Degradable pre-coated film and method for preparing the same

Abstract

This invention relates to the field of pre-coated film preparation technology, specifically to a biodegradable pre-coated film and its preparation method. The method includes adjusting the heat distortion temperature of a biodegradable substrate layer to 60-75°C; coating a biodegradable hot melt adhesive layer onto one side surface of the biodegradable substrate layer using a multi-segment temperature-controlled coating system to form a composite film; the biodegradable hot melt adhesive layer contains a second biodegradable resin with reversible crystallization properties, and its lower limit temperature for melting processing is 60-70°C; and subjecting the composite film to online heat setting treatment at a temperature lower than the melting point of the biodegradable hot melt adhesive layer. By using a low-melting-point biodegradable hot melt adhesive system and controlling the coating temperature at 60-90°C, low-temperature operation effectively avoids thermal degradation and thermal shrinkage deformation of the biodegradable substrate during processing. An online annealing step is added after coating to reduce internal stress in the film at 50-70°C, effectively solving the problem of easy curling and edge lifting of the biodegradable film after coating.

Description

Technical Field

[0001] This invention relates to the field of pre-coated film preparation technology, specifically to a biodegradable pre-coated film and its preparation method. Background Technology

[0002] Pre-coated film is a process in which a plastic film is pre-adhesiveized, rewound, and then thermally laminated with printed paper. It is widely used in the printing lamination industry. With increasing environmental protection requirements, biodegradable pre-coated film has become the industry's development direction.

[0003] Patent CN114517060A discloses a biodegradable pre-coated film and its preparation method. This patent uses a cellulose membrane as the substrate, and the adhesive layer material includes an adhesive solution, polyester, plant fibers, lactic acid, ethylene, biodegradable starch, PLA, and biodegradable oil. The preparation method includes: stepwise stirring and reacting the components of the adhesive solution at 45℃~85℃ to obtain a semi-finished adhesive solution; dehydrating the semi-finished adhesive solution to obtain a finished adhesive solution; then flattening and spreading the flattened adhesive solution into an adhesive layer; spraying a primer adhesive solution onto the cellulose membrane; and finally flattening and laminating the adhesive layer and the membrane layer together.

[0004] The existing technology has the following technical problems: High-temperature lamination can lead to degradation or deformation of biodegradable materials. In existing technologies, the preparation of the adhesive solution requires heating to 65℃~85℃, and the pre-coated film typically requires lamination temperatures of 80℃~120℃ or even higher when hot-pressed with paper. High temperatures can easily cause molecular chain breakage and thermal shrinkage deformation of biodegradable materials, affecting the quality of the lamination and the stability of its degradation performance.

[0005] Insufficient adhesion between the adhesive layer and the biodegradable substrate layer. Using the traditional offline coating method, the film is made first and then the adhesive is applied. The interfacial bonding between the adhesive layer and the biodegradable substrate is weak, and the film-adhesive separation is prone to occur during the use of the coated products.

[0006] Therefore, it is necessary to develop a method for preparing a biodegradable pre-coated film that can be laminated at a lower temperature and has strong interlayer bonding. Summary of the Invention

[0007] In order to overcome the defects in the prior art, the purpose of this invention is to provide a biodegradable pre-coated film and its preparation method, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides a method for preparing a biodegradable pre-coated film, comprising the following steps: S1. A biodegradable substrate layer is provided, the biodegradable substrate layer comprising a first biodegradable resin, and the heat distortion temperature of the biodegradable substrate layer is 60~75°C; S2. A biodegradable hot melt adhesive layer is coated on one side surface of the biodegradable substrate layer using a multi-segment temperature-controlled coating system to form a composite film; the biodegradable hot melt adhesive layer contains a second biodegradable resin with reversible crystallization properties, and the lower limit temperature of its melt processing window is 60℃~70℃. The multi-segment temperature-controlled coating system includes at least one adhesive supply segment with a temperature higher than the lower limit of the melt processing window, and a coating segment with a temperature lower than the heat distortion temperature of the biodegradable substrate layer, so that while the biodegradable hot melt adhesive layer is coated onto the biodegradable substrate layer in a molten state, the temperature of the biodegradable substrate layer is always lower than its heat distortion temperature. S3. The composite film obtained in step S2 is subjected to online heat setting treatment. The temperature of the online heat setting treatment is lower than the melting point of the biodegradable hot melt adhesive layer, so as to guide the directional crystallization of polymer molecular chains in the biodegradable hot melt adhesive layer and eliminate internal stress. S4. Cool and rewind to obtain a biodegradable pre-coated film roll.

