Biaxially oriented polylactic acid film with good toughness

Abstract

The invention discloses a biaxially oriented polylactic acid film with good toughness, and relates to the field of films. Comprising a first surface layer and a second surface layer, and the first surface layer and the second surface layer are the same in composition and are both composed of a macromolecular modifier, polylactic resin, a slipping agent and an anti-blocking agent; the core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, a dextrorotatory polylactic acid caprolactone random copolymer, a polylactic acid polyethylene glycol copolymer and a polylactic acid blend, and the polymer modifier is any one of a polylactic acid stereocomplex or a copolymer. According to the biaxially oriented polylactic acid film with good toughness, through specific composition and proportion design and a biaxially oriented process, the film has excellent mechanical properties and good heat resistance and degradability.

Description

Technical Field

[0001] The invention relates to the field of films, and in particular to a biaxially stretched polylactic acid film with good toughness. Background Art

[0002] With the depletion of petrochemical resources and the generation of a large amount of plastic waste, environmental and resource problems are becoming increasingly serious. Aliphatic polyesters with biomass sources and easily decomposed by microorganisms or active enzymes, such as polylactic acid and other degradable polymers, have attracted wide attention from researchers. Polylactic acid is a polymer obtained by polymerization with lactic acid as the main raw material. The raw material source is sufficient and renewable. The production process of polylactic acid is pollution-free, and the product can be biodegraded and realized in the cycle of nature. Therefore, it is an ideal green polymer material. Polylactic acid has good thermal stability and good solvent resistance. It can be processed in a variety of ways, such as extrusion, spinning, biaxial stretching, injection blow molding. In addition to being biodegradable, products made of polylactic acid have good biocompatibility, gloss, transparency, feel and heat resistance, and have certain antibacterial, flame retardant and UV resistance. Therefore, it has a wide range of uses and can be used as packaging materials, fibers and non-woven fabrics, etc. It is mainly used in PE shrink film, cold stretch sleeve film, cold shrink film, PE film, PE bag and other fields.

[0003] Polylactic acid can be obtained by direct polycondensation of lactic acid or ring-opening polymerization of lactide. The polylactic acid prepared by the condensation method has a relatively low molecular weight, while the ring-opening polymerization method can obtain polylactic acid with a high molecular weight and a narrow molecular weight distribution.

[0004] However, traditional polylactic acid films have problems such as insufficient toughness and easy breakage, which limits their application scope.

[0005] To this end, the present invention provides a biaxially stretched polylactic acid film with good toughness. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a biaxially stretched polylactic acid film with good toughness.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0008] Preferably, the mass ratio of the components of the first surface layer and the second surface layer is: 10-20 parts of polymer modifier, 75-85 parts of polylactic acid resin, 0.1-1 part of lubricant, and 0.5-1 part of anti-blocking agent.

[0009] Preferably: the mass ratio of the components of the core layer is: 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0010] Preferably, the polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

[0011] Preferably, the lubricant is any one of oleamide, erucamide, organosilicon compounds, polyesters of aliphatic polyacids and polyols, and saturated fatty alcohol polycarboxylic acid esters.

[0012] Preferably, the anti-adhesive agent is any one of silicon dioxide, wax, fatty acid metal salt, calcium carbonate, and silicone polymer.

[0013] Preferably: the method for preparing the biaxially oriented polylactic acid film comprises the following steps: S1: mixing materials, mixing the raw materials of the first surface layer and the second surface layer evenly according to the mass percentage, and then mixing the raw materials of the core layer evenly according to the mass percentage; S2: Melting, heating and melting the evenly mixed raw materials of the first surface layer and the second surface layer respectively, and extruding the molten raw materials into a film through a co-extruder; S3: Co-extrusion, heating and melting the raw material of the core layer, and extruding the molten raw material of the core layer between the first surface layer and the second surface layer through a co-extruder to form a three-layer film; S4: stretching, biaxially stretching the three-layer film; S5: Cooling and post-processing, cooling and cutting the stretched film and then processing it to make a finished film.

[0014] Preferably: in the step S2, the heating and melting temperature is 180-240 degrees Celsius.

[0015] Preferably: the step S4 comprises the following steps: S41: Preheating: preheating the casting before stretching, the preheating temperature is 40-80 degrees Celsius; S42: longitudinal stretching, the film is longitudinally stretched at a temperature of 60-80 degrees Celsius and a stretching ratio of 2.5-3.5 times; S43: Transverse stretching: after longitudinal stretching, the film is stretched transversely, the stretching temperature is 60-130 degrees Celsius, and the stretching ratio is 2-4 times.

[0016] Preferably: it is used in the fields of PE shrink film, cold stretch sleeve film, cold shrink film, PE film and PE bag.

