A biodegradable high oxygen barrier transfer paper and its preparation method

Abstract

This invention relates to the field of environmentally friendly packaging materials, and discloses a biodegradable high oxygen barrier transfer paper and its preparation method. The transfer paper, from bottom to top, consists of a base paper layer, a natural rubber-based pressure-sensitive adhesive layer, a natural rubber top layer, a PVA oxygen barrier middle layer, and a natural rubber bottom layer. The natural rubber is selected from cis-polyisoprene emulsion, which has been degraded using an alkyllithium / N,N,N',N'-tetramethylethylenediamine system to improve film-forming properties. The PVA oxygen barrier middle layer serves as the core functional layer, relying on the protection of the natural rubber layer to reduce the impact of moisture. The natural rubber-based pressure-sensitive adhesive layer ensures strong adhesion between the coating and the base paper, and contains no synthetic plastic components. The resulting transfer paper has an oxygen permeability of <5 cm⁻¹. 3 / (m 2 (24h·atm), soil degradation rate >65% within 60 days. In addition, the added modified nanocellulose can improve the coating's tensile strength, oxygen barrier properties, antibacterial properties, flame retardancy and hydrophobicity.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly packaging materials technology, specifically relating to a biodegradable high oxygen barrier transfer paper and its preparation method. Background Technology

[0002] Driven by the "plastic ban" and the demand for sustainable development, biodegradable oxygen-barrier packaging materials have become a research hotspot. Polyvinyl alcohol (PVA) is an ideal functional component due to its excellent oxygen barrier properties, but its direct application suffers from weak bonding and poor resistance to damp heat. Existing technologies often use synthetic materials such as styrene-butadiene latex to composite with PVA, but styrene-butadiene latex is non-degradable, and the synthetic adhesives used in conjunction with it can easily cause environmental burden. In addition, when traditional PVA emulsions are composited with most water-based coatings (such as acrylic and polyurethane emulsions), there are two major problems: First, the interlayer adhesion is weak, as the polarity of PVA's strong polar hydroxyl groups is poorly matched with the polarity of other coatings, resulting in insufficient intermolecular forces; second, it is prone to peeling when exposed to moisture. In high humidity environments, PVA absorbs moisture and expands (expansion rate 15~20%), leading to a sharp increase in interfacial stress and causing interlayer delamination.

[0003] Natural rubber, as a renewable biomass material, possesses good elasticity and biodegradability. In the natural environment, it can be decomposed into water and carbon dioxide by microorganisms. While natural rubber has weak adhesion to PET substrates but strong adhesion to paper fibers, it holds potential as a transfer coating carrier. However, its high molecular weight, poor film-forming properties, and unclear interfacial synergistic mechanism with PVA limit its application in oxygen-barrier transfer paper. Furthermore, existing oxygen-barrier packaging materials have deficiencies in antibacterial, flame-retardant, and hydrophobic properties. Enhancing the functionality of existing oxygen-barrier packaging materials can not only broaden their application areas but also increase their competitiveness in high-value-added markets, which is of great significance for promoting the green upgrading of packaging materials. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a biodegradable high oxygen barrier transfer paper and its preparation method, solving the problems of existing oxygen barrier transfer papers relying on non-degradable synthetic components and lacking environmental friendliness, while endowing the material with good tensile strength, oxygen barrier properties, antibacterial properties, flame retardant properties and hydrophobic properties.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A biodegradable high oxygen barrier transfer paper includes a base paper layer, a natural rubber-based pressure-sensitive adhesive layer and a transfer coating layer arranged sequentially from bottom to top. The transfer coating layer has a sandwich composite structure, consisting of a natural rubber bottom layer, a PVA oxygen barrier middle layer and a natural rubber top layer.

[0007] Both the natural rubber bottom layer and the natural rubber top layer are formed by coating and curing with a coating liquid, which includes the following components by weight: 30-45 parts of degraded natural rubber latex, 1-3 parts of modified nanocellulose, 0.2-0.5 parts of leveling agent, and 52-68 parts of deionized water.

[0008] The degraded natural rubber latex is natural rubber latex treated with an alkyl lithium / N,N,N',N'-tetramethylethylenediamine system, resulting in a number average molecular weight of 5000~10000.

[0009] The modified nanocellulose is prepared by grafting a functionalized silane coupling agent, which is prepared by a substitution reaction between a modified DOPO derivative and 3-chloropropyltrimethoxysilane, onto the surface of nanocellulose.

[0010] The modified DOPO derivative was prepared by ring-opening reaction of glycidyl neodecanoate with 3,4-dihydroxybenzaldehyde to obtain an aldehyde intermediate, followed by Schiff base reaction of 1,5-diaminonaphthalene with the aldehyde intermediate to obtain a Schiff base intermediate, which was then subjected to an addition reaction with DOPO to obtain the DOPO derivative. Subsequently, the bromo-substituted DOPO derivative was prepared by substitution reaction of the DOPO derivative with 1,5-dibromobutane, and then subjected to quaternization reaction with 3-pyridineboronic acid to obtain the DOPO derivative.

[0011] Preferably, the dry film thickness of the natural rubber bottom layer and the natural rubber top layer is 3~6μm; the dry film thickness of the PVA oxygen barrier middle layer is 5~12μm.

[0012] Preferably, the natural rubber latex is a cis-polyisoprene emulsion with a solid content ≥50%; and the leveling agent is a natural plant wax emulsion.

