Polylactic acid aluminum laminated film and preparation method thereof

Abstract

The invention discloses a polylactic acid aluminum laminated film and a preparation method thereof, and belongs to the field of films. The polylactic acid aluminum laminated film comprises a polylactic acid film material, a polyurethane coating and an aluminum laminated layer which are arranged in sequence, the polyurethane coating is formed by curing a polyurethane coating, and the polyurethane coating is subjected to plasma surface treatment. The polyurethane coating is prepared from the following raw materials in parts by weight: 70-80 parts of hydroxyl acrylate emulsion, 1-1.5 parts of isocyanate modified cellulose, 7-9 parts of an isocyanate curing agent, 2-4 parts of an auxiliary agent and 20-30 parts of water. The preparation method has the effects of improving the adhesive force between the polylactic acid film and the aluminum layer and improving the durability of the polylactic acid aluminized film.

Description

Technical Field

[0001] The present application relates to the field of thin films, and in particular to a polylactic acid aluminum-plated film and a preparation method thereof. Background Art

[0002] As a new type of bio-based renewable biodegradable material, polylactic acid (PLA) has shown great potential in the field of environmental protection. Polylactic acid is made from starch raw materials extracted from renewable plant resources such as corn and cassava. Under the action of microorganisms in nature, it can be completely degraded under certain conditions and eventually converted into harmless carbon dioxide and water. It will not pollute the environment and is a recognized environmentally friendly material.

[0003] However, polylactic acid film has certain deficiencies in oxygen barrier and water vapor barrier properties. This defect limits its direct application in the packaging industry. The packaging industry has strict requirements on the barrier properties of products, especially for food and medicines that need to be stored for a long time.

[0004] The current improvement method in the industry is to plate aluminum on the surface of the polylactic acid film, using the dense barrier properties of the aluminum layer to improve the barrier properties of the polylactic acid film. However, the aluminum layer has poor adhesion to the surface of the polylactic acid film and the durability of the adhesion is low, which affects the application and promotion of polylactic acid aluminum-plated film. Summary of the invention

[0005] In order to improve the adhesion between the polylactic acid film and the aluminum layer and enhance the durability of the polylactic acid aluminum-plated film, the present application provides a polylactic acid aluminum-plated film and a preparation method thereof.

[0006] In the first aspect, the polylactic acid aluminum-plated film provided in the present application adopts the following technical solution: A polylactic acid aluminum-plated film comprises a polylactic acid film material, a polyurethane coating and an aluminum-plated layer arranged in sequence, wherein the polyurethane coating is formed by curing a polyurethane coating, the polyurethane coating is subjected to plasma surface treatment, and the polyurethane coating is prepared from raw materials containing the following parts by weight: 70-80 parts of hydroxy acrylate emulsion; 1-1.5 parts of isocyanate-modified cellulose; 7-9 parts of isocyanate curing agent; 2 to 4 parts of additives; 20-30 parts of water.

[0007] By adopting the above technical solution, a polyurethane coating is provided as a bonding layer between the polylactic acid film and the aluminum-plated layer, which can effectively improve the bonding force between the polylactic acid film and the aluminum-plated layer. The isocyanate-modified cellulose is added to the polyurethane coating, and the interface compatibility of the cellulose with the polyurethane structure is improved after the isocyanate modification, thereby improving the dispersibility of the cellulose in the polyurethane coating. The cellulose not only improves the cross-linking density inside the polyurethane coating, but also enhances the interface interaction of the polyurethane coating, which can effectively improve the bonding force between the polyurethane coating and the aluminum-plated layer and between the polyurethane coating and the polylactic acid film, thereby enhancing the adhesion of the aluminum-plated layer on the surface of the polylactic acid film.