[0017] The beneficial effects of the present invention are: The biaxially stretched polylactic acid film with good toughness of the present invention has excellent mechanical properties, good heat resistance and degradability through specific composition and proportion design and biaxial stretching process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention provides a flow chart for preparing a biaxially stretched polylactic acid film with good toughness. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described in detail below in conjunction with specific implementation methods.

[0020] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "set" should be understood in a broad sense, for example, they can be fixedly connected or set, or detachably connected or set, or integrally connected or set. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] Embodiment 1: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0022] Embodiment 2: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0023] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts of polymer modifier, 75 parts of polylactic acid resin, 0.1 parts of lubricant, and 0.5 parts of anti-blocking agent.

[0024] The components of the core layer are composed of 15 parts of racemic polylactic acid, 10 parts of acrylic acid grafted polylactic acid, 5 parts of lignin grafted polylactic acid, 5 parts of carboxylated nanocellulose grafted polylactic acid, 10 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10 parts of polylactic acid polyethylene glycol copolymer, and 10 parts of polylactic acid blend.

[0025] Embodiment 3: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0026] The mass ratio of the components of the first surface layer and the second surface layer is: 20 parts of polymer modifier, 85 parts of polylactic acid resin, 1 part of lubricant, and 1 part of anti-blocking agent.

[0027] The components of the core layer are composed of 25 parts by weight of racemic polylactic acid, 20 parts by weight of acrylic acid grafted polylactic acid, 15 parts by weight of lignin grafted polylactic acid, 15 parts by weight of carboxylated nanocellulose grafted polylactic acid, 20 parts by weight of dextrorotatory polylactic acid caprolactone random copolymer, 20 parts by weight of polylactic acid polyethylene glycol copolymer, and 20 parts by weight of polylactic acid blend.

[0028] Embodiment 4: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0029] The mass ratio of the components of the first surface layer and the second surface layer is: 15 parts of polymer modifier, 80 parts of polylactic acid resin, 0.5 parts of lubricant, and 0.75 parts of anti-blocking agent.

[0030] The components of the core layer are composed of 20 parts by weight of racemic polylactic acid, 15 parts of acrylic acid grafted polylactic acid, 10 parts of lignin grafted polylactic acid, 10 parts of carboxylated nanocellulose grafted polylactic acid, 15 parts of dextrorotatory polylactic acid caprolactone random copolymer, 15 parts of polylactic acid polyethylene glycol copolymer, and 15 parts of polylactic acid blend.

[0031] Embodiment 5: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0032] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0033] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0034] The polymer modifier is a polylactic acid stereocomplex.

[0035] The lubricant is oleamide.

[0036] The anti-adhesive agent is silicon dioxide.

[0037] Embodiment 6: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0038] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0039] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0040] The polymer modifier is any one of the copolymers.

[0041] The lubricant is erucamide.

[0042] The anti-blocking agent is wax.

[0043] Embodiment 7: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0044] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0045] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0046] The polymer modifier is a polylactic acid stereocomplex.

[0047] The lubricant is an organic silicon compound.

[0048] The anti-blocking agent is a fatty acid metal salt.

[0049] Embodiment 8: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0050] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0051] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0052] The polymer modifier is any one of the copolymers.

[0053] The lubricant is a polyester of aliphatic polybasic acid and polyol.

[0054] The anti-adhesion agent is calcium carbonate.

[0055] Embodiment 9: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0056] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0057] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0058] The polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

[0059] The lubricant is a saturated fatty alcohol polycarboxylic acid ester.

[0060] The anti-adhesive agent is an organic silicon polymer.

[0061] Example 10 A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0062] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0063] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0064] The polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

[0065] The lubricant is any one of oleic acid amide, erucic acid amide, organic silicon compound, polyester of aliphatic polybasic acid and polyol, and saturated fatty alcohol polycarboxylic acid ester.

[0066] The anti-adhesive agent is any one of silicon dioxide, wax, fatty acid metal salt, calcium carbonate and organic silicon polymer.

[0067] The method for preparing the biaxially oriented polylactic acid film comprises the following steps: S1: mixing materials, mixing the raw materials of the first surface layer and the second surface layer evenly according to the mass percentage, and then mixing the raw materials of the core layer evenly according to the mass percentage; S2: Melting, heating and melting the evenly mixed raw materials of the first surface layer and the second surface layer respectively, and extruding the molten raw materials into a film through a co-extruder; S3: Co-extrusion, heating and melting the raw material of the core layer, and extruding the molten raw material of the core layer between the first surface layer and the second surface layer through a co-extruder to form a three-layer film; S4: stretching, biaxially stretching the three-layer film; S5: Cooling and post-processing, cooling and cutting the stretched film and then processing it to make a finished film.