[0013] Preferably, the method for preparing the modified nanocellulose includes the following steps:

[0014] ① Take 3,4-dihydroxybenzaldehyde and N,N-dimethylformamide in a reactor, add potassium carbonate catalyst, heat to 80~95℃, slowly add glycidyl neodecanoate, stir the reaction for 4~6h, and after the reaction is completed, extract, wash and purify to prepare aldehyde intermediate;

[0015] ② Dissolve 1,5-diaminonaphthalene and aldehyde intermediate in ethanol respectively, add them to the reactor under a nitrogen atmosphere, stir and react at 75~85℃ for 2~3h, wash, filter and dry after the reaction is completed to prepare Schiff base intermediate;

[0016] ③ Dissolve the Schiff base intermediate and DOPO in ethanol respectively, add them to the reactor under a nitrogen atmosphere, and stir the reaction at 75~85℃ for 5~6h. After the reaction is completed, wash, filter and dry to prepare DOPO derivative.

[0017] ④ Take DOPO derivative, 1,5-dibromobutane and dimethyl sulfoxide in a reactor, add potassium carbonate catalyst, stir and react at 85~90℃ for 6~8h, and after the reaction is completed, wash and dry to prepare bromine-substituted DOPO derivative.

[0018] ⑤ Take the bromine-substituted DOPO derivative, 3-pyridineboronic acid and dimethyl sulfoxide in a reactor, stir and react at 65~75℃ for 12~16h. After the reaction is completed, filter, wash and dry to prepare the modified DOPO derivative.

[0019] ⑥ Take the modified DOPO derivative and N,N-dimethylformamide in a reactor, add 3-chloropropyltrimethoxysilane and triethylamine, stir and react at 75~85℃ for 5~7h, and after the reaction is completed, filter under reduced pressure and evaporate by rotary evaporation to prepare the functionalized silane coupling agent.

[0020] ⑦ Disperse nanocellulose ultrasonically in anhydrous ethanol and deionized water, then add functionalized silane coupling agent, and stir at 55~70℃ for 6~8h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0021] Preferably, in step ①, the molar ratio of 3,4-dihydroxybenzaldehyde and glycidyl neodecanoate is 1:1 to 1.1; in step ②, the molar ratio of 1,5-diaminonaphthalene and aldehyde intermediate is 1 to 1.2:1; and in step ③, the molar ratio of Schiff base intermediate and DOPO is 1:1 to 1.1.

[0022] Preferably, the PVA oxygen barrier middle layer comprises the following components by weight: 75-90 parts PVA emulsion, 1-3 parts glycerol, 0.3-0.6 parts silane coupling agent, and 10-25 parts deionized water; the solid content of the PVA emulsion is 8-12%, the degree of polymerization of PVA is 1700-2400, and the degree of alcoholysis is 86-89%.

[0023] Preferably, the natural rubber-based pressure-sensitive adhesive layer is an aqueous system comprising the following components by weight: 20-30 parts of degraded natural rubber latex, 50-70 parts of hydrogenated rosin glycerol ester tackifying resin emulsion, 10-20 parts of lanolin softener emulsion, and 2-5 parts of antioxidant; the dry film thickness of the natural rubber-based pressure-sensitive adhesive layer is 8-15 μm, the 180° peel strength is ≥4.5 N / 2.5 cm, and the solid content is 40-50%.

[0024] Preferably, the base paper layer has a basis weight of 80~150 g / m³. 2 It is made of all-wood pulp or bagasse pulp, with a moisture content of 6-8%, a surface roughness of ≤2μm, and a biodegradability of ≥80% within 60 days.

[0025] The preparation method of the biodegradable high oxygen barrier transfer paper as described above includes the following steps:

[0026] S1. Pretreatment of PET substrate: Select a corona-free PET film with a thickness of 50~100μm, wipe it clean with a 70~80% ethanol solution, and dry it at 50~60℃ for 5~10min for later use.

[0027] S2. Preparation of natural rubber base layer: Weigh each component according to the weight parts, mix and stir the degraded natural rubber latex, modified nanocellulose, leveling agent and deionized water for 20~30min, apply it to the surface of the pretreated PET substrate using a micro-gravure plate at a coating speed of 15~25m / min, and dry it with hot air at 60~70℃ for 15~25min to form the natural rubber base layer.

[0028] S3, Preparation of PVA oxygen barrier middle layer: PVA emulsion, glycerin, silane coupling agent and deionized water are mixed and stirred and allowed to stand for degassing for 30-40 minutes. The mixture is then applied to the surface of the natural rubber base layer using a slit coating at a speed of 15-25 m / min. It is then pre-dried at 40-50℃ for 10-15 minutes and then dried at 60-65℃ for 20-30 minutes to form the PVA oxygen barrier middle layer.

[0029] S4. Preparation of the top layer of natural rubber: Using the same coating liquid and process parameters as in step S2, the coating is applied to the surface of the PVA oxygen barrier middle layer and dried to form a transfer coating of “natural rubber bottom layer - PVA oxygen barrier middle layer - natural rubber top layer”, and then cooled to room temperature.