[0009] As a further improvement to this technical solution, the temperature of the online heat setting treatment in step S3 is 45~65℃, the treatment time is 1~5min, and the cooling rate is 1~5℃ / min, so as to promote the formation of a high cohesive strength crystalline layer in the biodegradable hot melt adhesive layer.

[0010] As a further improvement to this technical solution, the second biodegradable resin is polycaprolactone, with a melt index of 10~25g / 10min at 160℃ and 2.16kg and a melting point of 58~62℃.

[0011] As a further improvement to this technical solution, the parameters of the multi-segment temperature-controlled coating system in step S2 are: adhesive supply section temperature 85~90℃, coating head temperature 70~80℃, and coating roller temperature 60~70℃.

[0012] As a further improvement to this technical solution, the first biodegradable resin is a blend of polylactic acid and polybutylene terephthalate, with a mass ratio of 60:40 to 80:20.

[0013] As a further improvement to this technical solution, the thickness of the biodegradable substrate layer is 12~30μm, and the coating thickness of the biodegradable hot melt adhesive layer is 8~20μm.

[0014] As a further improvement to this technical solution, the multi-segment temperature-controlled coating system adopts slit extrusion coating or micro-gravure coating.

[0015] As a further improvement to this technical solution, it also includes a step of hot-pressing the biodegradable pre-coated film roll with paper at a lamination temperature of 65~85°C, wherein the lamination temperature is lower than the heat distortion temperature of the biodegradable substrate layer.

[0016] As a further improvement to this technical solution, the biodegradable hot melt adhesive layer also includes a tackifying resin, which accounts for 5-15% of the total mass of the biodegradable hot melt adhesive layer.

[0017] On the other hand, the present invention provides a biodegradable pre-coated film, which is made by the above-mentioned method for preparing a biodegradable pre-coated film, including a biodegradable substrate layer, which is composed of a blend of polylactic acid and polybutylene terephthalate, wherein the mass ratio of polylactic acid to polybutylene terephthalate is 60:40 to 80:20, and the thickness is 12 to 30 μm; The biodegradable hot melt adhesive layer located on one side of the biodegradable substrate layer is composed of a blend of polycaprolactone and tackifying resin, wherein the polycaprolactone content is 85~95wt% and the thickness of the biodegradable hot melt adhesive layer is 8~20μm. The biodegradable hot melt adhesive layer forms a crystalline layer with high cohesive strength after cooling, and the peel strength of the biodegradable pre-coated film and paper after hot pressing at 65~85℃ and 0.5MPa is ≥2.5N / 15mm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The biodegradable pre-coated film and its preparation method adopt a low-melting-point biodegradable hot melt adhesive system and control the coating temperature at 60℃~90℃, which is much lower than the coating and lamination temperature of traditional pre-coated films. Low-temperature operation can effectively avoid thermal degradation and thermal shrinkage deformation of biodegradable substrates during processing, and ensure the stability of the mechanical properties and degradation performance of the film.

[0019] 2. The biodegradable pre-coated film and its preparation method add an online annealing step after coating, so that the film can eliminate internal stress under the condition of 50℃~70℃, effectively solving the problem of easy curling and edge lifting of biodegradable film after coating, and improving the flatness and dimensional stability of coated products.

[0020] 3. The biodegradable pre-coated film and its preparation method adopt the method of directly coating the substrate surface in a molten state. The hot melt adhesive and the substrate form good melt penetration and mechanical interlocking at the interface, and the interlayer peel strength is significantly improved. Attached Figure Description

[0021] The accompanying drawings described herein are for illustrative purposes only. The shapes and proportions of the components in the drawings are merely schematic and intended to aid in understanding the invention. They are not intended to specifically limit the shapes and proportions of the components of the invention.