[0008] Isocyanate-modified cellulose also increases the number of active sites for the polyurethane coating to receive plasma treatment. After the isocyanate-modified cellulose is treated with plasma, the number of active groups on the surface increases, which effectively improves the surface activity of the polyurethane coating, enhances the fixation of aluminum during aluminum plating, further enhances the bonding force between the polyurethane coating and the polylactic acid film, and improves the adhesion durability of the aluminum plating layer.

[0009] Optionally, the isocyanate-modified cellulose is prepared by the reaction of isocyanate and cellulose, wherein the isocyanate includes aromatic monoisocyanate and aliphatic diisocyanate.

[0010] By adopting the above technical scheme, the aromatic monoisocyanate has the characteristics of benzene ring rigidity, which can improve the adhesion between the polyurethane system and the cellulose interface. The aliphatic diisocyanate can achieve cross-linking between celluloses, forming a network fiber structure at the interface of the polyurethane coating, and improving the adhesion of the aluminum-plated film on the surface of the polyurethane coating.

[0011] Optionally, the isocyanate-modified cellulose is prepared by reacting cellulose with isocyanate in a mass ratio of 1:(0.48-0.65), and the isocyanate includes 4-n-butylphenol isocyanate and hexamethylene diisocyanate in a mass ratio of 1:(0.2-0.3).

[0012] By adopting the above technical scheme, the proportion of isocyanate accessed to the cellulose surface is controlled to improve the cross-linking density inside the polyurethane coating; the 4-n-butylphenol isocyanate has an n-butyl chain at the end, which forms a good entanglement with the polyurethane chain segment, thereby improving the density of the polyurethane coating and improving the barrier properties. The proportion of 4-n-butylphenol isocyanate and hexamethylene diisocyanate is controlled to keep the cross-linking between cellulose at a low level, prevent excessive cross-linking and agglomeration, give full play to the interfacial interaction, and thus improve the durability of the polylactic acid aluminum-plated film.

[0013] Optionally, the auxiliary agent includes one or both of a leveling agent and a thickener.

[0014] Optionally, the hydroxyacrylate emulsion is prepared from the following raw materials in parts by weight: 45-55 parts of hydroxy acrylate monomer; 2-5 parts of short-chain aliphatic acrylate monomer; 2 to 5 parts of long-chain aliphatic acrylate monomer; 2-3 parts of emulsifier; Initiator 0.2-0.6 parts; 60-70 parts of water.

[0015] By adopting the above technical scheme, with the combination of short-chain aliphatic and long-chain aliphatic acrylate monomers, not only the interfacial interaction of the polyurethane coating is enhanced, but also the interfacial bonding ability with isocyanate-modified cellulose is improved, further improving the bonding durability of the polyurethane coating.

[0016] Optionally, the short-chain aliphatic acrylate monomer includes one or more of methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate and propyl methacrylate; the long-chain aliphatic acrylate monomer includes one or more of dodecyl methacrylate, tetradecyl methacrylate and hexadecyl methacrylate.

[0017] Optionally, the hydroxyacrylate is selected from one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

[0018] Optionally, the emulsifier includes one or both of sodium lauryl sulfate and sodium stearate.

[0019] Optionally, the initiator includes one or both of potassium persulfate and ammonium persulfate.

[0020] Optionally, the isocyanate curing agent is a water-dispersible polyisocyanate based on hexamethylene diisocyanate.

[0021] By adopting the above technical scheme, the water-dispersible polyisocyanate based on hexamethylene diisocyanate is suitable for forming a stable cross-linking structure with the hydroxy acrylate emulsion, and the cross-linking structure is dense.

[0022] Optionally, the thickness of the polylactic acid film is 15 to 20 μm.

[0023] Optionally, the aluminum plating layer has a thickness of 400 to 450 angstroms.

[0024] Optionally, the thickness of the polyurethane coating is 0.1-0.3 μm.