[0030] S5. Coating of natural rubber-based pressure-sensitive adhesive layer: Weigh each component according to the weight parts, mix the degraded natural rubber latex, hydrogenated rosin glycerol ester tackifying resin emulsion, lanolin softener emulsion, and antioxidant evenly, coat it on the surface of the top layer of natural rubber, and dry it at 60~65℃ for 10~20min to form a natural rubber-based pressure-sensitive adhesive layer.

[0031] S6. Lamination and Transfer: Lay the PET-transfer coating with a natural rubber-based pressure-sensitive adhesive layer onto the pretreated base paper layer. The lamination pressure is 0.3~0.6MPa, the lamination speed is 10~20m / min, the pressure roller temperature is 40~50℃, and after lamination, let it stand for 15~20min. Then, remove the PET substrate by peeling it off at a 180° peeling speed of 5~10m / min.

[0032] S7. Post-treatment: Dry the transferred paper at 55~65℃ for 20~40 min to prepare biodegradable high oxygen barrier transfer paper.

[0033] Preferably, the pretreatment method of the base paper in step S6 is as follows: the base paper is dried at 50~60℃ to a moisture content of 6~8% to ensure a smooth surface without warping; the moisture content of the coating after drying in steps S2 and S4 is <1%; and the light transmittance of the PVA oxygen barrier layer after drying in step S3 is ≥90%.

[0034] The beneficial effects of this invention are:

[0035] The biodegradable high oxygen barrier transfer paper prepared by this invention consists of, from bottom to top, a base paper layer, a natural rubber-based pressure-sensitive adhesive layer, a natural rubber top layer, a PVA oxygen barrier middle layer, and a natural rubber bottom layer. The natural rubber bottom and top layers form a symmetrical structure, utilizing the weak van der Waals forces between natural rubber and PET to achieve precise peeling. Simultaneously, modified nanocellulose enhances the interfacial bonding with PVA. The PVA oxygen barrier middle layer serves as the core functional layer, relying on the protection of the natural rubber layer to reduce the impact of moisture. The natural rubber-based pressure-sensitive adhesive layer ensures strong adhesion between the coating and the base paper. Furthermore, it contains no synthetic plastic components, resulting in an oxygen permeability of <5 cm⁻¹. 3 / (m 2 With a degradation rate of >65% in soil within 60 days (24h·atm), it can be widely used in environmentally friendly packaging scenarios such as food and pharmaceuticals. The modified nanocellulose added in this invention utilizes its hydroxyl groups to form hydrogen bonds with PVA, thereby improving the coating's tensile strength, oxygen barrier properties, antibacterial properties, flame retardant properties, and hydrophobic properties. The PVA selected is partially alcoholyzable, and glycerol is added as a plasticizer to improve the brittleness problem. The silane coupling agent enhances the interfacial compatibility with natural rubber, ensuring stable interlayer bonding. The natural rubber-based pressure-sensitive adhesive layer adopts a fully bio-based formula, using degraded natural rubber as the elastic matrix, combined with hydrogenated rosin glycerol ester tackifying resin and lanolin softener. The 180° peel force is ≥4.5N / 2.5cm, meeting the requirements of the transfer process and achieving a degradation rate of over 60%.

[0036] In this invention, the natural rubber used is cis-polyisoprene emulsion, which is degraded using an alkyllithium / N,N,N',N'-tetramethylethylenediamine system to reduce the molecular weight to 5000-10000, improving film-forming properties. Although the main chain of the natural latex (cis-polyisoprene system) is non-polar, it contains naturally occurring residual polar groups (-COOH, -OH, content 0.5-2%), which can form hydrogen bonds and van der Waals forces with the -OH groups of PVA. Furthermore, the polar groups are evenly distributed, avoiding the problem of "excessive crosslinking and stress concentration due to high-density carboxyl groups" found in acrylic emulsions. This results in moderate and stable intermolecular bonding. During film formation, the elastic particles of the natural latex accumulate to form a porous structure, while the PVA emulsion... It can penetrate into the pores and solidify, forming a micro-anchoring structure of "PVA embedded in latex pores", upgrading the intermolecular bonding to a dual "chemical and physical" bonding. The adhesion is 30-50% higher than that of latex-free systems. The moisture absorption and expansion rate of natural latex is only 1-2% (far lower than the 15-20% of PVA), and the elongation at break is 800-1000%. The high elasticity can disperse the interfacial shear force generated by the moisture absorption and expansion of PVA through deformation, avoiding peeling caused by stress concentration. In addition, the interfacial bonding force (hydrogen bond and anchoring) between natural latex and PVA is stronger than the bonding force between water molecules and PVA. Water molecules are difficult to replace the interfacial interaction between the two to form a "weak hydration layer", preventing the PVA layer from falling off due to moisture.

[0037] This invention utilizes a ring-opening reaction between glycidyl neodecanoate and a hydroxyl group in 3,4-dihydroxybenzaldehyde to prepare an aldehyde intermediate. Then, a Schiff base intermediate prepared by reacting a terminal amino group of 1,5-diaminonaphthalene with the aldehyde intermediate undergoes an addition reaction with the PH bond in DOPO to prepare a DOPO derivative. Subsequently, an ungrafted amino group in the DOPO derivative undergoes a substitution reaction with a terminal bromine atom in 1,5-dibromobutane to prepare a bromine-substituted DOPO derivative. This bromine-substituted DOPO derivative is then quaternized with 3-pyridineboronic acid to prepare a modified DOPO derivative. The remaining hydroxyl groups in the modified DOPO derivative undergo a substitution reaction with 3-chloropropyltrimethoxysilane to prepare a functionalized silane coupling agent. Finally, the silanol groups generated by the hydrolysis of the functionalized silane coupling agent undergo a dehydration condensation reaction with the hydroxyl groups on the surface of nanocellulose to prepare modified nanocellulose.

