A PBS laminated material and a preparation method and application thereof

Abstract

The application discloses PBS laminating material and a preparation method and application thereof, and belongs to the technical field of high polymer materials. The PBS laminating material comprises a functional layer A and an adhesion layer B which are directly attached to each other, the functional layer A comprises polyglycolic acid, surface modified bamboo powder, a multifunctional epoxy compatibilizer, a carbodiimide stabilizer, an antioxidant, a nucleating agent, a laminating rheological aid and a polybutylene succinate-based resin, and the adhesion layer B comprises a functional polybutylene succinate-based adhesion resin, a multifunctional epoxy chain extender, an antioxidant and PBS and / or PBSA. In the preparation, the PBS-based resin is first made into a continuous phase, then the surface modified bamboo powder is pre-wetted and dispersed, and then the PGA is added in the later stage and the residence time is controlled, so that the obtained material has high rigidity, good film forming stability, paper base adhesion and heat sealing performance, and is suitable for food packaging paper, paper cups, paper bowls, express packaging paper and paper-based heat sealing packaging.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a PBS coating material, its preparation method, and its application. Background Technology

[0002] With the increasing demand for biodegradable materials in paper-based packaging, food packaging, and disposable catering packaging, replacing traditional polyethylene lamination layers with biodegradable polyester has become an important development direction for paper-based composite materials. Polybutylene succinate (PBS) has good biodegradability, flexibility, and processing performance, making it suitable for use in paper-based lamination materials. However, its rigidity, heat resistance, and barrier properties are relatively insufficient. Under thin-layer lamination and high-speed processing conditions, it may also experience problems such as insufficient melt strength, uneven film surface, unstable edges, or insufficient heat-sealing performance.

[0003] To improve the performance of PBS materials, existing technologies typically incorporate polyglycolic acid (PGA), inorganic fillers, or natural fiber fillers. PGA possesses high strength, high rigidity, and good barrier properties, but its compatibility with PBS is insufficient, and its processing window is narrow. It is also prone to degradation at high temperatures and long residence times, leading to problems such as melt viscosity fluctuations, film defects, pinholes, or film breakage. Bamboo powder is widely available and inexpensive, and can be used to improve material rigidity and reduce costs. However, bamboo powder has many hydroxyl groups on its surface, high hygroscopicity, and weak interfacial bonding with the polyester matrix. Direct addition can easily lead to agglomeration, filler exposure, pinholes, film roughness, and decreased mechanical properties.

[0004] Furthermore, paper-based coating materials not only require the coating layer itself to have good rigidity, heat resistance, barrier properties, and film-forming stability, but also require the coating layer to form a stable adhesion with the paper base and maintain good heat-sealing performance. If a functional system containing a high proportion of PGA and bamboo powder is directly laminated with the paper base, the adhesion effect and heat-sealing strength of the paper base are easily reduced due to the high rigidity of the functional layer, local exposure of fillers, or insufficient interfacial wettability. If an adhesive layer is simply added, interlayer separation may occur during heat sealing, folding, die-cutting, or subsequent use due to the lack of effective interfacial compatibility or reactive bridging between the functional layer and the adhesive layer.

[0005] Therefore, in PBS-based biodegradable coating materials, how to improve functional performance by introducing PGA and bamboo powder while reducing melt fluctuations and film defects caused by high-temperature processing degradation of PGA and poor filler dispersion, and taking into account the stability of paper substrate adhesion and interlayer bonding, still needs further improvement. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a PBS coating material, its preparation method, and its application. By setting up a functional layer A and an adhesive layer B that are directly bonded to each other, and by combining surface-modified bamboo powder, multifunctional epoxy compatibilizers, carbodiimide stabilizers, and a segmented feeding process, the compatibility and coating processing stability of the PBS / PGA / bamboo powder three-phase system are improved. Furthermore, the rigidity, heat resistance, paper-based adhesion, heat-sealing performance, and interlayer bonding strength between functional layer A and adhesive layer B are also enhanced.

[0007] To achieve the above objectives, the present invention provides a PBS coating material, wherein the PBS coating material comprises a functional layer A and an adhesive layer B directly bonded together. Based on 100 parts by weight of the raw materials of the functional layer A, the functional layer A comprises: 10-20 parts of polyglycolic acid, 8-15 parts of surface-modified bamboo powder, 0.2-0.8 parts of a multifunctional epoxy compatibilizer, 0.05-0.4 parts of a carbodiimide stabilizer, 0.05-0.3 parts of an antioxidant, 0.05-0.5 parts of a nucleating agent, and 0.05-0.4 parts of a coating rheology modifier, with the balance being polybutylene succinate-based resin. Based on 100 parts by weight of the raw materials for the tackifying layer B, the tackifying layer B comprises: 8-20 parts of functionalized polybutylene succinate-based tackifying resin, 0.05-0.3 parts of multifunctional epoxy chain extender, and 0.05-0.3 parts of antioxidant, with the balance being polybutylene succinate and / or polybutylene adipate. The functionalized polybutylene succinate-based tackifying resin is maleic anhydride-grafted polybutylene succinate and / or glycidyl methacrylate-grafted polybutylene succinate.