[0025] In the second aspect, the present application provides a method for preparing a polylactic acid aluminum-plated film using the following technical solution: A method for preparing a polylactic acid aluminum-plated film comprises the following steps: The hydroxy acrylate emulsion and the isocyanate modified cellulose are stirred and mixed, and heated to 40-45° C., and then the isocyanate curing agent, the auxiliary agent and water are added and mixed, and the heating is stopped after stirring evenly, and the stirring is continued for 20-60 minutes to obtain the polyurethane coating; Applying polyurethane coating on one side of the polylactic acid film, drying and curing to form a polyurethane coating; The surface of the polyurethane coating is subjected to plasma treatment, and then aluminum is vacuum evaporated on the surface of the polyurethane coating to form an aluminum-plated layer, which is then dried and solidified to obtain a polylactic acid aluminum-plated film.

[0026] By adopting the above technical solution, before vacuum evaporation of aluminum on the surface of the polyurethane coating, it is first subjected to plasma treatment, thereby increasing the surface activity of the polyurethane coating to be compatible with the interface of aluminum, thereby improving the adhesion between the aluminum layer and the polyurethane coating.

[0027] Optionally, the method for preparing the isocyanate-modified cellulose comprises the following steps: The cellulose is dispersed in an organic solvent, and isocyanate is added after heating. The reaction is stirred until the -NCO content in the reaction system is less than 0.1%, and then the reaction is stopped, filtered, washed, and dried to obtain isocyanate-modified cellulose.

[0028] By adopting the above technical solution, the hydroxyl group of cellulose reacts and combines with isocyanate to modify the surface structure of cellulose.

[0029] Optionally, the preparation method of the hydroxyacrylate emulsion comprises the following steps: Disperse part of the emulsifier evenly in water, then add hydroxy acrylate monomer, short-chain aliphatic acrylate monomer, and long-chain aliphatic acrylate monomer to mix, increase the temperature, gradually add initiator to react, add the remaining emulsifier, and obtain hydroxy acrylate emulsion after the reaction is completed.

[0030] Optionally, the working gas in the plasma treatment method is air, the working gas flow rate is 2000-2500 sccm, and the plasma treatment power is 3-5 kW.

[0031] By adopting the above technical solution and adjusting the parameters of the plasma treatment, the surface activity of the polyurethane coating can be fully improved and the influence on the stability of the polyurethane coating can be reduced.

[0032] In summary, this application has the following beneficial effects: 1. The present application sets a polyurethane coating as a bonding layer between the polylactic acid film and the aluminum-plated layer, which can effectively improve the bonding force between the polylactic acid film and the aluminum-plated layer. The isocyanate-modified cellulose is added to the polyurethane coating. The interface compatibility of the cellulose with the polyurethane structure is improved after the isocyanate modification, thereby improving the dispersibility of the cellulose in the polyurethane coating. The cellulose not only improves the cross-linking density inside the polyurethane coating, but also enhances the interface interaction of the polyurethane coating, which can effectively improve the bonding force between the polyurethane coating and the aluminum-plated layer and between the polyurethane coating and the polylactic acid film, thereby enhancing the adhesion of the aluminum-plated layer on the surface of the polylactic acid film.

[0033] 2. After the isocyanate-modified cellulose is treated with plasma, the active groups on the surface increase, which effectively improves the surface activity of the polyurethane coating. In addition, the aromatic monoisocyanate has the characteristics of benzene ring rigidity, which can improve the adhesion between the polyurethane system and the cellulose interface. The aliphatic diisocyanate can achieve cross-linking between cellulose and form a network fiber structure at the interface of the polyurethane coating, improve the adhesion of the aluminum-plated film on the surface of the polyurethane coating, enhance the fixation of aluminum during aluminum plating, further enhance the bonding between the polyurethane coating and the polylactic acid film, and improve the adhesion and durability of the aluminum-plated layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a layer structure diagram of the polylactic acid aluminum-coated film of Examples 1-2 of the present application.