[0038] The functionalized silane coupling agent prepared in this invention incorporates 1,5-diaminonaphthalene, which has good thermal stability and can release smoke and flame-retardant gases that inhibit combustion at high temperatures. DOPO, a commonly used organophosphorus flame retardant, is introduced, and the flame-retardant performance of the material is improved by leveraging the synergistic flame-retardant effect of NP-Si elements through the introduction of 3-chloropropyltrimethoxysilane. Simultaneously, the introduction of a quaternary ammonium salt structure with antibacterial activity and boric acid units with good bacterial capture ability endows the material with good antibacterial properties and durability. Furthermore, the introduced tertiary carbonate hydrophobic groups enhance the hydrophobic properties of the material to a certain extent. In addition, the functionalized silane coupling agent is grafted onto the surface of nanocellulose through strong chemical bonds, improving the defect of poor dispersion of nanocellulose and avoiding performance defects caused by nanocellulose agglomeration. This also facilitates long-lasting antibacterial, flame-retardant, and hydrophobic effects. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1 A method for preparing degraded natural rubber latex, comprising the following steps: natural rubber latex (cis-polyisoprene) with a solid content of 50% is degraded at room temperature for 10 min in an alkyllithium / N,N,N',N'-tetramethylethylenediamine system, with the number average molecular weight controlled at 8000, to obtain degraded natural rubber latex.

[0041] Example 2 A method for preparing modified nanocellulose includes the following steps:

[0042] ① Take 13.8g of 3,4-dihydroxybenzaldehyde and 120mL of N,N-dimethylformamide in a reactor, add 19.3g of potassium carbonate catalyst, heat to 85℃, slowly add 22.8g of neodecanoic acid glycidyl ester, stir the reaction for 5h, and after the reaction is completed, extract, wash and purify to prepare the aldehyde intermediate;

[0043] ② Dissolve 12.7g of 1,5-diaminonaphthalene and 29.3g of aldehyde intermediate in 100mL of ethanol respectively, add them to the reactor under a nitrogen atmosphere, and stir at 80℃ for 2.5h. After the reaction is completed, wash, filter and purify to prepare Schiff base intermediate;

[0044] ③ Dissolve 25.3g of Schiff base intermediate and 10.8g of DOPO in 100mL of ethanol respectively, add them to the reactor under a nitrogen atmosphere, stir at 80℃ for 6h, and after the reaction is completed, wash, filter and dry to prepare DOPO derivative;

[0045] ④ Take 21.7g of DOPO derivative, 20.7g of 1,5-dibromobutane and 200mL of dimethyl sulfoxide into a reactor, add 0.2g of potassium carbonate catalyst, and stir the reaction at 85℃ for 7h. After the reaction is completed, wash and dry to prepare bromine-substituted DOPO derivative.

[0046] ⑤ Take 17.4g of bromine-substituted DOPO derivative, 2.5g of 3-pyridineboronic acid and 120mL of dimethyl sulfoxide in a reactor, stir and react at 70℃ for 14h. After the reaction is completed, filter, wash and dry to prepare the modified DOPO derivative.

[0047] ⑥ Take 14.9g of modified DOPO derivative and 100mL of N,N-dimethylformamide in a reactor, add 3.9g of 3-chloropropyltrimethoxysilane and 1.5g of triethylamine, stir and react at 80℃ for 6h, and after the reaction is completed, filter under reduced pressure and evaporate by rotary evaporation to prepare functionalized silane coupling agent;

[0048] ⑦ Take 10g of nanocellulose and ultrasonically disperse it in 90mL of anhydrous ethanol and 20mL of deionized water. Then add 5.7g of functionalized silane coupling agent and stir at 60℃ for 7h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0049] Example 3 A natural rubber bottom layer and a natural rubber top layer are both formed by coating and curing with a coating liquid. The coating liquid includes the following components by weight: 33 parts of degraded natural rubber latex prepared in Example 1, 1.2 parts of modified nanocellulose prepared in Example 2, 0.2 parts of leveling agent natural plant wax emulsion, and 54 parts of deionized water.

[0050] A PVA oxygen barrier middle layer comprises the following components in parts by weight: 77 parts of PVA emulsion with a solid content of 10% (degree of polymerization of 2000 and degree of alcoholysis of 88%), 1.2 parts of glycerol, 0.3 parts of KH550 silane coupling agent, and 10.4 parts of deionized water;

[0051] A natural rubber-based pressure-sensitive adhesive layer comprises the following components in parts by weight: 21 parts of degraded natural rubber latex prepared in Example 1, 52 parts of hydrogenated rosin glycerol ester tackifying resin emulsion, 11 parts of lanolin softener emulsion, and 2.2 parts of antioxidant 4020;

[0052] A method for preparing a biodegradable high oxygen barrier transfer paper includes the following steps:

[0053] S1. Pretreatment of PET substrate: Select a 75μm thick corona-free PET film, wipe it clean with a 75% ethanol solution, and dry it at 60℃ for 8 minutes for later use.