[0008] Further, the polybutylene succinate-based resin is polybutylene succinate, or a blend of polybutylene succinate and polybutylene succinate-adipate. When the polybutylene succinate-based resin is a blend of polybutylene succinate and polybutylene succinate-adipate, the proportion of polybutylene succinate in the total mass of the polybutylene succinate-based resin is not less than 70 wt%. Through the above limitations, while maintaining the film-forming ability of the PBS continuous phase, the material toughness and coating process adaptability can be appropriately adjusted, avoiding weakening of the rigidity and heat resistance of functional layer A due to excessive flexible components.

[0009] Further, the surface-modified bamboo powder includes a bamboo powder core material and a polyester affinity modification layer located on the surface of the bamboo powder core material. The polyester affinity modification layer contains a coating component formed by epoxy silane coupling residues and maleic anhydride-grafted polybutylene succinate, wherein the amount of maleic anhydride-grafted polybutylene succinate is 2–10 wt% of the bamboo powder core material. The particle size D50 of the surface-modified bamboo powder is 5–30 μm, and the moisture content is not higher than 0.3 wt%. Through epoxy silane coupling treatment and maleic anhydride-grafted polybutylene succinate coating modification, the surface hydrophilicity of the bamboo powder can be reduced, the interfacial bonding force between the bamboo powder and the PBS-based continuous phase can be improved, and the aggregation and interfacial defects of the bamboo powder in the coating layer can be reduced.

[0010] Furthermore, both the multifunctional epoxy compatibilizer and the multifunctional epoxy chain extender are styrene-methacrylate-glycidyl methacrylate copolymers. The multifunctional epoxy compatibilizer, used in functional layer A, facilitates reaction with the terminal carboxyl or hydroxyl groups of PBS and PGA, improving the interfacial compatibility between the PBS / PGA phases and enhancing melt strength and film stability. The multifunctional epoxy chain extender, used in tackifying layer B, improves the melt strength and interfacial reactivity of tackifying layer B. The carbodiimide stabilizer is preferably polycarbodiimide, used to inhibit the hydrolytic degradation of the polyester material during processing and use. The antioxidant is a combination of hindered phenolic antioxidants and phosphite antioxidants. Preferably, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The nucleating agent is one or more of talc, nano-silica, and nano-montmorillonite. The rheology modifier for film coating is polyester wax and / or branched polybutylene succinate.

[0011] Further, the mass ratio of functional layer A to tackifying layer B is 75:25 to 92:8. The grafting rate of maleic anhydride-grafted polybutylene succinate or glycidyl methacrylate-grafted polybutylene succinate is 0.3 to 2.0 wt%. By controlling the ratio of functional layer A to tackifying layer B, functional layer A can provide the main rigidity, heat resistance, and barrier properties, while tackifying layer B maintains sufficient thickness to improve adhesion and heat-sealing performance with the paper base.

[0012] This invention also provides a method for preparing the PBS coating material, comprising the following steps: drying bamboo powder at 80-105℃ for 4-8 hours, then sequentially treating it with an epoxy silane coupling agent and modifying it by grafting maleic anhydride onto polybutylene succinate to obtain surface-modified bamboo powder. Preferably, the epoxy silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane (KH-560); preparing functional layer A granules using a twin-screw extruder with a first, second, and third feed port, wherein the first, second, and third feed ports are sequentially arranged along the material conveying direction; adding polybutylene succinate-based resin, an antioxidant, and a first portion of multifunctional epoxy compatibilizer through the first feed port, causing the polybutylene succinate-based resin to melt and form a continuous phase; adding surface-modified bamboo powder, a nucleating agent, and a coating rheology modifier through the second feed port, thereby modifying the surface. Bamboo powder is pre-wetted and dispersed in the continuous phase; polyglycolic acid, carbodiimide stabilizer, and a second part of multifunctional epoxy compatibilizer are added through the third feed port for reaction, compatibilization, and dispersion, and the average residence time of polyglycolic acid from the third feed port to the outlet of the twin-screw extruder is controlled to be 30-120s; after vacuum devolatilization, cooling, and pelletizing, functional layer A granules are obtained; polybutylene succinate and / or polybutylene adipate, functionalized polybutylene succinate-based tackifying resin, multifunctional epoxy chain extender, and antioxidant are melt-blended to obtain tackifying layer B granules; the functional layer A granules and the tackifying layer B granules are plasticized by two extruders respectively, and then composited in a co-extrusion die to form a double-layer melt film, with the tackifying layer B located on the side facing the paper base and the functional layer A located on the side away from the paper base, and then traction and cooling are performed to obtain the PBS coating material.

