Degradable bio-based hot-melt pressure-sensitive adhesive label paper and preparation method thereof

Abstract

The invention relates to the technical field of functional label paper, in particular to degradable bio-based hot-melt pressure-sensitive adhesive label paper and a preparation method thereof.The degradable bio-based hot-melt pressure-sensitive adhesive label paper comprises a base material layer, a hot-melt pressure-sensitive adhesive layer and a release layer; 30-50 parts of the base material layer is a polylactic acid / bamboo fiber / nanocellulose composite film; 40-60 parts of the adhesive layer contains poly (butylene adipate-butylene terephthalate) and the like, and contains a composite toughening agent; and 5-10 parts of a release layer is a beewax / chitosan / montmorillonite coating. The mechanical and adhesive properties of the label paper are improved, and the label paper is good in weather resistance, full-degradable, environment-friendly, stable in process, suitable for the fields of food and medicine and capable of supporting industrialization.

Description

Technical Field

[0001] This invention relates to the field of functional label paper technology, specifically to a biodegradable bio-based hot melt pressure-sensitive adhesive label paper and its preparation method. Background Technology

[0002] With increasing global environmental awareness and the implementation of policies such as the "plastic ban," the white pollution problem caused by traditional petroleum-based polymer label paper, which is difficult to degrade, is becoming increasingly prominent. Currently, most hot-melt pressure-sensitive adhesive label papers on the market use non-degradable resins such as polyethylene and polypropylene as the base material, combined with petroleum-based adhesives such as styrene-isoprene-styrene block copolymer (SIS) and acrylates. Their degradation cycle in the natural environment can take decades, and they release toxic gases when incinerated, which does not meet the requirements of sustainable development.

[0003] While some progress has been made in the research and development of biodegradable label paper, numerous technical bottlenecks remain. Regarding the substrate, single polylactic acid (PLA) films have insufficient mechanical properties, with an elongation at break of only 30-50%, and poor water resistance, making them prone to deformation in humid environments. While natural materials such as bamboo fiber are biodegradable, their poor compatibility with polymer matrices leads to a decline in material mechanical properties when directly mixed. At the adhesive level, bio-based hot melt adhesives mostly rely on single polyester or polyether systems, such as polybutylene adipate (PBA) and polylactic acid (PLA), which suffer from low bonding strength (initial tack ≤ 5# steel ball) and poor temperature resistance (easily overflowing above 60℃), making it difficult to meet the requirements of the food and pharmaceutical industries.

[0004] In terms of toughening modification, traditional methods often involve adding small-molecule plasticizers such as glycerol and citric acid. While these can improve material flexibility, they can lead to adhesive migration, decreased adhesion, and the easy release of small molecules, causing secondary pollution. In antioxidant systems, synthetic antioxidants (such as BHT and Irganox 1010) are effective, but their poor biocompatibility does not meet safety standards for food contact materials. Regarding release layer design, existing products mostly use silicone oil coatings, which are not only non-degradable but also contaminate the substrate during recycling, affecting reuse efficiency.

[0005] Furthermore, the interfacial compatibility of bio-based materials is a key factor limiting performance improvement. The peel strength between the substrate and the adhesive layer is generally below 2N / 15mm, leading to easy label detachment. Inorganic fillers (such as nano-hydroxyapatite) are unevenly dispersed in the organic matrix, easily forming aggregates, which actually reduces the material's mechanical properties. Simultaneously, in existing manufacturing processes, high-temperature melting accelerates the degradation of bio-based materials, resulting in a molecular weight decrease of over 30%, further deteriorating product performance.

[0006] To address the aforementioned challenges, the development of hot-melt pressure-sensitive adhesive label paper that combines high mechanical properties, excellent adhesion, and full biodegradability has become an urgent industry need. Achieving a balance between material performance and environmental requirements through multi-component synergistic design, interface modification optimization, and process innovation is currently a research hotspot and a key challenge in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a biodegradable bio-based hot-melt pressure-sensitive adhesive label paper and its preparation method.

