A biaxially oriented polylactic acid film with good toughness and its preparation method

Abstract

The application discloses a kind of bi-directional stretch polylactic acid film with good toughness and preparation method thereof, the bi-directional stretch polylactic acid film with good toughness includes upper surface layer, middle layer and lower surface layer;25-89 parts of polylactic acid, 1-15 parts of silicon-containing epoxidized cardanol-methyl methacrylate glycidyl ester polymer and 10-60 parts of polylactic acid block copolymer are used to form the middle layer by mass fraction, the upper surface layer and the lower surface layer are all composed of 25-88 parts of polylactic acid, 1-15 parts of silicon-containing epoxidized cardanol-methyl methacrylate glycidyl ester polymer, 10-50 parts of polylactic acid block copolymer and 1-10 parts of functional master batch;The bi-directional stretch polylactic acid film with good toughness prepared by the method not only has excellent toughness, but also has good mechanical properties, is completely biodegradable, and is suitable for food, drug, daily chemical product, medical device and other packaging fields.

Description

Technical Field

[0001] This invention belongs to the field of flexible film packaging technology, specifically relating to a biaxially oriented polylactic acid film with good toughness and its preparation method. Background Technology

[0002] In the packaging industry, the application of plastic products has brought great convenience to people's lives. Plastic packaging has become an indispensable packaging material for human survival and social development. While providing great convenience, the recycling and disposal of waste packaging products is also a major headache. Due to the non-degradability of ordinary plastics, waste plastic products can generally only be disposed of through incineration or landfill. However, incineration produces a large amount of toxic and harmful gases, while landfilling occupies a large amount of land, affecting crop cultivation, and the occupied land cannot be restored for a long time, affecting the sustainable use of land. With the annual increase in the use of plastic packaging products, environmental pollution problems are becoming more prominent. Therefore, achieving the environmental friendliness and sustainable development of plastic packaging products has become an attractive yet challenging task.

[0003] Biodegradable packaging materials possess the functions and properties of traditional plastics, and under certain conditions (such as temperature and humidity), they can gradually degrade and be reduced to carbon dioxide and water by microorganisms in soil and water or by ultraviolet radiation from sunlight, and then reintroduce into the ecosystem in a non-toxic manner. Therefore, promoting and using biodegradable plastic products is particularly urgent and is currently an effective way to solve the problem of "white pollution".

[0004] Currently, there are various pathways to achieve biodegradability, including photodegradation, photobiodegradation, photooxidative biodegradation, high-starch-content biodegradation, and fully biodegradable materials, such as starch-based biomaterials, PBS, PBAT, and PLA. Among these material categories, polylactic acid (PLA) is a commercially mature product. It is a fully bio-based biodegradable material. PLA has high mechanical strength but poor toughness, which cannot meet practical packaging requirements.

[0005] Therefore, how to obtain a biaxially oriented polylactic acid film with good toughness has become an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a biaxially oriented polylactic acid (PLA) film with good toughness and its preparation method. This PLA film with good toughness not only possesses excellent toughness but also exhibits good mechanical properties and is completely biodegradable, making it suitable for packaging applications in food, pharmaceuticals, daily chemicals, and medical devices.

[0007] The present invention adopts the following technical solution:

[0008] A biaxially oriented polylactic acid (PLA) film with good toughness, comprising an upper layer, an intermediate layer, and a lower layer; by mass parts, the intermediate layer is composed of 25-89 parts of PLA, 1-15 parts of a silicon-containing epoxidized cashew nut shell polymer (CPMP-Glyceryl methacrylate), and 10-60 parts of PLA block copolymer; the upper and lower layers are each composed of 25-88 parts of PLA, 1-15 parts of a CPMP-Glyceryl methacrylate ...

[0009] Preferably, the specific preparation method of the silicon-containing epoxidized cashew nut shell powder-glycidyl methacrylate polymer is as follows:

[0010] S1A. Dissolve 100-200 parts by weight of cashew phenol in 100-600 parts by weight of chlorobenzene, then add 50-100 parts by weight of oxalic acid, followed by adding 20-120 parts by weight of 20%-40% aqueous hydrogen peroxide solution in multiple portions, raise the temperature to 40-80°C, and react for 2-12 hours under chlorobenzene reflux conditions.