[0022] Figure 1 This is a flowchart illustrating the overall process flow of the present invention. Figure 2These are comparison diagrams of peel strength in various embodiments and comparative examples of the present invention; Figure 3 This is a comparison chart of the heat shrinkage rates of various embodiments and comparative examples of the present invention. Detailed Implementation

[0023] The specific embodiments described herein are for illustrative purposes only. Under the guidance of this invention, any possible variations of the invention by those skilled in the art should be considered within its scope. The directional terms used herein are based on the orientations shown in the accompanying drawings and are for ease of description and simplification; therefore, they should not be construed as limitations on the invention. Furthermore, in the description of this invention, "several" has two or more meanings unless otherwise explicitly specified.

[0024] Please see Figures 1-3 As shown, the present invention provides a biodegradable pre-coated film, including a biodegradable substrate layer composed of a blend of polylactic acid and polybutylene terephthalate, wherein the mass ratio of polylactic acid to polybutylene terephthalate is 60:40 to 80:20, and the thickness is 12~30μm. The biodegradable hot melt adhesive layer located on one side of the biodegradable substrate layer is composed of a blend of polycaprolactone and tackifying resin, wherein the polycaprolactone content is 85~95wt% and the thickness of the biodegradable hot melt adhesive layer is 8~20μm. The biodegradable hot melt adhesive layer forms a crystalline layer with high cohesive strength after cooling. The peel strength of the biodegradable pre-coated film and paper after hot pressing at 65~85℃ and 0.5MPa is ≥2.5N / 15mm.

[0025] The heat distortion temperature of biodegradable substrate layers is typically 60-75℃, while the lower limit of the melt processing window for biodegradable hot melt adhesive layers is also 60-70℃. For the hot melt adhesive to fully melt and achieve good coating and adhesion, the temperature must be ≥60℃; however, once it approaches or exceeds 60℃, the substrate layer is at risk of heat deformation and shrinkage. This processing window is extremely narrow, and simply lowering the temperature cannot solve the problem, because lowering it to the point where the adhesive will not melt, and raising it to the point where the film deforms. PCL (polycaprolactone) is a biodegradable resin with reversible crystallization properties. Its adhesive strength does not come from the tackiness of pressure-sensitive adhesives, but from the crystallization process during cooling—forming a crystalline layer with high cohesive strength.

[0026] The method for preparing the biodegradable pre-coated film of the present invention includes the following steps: S1. A biodegradable substrate layer is provided, the biodegradable substrate layer comprising a first biodegradable resin, and the heat distortion temperature of the biodegradable substrate layer is 60~75℃; The first biodegradable resin is a blend of polylactic acid and polybutylene terephthalate (PET) in a mass ratio of 60:40 to 80:20.

[0027] S2. A biodegradable hot melt adhesive layer is coated on one side of the biodegradable substrate layer using a multi-segment temperature-controlled coating system to form a composite film. The biodegradable hot melt adhesive layer contains a second biodegradable resin with reversible crystallization properties, and its lower limit temperature of the melt processing window is 60℃~70℃. The thickness of the biodegradable substrate layer is 12~30μm, and the coating thickness of the biodegradable hot melt adhesive layer is 8~20μm.

[0028] The second biodegradable resin is polycaprolactone, with a melt index of 10~25g / 10min at 160℃ and 2.16kg and a melting point of 58~62℃.

[0029] The multi-segment temperature-controlled coating system includes at least one adhesive supply segment with a temperature higher than the lower limit of the melt processing window and a coating segment with a temperature lower than the heat distortion temperature of the biodegradable substrate layer, so that while the biodegradable hot melt adhesive layer is coated onto the biodegradable substrate layer in a molten state, the temperature of the biodegradable substrate layer is always lower than its heat distortion temperature. The parameters of the multi-segment temperature-controlled coating system in step S2 are: adhesive supply section temperature 85~90℃, coating head temperature 70~80℃, and coating roller temperature 60~70℃.

[0030] S3. The composite film obtained in step S2 is subjected to online heat setting treatment. The temperature of the online heat setting treatment is lower than the melting point of the biodegradable hot melt adhesive layer, so as to guide the directional crystallization of polymer molecular chains in the biodegradable hot melt adhesive layer and eliminate internal stress. In step S3, the online heat setting temperature is 45~65℃, the processing time is 1~5min, and the cooling rate is 1~5℃ / min, so as to promote the formation of a high cohesive strength crystalline layer in the degradable hot melt adhesive layer.

[0031] S4. Cool and rewind to obtain a biodegradable pre-coated film roll.

[0032] The multi-segment temperature-controlled coating system uses slit extrusion coating or micro-gravure coating, which are existing technologies and will not be described in detail here.