[0008] A biodegradable bio-based hot-melt pressure-sensitive adhesive label paper includes a substrate layer, a hot-melt pressure-sensitive adhesive layer, and a release layer, in parts by weight: 30-50 parts substrate layer, 40-60 parts hot-melt pressure-sensitive adhesive layer, and 5-10 parts release layer; the substrate layer is composed of a composite film of polylactic acid, bamboo fiber, and nanocellulose in a mass ratio of 5:3:2; the hot-melt pressure-sensitive adhesive layer includes 30-40 parts polybutylene adipate-butylene terephthalate and 10 parts epoxidized soybean oil. -15 parts, modified rosin glycerol ester 15-20 parts, nano hydroxyapatite 5-8 parts, composite toughening agent 3-6 parts, bio-based antioxidant 2-4 parts, polybutylene succinate-polycaprolactone block copolymer 5-10 parts; the release layer is composed of a composite coating of beeswax, chitosan, and montmorillonite, with a mass ratio of 6:3:1; wherein the composite toughening agent is prepared by coupling polylactic acid and polyethylene glycol monomethyl ether through isophorone diisocyanate, the reaction formula is: .

[0009] Preferably, the substrate layer surface is further modified by grafting: after plasma treatment, it is immersed in a 1-2wt% dopamine solution for 60-90 minutes to form a polydopamine transition layer; the plasma treatment power is 300-400W, the argon flow rate is 15-20sccm, and the treatment time is 2-3 minutes.

[0010] Preferably, it also includes synergistic modification with modified rosin glycerol ester: prepared by reacting rosin glycerol ester, maleic anhydride and itaconic acid at a mass ratio of 10:1:0.5 at 120-130℃ for 2-3 hours, with an acid value of 45-55 mgKOH / g, a softening point of 90-100℃, and a compatibility parameter δ difference of ≤0.5(J / cm³)¹ / ² with polybutylene adipate-butylene terephthalate.

[0011] Preferably, nano-hydroxyapatite is modified by composite modification of γ-aminopropyltriethoxysilane and sodium alginate: first, it is coupled with silane, then mixed with 2wt% sodium alginate solution and sonicated for 30 min, with a particle size of 50-80 nm, a total surface amino and carboxyl group density of 1.5-2.0 mmol / g, and a dispersion of ≥95% in the colloidal layer.

[0012] Preferably, the bio-based antioxidant is a compound of tea polyphenols, rosemary extract and vitamin E in a mass ratio of 3:2:1, with a total phenol content of ≥80%, and 0.5-1wt% limonene added as a synergist. After 72 hours of thermo-oxidative aging at 100°C, the weight loss of the gel layer is ≤3%, and the elongation at break is retained at ≥85%.

[0013] Preferably, the montmorillonite in the release layer is modified by hexadecyltrimethylammonium bromide intercalation, the interlayer spacing is increased to 3.5-4.0 nm, the release layer thickness is 3-5 μm, the release force is 5-10 g / 15 mm, the release force change rate is ≤5% after being placed at 60℃ for 72 h, and the water vapor permeability is reduced by 30-40%.

[0014] Preferably, the method for preparing the biodegradable bio-based hot-melt pressure-sensitive adhesive label paper includes: Substrate preparation: Polylactic acid, bamboo fiber and nanocellulose are melt-blended in a twin-screw extruder, and a film with a thickness of 20-30μm is obtained by casting. The film is then treated with plasma and dopamine for later use. Preparation of composite toughening agent: Polylactic acid, polyethylene glycol monomethyl ether and isophorone diisocyanate were added to the reactor at a molar ratio of 1:0.8:0.5, stirred at 100-110℃ under nitrogen protection for 1.5-2h, and vacuum degassing for 30min to obtain the product.