[0011] S2A: Separate the organic matter, wash it 1-5 times with an alkaline saturated aqueous solution, then wash it 1-6 times with distilled water, remove the solvent by reduced pressure in a rotary evaporator, and dry the obtained product under vacuum at 50-80°C for 1-5 hours to obtain epoxidized cashew phenol.

[0012] S3A: 100-200 parts by mass of epoxidized cashew nut shell, 10-100 parts by mass of 2-bromo-1-butene, and 50-400 parts by mass of magnesium hydroxide are added to a reactor and reacted at a temperature of 20-80°C for 6-30 hours. Then, the alkylated epoxidized cashew nut shell is obtained by filtration, separation, purification, and drying.

[0013] S4A: 100-300 parts by weight of alkylated epoxy cashew phenol, 0.1-5 parts by weight of hexachloroplatinic acid, 10-80 parts by weight of phenyltriethoxysilane, and 1-10 parts by weight of glycidyl methacrylate are reacted at 50-80°C for 1-16 hours to obtain a silicon-containing epoxy cashew phenol-glycidyl methacrylate polymer.

[0014] Preferably, the specific preparation method of the polylactic acid block copolymer is as follows:

[0015] S1B. Add 100-200 parts by mass of lactic acid and 10-500 parts by mass of cyclohexane to a distillation flask, control the temperature at 100-150℃, and distill for 2-20 hours to obtain distillate A, and make its water content below 3wt%.

[0016] S2B: Add 96-99.98 parts by mass of distillate A, 0.01-1 parts by mass of catalyst, and 0.01-3 parts by mass of stabilizer to the reactor, introduce N2 or inert gas and circulate it 2-6 times, while simultaneously turning on the agitator and controlling the stirring speed at 50-250 r / min, raise the temperature to 150-210℃, and melt-condense under a pressure of 1-1500 Pa for 5-30 hours to obtain prepolymer B;

[0017] S3B: Add 30-79 parts by weight of prepolymer B, 20-50 parts by weight of 6-caprolactone and 1-20 parts by weight of hydroxyethyl methacrylate to a reactor, introduce N2 or inert gas and circulate it 2-6 times, while turning on the agitator and controlling the stirring speed at 50-350 r / min, raise the temperature to 130-185℃, and react for 10-60 hours under a pressure of 1-800 Pa to obtain block prepolymer C;

[0018] S4B. Block prepolymer C is dissolved in acetone, precipitated and washed with ethanol, and washed with distilled water in sequence. It is then vacuum dried at 30-60°C to obtain a white powdered polylactic acid block copolymer.

[0019] Preferably, the catalyst in step S2B is any one or a mixture of at least two of Zn(NO3)2, Zn(ClO4)2, Zn(BF4)2, malonic acid, azelaic acid, nonadecanedioic acid, phthalic acid, isophthalic acid, and glutaric anhydride in any proportion.

[0020] Preferably, the stabilizer in step S2B is phosphorous acid.

[0021] Preferably, by weight, the functional masterbatch comprises 0.5-8 parts of lubricant, 3-10 parts of opening agent, 0.5-5 parts of antioxidant, and 77-96 parts of polylactic acid; the lubricant is one or both of erucamide and oleamide; the opening agent is one or more of silica, calcium carbonate, diatomaceous earth, and talc; the antioxidant is a mixture of one or more of phosphites and phenols; the functional masterbatch is obtained by melt extrusion, stranding, cooling, pelletizing, and drying using a twin-screw extruder at a temperature of 145-200°C.

[0022] Preferably, the thickness of the biaxially oriented polylactic acid film with good toughness is 15–60 μm; wherein the thickness of the upper and lower surface layers is 1–3 μm, and the thickness of the intermediate layer is 9–58 μm.

[0023] A method for preparing a biaxially oriented polylactic acid film with good toughness specifically includes the following steps:

[0024] S1C. Dry the raw materials to control the moisture content of the raw materials to below 100 ppm;

[0025] S2C: The raw materials for the upper, middle and lower layers are mixed according to the formula ratio and dispersed evenly by a high-speed mixer. Then, they are melted and plasticized by their respective extruders at a temperature of 145-200°C and extruded through a T-die.

[0026] S3C: A low-pressure air knife is used to attach the melt onto a cold drum to form a thick sheet, wherein the thickness of the sheet is 120-550 μm and the temperature of the cold drum is 6-30℃.

[0027] S4C. Pre-treatment is performed by immersing the thick sheet in a water bath at 15-90°C.