[0035] Description of reference numerals: 1. Polylactic acid film; 2. Polyurethane coating; 3. Aluminum coating. DETAILED DESCRIPTION

[0036] The following is combined with Figure 1 This application is described in further detail.

[0037] Preparation Example 1 The preparation method of isocyanate-modified cellulose comprises the following steps: Weigh 1 kg of cellulose, 0.48 kg of isocyanate, and 5 L of an organic solvent.

[0038] The cellulose is specifically microcrystalline cellulose with a polymerization degree of 200 and a particle size of 20 to 30 nm; the isocyanate is specifically composed of 0.4 kg of 4-n-butylphenol isocyanate and 0.08 kg of hexamethylene diisocyanate; and the organic solvent is specifically toluene.

[0039] The cellulose is dispersed in an organic solvent, heated to 55°C, and isocyanate is added thereto. The reaction is stirred until the -NCO content in the reaction system is less than 0.1%, and then the reaction is stopped. The cellulose is filtered, washed, and dried to obtain isocyanate-modified cellulose.

[0040] Preparation Example 2 The preparation method of isocyanate-modified cellulose, the difference between this preparation example and preparation example 1 lies in the different ratios of raw materials.

[0041] 1 kg of cellulose, 0.65 kg of isocyanate, and 5 L of organic solvent.

[0042] The cellulose is specifically microcrystalline cellulose with a degree of polymerization of 200 and a particle size of 20 to 30 nm; the isocyanate is specifically composed of 0.5 kg of 4-n-butylphenol isocyanate and 0.15 kg of hexamethylene diisocyanate; and the organic solvent is specifically toluene.

[0043] Preparation Example 3 The preparation method of isocyanate-modified cellulose, the difference between this preparation example and preparation example 1 is that the specific selection of isocyanate is different.

[0044] The isocyanate specifically consisted of 0.27 kg of phenyl isocyanate and 0.08 kg of hexamethylene diisocyanate.

[0045] Preparation Example 4 The preparation method of isocyanate-modified cellulose, the difference between this preparation example and preparation example 1 is that the specific selection of isocyanate is different.

[0046] Specifically, the isocyanate was 0.48 kg of 4-n-butylphenol isocyanate.

[0047] Preparation Example 5 The preparation method of isocyanate-modified cellulose, the difference between this preparation example and preparation example 1 is that the specific selection of isocyanate is different.

[0048] The isocyanate specifically consists of 0.4 kg of 4-n-butylphenol isocyanate and 0.12 kg of 4'4-diphenylmethane diisocyanate.

[0049] Preparatory Example 1 The preparation method of hydroxy acrylate emulsion comprises the following steps: Weigh 4.5 kg of hydroxy acrylate monomer, 0.2 kg of short-chain aliphatic acrylate monomer, 0.2 kg of long-chain aliphatic acrylate monomer, 0.2 kg of emulsifier, 0.02 kg of initiator, and 6 L of water.

[0050] The hydroxy acrylate monomer is specifically hydroxyethyl methacrylate; the short-chain aliphatic acrylate monomer is specifically methyl acrylate; the long-chain aliphatic acrylate monomer is specifically dodecyl methacrylate; the emulsifier is specifically sodium dodecyl sulfate; the initiator is specifically ammonium persulfate, and the initiator is pre-dissolved in 0.5L water to obtain an initiator solution for use.

[0051] The emulsifier accounting for 50wt% of the total mass of the emulsifier is evenly dispersed in 5.5L of water, and then the hydroxy acrylate monomer, the short-chain aliphatic acrylate monomer and the long-chain aliphatic acrylate monomer are added and mixed, the temperature is raised to 80°C, and the initiator solution is gradually added dropwise to react. The initiator is added dropwise within 1.5h, and the remaining emulsifier is added after 1h of the initiator addition. After the initiator is added dropwise, the reaction is continued for 3.5h. After the reaction is completed, the temperature is cooled to obtain a hydroxy acrylate emulsion.