[0054] S2. Preparation of natural rubber base layer: Weigh each component according to the weight parts, mix and stir the degraded natural rubber latex, modified nanocellulose, leveling agent and deionized water for 25 min, and apply it to the surface of the pretreated PET substrate using a micro-gravure coating at a coating speed of 20 m / min. Dry it with hot air at 70℃ for 20 min to form a 5 μm natural rubber base layer.

[0055] S3, Preparation of PVA oxygen barrier middle layer: PVA emulsion with a solid content of 10%, glycerin, KH550 silane coupling agent and deionized water were mixed and stirred, and then allowed to stand for degassing for 35 min. The mixture was then applied to the surface of the natural rubber base layer by slit coating at a coating speed of 20 m / min. It was first pre-dried at 45℃ for 12 min, and then dried at 65℃ for 25 min to form a 10 μm PVA oxygen barrier middle layer.

[0056] S4. Preparation of natural rubber top layer: Using the same coating liquid and process parameters as in step S2, the PVA oxygen barrier middle layer is coated and dried to form a 5μm natural rubber top layer. The total thickness of the "natural rubber bottom layer-PVA oxygen barrier middle layer-natural rubber top layer" transfer coating is 20μm. Cool to room temperature.

[0057] S5. Coating of natural rubber-based pressure-sensitive adhesive layer: Weigh each component according to the weight parts, mix the degraded natural rubber latex, hydrogenated rosin glycerol ester tackifying resin emulsion, lanolin softener emulsion, and antioxidant evenly, coat it on the surface of the top layer of natural rubber, and dry it at 65℃ for 15 minutes to form a 12μm natural rubber-based pressure-sensitive adhesive layer.

[0058] S6. Lamination and Transfer: The base paper layer uses a basis weight of 120g / m³. 2 The bagasse pulp paper was dried to a moisture content of 7%. The PET-transfer coating was then laminated to the base paper layer at a lamination pressure of 0.5 MPa, a lamination speed of 15 m / min, and a pressing roller temperature of 45°C. After lamination, the paper was left to stand for 18 min. The PET substrate was then removed by peeling at a 180° peeling speed of 8 m / min.

[0059] S7. Post-treatment: Dry the transferred paper at 60℃ for 30 min to prepare biodegradable high oxygen barrier transfer paper.

[0060] Example 4 A natural rubber bottom layer and a natural rubber top layer are both formed by coating and curing with a coating liquid. The coating liquid includes the following components by weight: 40 parts of degraded natural rubber latex prepared in Example 1, 2 parts of modified nanocellulose prepared in Example 2, 0.3 parts of leveling agent natural plant wax emulsion, and 57.7 parts of deionized water.

[0061] A PVA oxygen barrier middle layer comprises the following components in parts by weight: 85 parts of PVA emulsion with a solid content of 10% (degree of polymerization of 2000 and degree of alcoholysis of 88%), 2 parts of glycerol, 0.4 parts of KH550 silane coupling agent, and 12.6 parts of deionized water.

[0062] A natural rubber-based pressure-sensitive adhesive layer comprises the following components in parts by weight: 25 parts of the degraded natural rubber latex prepared in Example 1, 60 parts of hydrogenated rosin glycerol ester tackifying resin emulsion, 15 parts of lanolin softener emulsion, and 3 parts of antioxidant 4020.

[0063] The preparation method of a biodegradable high oxygen barrier transfer paper is the same as in Example 3.

[0064] Example 5 A natural rubber bottom layer and a natural rubber top layer are both formed by coating and curing with a coating liquid. The coating liquid includes the following components by weight: 44 parts of degraded natural rubber latex prepared in Example 1, 2.7 parts of modified nanocellulose prepared in Example 2, 0.4 parts of leveling agent natural plant wax emulsion, and 63 parts of deionized water.

[0065] A PVA oxygen barrier middle layer comprises the following components in parts by weight: 89 parts of PVA emulsion with a solid content of 10% (degree of polymerization of 2000 and degree of alcoholysis of 88%), 2.6 parts of glycerol, 0.5 parts of KH550 silane coupling agent, and 22 parts of deionized water.

[0066] A natural rubber-based pressure-sensitive adhesive layer comprises the following components in parts by weight: 28 parts of degraded natural rubber latex prepared in Example 1, 66 parts of hydrogenated rosin glycerol ester tackifying resin emulsion, 17 parts of lanolin softener emulsion, and 4.3 parts of antioxidant 4020;

[0067] The preparation method of a biodegradable high oxygen barrier transfer paper is the same as in Example 3.

[0068] Comparative Example 1: A method for preparing modified nanocellulose includes the following steps:

[0069] ① Take 13.8g of 3,4-dihydroxybenzaldehyde and 120mL of N,N-dimethylformamide in a reactor, add 19.3g of potassium carbonate catalyst, heat to 85℃, slowly add 22.8g of neodecanoic acid glycidyl ester, stir the reaction for 5h, and after the reaction is completed, extract, wash and purify to prepare the aldehyde intermediate;

[0070] ② Dissolve 12.7g of 1,5-diaminonaphthalene and 29.3g of aldehyde intermediate in 100mL of ethanol respectively, add them to the reactor under a nitrogen atmosphere, and stir at 80℃ for 2.5h. After the reaction is completed, wash, filter and purify to prepare Schiff base intermediate;