[0033] It also includes a step of hot-pressing the biodegradable pre-coated film roll with paper at a lamination temperature of 65~85°C, where the lamination temperature is lower than the heat distortion temperature of the biodegradable substrate layer.

[0034] The biodegradable hot melt adhesive layer also contains tackifying resin, which accounts for 5 to 15% of the total mass of the biodegradable hot melt adhesive layer.

[0035] This invention is not simply about replacing the material with a lower melting point or lowering the coating temperature, but rather about providing a synergistic overall process solution.

[0036] I. Multi-stage temperature-controlled coating system To address the short temperature processing window, the coating system employs a multi-segment independent temperature control design: Adhesive supply section: 85~90℃, to ensure the hot melt adhesive is fully melted and achieves good flowability; Coating head: 70~80℃, melt metering and uniform distribution; Coating roller / substrate side: 60~70℃, always below the heat distortion temperature of the substrate; The hot melt adhesive melts instantly at high temperatures in the adhesive supply section, while rapidly cooling down in the coating roller section that contacts the substrate. This ensures that while the hot melt adhesive is coated onto the substrate in a molten state, the substrate temperature remains consistently below its heat distortion temperature. This dynamic temperature gradient control, designed specifically for the heat-sensitive characteristics of biodegradable materials, is a technical challenge that traditional non-biodegradable pre-coated films (such as BOPP) simply do not need to address.

[0037] II. Online heat setting treatment To address the reversible crystallization of PCL, the composite film was subjected to online annealing after coating. Temperature: 45~65℃, lower than the melting point of PCL (58~62℃) and higher than its crystallization initiation temperature; Time: 1~5 minutes; Cooling rate: 1~5℃ / min, slow cooling; Within a temperature range below the melting point but sufficient to support molecular chain movement, PCL molecular chains are guided to align and crystallize, forming a crystalline layer with high cohesive strength. Simultaneously, slow cooling releases the internal stress accumulated in the composite film during coating, preventing curling and edge lifting during subsequent film application. In other words, PCL-based hot melt adhesives, even without non-degradable frameworks such as epoxy resins, can still form a structurally stable, non-overflowing adhesive layer, achieving true full degradation of the biodegradable pre-coated film.

[0038] Example 1

[0039] (I) Preparation of biodegradable pre-coated film L1. Polylactic acid (PLA resin) and polybutylene terephthalate adipate (PBAT resin) are mixed at a mass ratio of 70:30, and then melt-blended and cast using a twin-screw extruder at 160℃~180℃ to obtain a biodegradable substrate film with a thickness of 20μm.

[0040] L2. Polycaprolactone (PCL resin, melt index approximately 17g / 10min@160℃ / 2.16kg) and PLA resin were mixed at a mass ratio of 80:20. Tackifying resin (rosin glycerol ester) accounting for 10% of the total mass of the blend was added. Under multi-stage temperature control conditions of 85℃ in the glue supply section, 75℃ in the coating head, and 65℃ in the coating roller, the mixture was coated onto the surface of a biodegradable substrate film by slit extrusion coating, with a coating thickness of 12μm.

[0041] L3. The coated composite film is annealed online at 60°C for 3 minutes, then cooled to room temperature and wound up to obtain a biodegradable pre-coated film roll.

[0042] (ii) Performance Testing The obtained pre-coated film and coated paper are hot-pressed together on a laminating machine under the following conditions: temperature 75℃, pressure 0.5MPa, and speed 15m / min.

[0043] Test results: Peel strength: ≥2.5N / 15mm (tested according to GB / T2792 standard); Lamination smoothness: No warping, no curling, visually smooth; Heat shrinkage rate (75℃ / 5min): ≤1.5%.

[0044] Example 2

[0045] (I) Preparation of biodegradable pre-coated film N1. PLA resin and PBAT resin are mixed at a mass ratio of 60:40 and blown into a film to obtain a biodegradable substrate film with a thickness of 15μm.

[0046] N2. Mix PCL resin and PLA resin at a mass ratio of 90:10, add 5% of tackifying resin by mass of the blend, and coat the substrate surface by microgravure coating at a coating temperature of 70℃, with a coating thickness of 8μm.

[0047] N3. After coating, the composite film is annealed online at 55°C for 2 minutes, then cooled and wound up.