[0013] Furthermore, the second feed port is located at 35-55% of the effective length of the twin-screw extruder screw, and the third feed port is located at 60-80% of the effective length of the twin-screw extruder screw. By setting the feed positions as described above, the PBS-based resin can first form a continuous melt, then the surface-modified bamboo powder can be fully pre-wetted and dispersed in the continuous phase. Subsequently, the PGA completes melting dispersion and compatibilization within a shorter high-temperature residence time, thereby reducing the degradation risk caused by prolonged high-temperature residence of PGA and improving the melt stability and film uniformity of functional layer A.

[0014] Furthermore, the temperature of the polybutylene succinate-based resin plasticizing section of the twin-screw extruder is 120–165°C, the temperature of the surface-modified bamboo powder wetting and dispersion section is 150–185°C, the temperature of the transition section before the addition of polyglycolic acid is 190–210°C, the temperature of the polyglycolic acid reaction and dispersion section is 215–235°C, the temperature of the vacuum devouring section is 220–235°C, and the vacuum devouring pressure is -0.06–-0.095 MPa. The first part of the multifunctional epoxy compatibilizer accounts for 20–60 wt% of the total multifunctional epoxy compatibilizer, and the second part of the multifunctional epoxy compatibilizer is the remaining part. By controlling the temperature in stages and adding the multifunctional epoxy compatibilizer in stages, the formation of the PBS continuous phase, the wetting and dispersion of bamboo powder, and the post-reaction compatibilization of PGA can be taken into account, thereby improving the overall processing stability of the material.

[0015] Furthermore, the polyglycolic acid is dried at 60–90°C for 4–10 hours before being added to the third feed inlet, and the moisture content of the polyglycolic acid is not higher than 500 ppm. The melt temperature of the functional layer A granules is 220–240°C, the melt temperature of the tackifying layer B granules is 190–230°C, and the unit area mass of the double-layer melt film is 12–35 g / m². 2 The adhesive layer B has a unit area mass of 2-8 g / m³. 2 By controlling the moisture content of PGA and the unit area mass of the double-layer melt film, the continuity, thickness uniformity, and compatibility of the coating layer with the paper base can be further improved.

[0016] This invention also provides a paper-based composite article, comprising a paper base and a coating layer disposed on at least one surface of the paper base, the coating layer being formed of the aforementioned PBS coating material. The tackifying layer B is directly adhered to the surface of the paper base, and the functional layer A is located on the side of the tackifying layer B away from the paper base. The paper-based composite article can be food packaging paper, paper cups, paper bowls, kraft paper composite packaging, express delivery packaging paper, lunch box lining, or paper-based heat-sealed packaging.

[0017] Compared with the prior art, the present invention provides a PBS coating material, its preparation method and application, which has the following beneficial effects: 1. This invention employs a two-layer structure in which functional layer A and tackifying layer B are directly bonded together. Functional layer A primarily enhances rigidity, heat resistance, barrier properties, and film-forming stability, while tackifying layer B primarily serves to bond with the paper substrate and facilitate heat sealing. Compared to single-layer PBS / PGA / bamboo powder coating materials, this structure avoids the problem of decreased adhesion caused by direct contact between the high PGA and high bamboo powder functional systems and the paper substrate, thus balancing the performance of the outer layer and the composite performance of the inner paper substrate.

[0018] 2. This invention introduces surface-modified bamboo powder into functional layer A, and makes its surface contain epoxy silane coupling residues and a coating component formed by maleic anhydride grafted polybutylene succinate. This can improve the interfacial compatibility between bamboo powder and PBS-based resin, and reduce bamboo powder agglomeration and interfacial defects. At the same time, the combined use of multifunctional epoxy compatibilizers and carbodiimide stabilizers is beneficial to improving the reaction compatibilization effect and hydrolytic stability of the PBS / PGA system, and reducing melt fluctuations and film defects caused by PGA degradation during processing.

[0019] 3. The preparation method of this invention employs a segmented feeding and segmented temperature control process. First, the PBS-based resin forms a continuous phase. Then, the surface-modified bamboo powder is pre-wetted and dispersed within the continuous phase. Subsequently, PGA is added from the later stage, and its high-temperature residence time is controlled. This process helps reduce the degradation risk caused by prolonged high-temperature residence of PGA and improves the dispersion uniformity and melt rheological stability of the three-phase system. The resulting PBS-coated material is suitable for paper-based composite products such as food packaging paper, paper cups, paper bowls, kraft paper composite packaging, express packaging paper, lunch box liners, and paper-based heat-sealed packaging.

[0020] 4. The tackifying layer B of this invention uses a functionalized polybutylene succinate-based tackifying resin, namely maleic anhydride-grafted PBS and / or glycidyl methacrylate-grafted PBS. This functionalized PBS-based tackifying resin can not only interact or react with the hydroxyl groups on the paper substrate surface through anhydride groups or epoxy groups, thereby improving the adhesion between the tackifying layer B and the paper substrate, but also, under the high-temperature melting contact and pressure of the co-extrusion die, its residual active groups can also react in situ or interact with the multifunctional epoxy compatibilizer, PBS / PGA terminal carboxyl groups or terminal hydroxyl groups in functional layer A, forming a reactive bridging structure at the interface between functional layer A and tackifying layer B, thereby improving the interlayer bonding strength of the bilayer film and avoiding delamination or peeling during coating, heat sealing, folding, and subsequent use.