[0071] ③ Dissolve 25.3g of Schiff base intermediate and 10.8g of DOPO in 100mL of ethanol respectively, add them to the reactor under a nitrogen atmosphere, stir at 80℃ for 6h, and after the reaction is completed, wash, filter and dry to prepare DOPO derivative;

[0072] ④ Take 10.8g of DOPO derivative and 100mL of N,N-dimethylformamide in a reactor, add 3.9g of 3-chloropropyltrimethoxysilane and 1.5g of triethylamine, stir and react at 80℃ for 6h, and after the reaction is completed, filter under reduced pressure and evaporate by rotary evaporation to prepare functionalized silane coupling agent;

[0073] ⑤ Take 10g of nanocellulose and ultrasonically disperse it in 90mL of anhydrous ethanol and 20mL of deionized water. Then add 5.7g of functionalized silane coupling agent and stir at 60℃ for 7h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0074] Comparative Example 2: A method for preparing modified nanocellulose includes the following steps:

[0075] ① Take 13.8g of 3,4-dihydroxybenzaldehyde and 120mL of N,N-dimethylformamide in a reactor, add 19.3g of potassium carbonate catalyst, heat to 85℃, slowly add 22.8g of neodecanoic acid glycidyl ester, stir the reaction for 5h, and after the reaction is completed, extract, wash and purify to prepare the aldehyde intermediate;

[0076] ② Dissolve 12.7g of 1,5-diaminonaphthalene and 29.3g of aldehyde intermediate in 100mL of ethanol respectively, add them to the reactor under a nitrogen atmosphere, and stir at 80℃ for 2.5h. After the reaction is completed, wash, filter and purify to prepare Schiff base intermediate;

[0077] ③ Take 7.6g of Schiff base intermediate and 100mL of N,N-dimethylformamide in a reactor, add 3.9g of 3-chloropropyltrimethoxysilane and 1.5g of triethylamine, stir and react at 80℃ for 6h, and after the reaction is completed, filter under reduced pressure and evaporate by rotary evaporation to prepare functionalized silane coupling agent;

[0078] ④ Take 10g of nanocellulose and ultrasonically disperse it in 90mL of anhydrous ethanol and 20mL of deionized water. Then add 5.7g of functionalized silane coupling agent and stir at 60℃ for 7h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0079] Comparative Example 3: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the modified nanocellulose in Example 4 is replaced by an equal amount of the modified nanocellulose prepared in Comparative Example 1, and the remaining components and operating steps are the same as in Example 4.

[0080] Comparative Example 4: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the modified nanocellulose in Example 4 is replaced by an equal amount of the modified nanocellulose prepared in Comparative Example 2, and the remaining components and operating steps are the same as in Example 4.

[0081] Comparative Example 5: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the modified nanocellulose in Example 4 is replaced with an equal amount of nanocellulose, and the remaining components and operating steps are the same as in Example 4.

[0082] Comparative Example 6: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the biodegradable natural rubber latex in Example 4 was replaced by an equal amount of natural rubber latex with a solid content of 50% (cis-polyisoprene). No degradation treatment was performed. The remaining components and operating steps were the same as in Example 4.

[0083] Comparative Example 7: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the biodegradable natural rubber latex in Example 4 was replaced with styrene-butadiene latex in equal amounts, and the natural rubber-based pressure-sensitive adhesive was replaced with acrylic pressure-sensitive adhesive in equal amounts. The remaining components and operating steps were the same as in Example 4.

[0084] Comparative Example 8: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the biodegradable natural rubber latex added to the coating liquid in Example 4 was replaced with an equal amount of water-based acrylic emulsion, and the remaining components and operating steps were the same as in Example 4.

[0085] Comparative Example 9: A method for preparing a biodegradable high oxygen barrier transfer paper. Compared with Example 4, the biodegradable natural rubber latex added to the coating liquid in Example 4 was replaced with an equal amount of waterborne polyurethane emulsion, and the remaining components and operating steps were the same as in Example 4.

[0086] Performance testing

[0087] A. The biodegradable high oxygen barrier transfer papers prepared in Examples 3-5 and Comparative Examples 3-7 were subjected to tensile strength testing according to GB / T 12914-2018. Before the test, the paper samples were placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 12 hours to equilibrate the moisture. The tensile index was calculated by dividing the average tensile strength (N / m) of the paper in the longitudinal and transverse directions by the basis weight (g / m³). 2The oxygen permeability was measured using an oxygen permeability tester; the antibacterial rate was tested according to GB / T 21866-2008, with Staphylococcus aureus and Escherichia coli as the test species; the water contact angle was tested using a PZ-200SD contact angle meter; the flame retardant performance of the sample was evaluated by the limiting oxygen index; the biodegradability of the sample after 60 days of landfill was determined according to GB / T 19277.1-2025, and the data results are shown in Table 1.

[0088] Table 1 Sample performance test results

[0089]

[0090] Note: In Comparative Example 6 of Table 1, cracks in the coating were not detected ("-" indicates that they were not detected).