[0048] (ii) Performance Testing The bonding conditions are the same as in Example 1.

[0049] Test results: Peel strength: ≥2.2N / 15mm; Film flatness: No warping, no curling; Heat shrinkage rate (75℃ / 5min): ≤1.8%.

[0050] Example 3

[0051] (I) Preparation of biodegradable pre-coated film M1. A biodegradable substrate film with a thickness of 25μm is prepared by casting pure PLA resin. The substrate is preheated at 45℃ before casting.

[0052] M2. Mix PCL resin and PLA resin at a mass ratio of 70:30, add 15% of tackifying resin by mass of the blend, and apply the coating with a thickness of 16μm by slit extrusion under multi-stage temperature control conditions of 90℃ in the glue supply section, 80℃ in the coating head, and 70℃ in the coating roller.

[0053] M3, the coated composite film is annealed online at 65°C for 3 minutes, then cooled and wound up.

[0054] (ii) Performance Testing The bonding conditions are the same as in Example 1.

[0055] Test results: Peel strength: ≥2.8N / 15mm; Film flatness: No warping, no curling; Heat shrinkage rate (75℃ / 5min): ≤1.2%.

[0056] Comparative Example 1 (without annealing) The difference from Example 1 is that the online annealing process in step L3 is omitted, and the coating is directly cooled and wound up.

[0057] Test results: Peel strength: 2.3 N / 15 mm (lower than Example 1); Lamination smoothness: Slight curling is observed, with the edges lifting up to a height of approximately 3-5 mm; Heat shrinkage rate (75℃ / 5min): 2.8% (significantly higher than Example 1).

[0058] Comparative Example 2 (Conventional High-Temperature Coating) The difference from Example 1 is that the coating temperature is 120°C, which is the standard temperature for conventional processes.

[0059] Test results: Peel strength: 2.0 N / 15 mm; Film flatness: The film shows obvious shrinkage and deformation, with a heat shrinkage rate as high as 4.5%; The substrate film experienced localized melting and adhesion, making normal winding impossible.

[0060] Comparative Example 3 (Non-degradable substrate reference) The PLA / PBAT biodegradable substrate in Example 1 was replaced with a conventional BOPP film (20 μm thick), and the other conditions were the same as in Example 1.

[0061] Test results: Peel strength: 2.6 N / 15 mm; Comparative Example 3 is for reference only, illustrating that the biodegradable pre-coated film prepared by the low-temperature process of this invention has reached the peel strength level of conventional non-degradable pre-coated films. The relevant experimental parameters and results of the above embodiments and comparative examples are shown in Table 1.

[0062] Table 1 Data Summary As can be seen from Table 1: In Examples 1-3, under the conditions of low-temperature coating and online annealing, the peel strength reached more than 2.2 N / 15 mm, the heat shrinkage rate was controlled below 1.8%, and the film flatness was excellent.

[0063] Comparative Example 1, without annealing treatment, did not eliminate the internal stress of the film, resulting in obvious curling after coating and a significant increase in thermal shrinkage rate to 2.8%.

[0064] Comparative Example 2 used conventional 120℃ high-temperature coating, which caused severe thermal shrinkage of the biodegradable substrate, making normal production impossible.

[0065] like Figure 2 As shown, the peel strength of all three embodiments is ≥2.2N / 15mm, with Embodiment 3 even reaching 2.8N / 15mm. In contrast, Comparative Example 1, without annealing treatment, has a lower peel strength (2.3N / 15mm); Comparative Example 2, due to substrate damage caused by a high temperature of 120℃, has a significantly reduced peel strength of 2.0N / 15mm. This directly proves that the present invention, through low-temperature processing and online heat setting, not only avoids heat damage but also achieves higher adhesive strength due to the full crystallization of PCL.

[0066] like Figure 3 As shown, in Examples 1-3, the introduction of online heat setting fully released internal stress, and the thermal shrinkage rate was firmly controlled below 1.8%. In contrast, Comparative Example 1, although employing low-temperature coating, omitted heat setting, resulting in a shrinkage rate of 2.8% after coating due to residual stress within the film; Comparative Example 2, where thermal shrinkage occurred during the coating stage, ultimately achieved a shrinkage rate as high as 4.5%. This strongly demonstrates that low-temperature coating and online heat setting are two indispensable synergistic steps, and the low shrinkage rate effect achieved by their combination cannot be achieved by a single step.