[0028] S5C: After heating the thick sheet, the polylactic acid film is simultaneously biaxially stretched using a Bruckner magnetic levitation synchronous biaxial stretching device, wherein the stretching temperature is 90~185℃ and the stretching ratio is 2.5*2.5~3.8*3.8.

[0029] S6C. The stretched film undergoes heat setting at a temperature of 140–195°C for 5–50 seconds. The film is then cooled and post-treated with corona discharge at a power of 8–18 W / min / m. 2 And collect the roll;

[0030] S7C. The wound biaxially oriented polylactic acid film is cut as required to obtain the biaxially oriented polylactic acid film with good toughness and a film thickness of 15-60 μm.

[0031] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0032] 1. The biaxially oriented polylactic acid (PLA) film with good toughness prepared by this invention overcomes the shortcomings of insufficient toughness of PLA itself. The carbon-15 straight chain containing unsaturated double bonds in the meta-position of the cashew phenol component in the silicon epoxidized cashew phenol-glycidyl methacrylate copolymer provides good toughness to the system. It has a wide range of applications, good product appearance, good performance, and is easy to process. The production process is simple, the production efficiency is high, and it is easy to industrialize. This biaxially oriented polylactic acid film with good toughness can be completely degraded under natural conditions. It is non-toxic, harmless, and hygienic, and can completely solve the problem of white pollution. It is a green and environmentally friendly packaging material that conforms to the trend of environmental protection.

[0033] 2. This invention improves the mechanical strength, thermal stability, and compatibility with polylactic acid (PLA) of the film by adding a silicon-containing epoxidized cashew nut shell copolymer. In the PLA block copolymer, PLA acts as the hard segment, while poly6-caprolactone acts as the soft segment. The soft segment possesses the elasticity of rubber, thus providing good toughness for the entire system. This component also exhibits excellent compatibility. Through the combination and blending of various biodegradable materials, the properties of each component can complement each other, resulting in superior performance compared to a single-component structure. A rational film layer structure design ensures that the functions of each layer work in harmony, leading to a film with even better performance.

[0034] 3. Through reasonable formulation design and film layer structure design, this invention achieves good mutual coordination between the various functional layers and formulations of the film, and achieves complementary advantages and strong synergy between the layers and formulations, forming an inseparable organic whole. This provides a biaxially oriented polylactic acid film with good toughness, complete degradability, high mechanical strength and good optical properties, which can be widely used in various packaging fields. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the biaxially oriented polylactic acid film with good toughness according to the present invention.

[0036] The reference numerals in the figure are as follows:

[0037] 30. Top layer; 20. Middle layer; 10. Bottom layer. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] In the description of this invention, it should be noted that the terms used in this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and should not be construed as limiting the invention; it should be further understood that the terms used in this invention should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this invention.

[0040] refer to Figure 1 As shown.

[0041] Example 1

[0042] A biaxially oriented polylactic acid (PLA) film with good toughness, comprising an upper surface layer 30, an intermediate layer 20, and a lower surface layer 10; by mass parts, the intermediate layer 20 is composed of 60 parts of PLA, 10 parts of a silicon-containing epoxidized cashew nut shell polymer-glycidyl methacrylate polymer, and 30 parts of PLA block copolymer; the upper surface layer 30 and the lower surface layer 10 are each composed of 55 parts of PLA, 10 parts of a silicon-containing epoxidized cashew nut shell polymer-glycidyl methacrylate polymer, 30 parts of PLA block copolymer, and 5 parts of functional masterbatch.

[0043] The specific preparation method of the silicon-containing epoxidized cashew nut phenol-glycidyl methacrylate polymer is as follows:

[0044] S1A. Dissolve 150 parts by weight of cashew phenol in 300 parts by weight of chlorobenzene, then add 80 parts by weight of oxalic acid, followed by adding 80 parts by weight of 30% hydrogen peroxide aqueous solution in multiple portions, heat to 60°C, and react for 8 hours under chlorobenzene reflux conditions.

[0045] S2A. The organic matter was separated, washed three times with an alkaline saturated aqueous solution, then washed three times with distilled water, and the solvent was removed by reduced pressure in a rotary evaporator. The resulting product was dried under vacuum at 60°C for 3 hours to obtain epoxidized cashew phenol.