[0091] As can be seen from the data in Table 1, the biodegradable high oxygen barrier transfer paper prepared in Examples 3-5 of this invention has high tensile strength and an oxygen permeability of <5cm. 3 / (m 2 (24h·atm), soil degradation rate >65% within 60 days, while also possessing good antibacterial, flame retardant, and hydrophobic properties. The modified nanocellulose added in Comparative Example 3 did not contain quaternary ammonium salt structures or boric acid units, and the modified nanocellulose added in Comparative Example 4 did not contain quaternary ammonium salt structures, boric acid units, or DOPO. Comparative Example 5 did not undergo any modification treatment of the nanocellulose. The measured antibacterial rates in Comparative Examples 3-5 were lower than those in Examples 3-5, indicating that quaternary ammonium salt structures and boric acid units can improve the antibacterial properties of the material. Furthermore, the limiting oxygen index in Comparative Examples 4-5 was lower than that in Examples 3-5, because no organophosphorus flame retardant was grafted. The limiting oxygen index in Comparative Example 5 was further lower than that in Comparative Example 4, indicating that NP-Si synergistic flame retardancy is beneficial for further improving the flame retardant properties of the material. Additionally, the measured values ​​of the comparative examples... In Comparative Example 5, the tensile index and water contact angle were lower than those in Examples 3-5, while the oxygen permeability was higher. This may be due to the agglomeration of nanocellulose, which reduced mechanical properties and oxygen barrier properties. In Comparative Example 6, no degradation treatment was performed on the natural rubber latex, and the measured oxygen permeability was significantly higher than that in Examples 3-5. This is because the molecular weight of natural rubber is too high (>100,000), causing cracks during film formation and reducing oxygen barrier properties. In Comparative Example 7, the degraded natural rubber latex was replaced with an equal amount of styrene-butadiene latex, and the natural rubber-based pressure-sensitive adhesive was replaced with an equal amount of acrylic pressure-sensitive adhesive. The measured degradation rate was significantly lower than that in Examples 3-5, and there were synthetic plastic residues, which did not meet environmental protection requirements.

[0092] B. The interlayer adhesion of the biodegradable high oxygen barrier transfer paper prepared in Examples 3-5 and Comparative Examples 8-9 was tested, and the data results are shown in Table 2.

[0093] Table 2 Results of interlayer adhesion test on samples

[0094]

[0095] As can be seen from the data results in Table 2, the degraded natural rubber latex prepared in Examples 3-5 of the present invention can serve as an "interface bridge" to simultaneously solve the problems of adhesion and moisture stability, and achieve long-term bonding between PVA and the coating / substrate. However, water molecules at the interface between PVA and acrylic / polyurethane are prone to destroying the original bond, leading to moisture-induced peeling.

[0096] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0097] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A biodegradable high oxygen barrier transfer paper, characterized in that, It includes a base paper layer, a natural rubber-based pressure-sensitive adhesive layer and a transfer coating layer arranged from bottom to top. The transfer coating layer has a sandwich composite structure, consisting of a natural rubber bottom layer, a PVA oxygen barrier middle layer and a natural rubber top layer. Both the natural rubber bottom layer and the natural rubber top layer are formed by coating and curing with a coating liquid, which includes the following components by weight: 30-45 parts of degraded natural rubber latex, 1-3 parts of modified nanocellulose, 0.2-0.5 parts of leveling agent, and 52-68 parts of deionized water. The degraded natural rubber latex is natural rubber latex treated with an alkyl lithium / N,N,N',N'-tetramethylethylenediamine system, resulting in a number average molecular weight of 5000~10000. The modified nanocellulose is prepared by grafting a functionalized silane coupling agent, which is prepared by a substitution reaction between a modified DOPO derivative and 3-chloropropyltrimethoxysilane, onto the surface of nanocellulose. The modified DOPO derivative is prepared by ring-opening reaction of glycidyl neodecanoate with 3,4-dihydroxybenzaldehyde to prepare an aldehyde intermediate, then by Schiff base reaction of 1,5-diaminonaphthalene with the aldehyde intermediate to prepare a Schiff base intermediate, which is then added to DOPO to obtain the DOPO derivative. Subsequently, the DOPO derivative is substituted with 1,5-dibromobutane to prepare a bromo-substituted DOPO derivative, which is then quaternized with 3-pyridineboronic acid. The PVA oxygen barrier middle layer comprises the following components by weight: 75-90 parts PVA emulsion, 1-3 parts glycerol, 0.3-0.6 parts silane coupling agent, and 10-25 parts deionized water; the PVA emulsion has a solid content of 8-12%, a degree of polymerization of PVA of 1700-2400, and a degree of alcoholysis of 86-89%; The natural rubber-based pressure-sensitive adhesive layer is an aqueous system comprising the following components by weight: 20-30 parts of degraded natural rubber latex, 50-70 parts of hydrogenated rosin glyceryl ester tackifying resin emulsion, 10-20 parts of lanolin softener emulsion, and 2-5 parts of antioxidant; the dry film thickness of the natural rubber-based pressure-sensitive adhesive layer is 8-15 μm, the 180° peel strength is ≥4.5 N / 2.5 cm, and the solid content is 40-50%.

2. The biodegradable high oxygen barrier transfer paper according to claim 1, characterized in that, The dry film thickness of the natural rubber bottom layer and the natural rubber top layer is 3~6μm; the dry film thickness of the PVA oxygen barrier middle layer is 5~12μm.

3. The biodegradable high oxygen barrier transfer paper according to claim 1, characterized in that, The natural rubber latex is a cis-polyisoprene emulsion with a solid content ≥50%; the leveling agent is a natural plant wax emulsion.

