A kind of polylactic acid aluminum-plated film and preparation method thereof

Abstract

This application discloses a polylactic acid aluminum-coated film and its preparation method, belonging to the field of thin films. The polylactic acid aluminum-coated film comprises a polylactic acid film material, a polyurethane coating, and an aluminum-coated layer arranged in sequence. The polyurethane coating is formed by curing a polyurethane coating, which has been subjected to plasma surface treatment. The polyurethane coating is prepared from the following raw materials in parts by weight: 70-80 parts hydroxyacrylate emulsion, 1-1.5 parts isocyanate-modified cellulose, 7-9 parts isocyanate curing agent, 2-4 parts auxiliary agent, and 20-30 parts water. This application improves the adhesion between the polylactic acid film and the aluminum layer, thereby increasing the durability of the polylactic acid aluminum-coated film.

Description

Technical Field

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

[0002] Polylactic acid (PLA), a new bio-based, renewable, biodegradable material, has shown great potential in the environmental protection field. Made from starch extracted from renewable plant resources such as corn and cassava, PLA is completely degraded under specific conditions by microorganisms in nature, ultimately converting into harmless carbon dioxide and water. It poses no environmental pollution and is recognized as an environmentally friendly material.

[0003] However, polylactic acid films have certain deficiencies in their oxygen and water vapor barrier properties, limiting their direct application in the packaging industry, which has stringent requirements for product barrier properties, especially for foods and pharmaceuticals that require long-term storage.

[0004] The current improvement method in the industry is to plate aluminum on the surface of 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 present application provides a polylactic acid aluminum-plated film adopting the following technical solution:

[0007] 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:

[0008] 70-80 parts of hydroxy acrylate emulsion;

[0009] 1-1.5 parts of isocyanate-modified cellulose;

[0010] 7-9 parts of isocyanate curing agent;

[0011] 2 to 4 parts of additives;

[0012] 20-30 parts of water.

[0013] 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, effectively improving the bonding strength between the polylactic acid film and the aluminum-plated layer. The isocyanate-modified cellulose is incorporated into the polyurethane coating. The isocyanate-modified cellulose improves the interfacial compatibility with the polyurethane structure, thereby improving the dispersibility of the cellulose in the polyurethane coating. The cellulose not only increases the crosslinking density within the polyurethane coating but also enhances the interfacial interaction of the polyurethane coating, effectively improving the bonding strength between the polyurethane coating and the aluminum-plated layer, as well as between the polyurethane coating and the polylactic acid film, thereby enhancing the adhesion of the aluminum-plated layer to the surface of the polylactic acid film.

[0014] Isocyanate-modified cellulose also increases the number of active sites on the polyurethane coating that can be treated with plasma. After the isocyanate-modified cellulose is treated with plasma, the number of active groups on the surface increases, effectively improving the surface activity of the polyurethane coating, enhancing the fixation of aluminum during aluminum plating, further enhancing the bonding force between the polyurethane coating and the polylactic acid film, and improving the adhesion and durability of the aluminum plating layer.

[0015] Optionally, the isocyanate-modified cellulose is prepared by reacting isocyanate with cellulose, and the isocyanate includes aromatic monoisocyanate and aliphatic diisocyanate.

[0016] By adopting the above technical solution, 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.

[0017] 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).

[0018] By adopting the above technical solution, the proportion of isocyanate access 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 ratio of 4-n-butylphenol isocyanate and hexamethylene diisocyanate is controlled to keep the cross-linking between the cellulose fibers 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-coated film.

[0019] Optionally, the auxiliary agent includes one or both of a leveling agent and a thickener.

[0020] Optionally, the hydroxyacrylate emulsion is prepared from the following raw materials in parts by weight:

[0021] 45-55 parts of hydroxy acrylate monomer;

[0022] 2-5 parts of short-chain aliphatic acrylate monomer;

[0023] 2-5 parts of long-chain aliphatic acrylate monomer;

[0024] 2-3 parts of emulsifier;

[0025] 0.2-0.6 parts of initiator;

[0026] 60-70 parts of water.

[0027] By adopting the above technical solution, in combination with 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.

[0028] 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.

[0029] Optionally, the hydroxyacrylate is selected from one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

[0030] Optionally, the emulsifier includes one or both of sodium lauryl sulfate and sodium stearate.

[0031] Optionally, the initiator includes one or both of potassium persulfate and ammonium persulfate.

[0032] Optionally, the isocyanate curing agent is a water-dispersible polyisocyanate based on hexamethylene diisocyanate.

[0033] By adopting the above technical solution, 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.

[0034] Optionally, the thickness of the polylactic acid film is 15 to 20 μm.

[0035] Optionally, the thickness of the aluminum plating layer is 400 to 450 angstroms.