[0021] 5. This invention improves the interfacial bonding and compatibility between bamboo powder and the PBS-based continuous phase, between PBS and PGA phases, and between functional layer A and tackifying layer B by combining surface-modified bamboo powder, multifunctional epoxy compatibilizers, carbodiimide stabilizers, and functionalized PBS-based tackifying resins. It also reduces the impact of PGA processing degradation on melt stability. This reduces defects such as filler agglomeration, phase separation, pinholes, and film breakage, resulting in a material with good rigidity, heat resistance, barrier properties, paper-based adhesion, heat-sealing performance, and interlayer bonding strength. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the preparation method of the present invention; Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In the following examples and comparative examples, polybutylene succinate is referred to as PBS, polybutylene adipate is referred to as PBSA, and polyglycolic acid is referred to as PGA. Maleic anhydride-grafted PBS and glycidyl methacrylate-grafted PBS can be commercially available products, or they can be prepared by melt extrusion of PBS, the corresponding graft monomers, and a peroxide initiator. The multifunctional epoxy compatibilizer and multifunctional epoxy chain extender are both commercially available styrene-methacrylate-glycidyl methacrylate multifunctional epoxy copolymers with an epoxy equivalent of 280-320 g / eq and a number average molecular weight of 6000-8000. The carbodiimide stabilizer is polycarbodiimide. The antioxidant is a 1:1 mass mixture of hindered phenolic antioxidant (antioxidant 1010) and phosphite antioxidant (antioxidant 168). The epoxy silane coupling agent used is γ-glycidoxypropyltrimethoxysilane (KH-560). The nucleating agent used is talc, nano-silica, or nano-montmorillonite. The membrane rheology modifier used is polyester wax and / or branched PBS.

[0025] To evaluate the paper-based composite performance of the obtained PBS coating materials, the PBS coating materials prepared in each example and comparative example were coated online with 250g / m² food-grade packaging paper with the tackifying layer B facing the paper base to obtain test paper-based composite samples. Example

[0026] The raw materials for functional layer A, based on 100 parts by weight, include: 71.65 parts PBS, 15 parts PGA, 12 parts surface-modified bamboo powder, 0.5 parts multifunctional epoxy compatibilizer, 0.2 parts polycarbodiimide, 0.15 parts antioxidant, 0.3 parts talc, and 0.2 parts branched PBS.

[0027] The raw materials for tackifying layer B, based on 100 parts by weight, include: 85.70 parts of PBS / PBSA blended resin, 14 parts of functionalized PBS-based tackifying resin, 0.15 parts of multifunctional epoxy chain extender, and 0.15 parts of antioxidant. The mass ratio of PBS to PBSA in the PBS / PBSA blended resin is 85:15; the functionalized PBS-based tackifying resin is composed of maleic anhydride-grafted PBS and glycidyl methacrylate-grafted PBS in a mass ratio of 7:3, with a grafting rate of 1.0 wt%.

[0028] The preparation method of surface-modified bamboo powder is as follows: bamboo powder is dried at 95℃ for 6 hours to reduce its moisture content to 0.18 wt%; then, it is surface-treated with an epoxy silane coupling agent equivalent to 1.0 wt% of the bamboo powder mass; and then, maleic anhydride-grafted PBS equivalent to 6 wt% of the bamboo powder mass is added for melt coating modification to obtain surface-modified bamboo powder. The D50 particle size of the obtained surface-modified bamboo powder is 15 μm.

[0029] Functional layer A granules were prepared using a twin-screw extruder equipped with a first, second, and third feed port. The first feed port was located in the main feeding section, the second feed port was located at 45% of the effective screw length, and the third feed port was located at 70% of the effective screw length. PBS, antioxidants, and a first portion of multifunctional epoxy compatibilizer (40 wt% of the total multifunctional epoxy compatibilizer) are added through the first feed port. The PBS is melted in the PBS plasticizing section at 150°C to form a continuous phase. Surface-modified bamboo powder, talc, and branched PBS are added through the second feed port. The surface-modified bamboo powder is pre-wetted and dispersed in the PBS continuous phase in the wetting and dispersion section at 170°C. PGA is dried at 80°C for 8 hours to a moisture content of 350 ppm, and then added through the third feed port along with polycarbodiimide and the remaining multifunctional epoxy compatibilizer. The mixture sequentially passes through a PGA pre-addition transition section at 200°C, a PGA reaction and dispersion section at 225°C, and a vacuum devolatilization section at 228°C. The vacuum devolatilization pressure is -0.085 MPa. The average residence time of PGA from the third feed port to the outlet is controlled to be 75 s. After cooling and pelletizing, functional layer A granules are obtained.