[0068] Embodiment 11: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0069] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0070] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0071] The polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

[0072] The lubricant is any one of oleic acid amide, erucic acid amide, organic silicon compound, polyester of aliphatic polybasic acid and polyol, and saturated fatty alcohol polycarboxylic acid ester.

[0073] The anti-adhesive agent is any one of silicon dioxide, wax, fatty acid metal salt, calcium carbonate and organic silicon polymer.

[0074] The method for preparing the biaxially oriented polylactic acid film comprises the following steps: S1: mixing materials, mixing the raw materials of the first surface layer and the second surface layer evenly according to the mass percentage, and then mixing the raw materials of the core layer evenly according to the mass percentage; S2: Melting, heating and melting the evenly mixed raw materials of the first surface layer and the second surface layer respectively, and extruding the molten raw materials into a film through a co-extruder; S3: Co-extrusion, heating and melting the raw material of the core layer, and extruding the molten raw material of the core layer between the first surface layer and the second surface layer through a co-extruder to form a three-layer film; S4: stretching, biaxially stretching the three-layer film; S5: Cooling and post-processing, cooling and cutting the stretched film and then processing it to make a finished film.

[0075] In the step S2, the heating and melting temperature is 180 degrees Celsius.

[0076] The step S4 comprises the following steps: S41: Preheating: preheating the casting before stretching, the preheating temperature is 40 degrees Celsius; S42: longitudinal stretching, the film is longitudinally stretched at a temperature of 60 degrees Celsius and a stretching ratio of 2.5 times; S43: Transverse stretching: after longitudinal stretching, the film is stretched transversely, the stretching temperature is 60 degrees Celsius, and the stretching ratio is 2 times.

[0077] Embodiment 12: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0078] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0079] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0080] The polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

[0081] The lubricant is any one of oleic acid amide, erucic acid amide, organic silicon compound, polyester of aliphatic polybasic acid and polyol, and saturated fatty alcohol polycarboxylic acid ester.

[0082] The anti-adhesive agent is any one of silicon dioxide, wax, fatty acid metal salt, calcium carbonate and organic silicon polymer.

[0083] The method for preparing the biaxially oriented polylactic acid film comprises the following steps: S1: mixing materials, mixing the raw materials of the first surface layer and the second surface layer evenly according to the mass percentage, and then mixing the raw materials of the core layer evenly according to the mass percentage; S2: Melting, heating and melting the evenly mixed raw materials of the first surface layer and the second surface layer respectively, and extruding the molten raw materials into a film through a co-extruder; S3: Co-extrusion, heating and melting the raw material of the core layer, and extruding the molten raw material of the core layer between the first surface layer and the second surface layer through a co-extruder to form a three-layer film; S4: stretching, biaxially stretching the three-layer film; S5: Cooling and post-processing, cooling and cutting the stretched film and then processing it to make a finished film.

[0084] In the step S2, the heating and melting temperature is 240 degrees Celsius.

[0085] The step S4 comprises the following steps: S41: Preheating: preheating the casting before stretching, the preheating temperature is 80 degrees Celsius; S42: longitudinal stretching, the film is longitudinally stretched at a temperature of 80 degrees Celsius and a stretching ratio of 3.5 times; S43: Transverse stretching: after longitudinal stretching, the film is stretched transversely, the stretching temperature is 130 degrees Celsius, and the stretching ratio is 4 times.

[0086] Embodiment 13: A biaxially stretched polylactic acid film with good toughness, comprising: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

[0087] The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

[0088] The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

[0089] The polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

[0090] The lubricant is any one of oleic acid amide, erucic acid amide, organic silicon compound, polyester of aliphatic polybasic acid and polyol, and saturated fatty alcohol polycarboxylic acid ester.

[0091] The anti-adhesive agent is any one of silicon dioxide, wax, fatty acid metal salt, calcium carbonate and organic silicon polymer.

[0092] The method for preparing the biaxially oriented polylactic acid film comprises the following steps: S1: mixing materials, mixing the raw materials of the first surface layer and the second surface layer evenly according to the mass percentage, and then mixing the raw materials of the core layer evenly according to the mass percentage; S2: Melting, heating and melting the evenly mixed raw materials of the first surface layer and the second surface layer respectively, and extruding the molten raw materials into a film through a co-extruder; S3: Co-extrusion, heating and melting the raw material of the core layer, and extruding the molten raw material of the core layer between the first surface layer and the second surface layer through a co-extruder to form a three-layer film; S4: stretching, biaxially stretching the three-layer film; S5: Cooling and post-processing, cooling and cutting the stretched film and then processing it to make a finished film.