[0052] Preparatory Example 2 The preparation method of hydroxy acrylate emulsion, the difference between this preparation example and preparation example 1 is that the proportion of raw materials is different.

[0053] 5.5 kg of hydroxy acrylate monomer, 0.5 kg of short-chain aliphatic acrylate monomer, 0.5 kg of long-chain aliphatic acrylate monomer, 0.3 kg of emulsifier, 0.06 kg of initiator, and 7 L of water.

[0054] The hydroxy acrylate monomer is specifically hydroxyethyl methacrylate; the short-chain aliphatic acrylate monomer is specifically methyl acrylate; the long-chain aliphatic acrylate monomer is specifically dodecyl methacrylate; the emulsifier is specifically sodium dodecyl sulfate; and the initiator is specifically ammonium persulfate.

[0055] Preparatory Example 3 The preparation method of hydroxy acrylate emulsion, the difference between this preparation example and preparation example 1 is that the proportion of raw materials is different.

[0056] 4.5 kg of hydroxy acrylate monomer, 0.4 kg of short-chain aliphatic acrylate monomer, 0.2 kg of emulsifier, 0.02 kg of initiator, and 6 L of water.

[0057] The hydroxy acrylate monomer is specifically hydroxyethyl methacrylate; the short-chain aliphatic acrylate monomer is specifically methyl acrylate; the emulsifier is specifically sodium dodecyl sulfate; and the initiator is specifically ammonium persulfate.

[0058] Example 1 A polylactic acid aluminum-plated film, such as Figure 1 As shown, it includes a polylactic acid film material 1, a polyurethane coating 2 and an aluminum plating layer 3 which are arranged in sequence.

[0059] A method for preparing a polylactic acid aluminum-plated film comprises the following steps: Weigh 7 kg of hydroxy acrylate emulsion, 0.1 kg of isocyanate-modified cellulose, 0.7 kg of isocyanate curing agent, 0.2 kg of auxiliary agent, and 2 L of water.

[0060] Among them, the hydroxy acrylate emulsion comes from Preparatory Example 1; the isocyanate-modified cellulose comes from Preparation Example 1; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the auxiliary agent consists of 0.1 kg of leveling agent and 0.1 kg of thickener, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0061] The hydroxy acrylate emulsion and the isocyanate modified cellulose are stirred and mixed, heated to 40°C, and then the isocyanate curing agent, the auxiliary agent and water are added and mixed, and the heating is stopped after stirring evenly, and the stirring is continued for 60 minutes to obtain the polyurethane coating.

[0062] Take a polylactic acid film with a thickness of 20 μm and apply a polyurethane coating on one side of the polylactic acid film with a coating amount of 1 g / m 2 The substrate is then passed into a drying tunnel for drying and curing. The drying tunnel is divided into seven sections, and the temperatures of each section are 60°C, 80°C, 110°C, 120°C, 110°C, 105°C, and 100°C, forming a polyurethane coating with a thickness of 0.1μm.

[0063] The surface of the polyurethane coating is subjected to glow discharge plasma treatment, the working gas in the plasma treatment method is air, the working gas flow rate is 2000 sccm, and the plasma treatment power is 5 kW.

[0064] Finally, it was sent to the vacuum evaporation equipment to vacuum evaporate aluminum oxide on the surface of the polyurethane coating. During the vacuum evaporation process, the aluminum plating speed was 490m / s, the temperature of the heated aluminum wire was 1400℃, and the wire feeding speed of the aluminum wire was 700mm / min, forming an aluminum plating layer with a thickness of 400 angstroms. It was then dried and cured in an oven at 60℃ for 72 hours to obtain the polylactic acid aluminum-plated film.

[0065] Example 2 A polylactic acid aluminum-plated film, such as Figure 1 As shown, it includes a polylactic acid film material 1, a polyurethane coating 2 and an aluminum plating layer 3 which are arranged in sequence.