[0030] PBS / PBSA blended resin, functionalized PBS-based tackifying resin, multifunctional epoxy chain extender, and antioxidant were added to a twin-screw extruder and melt-blended, extruded, cooled, and pelletized at 185–205°C to obtain tackifying layer B granules. Subsequently, functional layer A granules and tackifying layer B granules were plasticized separately in two extruders, with the melt temperature of functional layer A granules controlled at 230°C and the melt temperature of tackifying layer B granules controlled at 210°C. The two melts were then co-extruded through a die to form a bilayer melt film, with tackifying layer B positioned on the side facing the paper substrate and functional layer A on the side away from the paper substrate. After traction and cooling, the PBS coating material was obtained. The resulting bilayer melt film had a unit area mass of 25 g / m². 2 The bulk density of the tackifying layer B is 3.8 g / m². 2 The mass ratio of functional layer A to adhesive layer B is approximately 85:15. Example

[0031] The raw materials for functional layer A, based on 100 parts by weight, include: 81.60 parts of PBS, 10 parts of PGA, 8 parts of surface-modified bamboo powder, 0.2 parts of multifunctional epoxy compatibilizer, 0.05 parts of polycarbodiimide, 0.05 parts of antioxidant, 0.05 parts of nano-silica, and 0.05 parts of polyester wax.

[0032] The raw materials for tackifying layer B, based on 100 parts by weight, include: 91.90 parts PBS, 8 parts functionalized PBS-based tackifying resin, 0.05 parts multifunctional epoxy chain extender, and 0.05 parts antioxidant. The functionalized PBS-based tackifying resin is maleic anhydride-grafted PBS with a grafting rate of 0.3 wt%.

[0033] This embodiment uses the same preparation steps as Example 1, except that: after drying the bamboo powder at 80°C for 4 hours, it is treated with an epoxy silane coupling agent and modified by maleic anhydride-grafted PBS coating. The amount of maleic anhydride-grafted PBS is 2wt% of the bamboo powder mass, and the resulting surface-modified bamboo powder has a D50 particle size of 5μm and a moisture content of 0.30wt%.

[0034] The second feed port is located at 35% of the effective screw length, and the third feed port is located at 60% of the effective screw length. The average residence time of PGA from the third feed port to the outlet is 30 seconds. The temperature of the PBS plasticizing section is 120℃, the temperature of the bamboo powder wetting and dispersing section is 150℃, the temperature of the transition section before PGA addition is 190℃, the temperature of the PGA reaction and dispersion section is 215℃, the temperature of the vacuum devolatilization section is 220℃, and the vacuum devolatilization pressure is -0.06MPa. After drying at 60℃ for 10 hours, the moisture content of PGA is 500ppm. The melt temperature of functional layer A granules is 220℃, the melt temperature of tackifying layer B granules is 190℃, and the unit area mass of the double-layer melt film is 12g / m². 2 The bulk density of the tackifying layer B is 3 g / m². 2 The mass ratio of functional layer A to adhesive layer B is 75:25. The remaining steps are the same as in Example 1. Example

[0035] The raw materials for functional layer A, based on 100 parts by weight, include: 62.6 parts PBS, 20 parts PGA, 15 parts surface-modified bamboo powder, 0.8 parts multifunctional epoxy compatibilizer, 0.4 parts polycarbodiimide, 0.3 parts antioxidant, 0.5 parts nano-montmorillonite, and 0.4 parts branched PBS.

[0036] The raw materials for tackifying layer B, based on 100 parts by weight, include: 79.40 parts of PBSA, 20 parts of functionalized PBS-based tackifying resin, 0.3 parts of multifunctional epoxy chain extender, and 0.3 parts of antioxidant. The functionalized PBS-based tackifying resin is PBS grafted with glycidyl methacrylate, with a grafting rate of 2.0 wt%.

[0037] This embodiment uses the same preparation steps as Example 1, except that: after drying the bamboo powder at 105°C for 8 hours, it is treated with an epoxy silane coupling agent and modified by maleic anhydride-grafted PBS coating. The amount of maleic anhydride-grafted PBS is 10 wt% of the bamboo powder mass, and the resulting surface-modified bamboo powder has a D50 particle size of 30 μm and a moisture content of 0.28 wt%.

[0038] The second feed port is located at 55% of the effective screw length, and the third feed port is located at 80% of the effective screw length. The average residence time of PGA from the third feed port to the outlet is 120 seconds. The temperature of the PBS plasticizing section is 165℃, the temperature of the bamboo powder wetting and dispersion section is 185℃, the temperature of the transition section before PGA addition is 210℃, the temperature of the PGA reaction and dispersion section is 235℃, the temperature of the vacuum devolatilization section is 235℃, and the vacuum devolatilization pressure is -0.095MPa. After drying at 90℃ for 4 hours, the moisture content of PGA is 420ppm. The melt temperature of functional layer A granules is 240℃, the melt temperature of tackifying layer B granules is 230℃, and the unit area mass of the double-layer melt film is 25g / m². 2 The bulk density of the tackifying layer B is 2 g / m². 2 The mass ratio of functional layer A to adhesive layer B is 92:8. The remaining steps are the same as in Example 1. Example

[0039] The raw material composition of functional layer A and tackifying layer B is the same as in Example 1. The preparation method of surface-modified bamboo powder is the same as in Example 1. The second feed port is located at 45% of the effective screw length, and the third feed port is located at 70% of the effective screw length. The average residence time of PGA from the third feed port to the outlet is 75 seconds. The unit area mass of the double-layer melt film is 35 g / m². 2 The bulk density of the tackifying layer B is 8 g / m². 2 The mass ratio of functional layer A to adhesive layer B is approximately 77:23. The remaining steps are the same as in Example 1.