4. The biodegradable high oxygen barrier transfer paper according to claim 1, characterized in that, The preparation method of the modified nanocellulose includes the following steps: ① Take 3,4-dihydroxybenzaldehyde and N,N-dimethylformamide in a reactor, add potassium carbonate catalyst, heat to 80~95℃, slowly add glycidyl neodecanoate, stir the reaction for 4~6h, and after the reaction is completed, extract, wash and purify to prepare aldehyde intermediate; ② Dissolve 1,5-diaminonaphthalene and aldehyde intermediate in ethanol respectively, add them to the reactor under a nitrogen atmosphere, stir and react at 75~85℃ for 2~3h, wash, filter and dry after the reaction is completed to prepare Schiff base intermediate; ③ Dissolve the Schiff base intermediate and DOPO in ethanol respectively, add them to the reactor under a nitrogen atmosphere, and stir the reaction at 75~85℃ for 5~6h. After the reaction is completed, wash, filter and dry to prepare DOPO derivative. ④ Take DOPO derivative, 1,5-dibromobutane and dimethyl sulfoxide in a reactor, add potassium carbonate catalyst, stir and react at 85~90℃ for 6~8h, and after the reaction is completed, wash and dry to prepare bromine-substituted DOPO derivative. ⑤ Take the bromine-substituted DOPO derivative, 3-pyridineboronic acid and dimethyl sulfoxide in a reactor, stir and react at 65~75℃ for 12~16h. After the reaction is completed, filter, wash and dry to prepare the modified DOPO derivative. ⑥ Take the modified DOPO derivative and N,N-dimethylformamide in a reactor, add 3-chloropropyltrimethoxysilane and triethylamine, stir and react at 75~85℃ for 5~7h, and after the reaction is completed, filter under reduced pressure and evaporate by rotary evaporation to prepare the functionalized silane coupling agent. ⑦ Disperse nanocellulose ultrasonically in anhydrous ethanol and deionized water, then add functionalized silane coupling agent, and stir at 55~70℃ for 6~8h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

5. The biodegradable high oxygen barrier transfer paper according to claim 4, characterized in that, In step ①, the molar ratio of 3,4-dihydroxybenzaldehyde to neodecanoic acid glycidyl ester is 1:1 to 1.1; in step ②, the molar ratio of 1,5-diaminonaphthalene to the aldehyde intermediate is 1 to 1.2:1; and in step ③, the molar ratio of Schiff base intermediate to DOPO is 1:1 to 1.

1.

6. The biodegradable high oxygen barrier transfer paper according to claim 1, characterized in that, The base paper layer has a basis weight of 80~150g / m³. 2 It is made of all-wood pulp or bagasse pulp, with a moisture content of 6-8%, a surface roughness of ≤2μm, and a biodegradability of ≥80% within 60 days.

7. The method for preparing biodegradable high oxygen barrier transfer paper according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Pretreatment of PET substrate: Select a corona-free PET film with a thickness of 50~100μm, wipe it clean with a 70~80% ethanol solution, and dry it at 50~60℃ for 5~10min for later use. S2. Preparation of natural rubber base layer: Weigh each component according to the weight parts, mix and stir the degraded natural rubber latex, modified nanocellulose, leveling agent and deionized water for 20~30min, apply it to the surface of the pretreated PET substrate using a micro-gravure plate at a coating speed of 15~25m / min, and dry it with hot air at 60~70℃ for 15~25min to form the natural rubber base layer. S3, Preparation of PVA oxygen barrier middle layer: PVA emulsion, glycerin, silane coupling agent and deionized water are mixed and stirred and allowed to stand for degassing for 30-40 minutes. The mixture is then applied to the surface of the natural rubber base layer using a slit coating at a speed of 15-25 m / min. It is then pre-dried at 40-50℃ for 10-15 minutes and then dried at 60-65℃ for 20-30 minutes to form the PVA oxygen barrier middle layer. S4. Preparation of natural rubber top layer: Using the same coating liquid and process parameters as in step S2, coat and dry the PVA oxygen barrier middle layer to form a natural rubber top layer, and cool to room temperature; S5. Coating of natural rubber-based pressure-sensitive adhesive layer: Weigh each component according to the weight parts, mix the degraded natural rubber latex, hydrogenated rosin glycerol ester tackifying resin emulsion, lanolin softener emulsion, and antioxidant evenly, coat it on the surface of the top layer of natural rubber, and dry it at 60~65℃ for 10~20min to form a natural rubber-based pressure-sensitive adhesive layer. S6. Lamination and Transfer: Lay the PET-transfer coating with a natural rubber-based pressure-sensitive adhesive layer onto the pretreated base paper layer. The lamination pressure is 0.3~0.6MPa, the lamination speed is 10~20m / min, the pressure roller temperature is 40~50℃, and after lamination, let it stand for 15~20min. Then, remove the PET substrate by peeling it off at a 180° peeling speed of 5~10m / min. S7. Post-treatment: Dry the transferred paper at 55~65℃ for 20~40 min to prepare biodegradable high oxygen barrier transfer paper.

8. The method for preparing biodegradable high oxygen barrier transfer paper according to claim 7, characterized in that, The pretreatment method for the base paper layer in step S6 is as follows: the base paper is dried at 50~60℃ to a moisture content of 6~8% to ensure a smooth surface without warping; the moisture content of the coating after drying in steps S2 and S4 is <1%; the light transmittance of the PVA oxygen barrier layer after drying in step S3 is ≥90%.

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