[0046] S3A. 150 parts by mass of epoxidized cashew nut powder, 50 parts by mass of 2-bromo-1-butene and 200 parts by mass of magnesium hydroxide were added to a reactor and reacted at 60°C for 20 hours. Then, alkylated epoxidized cashew nut powder was obtained by filtration, separation, purification and drying.

[0047] S4A. 150 parts by weight of alkylated epoxy cashew phenol, 3 parts by weight of hexachloroplatinic acid, 50 parts by weight of phenyltriethoxysilane and 5 parts by weight of glycidyl methacrylate were reacted at 60°C for 10 hours to obtain a silicon-containing epoxy cashew phenol-glycidyl methacrylate polymer.

[0048] The specific preparation method of the polylactic acid block copolymer is as follows:

[0049] S1B. Add 160 parts by mass of lactic acid and 300 parts by mass of cyclohexane to a distillation flask, control the temperature at 120°C, and distill for 10 hours to obtain distillate A, and make its water content less than 2 wt%.

[0050] S2B: Add 98.5 parts by mass of distillate A, 0.5 parts by mass of catalyst, and 1 part by mass of stabilizer to the reactor, introduce N2 or inert gas and circulate it 4 times, while turning on the agitator and controlling the stirring speed at 120 r / min, raise the temperature to 180℃, and melt polycondense under a pressure of 900 Pa for 20 hours to obtain prepolymer B;

[0051] S3B, add 55 parts by weight of prepolymer B, 35 parts by weight of 6-caprolactone and 10 parts by weight of hydroxyethyl methacrylate to the reactor, introduce N2 or inert gas and circulate it 4 times, while turning on the agitator and controlling the stirring speed at 250 r / min, raise the temperature to 155℃, and react for 40 hours under a pressure of 600 Pa to obtain block prepolymer C;

[0052] S4B. Block prepolymer C was dissolved in acetone, precipitated and washed with ethanol, and washed with distilled water in sequence. It was then vacuum dried at 45°C to obtain a white powdered polylactic acid block copolymer.

[0053] The catalyst in step S2B is a mixture of Zn(NO3)2, azelaic acid, and glutaric anhydride in a ratio of 1:1:1.

[0054] The stabilizer in step S2B is phosphorous acid.

[0055] The functional masterbatch comprises, by weight, 5 parts lubricant, 8 parts opening agent, 3 parts antioxidant and 84 parts polylactic acid; the lubricant is erucamide; the opening agent is silica; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a 2:1 ratio; the functional masterbatch is obtained by melt extrusion, stranding, cooling, pelletizing and drying at 185°C using a twin-screw extruder.

[0056] The thickness of the biaxially oriented polylactic acid film with good toughness is 25 μm; wherein the thickness of the upper surface layer 30 and the lower surface layer 10 is 2 μm, and the thickness of the intermediate layer 20 is 21 μm.

[0057] A method for preparing a biaxially oriented polylactic acid film with good toughness specifically includes the following steps:

[0058] S1C. Dry the raw materials to control the moisture content of the raw materials to below 90 ppm;

[0059] S2C: The raw materials of the upper surface layer 30, the middle layer 20 and the lower surface layer 10 are mixed according to the formula ratio and dispersed evenly by a high-speed mixer. Then, they are melted and plasticized by their respective extruders at a temperature of 185°C and extruded through a T-die.

[0060] S3C: A low-pressure air knife is used to attach the melt onto a cold drum to form a thick sheet, wherein the thickness of the sheet is 350μm and the temperature of the cold drum is 15℃.

[0061] S4C. Pre-treatment involves immersing the thick sheet in a 55°C water bath.

[0062] S5C: After heating the thick sheet, the polylactic acid film is simultaneously biaxially stretched using a Bruckner magnetic levitation synchronous biaxial stretching device, wherein the stretching temperature is 160℃ and the stretching ratio is 3.5*3.5.

[0063] S6C. The stretched film undergoes heat setting at 175℃ for 20 seconds. The film is then cooled and subjected to corona treatment at a power of 12 W / min / m. 2 And collect the roll;

[0064] S7C. The wound biaxially oriented polylactic acid film is cut as required to obtain the biaxially oriented polylactic acid film with good toughness and a film thickness of 25 μm.