[0015] Preferably, the process also includes a hot-melt pressure-sensitive adhesive preparation step: polybutylene adipate-butylene terephthalate, polybutylene succinate-polycaprolactone block copolymer, and epoxidized soybean oil are added to a twin-screw extruder and melted for 5 minutes. Modified rosin glycerol ester, composite toughening agent, and nano hydroxyapatite are added, and the mixture is stirred at 600 rpm for 20 minutes. Finally, a bio-based antioxidant is added, and the mixture is stirred for another 10-15 minutes. The vacuum degree is maintained at -0.09 MPa, and the melt flow rate is controlled at 15-20 g / 10 min.

[0016] Preferably, the process also includes a composite molding step: hot melt adhesive is uniformly coated onto the substrate layer using a precision slot coater, and then dried by infrared to form an adhesive layer with a dry film thickness of 15-20μm; the adhesive layer is then pressed together with the release layer by a heated composite roller for 5-8s, and after being wound up, it is cured at 23℃ and 50%RH for 24h to ensure that the initial tack reaches the level of 8-10# steel balls.

[0017] Preferably, the release layer preparation step is also included: dispersing modified montmorillonite in a 5wt% chitosan aqueous solution, ultrasonically dispersing for 30 min, adding molten beeswax, and emulsifying by high-speed shearing for 30 min to form an emulsion with a solid content of 20wt%; coating it onto a PET release substrate using a microgravure coating method, drying it with hot air for 10-15 min to form a release layer with a thickness of 3-5μm, and then subjecting it to corona treatment after curing.

[0018] Compared with existing technologies, the beneficial effects of this invention are: 1. The substrate layer adopts a polylactic acid / bamboo fiber / nanocellulose composite system. After surface modification with dopamine, the hydroxyl density is increased to 2.5-3.0 mmol / m², and the peel strength from the adhesive layer reaches 3.5-4.0 N / 15 mm, which is 75% higher than that of traditional materials. The composite toughening agent constructs a branched structure through isophorone diisocyanate, which increases the elongation at break of the adhesive layer to 150-180%, solving the brittleness problem of bio-based materials.

[0019] 2. Modified rosin glycerol ester is synergistically modified with maleic anhydride and itaconic acid. The difference in compatibility parameters with the polyester matrix is ​​≤0.5 (J / cm³)¹ / ². The initial tack reaches 8-10# steel ball and the holding power is ≥24h. The bio-based antioxidant compound system makes the weight loss rate of the adhesive layer ≤3% after 100℃ thermo-oxidative aging, which is better than existing bio-based materials.

[0020] 3. The release layer uses a montmorillonite-modified beeswax / chitosan system, which is completely degradable and has excellent release force stability; the components comply with FDA 21CFR 177 standards and are suitable for sensitive fields such as food and medicine.

[0021] 4. Stepwise melt blending and vacuum degassing processes reduce the degradation of bio-based materials, and the melt flow rate is stabilized at 15-20g / 10min; microgravure coating and heated composite roller pressing ensure the uniformity of the adhesive layer, reducing the scrap rate to below 1%. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for preparing biodegradable bio-based hot-melt pressure-sensitive adhesive label paper proposed in this invention; Figure 2 This is a line graph comparing the peel strength and initial tack of the examples and comparative examples; Figure 3 This is a bar chart comparing the weight loss rate and release force change rate under thermo-oxidative aging of the examples and comparative examples; Figure 4 This is a radar comparison chart created by standardizing the dimensions of the performance test results of the examples and comparative examples. Detailed Implementation

[0023] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: Example 1 Substrate layer preparation: 30 parts of polylactic acid (PLA, molecular weight 80,000), 18 parts of bamboo fiber (length 100-200 μm), and 12 parts of nanocellulose (diameter 20-50 nm) were weighed at a mass ratio of 5:3:2 and added to a twin-screw extruder. The mixture was melt-blended at 170℃ in zone one, 180℃ in zone two, and 175℃ in zone three at a speed of 300 rpm for 8 minutes. After cooling at 60℃, the mixture was rolled into a 25 μm thick film. Plasma treatment: 350 W power, argon flow rate 18 sccm, time 2.5 minutes; immersion in a 1.5 wt% dopamine solution (pH 8.5) for 75 minutes; after drying, the surface hydroxyl density was 2.8 mmol / m².