[0067] It should be noted that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a degradable pre-coated film, characterized by: Includes the following steps: S1. A biodegradable substrate layer is provided, the biodegradable substrate layer comprising a first biodegradable resin, and the heat distortion temperature of the biodegradable substrate layer is 60~75°C; S2. A biodegradable hot melt adhesive layer is coated on one side surface of the biodegradable substrate layer using a multi-segment temperature-controlled coating system to form a composite film; the biodegradable hot melt adhesive layer contains a second biodegradable resin with reversible crystallization properties, and the lower limit temperature of its melt processing window is 60℃~70℃. The multi-segment temperature-controlled coating system includes at least one adhesive supply segment with a temperature higher than the lower limit of the melt processing window, and a coating segment with a temperature lower than the heat distortion temperature of the biodegradable substrate layer, so that while the biodegradable hot melt adhesive layer is coated onto the biodegradable substrate layer in a molten state, the temperature of the biodegradable substrate layer is always lower than its heat distortion temperature. S3. The composite film obtained in step S2 is subjected to online heat setting treatment. The temperature of the online heat setting treatment is lower than the melting point of the biodegradable hot melt adhesive layer, so as to guide the directional crystallization of polymer molecular chains in the biodegradable hot melt adhesive layer and eliminate internal stress. S4. Cool and rewind to obtain a biodegradable pre-coated film roll.

2. The method for preparing the biodegradable pre-coated film according to claim 1, characterized in that, The temperature of the online heat setting treatment in step S3 is 45~65℃, the treatment time is 1~5min, and the cooling rate is 1~5℃ / min, so as to promote the formation of a high cohesive strength crystalline layer in the biodegradable hot melt adhesive layer.

3. The method for preparing the biodegradable pre-coated film according to claim 2, characterized in that, The second biodegradable resin is polycaprolactone, with a melt index of 10~25g / 10min at 160℃ and 2.16kg and a melting point of 58~62℃.

4. The method for preparing the biodegradable pre-coated film according to claim 3, characterized in that, The parameters of the multi-segment temperature-controlled coating system in step S2 are: adhesive supply section temperature 85~90℃, coating head temperature 70~80℃, and coating roller temperature 60~70℃.

5. The method for preparing the biodegradable pre-coated film according to claim 4, characterized in that, The first biodegradable resin is a blend of polylactic acid and polybutylene terephthalate, with a mass ratio of 60:40 to 80:

20.

6. The method for preparing the biodegradable pre-coated film according to claim 5, characterized in that, The thickness of the biodegradable substrate layer is 12~30μm, and the coating thickness of the biodegradable hot melt adhesive layer is 8~20μm.

7. The method for preparing the biodegradable pre-coated film according to claim 6, characterized in that, The multi-segment temperature-controlled coating system employs slit extrusion coating or micro-gravure coating methods.

8. The method for preparing the biodegradable pre-coated film according to claim 7, characterized in that, It also includes a step of hot-pressing the biodegradable pre-coated film roll with paper at a lamination temperature of 65~85°C, wherein the lamination temperature is lower than the heat distortion temperature of the biodegradable substrate layer.

9. The method for preparing the biodegradable pre-coated film according to claim 8, characterized in that, The biodegradable hot melt adhesive layer further comprises a tackifying resin, which accounts for 5-15% of the total mass of the biodegradable hot melt adhesive layer.

10. A biodegradable pre-coated film, prepared by the method for preparing the biodegradable pre-coated film according to claim 9, characterized in that: It includes a biodegradable substrate layer composed of a blend of polylactic acid and polybutylene terephthalate, wherein the mass ratio of polylactic acid to polybutylene terephthalate is 60:40 to 80:20, and the thickness is 12 to 30 μm. The biodegradable hot melt adhesive layer located on one side of the biodegradable substrate layer is composed of a blend of polycaprolactone and tackifying resin, wherein the polycaprolactone content is 85~95wt% and the thickness of the biodegradable hot melt adhesive layer is 8~20μm. The biodegradable hot melt adhesive layer forms a crystalline layer with high cohesive strength after cooling, and the peel strength of the biodegradable pre-coated film and paper after hot pressing at 65~85℃ and 0.5MPa is ≥2.5N / 15mm.

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