[0040] Comparative Example 1 This comparative example is basically the same as Example 1, except that no multifunctional epoxy compatibilizer and carbodiimide stabilizer are added to functional layer A, and an equal amount of PBS is used to make up the difference; no multifunctional epoxy chain extender is added to tackifying layer B, and an equal amount of PBS / PBSA blended resin is used to make up the difference. The remaining raw materials, layer structures and preparation conditions are the same as in Example 1.

[0041] Comparative Example 2 This comparative example is basically the same as Example 1, except that polyglycolic acid is not added to functional layer A, and it is supplemented with an equal amount of PBS. The other conditions are the same as in Example 1.

[0042] Comparative Example 3 This comparative example is basically the same as Example 1, except that the surface-modified bamboo powder in functional layer A is replaced with unmodified bamboo powder. The unmodified bamboo powder is dried at 95°C for 6 hours and then directly added to the second feed port. The other conditions are the same as in Example 1.

[0043] Comparative Example 4 This comparative example is basically the same as Example 1, except that all raw materials for functional layer A are added at once through the first feed port, instead of using the method of pre-wetting the surface-modified bamboo powder in the middle section and adding polyglycolic acid in the later section. The average residence time of polyglycolic acid in the high-temperature zone is approximately 220 seconds. All other conditions are the same as in Example 1.

[0044] Comparative Example 5 This comparative example is basically the same as Example 1, except that the tackifying layer B is not provided, and only the functional layer A from Example 1 is used as a single-layer coating material. The unit area mass of the single-layer coating material is 25 g / m². 2 The remaining conditions are the same as in Example 1.

[0045] Comparative Example 6 This comparative example is basically the same as Example 1, except that the average residence time of polyglycolic acid (PGA) from the third feed port to the outlet of the twin-screw extruder is 150 seconds by adjusting the position of the third feed port, the screw combination, or the screw speed. Except for the average residence time of PGA mentioned above, the raw material composition, temperature of each section, vacuum devolatilization conditions, co-extrusion coating conditions, unit area mass of the double-layer melt film, and the mass ratio of functional layer A to tackifying layer B are all the same as in Example 1.

[0046] The PBS coating materials and paper-based composite products prepared in the examples and comparative examples were conditioned for 24 hours at a temperature of 23±2℃ and a relative humidity of 50±10% before being tested.

[0047] Tensile strength and tensile modulus of elasticity were tested according to GB / T 1040.3-2006. Paper-based / coated layer peel strength was tested according to GB / T 8808-1988, with a sample width of 15 mm. Heat-sealing strength between coated and coated surfaces was tested according to QB / T2358-1998, with a heat-sealing temperature of 150℃, a heat-sealing pressure of 0.2 MPa, and a heat-sealing time of 1 s. Oxygen permeability was tested according to GB / T 19789-2021, with a test temperature of 23℃ and a relative humidity of 0%. Cobb60 water absorption was tested according to GB / T1540-2002, with the test surface being the coated surface.

[0048] Processing stability evaluation method: The number of pinholes was tested using the dye penetration method. A 100mm×100mm paper-based composite sample was taken, and a 0.5wt% methylene blue aqueous solution was evenly coated on the coated surface. After keeping it for 60s, the surface dye was wiped off, and the number of visible penetration points on the back or cross-section of the paper base was recorded and converted into the number of pinholes per square meter.

[0049] The number of times the membrane breaks during continuous coating was tested using the continuous operation evaluation method: the membrane was continuously run for 60 minutes at a traction speed of 80 m / min, and the number of times the membrane broke, the edge ruptured, or the continuous traction could not be completed was recorded.

[0050] A / B interlayer peel strength test: During the test, a bilayer melt film of functional layer A and tackifying layer B was prepared using the same co-extrusion process as that used for paper-based composites, but without being composited with the paper base, resulting in an independent bilayer film sample. To facilitate the formation of the peel initiation end, a polytetrafluoroethylene sheet or other inert separator can be locally placed at the initiation end of the bilayer film to form a pre-peeling tongue. The separator is only located at the peel initiation end and does not enter the effective test section. After the obtained bilayer film is conditioned for 24 hours at a temperature of 23±2℃ and a relative humidity of 50±10%, it is cut into 15mm wide samples. Functional layer A and tackifying layer B are pre-peeled along the interface direction, and a T-type peel test is performed according to GB / T 8808-1988. The average peel force of the stable peel section is recorded, and the result is expressed as N / 15mm. For single-layer coated materials, since there is no interface between functional layer A and tackifying layer B, the A / B interlayer peel strength is not applicable.