[0024] Preparation of composite toughening agent: 10 parts of polylactic acid (molecular weight 50,000), 8 parts of polyethylene glycol monomethyl ether (molecular weight 2,000), and 5 parts of isophorone diisocyanate were added to a reaction vessel. The mixture was stirred at 105℃ under nitrogen protection for 1.8 h, and then degassed under vacuum at -0.09 MPa for 30 min to obtain a toughening agent with a number average molecular weight of 9,000 and a branching degree of 1.3.

[0025] Preparation of hot-melt pressure-sensitive adhesive: 35 parts of polybutylene adipate-butylene terephthalate, 7 parts of polybutylene succinate-polycaprolactone block copolymer, and 12 parts of epoxidized soybean oil were added to a twin-screw extruder (zone 1 140℃, zone 2 150℃, zone 3 160℃) and melted for 5 min. 18 parts of modified rosin glycerol ester (rosin glycerol ester: maleic anhydride: itaconic acid = 10:1:0.5, reacted at 125℃ for 2.5 h), 4 parts of composite toughening agent, and 6 parts of composite modified nano-hydroxyapatite (silane: sodium alginate = 10:1 modified) were added, and stirred at 600 rpm for 20 min. Finally, 3 parts of bio-based antioxidant (tea polyphenols: rosemary: vitamin E = 3:2:1, containing 0.8 wt% limonene) were added, and stirred for 12 min. The melt flow rate was 18 g / 10 min (190℃, 2.16 kg).

[0026] Release layer preparation: 1 part montmorillonite (reacted with hexadecyltrimethylammonium bromide at a ratio of 10:1 at 80℃ for 2 h) was dispersed in 30 parts 5 wt% chitosan aqueous solution (dissolved in 1 wt% acetic acid), and sonicated at 400 W for 30 min. 6 parts molten beeswax (65℃) were added, and emulsified at 1500 rpm for 30 min to obtain a 20 wt% emulsion. This emulsion was microgravated onto a PET substrate and dried at 60℃ for 12 min to form a 4 μm release layer, followed by corona treatment (tension 30 N, 50 W / m²).

[0027] Composite molding: Hot melt adhesive is coated onto the substrate using a 165℃ slot coater (speed 12m / min) and dried at 85℃ using infrared technology to form an 18μm adhesive layer. It is then pressed with the release layer by an 85℃ composite roller (0.4MPa) for 6s, cured at 23℃ and 50%RH for 24h, and has an initial tack of 9# steel balls.

[0028] Example 2 Substrate layer preparation: 24 parts of polylactic acid (PLA, molecular weight 80,000), 14.4 parts of bamboo fiber (length 100-200 μm), and 9.6 parts of nanocellulose (diameter 20-50 nm) were weighed at a mass ratio of 5:3:2 and added to a twin-screw extruder. The mixture was melt-blended at 170℃ in zone one, 180℃ in zone two, and 175℃ in zone three, at a speed of 300 rpm for 8 minutes. After cooling at 60℃, the mixture was rolled into a 20 μm thick film. Plasma treatment: 300 W power, argon flow rate 15 sccm, time 2 minutes; immersion in 1 wt% dopamine solution (pH 8.5) for 60 minutes; after drying, the surface hydroxyl density was 2.5 mmol / m².

[0029] Preparation of composite toughening agent: 10 parts of polylactic acid (molecular weight 50,000), 8 parts of polyethylene glycol monomethyl ether (molecular weight 2,000), and 5 parts of isophorone diisocyanate were added to a reaction vessel. The mixture was stirred at 100℃ under nitrogen protection for 1.5 h, and then degassed under vacuum at -0.09 MPa for 30 min to obtain a toughening agent with a number average molecular weight of 8,000 and a branching degree of 1.2.