[0066] A method for preparing a polylactic acid aluminum-plated film comprises the following steps: Weigh 8 kg of hydroxy acrylate emulsion, 0.15 kg of isocyanate-modified cellulose, 0.9 kg of isocyanate curing agent, 0.4 kg of auxiliary agent, and 3 L of water.

[0067] Among them, the hydroxy acrylate emulsion comes from Preparatory Example 2; the isocyanate-modified cellulose comes from Preparation Example 2; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the auxiliary agent consists of 0.2 kg of leveling agent and 0.2 kg of thickener, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0068] The hydroxy acrylate emulsion and the isocyanate modified cellulose are stirred and mixed, heated to 45°C, and then the isocyanate curing agent, the auxiliary agent and water are added and mixed, and the heating is stopped after stirring evenly, and the stirring is continued for 20 minutes to obtain the polyurethane coating.

[0069] Take a polylactic acid film with a thickness of 20 μm and apply a polyurethane coating on one side of the polylactic acid film with a coating amount of 1 g / m 2 The substrate is then passed into a drying tunnel for drying and curing. The drying tunnel is divided into seven sections, and the temperatures of each section are 60°C, 80°C, 110°C, 120°C, 110°C, 105°C, and 100°C, forming a polyurethane coating with a thickness of 0.1μm.

[0070] The surface of the polyurethane coating was subjected to a plasma treatment in a glow discharge manner. The working gas in the plasma treatment method was air, the working gas flow rate was 2500 sccm, and the power of the plasma treatment was 3 kW.

[0071] Finally, it was sent to the vacuum evaporation equipment to vacuum evaporate aluminum oxide on the surface of the polyurethane coating. During the vacuum evaporation process, the aluminum plating speed was 490m / s, the temperature of the heated aluminum wire was 1400℃, and the wire feeding speed of the aluminum wire was 700mm / min, forming an aluminum plating layer with a thickness of 400 angstroms. It was then dried and cured in an oven at 60℃ for 72 hours to obtain the polylactic acid aluminum-plated film.

[0072] Example 3 A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 1 is that the raw material ratio of the polyurethane coating is different.

[0073] 0.75 kg of hydroxy acrylate emulsion, 0.12 kg of isocyanate-modified cellulose, 0.82 kg of isocyanate curing agent, 0.3 kg of auxiliary agent, and 2.6 L of water.

[0074] Among them, the hydroxy acrylate emulsion is derived from Preparatory Example 1; the isocyanate-modified cellulose is derived from Preparation Example 1; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the auxiliary agent is composed of 0.15 kg of leveling agent and 0.15 kg of thickener, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0075] Example 4 A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 3 is that the sources of isocyanate-modified cellulose are different.

[0076] The isocyanate-modified cellulose was obtained from Preparation Example 3.

[0077] Example 5 A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 3 is that the sources of isocyanate-modified cellulose are different.

[0078] The isocyanate-modified cellulose was obtained from Preparation Example 4.

[0079] Example 6 A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 3 is that the sources of isocyanate-modified cellulose are different.

[0080] The isocyanate-modified cellulose was obtained from Preparation Example 5.

[0081] Example 7 A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 3 is that the sources of the hydroxyacrylate emulsion are different.

[0082] The hydroxyacrylate emulsion was derived from Preparatory Example 3.

[0083] Comparative Example 1 A method for preparing a polylactic acid aluminum-plated film. The difference between this comparative example and Example 3 is that the raw materials of the polyurethane coating are different.

[0084] Weigh 0.75 kg of hydroxy acrylate emulsion, 0.82 kg of isocyanate curing agent, 0.3 kg of auxiliary agent, and 2.6 L of water.

[0085] Among them, the hydroxy acrylate emulsion comes from Preparatory Example 1; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the auxiliary agent is composed of a leveling agent kg and a thickener kg, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0086] Comparative Example 2 A method for preparing a polylactic acid aluminum-plated film. The difference between this comparative example and Example 3 is that the raw materials of the polyurethane coating are different.