[0036] Optionally, the polyurethane coating has a thickness of 0.1 to 0.3 μm.

[0037] In a second aspect, the present application provides a method for preparing a polylactic acid aluminum-plated film using the following technical solutions:

[0038] A method for preparing a polylactic acid aluminum-plated film comprises the following steps:

[0039] The hydroxy acrylate emulsion and the isocyanate modified cellulose are stirred and mixed, and the mixture is heated to 40-45° C., and then the isocyanate curing agent, the auxiliary agent and water are added and mixed. After stirring evenly, the heating is stopped and the stirring is continued for 20-60 minutes to obtain a polyurethane coating.

[0040] Applying polyurethane coating on one side of the polylactic acid film, drying and curing it to form a polyurethane coating;

[0041] 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.

[0042] 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.

[0043] Optionally, the method for preparing the isocyanate-modified cellulose comprises the following steps:

[0044] 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. The cellulose is filtered, washed, and dried to obtain isocyanate-modified cellulose.

[0045] By adopting the above technical solution, the hydroxyl groups of cellulose react and combine with isocyanate to modify the surface structure of cellulose.

[0046] Optionally, the preparation method of the hydroxyacrylate emulsion comprises the following steps:

[0047] Part of the emulsifier is evenly dispersed in water, and then hydroxy acrylate monomer, short-chain aliphatic acrylate monomer, and long-chain aliphatic acrylate monomer are added and mixed. The temperature is increased, and the initiator is gradually added to react. The remaining emulsifier is added, and after the reaction is completed, a hydroxy acrylate emulsion is obtained.

[0048] 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.

[0049] 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 impact on the stability of the polyurethane coating can be reduced.

[0050] In summary, this application has the following beneficial effects:

[0051] 1. This application provides a polyurethane coating as a bonding layer between the polylactic acid film and the aluminum coating, effectively improving the bonding between the polylactic acid film and the aluminum coating. The isocyanate-modified cellulose incorporated into the polyurethane coating improves the interfacial compatibility of the cellulose with the polyurethane structure after isocyanate modification, thereby improving the dispersibility of the cellulose in the polyurethane coating. The cellulose not only increases the crosslinking density within the polyurethane coating but also enhances the interfacial interactions of the polyurethane coating, effectively improving the bonding between the polyurethane coating and the aluminum coating, as well as between the polyurethane coating and the polylactic acid film, thereby enhancing the adhesion of the aluminum coating to the surface of the polylactic acid film.

[0052] 2. After the isocyanate-modified cellulose is treated with plasma, the surface active groups 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 celluloses, forming a network fiber structure at the interface of the polyurethane coating, improving the adhesion of the aluminum-plated film to the polyurethane coating surface, and enhancing the fixation of aluminum during aluminum plating, further enhancing the bonding between the polyurethane coating and the polylactic acid film, and improving the adhesion and durability of the aluminum-plated layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a layer structure diagram of the polylactic acid aluminum-coated film of Examples 1-2 of the present application.

[0054] Description of reference numerals:

[0055] 1. Polylactic acid film; 2. Polyurethane coating; 3. Aluminum coating. DETAILED DESCRIPTION

[0056] The following is combined with Figure 1 This application is described in further detail.

[0057] Preparation Example 1

[0058] The preparation method of isocyanate-modified cellulose comprises the following steps:

[0059] Weigh 1 kg of cellulose, 0.48 kg of isocyanate, and 5 L of organic solvent.

[0060] 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 0.4 kg of 4-n-butylphenol isocyanate and 0.08 kg of hexamethylene diisocyanate; and the organic solvent is specifically toluene.

[0061] The cellulose is dispersed in an organic solvent, heated to 55°C, and isocyanate is added. 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.

[0062] Preparation Example 2

[0063] Preparation method of isocyanate-modified cellulose. The difference between this preparation example and Preparation Example 1 lies in the different ratios of raw materials.

[0064] 1 kg of cellulose, 0.65 kg of isocyanate, and 5 L of organic solvent.

[0065] 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.

[0066] Preparation Example 3

[0067] The preparation method of isocyanate-modified cellulose, the difference between this preparation example and Preparation Example 1 lies in the specific selection of isocyanate.

[0068] Specifically, the isocyanate consists of 0.27 kg of phenyl isocyanate and 0.08 kg of hexamethylene diisocyanate.

[0069] Preparation Example 4

[0070] The preparation method of isocyanate-modified cellulose, the difference between this preparation example and Preparation Example 1 lies in the specific selection of isocyanate.

[0071] Specifically, the isocyanate was 0.48 kg of 4-n-butylphenol isocyanate.

[0072] Preparation Example 5

[0073] The preparation method of isocyanate-modified cellulose, the difference between this preparation example and Preparation Example 1 lies in the specific selection of isocyanate.