[0030] Preparation of hot-melt pressure-sensitive adhesive: 30 parts of polybutylene adipate-butylene terephthalate, 5 parts of polybutylene succinate-polycaprolactone block copolymer, and 10 parts of epoxidized soybean oil were added to a twin-screw extruder (zone 1 140℃, zone 2 150℃, zone 3 160℃) and melted for 5 min. 15 parts of modified rosin glycerol ester (rosin glycerol ester: maleic anhydride: itaconic acid = 10:1:0.5, reacted at 120℃ for 2 h), 3 parts of composite toughening agent, and 5 parts of composite modified nano-hydroxyapatite (silane: sodium alginate = 10:1 modification) were added, and stirred at 600 rpm for 20 min. Finally, 2 parts of bio-based antioxidant (tea polyphenols: rosemary: vitamin E = 3:2:1, containing 0.5 wt% limonene) were added, and stirred for 10 min. The melt flow rate was 15 g / 10 min (190℃, 2.16 kg).

[0031] Release layer preparation: 0.8 parts of montmorillonite (reacted with hexadecyltrimethylammonium bromide at a ratio of 10:1 at 80℃ for 2 h) were dispersed in 24 parts of 5 wt% chitosan aqueous solution (dissolved in 1 wt% acetic acid), and sonicated at 400 W for 30 min. 4.8 parts of molten beeswax (60℃) were added, and emulsified at 1500 rpm for 30 min to obtain a 20 wt% emulsion. The emulsion was microgravated onto a PET substrate and dried at 60℃ for 10 min to form a 3 μm release layer, followed by corona treatment (tension 30 N, 50 W / m²).

[0032] Composite molding: Hot melt adhesive is coated onto the substrate using a 160℃ slot coater (speed 10m / min) and dried at 80℃ using infrared technology to form a 15μm adhesive layer. It is then pressed with the release layer using an 80℃ composite roller (0.3MPa) for 5s, cured at 23℃ and 50%RH for 24h, and has an initial tack of 8# steel balls.

[0033] Example 3 Substrate layer preparation: 36 parts of polylactic acid (PLA, molecular weight 80,000), 21.6 parts of bamboo fiber (length 100-200 μm), and 14.4 parts of nanocellulose (diameter 20-50 nm) were weighed at a mass ratio of 5:3:2 and added to a twin-screw extruder. The mixture was melt-blended at 170℃ in zone one, 180℃ in zone two, and 175℃ in zone three, at a speed of 300 rpm for 8 minutes. After cooling at 60℃, the mixture was rolled into a 30 μm thick film. Plasma treatment: 400 W power, argon flow rate 20 sccm, time 3 minutes; immersion in 2 wt% dopamine solution (pH 8.5) for 90 minutes; after drying, the surface hydroxyl density was 3.0 mmol / m².

[0034] Preparation of composite toughening agent: 10 parts of polylactic acid (molecular weight 50,000), 8 parts of polyethylene glycol monomethyl ether (molecular weight 2,000), and 5 parts of isophorone diisocyanate were added to a reaction vessel. The mixture was stirred at 110℃ under nitrogen protection for 2 hours and then degassed under vacuum at -0.09 MPa for 30 minutes to obtain a toughening agent with a number average molecular weight of 10,000 and a branching degree of 1.5.

[0035] Preparation of hot-melt pressure-sensitive adhesive: 40 parts of polybutylene adipate-butylene terephthalate, 10 parts of polybutylene succinate-polycaprolactone block copolymer, and 15 parts of epoxidized soybean oil were added to a twin-screw extruder (zone 1 140℃, zone 2 150℃, zone 3 160℃) and melted for 5 min. 20 parts of modified rosin glycerol ester (rosin glycerol ester: maleic anhydride: itaconic acid = 10:1:0.5, reacted at 130℃ for 3 h), 6 parts of composite toughening agent, and 8 parts of composite modified nano-hydroxyapatite (silane: sodium alginate = 10:1 modification) were added, and stirred at 600 rpm for 20 min. Finally, 4 parts of bio-based antioxidant (tea polyphenols: rosemary: vitamin E = 3:2:1, containing 1 wt% limonene) were added, and stirred for 15 min. The melt flow rate was 20 g / 10 min (190℃, 2.16 kg).