[0087] Weigh 0.75 kg of hydroxy acrylate emulsion, 0.12 kg of cellulose, 0.82 kg of isocyanate curing agent, 0.3 kg of auxiliary agent, and 2.6 L of water.

[0088] Among them, the hydroxy acrylate emulsion comes from Preparatory Example 1; the cellulose is specifically microcrystalline cellulose with a polymerization degree of 200; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the auxiliary agent is composed of a leveling agent kg and a thickener kg, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0089] Comparative Example 3 A method for preparing a polylactic acid aluminum-coated film. The difference between this comparative example and Example 3 is that before the polylactic acid film is coated with polyurethane coating, the polylactic acid film is first subjected to plasma treatment in a glow discharge manner. The working gas in the plasma treatment method is air, the working gas flow rate is 2000sccm, and the plasma treatment power is 5kW.

[0090] In addition, no plasma treatment was performed before the aluminum layer was evaporated on the surface of the polyurethane coating.

[0091] Performance Testing Adhesion of aluminized layer: refer to QB / T 2358-1998 “Test method for heat sealing strength of plastic film packaging bags”, heat seal layer of EAA film and aluminized layer of polylactic acid aluminized film, heat sealing temperature is 115℃, pressure is 0.4MPa, heat sealing time is 2s, and then use tensile testing machine to peel off aluminized layer from polylactic acid film to obtain adhesion data. The results are shown in Table 1.

[0092] Adhesion durability: The polylactic acid aluminum-plated film was placed in an oven at 120°C and 70% humidity for aging for 240 hours, and then the aluminum-plated layer adhesion test was performed. The results are shown in Table 1.

[0093] Barrier property: With reference to ASTM D-3985 and ASTM F-1249, the oxygen transmission rate and water vapor transmission rate of the polylactic acid aluminum-coated film were tested. The results are shown in Table 2.

[0094] Table 1 Adhesion(N / 15mm) Adhesion after aging (N / 15mm) Example 1 3.2 2.7 Example 2 3.0 2.5 Example 3 3.2 2.9 Example 4 3.0 2.3 Example 5 2.9 2.2 Example 6 2.9 2.3 Example 7 3.0 2.4 Comparative Example 1 2.4 1.4 Comparative Example 2 2.5 1.5 Comparative Example 3 2.7 1.9 Table 2 From Table 1 and Table 2, it can be seen that the polylactic acid aluminum-plated films prepared in Examples 1-3 perform well in terms of aluminum layer adhesion and aluminum layer adhesion durability, while ensuring good oxygen barrier properties and water vapor barrier properties. Compared with Comparative Examples 1-3, it can be seen that after adding isocyanate-modified cellulose to the polyurethane coating, the adhesion between the polyurethane coating and the aluminum-plated layer and between the polyurethane coating and the polylactic acid film material is enhanced, so the aluminum layer adhesion of the polylactic acid aluminum-plated film is improved. In addition, the polyurethane coating is plasma treated to further improve the bonding strength between the polyurethane coating and the aluminum-plated layer, thereby improving the adhesion durability of the aluminum layer.

[0095] Combining Example 3 with Examples 4-6 and Comparative Example 2, it can be seen that after cellulose is modified by isocyanate, the interfacial bonding ability of the polyurethane coating is significantly enhanced, and the appropriate selection of aromatic monoisocyanate and aliphatic diisocyanate can further improve the adhesion durability of the aluminum layer.

[0096] It can be seen from the combination of Example 3 and Example 7 that the polymerization of long-chain aliphatic acrylate monomers in the hydroxy acrylate emulsion can further improve the adhesion durability of the aluminum layer.