[0074] The isocyanate specifically consists of 0.4 kg of 4-n-butylphenol isocyanate and 0.12 kg of 4'4-diphenylmethane diisocyanate.

[0075] Preparatory Example 1

[0076] The preparation method of hydroxy acrylate emulsion comprises the following steps:

[0077] 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.

[0078] 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 lauryl sulfate; and the initiator is specifically ammonium persulfate. The initiator is pre-dissolved in 0.5 L of water to obtain an initiator solution for use.

[0079] An emulsifier accounting for 50 wt% of the total mass of the emulsifier is evenly dispersed in 5.5 L of water, and then a hydroxy acrylate monomer, a short-chain aliphatic acrylate monomer and a long-chain aliphatic acrylate monomer are added and mixed. The temperature is raised to 80° C., and an initiator solution is gradually added dropwise to react. The initiator is added dropwise within 1.5 hours. The remaining emulsifier is added 1 hour after the initiator is added dropwise. After the initiator is added dropwise, the reaction is continued for 3.5 hours. After the reaction is completed, the temperature is cooled to obtain a hydroxy acrylate emulsion.

[0080] Preparatory Example 2

[0081] The preparation method of the hydroxyacrylate emulsion is different from that of Preparative Example 1 in that the ratio of the raw materials is different.

[0082] 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.

[0083] 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 lauryl sulfate; and the initiator is specifically ammonium persulfate.

[0084] Preparatory Example 3

[0085] The preparation method of the hydroxyacrylate emulsion is different from that of Preparative Example 1 in that the ratio of the raw materials is different.

[0086] 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.

[0087] The hydroxy acrylate monomer is specifically hydroxyethyl methacrylate; the short-chain aliphatic acrylate monomer is specifically methyl acrylate; the emulsifier is specifically sodium lauryl sulfate; and the initiator is specifically ammonium persulfate.

[0088] Example 1

[0089] A polylactic acid aluminum-plated film, such as Figure 1 As shown, it includes a polylactic acid film 1, a polyurethane coating 2 and an aluminum plating layer 3 arranged in sequence.

[0090] A method for preparing a polylactic acid aluminum-plated film comprises the following steps:

[0091] 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.

[0092] Among them, the hydroxy acrylate emulsion is derived from Preparation 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 consists of 0.1 kg of a leveling agent and 0.1 kg of a thickener, specifically BYK-333, and the thickener is BYK-428.

[0093] The hydroxy acrylate emulsion and the isocyanate modified cellulose were stirred and mixed, heated to 40° C., and then the isocyanate curing agent, the auxiliary agent and the water were added and mixed. After stirring evenly, the heating was stopped and the stirring was continued for 60 minutes to obtain the polyurethane coating.

[0094] Take a polylactic acid film with a thickness of 20 μm and apply 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 in 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.

[0095] 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 2000 sccm, and the plasma treatment power was 5 kW.

[0096] 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 a 60℃ oven for 72 hours to obtain a polylactic acid aluminum-plated film.

[0097] Example 2

[0098] A polylactic acid aluminum-plated film, such as Figure 1As shown, it includes a polylactic acid film 1, a polyurethane coating 2 and an aluminum plating layer 3 arranged in sequence.

[0099] A method for preparing a polylactic acid aluminum-plated film comprises the following steps:

[0100] 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.

[0101] Among them, the hydroxyacrylate emulsion is derived from Preparation Example 2; the isocyanate-modified cellulose is derived 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 a leveling agent and 0.2 kg of a thickener, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0102] The hydroxy acrylate emulsion and the isocyanate modified cellulose were stirred and mixed, heated to 45° C., and then the isocyanate curing agent, the auxiliary agent and the water were added and mixed. After stirring evenly, the heating was stopped and the stirring was continued for 20 minutes to obtain the polyurethane coating.

[0103] Take a polylactic acid film with a thickness of 20 μm and apply 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 in 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.

[0104] 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 plasma treatment power was 3 kW.

[0105] 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 a 60℃ oven for 72 hours to obtain a polylactic acid aluminum-plated film.

[0106] Example 3

[0107] A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 1 lies in the different ratio of raw materials of the polyurethane coating.

[0108] 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.

[0109] Among them, the hydroxy acrylate emulsion is derived from Preparation 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 consists of 0.15 kg of a leveling agent and 0.15 kg of a thickener, specifically BYK-333, and the thickener is BYK-428.

[0110] Example 4

[0111] 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.

[0112] The isocyanate-modified cellulose was obtained from Preparation 3.

[0113] Example 5

[0114] 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.

[0115] The isocyanate-modified cellulose was obtained from Preparation Example 4.

[0116] Example 6

[0117] 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.