[0051] Heat distortion temperature test: During the test, the functional layer A granules or corresponding coating material are prepared into standard test strips by hot pressing or injection molding. After conditioning for 24 hours in an environment with a temperature of 23±2℃ and a relative humidity of 50±10%, the heat distortion temperature is tested according to the methods specified in GB / T 1634.1 and GB / T 1634.2.

[0052] Test Results

[0053] Results Analysis As shown in the table, Example 1, employing a superior component ratio, bamboo powder surface modification method, double-layer structure, and short-dwelling process after PGA, exhibits superior tensile strength, tensile modulus of elasticity, peel strength, heat seal strength, oxygen barrier properties, Cobb60 water absorption value, A / B interlayer peel strength, heat distortion temperature, and processing stability, resulting in the best overall performance. Example 2, at the lower limit of PGA and bamboo powder content, exhibits relatively lower material rigidity, barrier properties, and heat resistance. Example 3, at the upper limit of PGA and bamboo powder content, demonstrates good heat distortion temperature and barrier properties, but its paper-based peel strength, A / B interlayer peel strength, and processing stability are slightly lower than those of Example 1. In Example 4, the tackifying layer B has a higher unit area mass, maintaining a high level of paper-based adhesion, but due to the reduced proportion of functional layers, its mechanical properties, barrier properties, and heat resistance are slightly lower than those of Example 1.

[0054] In Comparative Example 1, the absence of multifunctional epoxy compatibilizers, carbodiimide stabilizers, and multifunctional epoxy chain extenders significantly reduced tensile strength, paper-based / coating layer peel strength, heat-sealing strength, A / B interlayer peel strength, and processing stability. This indicates that the reactive compatibilization and stabilization system not only improves PBS / PGA compatibility and melt stability but also enhances the interfacial bonding strength between functional layer A and tackifying layer B. In Comparative Example 2, without the addition of PGA, tensile modulus of elasticity, oxygen barrier properties, and heat distortion temperature all decreased significantly, demonstrating the important contribution of PGA to improving material rigidity, barrier properties, and heat-resistant dimensional stability. In Comparative Example 3, using unmodified bamboo powder, the number of pinholes and continuous coating failures significantly increased, while the A / B interlayer peel strength and paper-based peel strength decreased. This indicates that bamboo powder surface modification improves the interfacial compatibility between the filler and the PBS-based continuous phase, reducing filler agglomeration and film surface defects. Comparative Example 4 used a one-time feeding method, and the average residence time of PGA in the high-temperature zone was approximately 220 s. Its tensile strength, A / B interlayer peel strength, heat seal strength, and heat distortion temperature were all significantly lower than those of Example 1, while the number of pinholes and film breakages increased significantly. Comparative Example 5 did not include the tackifying layer B, and only used functional layer A as a single-layer coating material. Its paper base / coating layer peel strength, heat seal strength, and Cobb 60 water absorption value were significantly worse, indicating that the tackifying layer B plays a crucial role in the compatibility of the paper base composite. Comparative Example 6, under the same conditions as Example 1, only extended the average residence time of PGA from the third feed port to the discharge port to 150 s. The material properties also decreased, indicating that PGA is prone to degradation or melt fluctuation after a residence time in the high-temperature zone exceeds 120 s, thereby weakening the reinforcement, heat resistance, and barrier contributions of PGA.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A PBS coating material, characterized in that, The PBS coating material includes a functional layer A and an adhesive layer B that are directly bonded together. Based on a total of 100 parts by weight of raw materials for functional layer A, functional layer A comprises: 10-20 parts of polyglycolic acid, 8-15 parts of surface-modified bamboo powder, 0.2-0.8 parts of multifunctional epoxy compatibilizer, 0.05-0.4 parts of carbodiimide stabilizer, 0.05-0.3 parts of antioxidant, 0.05-0.5 parts of nucleating agent, and 0.05-0.4 parts of coating rheology aid, with the balance being polybutylene succinate-based resin; Based on a total of 100 parts by weight of raw materials for the tackifying layer B, the tackifying layer B comprises: 8-20 parts of functionalized polybutylene succinate-based tackifying resin, 0.05-0.3 parts of multifunctional epoxy chain extender, and 0.05-0.3 parts of antioxidant, with the remainder being polybutylene succinate and / or polybutylene adipate; The functionalized polybutylene succinate-based tackifying resin is maleic anhydride-grafted polybutylene succinate and / or glycidyl methacrylate-grafted polybutylene succinate.

2. The PBS coating material according to claim 1, characterized in that, The polybutylene succinate-based resin is polybutylene succinate, or a blend of polybutylene succinate and polybutylene adipate. When the polybutylene succinate-based resin is a blend of polybutylene succinate and polybutylene adipate, the proportion of polybutylene succinate to the total mass of the polybutylene succinate-based resin is not less than 70 wt%.

