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