[0097] This specific implementation manner is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the specific implementation manner as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A polylactic acid aluminum-plated film, characterized in that: The invention comprises a polylactic acid film material, a polyurethane coating and an aluminum-plated layer arranged in sequence, wherein the polyurethane coating is formed by curing the polyurethane coating, the polyurethane coating is subjected to plasma surface treatment, and the polyurethane coating is prepared from raw materials containing the following parts by weight: 70-80 parts of hydroxy acrylate emulsion; 1-1.5 parts of isocyanate-modified cellulose; Isocyanate curing agent 7-9 parts; 2~4 parts of additives; 20~30 parts of water.

2. The polylactic acid aluminum-plated film according to claim 1, characterized in that: The isocyanate-modified cellulose is prepared by the reaction of isocyanate and cellulose, wherein the isocyanate includes aromatic monoisocyanate and aliphatic diisocyanate.

3. The polylactic acid aluminum-plated film according to claim 1, characterized in that: The isocyanate-modified cellulose is prepared by reacting cellulose with isocyanate in a mass ratio of 1:(0.48-0.65), and the isocyanate comprises 4-n-butylphenol isocyanate and hexamethylene diisocyanate in a mass ratio of 1:(0.2-0.3).

4. The polylactic acid aluminum-plated film according to claim 1, characterized in that: The hydroxy acrylate emulsion is prepared from the following raw materials in parts by weight: 45-55 parts of hydroxy acrylate monomer; 2-5 parts of short-chain aliphatic acrylate monomer; 2-5 parts of long-chain aliphatic acrylate monomer; 2~3 parts of emulsifier; Initiator 0.2~0.6 parts; 60~70 parts of water.

5. The polylactic acid aluminum-plated film according to claim 4, characterized in that: The short-chain aliphatic acrylate monomer includes one or more of methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate and propyl methacrylate; the long-chain aliphatic acrylate monomer includes one or more of dodecyl methacrylate, tetradecyl methacrylate and hexadecyl methacrylate.

6. The polylactic acid aluminum-plated film according to claim 1, characterized in that: The isocyanate curing agent is a water-dispersible polyisocyanate based on hexamethylene diisocyanate.

7. A method for preparing a polylactic acid aluminum-plated film according to any one of claims 1 to 6, characterized in that: The following steps are involved: The hydroxy acrylate emulsion and the isocyanate modified cellulose are stirred and mixed, and heated to 40-45°C, and then the isocyanate curing agent, the auxiliary agent and water are added and mixed, and the heating is stopped after stirring evenly, and the stirring is continued for 20-60 minutes to obtain the polyurethane coating; Applying polyurethane coating on one side of the polylactic acid film, drying and curing to form a polyurethane coating; The surface of the polyurethane coating is subjected to plasma treatment, and then aluminum is vacuum evaporated on the surface of the polyurethane coating to form an aluminum-plated layer, which is then dried and solidified to obtain a polylactic acid aluminum-plated film.

8. The method for preparing a polylactic acid aluminum-plated film according to claim 7, characterized in that: The method for preparing the isocyanate-modified cellulose comprises the following steps: The cellulose is dispersed in an organic solvent, and isocyanate is added after heating. The reaction is stirred until the -NCO content in the reaction system is less than 0.1%, and then the reaction is stopped, filtered, washed, and dried to obtain isocyanate-modified cellulose.

9. The method for preparing a polylactic acid aluminum-plated film according to claim 7, characterized in that: The preparation method of the hydroxyacrylate emulsion comprises the following steps: Disperse part of the emulsifier evenly in water, then add hydroxy acrylate monomer, short-chain aliphatic acrylate monomer, and long-chain aliphatic acrylate monomer to mix, increase the temperature, gradually add initiator to react, add the remaining emulsifier, and obtain hydroxy acrylate emulsion after the reaction is completed.

10. The method for preparing a polylactic acid aluminum-plated film according to claim 7, characterized in that: The working gas in the plasma treatment method is air, the working gas flow rate is 2000~2500sccm, and the power of plasma treatment is 3~5kW.

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