3. The PBS coating material according to claim 1, characterized in that, The surface-modified bamboo powder includes a bamboo powder core material and a polyester affinity modification layer located on the surface of the bamboo powder core material; the polyester affinity modification layer contains a coating component formed by epoxy silane coupling residues and maleic anhydride-grafted polybutylene succinate, wherein the amount of maleic anhydride-grafted polybutylene succinate is 2-10 wt% of the bamboo powder core material; the particle size D50 of the surface-modified bamboo powder is 5-30 μm, and the moisture content is not higher than 0.3 wt%.

4. The PBS coating material according to claim 1, characterized in that, Both the multifunctional epoxy compatibilizer and the multifunctional epoxy chain extender are styrene-methacrylate-glycidyl methacrylate copolymers. The carbodiimide stabilizer is polycarbodiimide; The antioxidant is a combination of hindered phenolic antioxidants and phosphite antioxidants; The nucleating agent is one or more of talc, nano-silica, and nano-montmorillonite; The rheology modifier for the coating is polyester wax and / or branched polybutylene succinate.

5. The PBS coating material according to claim 1, characterized in that, The mass ratio of the functional layer A to the adhesive layer B is 75:25 to 92:8; The grafting rate of the maleic anhydride-grafted polybutylene succinate or glycidyl methacrylate-grafted polybutylene succinate is 0.3 to 2.0 wt%.

6. A method for preparing the PBS membrane material according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Bamboo powder is dried at 80-105℃ for 4-8 hours, and then treated with epoxy silane coupling agent and coated with maleic anhydride-grafted polybutylene succinate to obtain surface-modified bamboo powder. S2, Functional layer A granules are prepared using a twin-screw extruder with a first discharge port, a second discharge port and a third discharge port, wherein the first discharge port, the second discharge port and the third discharge port are arranged sequentially along the material conveying direction; S3, polybutylene succinate-based resin, antioxidant and first part of multifunctional epoxy compatibilizer are added from the first feed port, so that the polybutylene succinate-based resin melts to form a continuous phase. S4, surface-modified bamboo powder, nucleating agent and coating rheology aid are added through the second feed port to pre-wet and disperse the surface-modified bamboo powder in the continuous phase; S5, polyglycolic acid, carbodiimide stabilizer and the second part of multifunctional epoxy compatibilizer are added through the third feed port to react, compatibilize and disperse, and the average residence time of polyglycolic acid from the third feed port to the outlet of the twin-screw extruder is controlled to be 30-120s. S6, after vacuum devolatilization, cooling and pelletizing, yields functional layer A granules; S7, polybutylene succinate and / or polybutylene adipate, functionalized polybutylene succinate-based tackifying resin, multifunctional epoxy chain extender and antioxidant are melt-blended to obtain tackifying layer B granules. S8, the functional layer A granules and the tackifying layer B granules are plasticized by two extruders respectively, and then compounded in a co-extrusion die to form a double-layer melt film, with the tackifying layer B located on the side facing the paper base and the functional layer A located on the side away from the paper base. After traction and cooling, the PBS coating material is obtained.

7. The preparation method according to claim 6, characterized in that, The second feed port is located at 35-55% of the effective length of the screw in the twin-screw extruder; The third discharge port is located at 60-80% of the effective length of the screw in the twin-screw extruder.

8. The preparation method according to claim 6, characterized in that, In steps S3 to S6, the temperature of the plasticizing section of the twin-screw extruder for polybutylene succinate is 120–165°C, the temperature of the surface-modified bamboo powder wetting and dispersing section is 150–185°C, the temperature of the transition section before the addition of polyglycolic acid is 190–210°C, the temperature of the polyglycolic acid reaction and dispersion section is 215–235°C, the temperature of the vacuum devolatilization section is 220–235°C, and the vacuum devolatilization pressure is -0.06–-0.095 MPa. The first part of the multifunctional epoxy compatibilizer accounts for 20-60 wt% of the total multifunctional epoxy compatibilizer, and the second part of the multifunctional epoxy compatibilizer is the remaining part.

9. The preparation method according to claim 6, characterized in that, In step S5, the polyglycolic acid is dried at 60-90°C for 4-10 hours before being added to the third feed port, and the water content of the polyglycolic acid is not higher than 500 ppm. In step S8, the melt temperature of the functional layer A granules is 220–240°C, the melt temperature of the tackifying layer B granules is 190–230°C, and the unit area mass of the double-layer melt film is 12–35 g / m². 2 The adhesive layer B has a unit area mass of 2-8 g / m³. 2 .

10. A paper-based composite product, characterized in that, It includes a paper base and a coating layer disposed on at least one surface of the paper base, the coating layer being formed of the PBS coating material according to any one of claims 1 to 5; Wherein, the tackifying layer B is directly bonded to the paper base surface, and the functional layer A is located on the side of the tackifying layer B away from the paper base; The paper-based composite products include food packaging paper, paper cups, paper bowls, kraft paper composite packaging, express packaging paper, lunch box linings, or paper-based heat-sealed packaging.

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