[0036] Release layer preparation: 1 part montmorillonite (reacted with hexadecyltrimethylammonium bromide at a ratio of 10:1 at 80℃ for 2 h) was dispersed in 30 parts 5 wt% chitosan aqueous solution (dissolved in 1 wt% acetic acid), and sonicated at 400 W for 30 min. 6 parts molten beeswax (70℃) were added, and emulsified at 1500 rpm for 30 min to obtain a 20 wt% emulsion. This emulsion was microgravated onto a PET substrate and dried at 60℃ for 15 min to form a 5 μm release layer (montmorillonite interlayer spacing 4.0 nm), followed by corona treatment (tension 30 N, 50 W / m²).

[0037] Composite molding: Hot melt adhesive is coated onto the substrate using a 170℃ slot coater (speed 15m / min) and dried at 90℃ using infrared technology to form a 20μm adhesive layer. It is then pressed with the release layer by a 90℃ composite roller (0.5MPa) for 8s, cured at 23℃ and 50%RH for 24h, with an initial tack of 10# steel ball.

[0038] Example 4 Substrate layer preparation: 30 parts of polylactic acid (PLA, molecular weight 80,000), 18 parts of bamboo fiber (length 100-200 μm), and 12 parts of nanocellulose (diameter 20-50 nm) were weighed at a mass ratio of 5:3:2 and added to a twin-screw extruder. The mixture was melt-blended at 170℃ in zone one, 180℃ in zone two, and 175℃ in zone three, at a speed of 300 rpm for 8 minutes. After cooling at 60℃, the mixture was rolled into a 25 μm thick film. Plasma treatment: 350 W power, argon flow rate 18 sccm, time 2.5 minutes; immersion in a 1.5 wt% dopamine solution (pH 8.5) for 75 minutes; after drying, the surface hydroxyl density was 2.7 mmol / m².

[0039] Preparation of composite toughening agent: 10 parts of polylactic acid (molecular weight 50,000), 8 parts of polyethylene glycol monomethyl ether (molecular weight 2,000), and 5 parts of isophorone diisocyanate were added to a reaction vessel. The mixture was stirred at 105℃ under nitrogen protection for 1.8 h, and then degassed under vacuum at -0.09 MPa for 30 min to obtain a toughening agent with a number average molecular weight of 9,000 and a branching degree of 1.4.

[0040] Preparation of hot-melt pressure-sensitive adhesive: 35 parts of polybutylene adipate-butylene terephthalate, 8 parts of polybutylene succinate-polycaprolactone block copolymer, and 12 parts of epoxidized soybean oil were added to a twin-screw extruder (zone 1 140℃, zone 2 150℃, zone 3 160℃) and melted for 5 min. 18 parts of modified rosin glycerol ester (rosin glycerol ester: maleic anhydride: itaconic acid = 10:1:0.5, reacted at 125℃ for 2.5 h), 4 parts of composite toughening agent, and 7 parts of composite modified nano-hydroxyapatite (silane: sodium alginate = 10:1 modified) were added, and stirred at 600 rpm for 20 min. Finally, 3.5 parts of bio-based antioxidant (tea polyphenols: rosemary: vitamin E = 3:2:1, containing 0.9 wt% limonene) were added, and stirred for 12 min. The melt flow rate was 19 g / 10 min (190℃, 2.16 kg).

[0041] Release layer preparation: 1 part montmorillonite (reacted with hexadecyltrimethylammonium bromide at a ratio of 10:1 at 80℃ for 2.5 h) was dispersed in 30 parts 5 wt% chitosan aqueous solution (dissolved in 1 wt% acetic acid), and sonicated at 400 W for 30 min. 6 parts molten beeswax (65℃) were added, and emulsified at 1500 rpm for 30 min to obtain a 22 wt% emulsion. This emulsion was microgravated onto a PET substrate and dried at 60℃ for 12 min to form a 4 μm release layer, followed by corona treatment (tension 30 N, 50 W / m²).