[0118] The isocyanate-modified cellulose was obtained from Preparation Example 5.

[0119] Example 7

[0120] A method for preparing a polylactic acid aluminum-plated film. The difference between this embodiment and embodiment 3 is that the source of the hydroxyacrylate emulsion is different.

[0121] The hydroxyacrylate emulsion was derived from Preparatory Example 3.

[0122] Comparative Example 1

[0123] A method for preparing a polylactic acid aluminum-plated film. The difference between this comparative example and Example 3 lies in the different raw materials of the polyurethane coating.

[0124] 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.

[0125] The hydroxy acrylate emulsion is derived from Preparatory Example 1; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the additives are composed of a leveling agent kg and a thickener kg, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0126] Comparative Example 2

[0127] A method for preparing a polylactic acid aluminum-plated film. The difference between this comparative example and Example 3 lies in the different raw materials of the polyurethane coating.

[0128] 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.

[0129] The hydroxyacrylate emulsion is derived from Preparatory Example 1; the cellulose is specifically microcrystalline cellulose with a degree of polymerization of 200; the isocyanate curing agent can be a water-dispersible polyisocyanate based on hexamethylene diisocyanate, specifically Desmodur DA; the additives are composed of a leveling agent kg and a thickener kg, the leveling agent is specifically BYK-333, and the thickener is BYK-428.

[0130] Comparative Example 3

[0131] 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.

[0132] In addition, no plasma treatment is performed before the aluminum layer is evaporated on the surface of the polyurethane coating.

[0133] Performance Testing

[0134] Adhesion of the aluminized layer: Referring to QB / T 2358-1998 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags", the heat-sealing layer of the EAA film was heat-sealed to the aluminized layer of the polylactic acid aluminized film at a heat-sealing temperature of 115°C, a pressure of 0.4 MPa, and a heat-sealing time of 2 seconds. The aluminized layer was then peeled off from the polylactic acid film using a tensile testing machine to obtain adhesion data. The results are shown in Table 1.

[0135] Adhesion durability: The polylactic acid aluminum-plated film was placed in an oven at 120°C and 70% humidity for 240 hours, and then the aluminum-plated layer adhesion test was performed. The results are shown in Table 1.

[0136] Barrier properties: The oxygen transmission rate and water vapor transmission rate of the polylactic acid aluminum-coated film were tested with reference to ASTM D-3985 and ASTM F-1249. The results are shown in Table 2.

[0137] Table 1

[0138] 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

[0139] Table 2

[0140]

[0141]

[0142] From Table 1 and Table 2, it can be seen that the polylactic acid aluminized films prepared in Examples 1-3 perform well in terms of adhesion to the aluminum layer and durability of the adhesion to the aluminum layer, while ensuring good oxygen barrier properties and water vapor barrier properties. Compared with Comparative Examples 1-3, it can be seen that after the isocyanate-modified cellulose is added to the polyurethane coating, the adhesion to the aluminum layer of the polylactic acid aluminized film is improved due to the enhanced bonding between the polyurethane coating and the aluminum layer and between the polyurethane coating and the polylactic acid film. In addition, the polyurethane coating is plasma treated to further improve the bonding between the polyurethane coating and the aluminum layer, thereby improving the adhesion durability of the aluminum layer.

[0143] Combining Example 3 with Examples 4-6 and Comparative Example 2, it can be seen that after cellulose is modified with 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.

[0144] It can be seen from 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.

[0145] 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 as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A polylactic acid aluminum-plated film, characterized in that: The invention comprises a polylactic acid film, a polyurethane coating and an aluminum plating 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; 7-9 parts of isocyanate curing agent; 2~4 parts of additives; 20~30 parts water.

2. The polylactic acid aluminum-plated film according to claim 1, characterized in that: The isocyanate-modified cellulose is formed 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; 0.2~0.6 parts of initiator; 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 the mixture is heated to 40-45°C. Then, the isocyanate curing agent, the additive and water are added and mixed. After stirring evenly, the heating is stopped and the stirring is continued for 20-60 minutes to obtain a polyurethane coating. Applying polyurethane coating on one side of the polylactic acid film, drying and curing it 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, wherein: The preparation method of 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. The cellulose is filtered, washed, and dried to obtain isocyanate-modified cellulose.

9. The method for preparing a polylactic acid aluminum-plated film according to claim 7, wherein: The preparation method of the hydroxyacrylate emulsion comprises the following steps: Part of the emulsifier is evenly dispersed in water, and then hydroxy acrylate monomer, short-chain aliphatic acrylate monomer, and long-chain aliphatic acrylate monomer are added and mixed. The temperature is increased, and the initiator is gradually added to react. The remaining emulsifier is added, and after the reaction is completed, a hydroxy acrylate emulsion is obtained.

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

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