[0093] In the step S2, the heating and melting temperature is 210 degrees Celsius.

[0094] The step S4 comprises the following steps: S41: Preheating: preheating the casting before stretching, the preheating temperature is 60 degrees Celsius; S42: longitudinal stretching, the film is longitudinally stretched at a temperature of 70 degrees Celsius and a stretching ratio of 3 times; S43: Transverse stretching: after longitudinal stretching, the film is stretched transversely, the stretching temperature is 145 degrees Celsius, and the stretching ratio is 3 times.

[0095] Embodiment 13: A biaxially oriented polylactic acid film with good toughness is applied to the fields of PE shrink film, cold stretch sleeve film, cold shrink film, PE film and PE bag.

[0096] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A biaxially oriented polylactic acid film with good toughness, characterized in that: include: The first surface layer and the second surface layer have the same composition, which is composed of a polymer modifier, a polylactic acid resin, a lubricant, and an anti-blocking agent; The core layer is composed of racemic polylactic acid, acrylic acid grafted polylactic acid, lignin grafted polylactic acid, carboxylated nanocellulose grafted polylactic acid, dextrorotatory polylactic acid caprolactone random copolymer, polylactic acid polyethylene glycol copolymer, and polylactic acid blend.

2. The biaxially oriented polylactic acid film with good toughness according to claim 1, characterized in that: The mass ratio of the components of the first surface layer and the second surface layer is: 10 parts to 20 parts of polymer modifier, 75 parts to 85 parts of polylactic acid resin, 0.1 parts to 1 parts of lubricant, and 0.5 parts to 1 parts of anti-blocking agent.

3. The biaxially oriented polylactic acid film with good toughness according to claim 1, characterized in that: The components of the core layer are composed of 15-25 parts of racemic polylactic acid, 10-20 parts of acrylic acid grafted polylactic acid, 5-15 parts of lignin grafted polylactic acid, 5-15 parts of carboxylated nanocellulose grafted polylactic acid, 10-20 parts of dextrorotatory polylactic acid caprolactone random copolymer, 10-20 parts of polylactic acid polyethylene glycol copolymer, and 10-20 parts of polylactic acid blend.

4. The biaxially oriented polylactic acid film with good toughness according to claim 1, characterized in that: The polymer modifier is any one of a polylactic acid stereocomplex or a copolymer.

5. The biaxially oriented polylactic acid film with good toughness according to claim 1, characterized in that: The lubricant is any one of oleic acid amide, erucic acid amide, organic silicon compound, polyester of aliphatic polybasic acid and polyol, and saturated fatty alcohol polycarboxylic acid ester.

6. A biaxially oriented polylactic acid film with good toughness according to any one of claim 1, characterized in that: The anti-adhesive agent is any one of silicon dioxide, wax, fatty acid metal salt, calcium carbonate and organic silicon polymer.

7. A biaxially oriented polylactic acid film with good toughness according to any one of claims 1 to 6, characterized in that: The method for preparing the biaxially oriented polylactic acid film comprises the following steps: S1: mixing materials, mixing the raw materials of the first surface layer and the second surface layer evenly according to the mass percentage, and then mixing the raw materials of the core layer evenly according to the mass percentage; S2: Melting, heating and melting the evenly mixed raw materials of the first surface layer and the second surface layer respectively, and extruding the molten raw materials into a film through a co-extruder; S3: Co-extrusion, heating and melting the raw material of the core layer, and extruding the molten raw material of the core layer between the first surface layer and the second surface layer through a co-extruder to form a three-layer film; S4: stretching, biaxially stretching the three-layer film; S5: Cooling and post-processing, cooling and cutting the stretched film and then processing it to make a finished film.

8. The biaxially oriented polylactic acid film with good toughness according to claim 6, characterized in that: In the step S2, the heating and melting temperature is 180-240 degrees Celsius.

9. The biaxially oriented polylactic acid film with good toughness according to claim 6, characterized in that: The step S4 comprises the following steps: S41: Preheating: preheating the casting before stretching, the preheating temperature is 40-80 degrees Celsius; S42: longitudinal stretching, the film is longitudinally stretched at a temperature of 60-80 degrees Celsius and a stretching ratio of 2.5-3.5 times; S43: Transverse stretching: after longitudinal stretching, the film is stretched transversely, the stretching temperature is 60-130 degrees Celsius, and the stretching ratio is 2-4 times.

10. The biaxially oriented polylactic acid film with good toughness according to claim 1, characterized in that: It is used in the fields of PE shrink film, cold stretch sleeve film, cold shrink film, PE film and PE bag.

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