[0042] Composite molding: Hot melt adhesive is coated onto the substrate using a 165℃ slot coater (speed 12m / min) and dried at 85℃ using infrared technology to form an 18μm adhesive layer. It is then pressed with the release layer using an 85℃ composite roller (0.4MPa) for 7s, cured at 23℃ and 50%RH for 24h, and has an initial tack of 9# steel balls.

[0043] Comparative Example Substrate layer preparation: Weigh 40 parts of pure polylactic acid (PLA, molecular weight 80,000), add it to a twin-screw extruder (zone 1 170℃, zone 2 180℃) and melt-blend for 8 min, then cast into a film with a thickness of 25 μm. No plasma or dopamine treatment was performed, and the surface hydroxyl density was 0.5 mmol / m².

[0044] Preparation without composite toughening agent: 3 parts of glycerol are used directly as plasticizer.

[0045] Preparation of hot melt pressure-sensitive adhesive: 35 parts of polybutylene adipate and 12 parts of epoxidized soybean oil were added to a twin-screw extruder (zone 1 140℃, zone 2 150℃) and melted for 5 min. 18 parts of unmodified rosin glycerol ester, 6 parts of unmodified nano-hydroxyapatite, and 2 parts of BHT antioxidant were added, and the mixture was stirred at 600 rpm for 30 min without stepwise feeding. The melt flow rate was 8 g / 10 min (190℃, 2.16 kg).

[0046] Release layer preparation: Conventional silicone oil coating (5 parts) with a thickness of 4 μm was used, without montmorillonite modification or corona treatment.

[0047] Composite molding: Hot melt adhesive is applied to the substrate using a 150℃ slot coater (speed 12m / min) and allowed to air dry naturally to form an 18μm adhesive layer. It is then directly laminated with the release layer without heating, pressing, or curing. The initial tack is equivalent to a #4 steel ball.

[0048] The performance test results of the examples and comparative examples are shown in the table below: Table 1

[0049] The following table compares the interface performance and processability of the examples and comparative examples: Table 2

[0050] As can be seen from the two tables above, the performance of Examples 1-4 is comprehensively superior to that of the comparative examples. This is because the dopamine modification of the substrate increases the hydroxyl density, significantly enhancing the interfacial bonding with the adhesive layer; the synergistic effect of the composite toughening agent and block copolymer improves the elongation at break; and the composite-modified nano-hydroxyapatite exhibits a dispersion of over 95%, preventing performance degradation caused by agglomeration. The bio-based antioxidant system significantly reduces the weight loss rate due to thermo-oxidative aging, and the montmorillonite-modified release layer demonstrates improved stability, achieving a degradation rate of over 90% after 60 days. This fully demonstrates the synergistic advantages of this invention in terms of environmental friendliness and performance.

[0051] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A biodegradable bio-based hot-melt pressure-sensitive adhesive label paper, characterized in that, The product comprises a substrate layer, a hot-melt pressure-sensitive adhesive layer, and a release layer, in parts by weight: 30-50 parts substrate layer, 40-60 parts hot-melt pressure-sensitive adhesive layer, and 5-10 parts release layer; the substrate layer is composed of a composite film of polylactic acid, bamboo fiber, and nanocellulose in a mass ratio of 5:3:2; the hot-melt pressure-sensitive adhesive layer comprises 30-40 parts polybutylene adipate-butylene terephthalate, 10-15 parts epoxidized soybean oil, and modified rosin. The mixture comprises 15-20 parts glyceryl ester, 5-8 parts nano-hydroxyapatite, 3-6 parts composite toughening agent, 2-4 parts bio-based antioxidant, and 5-10 parts polybutylene succinate-polycaprolactone block copolymer; the release layer consists of a composite coating of beeswax, chitosan, and montmorillonite in a mass ratio of 6:3:1; the composite toughening agent is prepared by coupling polylactic acid and polyethylene glycol monomethyl ether via isophorone diisocyanate, and the reaction formula is as follows: 。 2. The biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 1, characterized in that, It also includes surface grafting modification of the substrate layer: after plasma treatment, it is immersed in a 1-2wt% dopamine solution for 60-90 minutes to form a polydopamine transition layer; the power of the plasma treatment is 300-400W, the argon flow rate is 15-20sccm, and the duration is 2-3 minutes.

3. The biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 2, characterized in that, It also includes the synergistic modification of modified rosin glycerol esters: prepared by reacting rosin glycerol esters, maleic anhydride and itaconic acid at a mass ratio of 10:1:0.5 at 120-130℃ for 2-3 hours.

4. The biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 3, characterized in that, Nano-hydroxyapatite was modified by composite modification with γ-aminopropyltriethoxysilane and sodium alginate: first, it was coupled with silane, then mixed with 2wt% sodium alginate solution and sonicated for 30 min. The particle size was 50-80 nm and the total density of amino and carboxyl groups on the surface was 1.5-2.0 mmol / g.

5. The biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 4, characterized in that, The bio-based antioxidant is a compound of tea polyphenols, rosemary extract and vitamin E in a mass ratio of 3:2:1, with a total phenol content of ≥80%. 0.5-1wt% limonene is added as a synergist. After 72 hours of thermo-oxidative aging at 100℃, the weight loss of the gel layer is ≤3%, and the elongation at break is retained at ≥85%.

6. The biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 5, characterized in that, The montmorillonite in the release layer is modified by hexadecyltrimethylammonium bromide intercalation, which increases the interlayer spacing to 3.5-4.0 nm, the release layer thickness to 3-5 μm, the release force to 5-10 g / 15 mm, the release force change rate to ≤5% after being placed at 60℃ for 72 h, and the water vapor permeability to be reduced by 30-40%.

7. A method for preparing the biodegradable bio-based hot-melt pressure-sensitive adhesive label paper as described in claim 6, comprising: Substrate preparation: Polylactic acid, bamboo fiber and nanocellulose are melt-blended in a twin-screw extruder, and a film with a thickness of 20-30μm is obtained by casting. The film is then treated with plasma and dopamine for later use. Preparation of composite toughening agent: Polylactic acid, polyethylene glycol monomethyl ether and isophorone diisocyanate were added to the reactor at a molar ratio of 1:0.8:0.5, stirred at 100-110℃ under nitrogen protection for 1.5-2h, and vacuum degassing for 30min to obtain the product.

8. The method for preparing biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 7, characterized in that, It also includes the following steps for preparing hot-melt pressure-sensitive adhesive: Polybutylene adipate-butylene terephthalate, polybutylene succinate-polycaprolactone block copolymer, and epoxidized soybean oil are added to a twin-screw extruder and melted for 5 minutes. Modified rosin glycerol ester, composite toughening agent, and nano hydroxyapatite are added and stirred at 600 rpm for 20 minutes. Finally, a bio-based antioxidant is added and stirring is continued for 10-15 minutes. The vacuum degree is maintained at -0.09 MPa, and the melt flow rate is controlled at 15-20 g / 10 min.

9. The method for preparing biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 8, characterized in that, It also includes a composite molding step: hot melt adhesive is evenly coated onto the substrate layer by a precision slot coater, and then dried by infrared to form an adhesive layer with a dry film thickness of 15-20μm; it is pressed with the release layer by a heated composite roller for 5-8s, and after being rolled up, it is cured at 23℃ and 50%RH for 24h to ensure that the initial tack reaches 8-10# steel ball.

10. The method for preparing biodegradable bio-based hot-melt pressure-sensitive adhesive label paper according to claim 9, characterized in that, It also includes the following steps for preparing the release layer: Modified montmorillonite is dispersed in a 5wt% chitosan aqueous solution, ultrasonically dispersed for 30 min, molten beeswax is added, and high-speed shear emulsification is performed for 30 min to form an emulsion with a solid content of 20wt%; it is then coated onto a PET release substrate using a microgravure coating method, dried with hot air for 10-15 min to form a release layer with a thickness of 3-5μm, and corona treatment is performed after curing.

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