[0065] Example 2

[0066] A biaxially oriented polylactic acid (PLA) film with good toughness, comprising an upper surface layer 30, an intermediate layer 20, and a lower surface layer 10; by mass parts, the intermediate layer 20 is composed of 75 parts of PLA, 5 parts of a silicon-containing epoxidized cashew nut shell polymer-glycidyl methacrylate polymer, and 20 parts of PLA block copolymer; the upper surface layer 30 and the lower surface layer 10 are each composed of 72 parts of PLA, 5 parts of a silicon-containing epoxidized cashew nut shell polymer-glycidyl methacrylate polymer, 20 parts of PLA block copolymer, and 3 parts of functional masterbatch.

[0067] The specific preparation method of the silicon-containing epoxidized cashew nut phenol-glycidyl methacrylate polymer is as follows:

[0068] S1A. Dissolve 120 parts by weight of cashew phenol in 150 parts by weight of chlorobenzene, then add 60 parts by weight of oxalic acid, followed by adding 30 parts by weight of 25% hydrogen peroxide aqueous solution in multiple portions, heat to 50°C, and react for 6 hours under chlorobenzene reflux conditions.

[0069] S2A. The organic matter was separated, washed twice with alkaline saturated aqueous solution, then washed twice with distilled water, and the solvent was removed by reduced pressure in a rotary evaporator. The resulting product was dried under vacuum at 60°C for 2 hours to obtain epoxidized cashew phenol.

[0070] S3A. 120 parts by mass of epoxidized cashew nut shell, 20 parts by mass of 2-bromo-1-butene and 80 parts by mass of magnesium hydroxide were added to a reactor and reacted at 40°C for 10 hours. Then, the alkylated epoxidized cashew nut shell was obtained by filtration, separation, purification and drying.

[0071] S4A. 120 parts by weight of alkylated epoxy cashew phenol, 0.5 parts by weight of hexachloroplatinic acid, 20 parts by weight of phenyltriethoxysilane, and 2 parts by weight of glycidyl methacrylate were reacted at 55°C for 3 hours to obtain a silicon-containing epoxy cashew phenol-glycidyl methacrylate polymer.

[0072] The specific preparation method of the polylactic acid block copolymer is as follows:

[0073] S1B. Add 120 parts by mass of lactic acid and 20 parts by mass of cyclohexane to a distillation flask, control the temperature at 110°C, and distill for 3 hours to obtain distillate A, and make its water content below 2.5 wt%.

[0074] S2B: Add 99.8 parts by mass of distillate A, 0.1 parts by mass of catalyst, and 0.1 parts by mass of stabilizer to the reactor, introduce N2 or inert gas and circulate it 3 times, while turning on the agitator and controlling the stirring speed at 60 r / min, raise the temperature to 160℃, and melt polycondense under a pressure of 1300 Pa for 8 hours to obtain prepolymer B;

[0075] S3B, add 70 parts by weight of prepolymer B, 25 parts by weight of 6-caprolactone and 5 parts by weight of hydroxyethyl methacrylate to the reactor, introduce N2 or inert gas and circulate it 3 times, at the same time turn on the agitator and control the stirring speed at 65 r / min, raise the temperature to 135℃, and react for 15 hours under a pressure of 750 Pa to obtain block prepolymer C;

[0076] S4B. Block prepolymer C was dissolved in acetone, precipitated and washed with ethanol, and washed with distilled water in sequence. It was then vacuum dried at 35°C to obtain a white powdered polylactic acid block copolymer.

[0077] The catalyst in step S2B is nonadecanedioic acid.

[0078] The stabilizer in step S2B is phosphorous acid.

[0079] The functional masterbatch comprises, by weight, 3 parts lubricant, 5 parts opening agent, 2 parts antioxidant and 90 parts polylactic acid; the lubricant is oleamide; the opening agent is talc; the antioxidant is a 1:1 mixture of antioxidant 1010 and antioxidant 168; the functional masterbatch is obtained by melt extrusion, stranding, cooling, pelletizing and drying at 155°C using a twin-screw extruder.

[0080] The thickness of the biaxially oriented polylactic acid film with good toughness is 20 μm; wherein the thickness of the upper surface layer 30 and the lower surface layer 10 are 1.5 μm and the thickness of the intermediate layer 20 is 17 μm.

[0081] A method for preparing a biaxially oriented polylactic acid film with good toughness specifically includes the following steps:

[0082] S1C. Dry the raw materials to control the moisture content of the raw materials to below 100 ppm;

[0083] S2C: The raw materials of the upper surface layer 30, the middle layer 20 and the lower surface layer 10 are mixed according to the formula ratio and dispersed evenly by a high-speed mixer. Then, they are melted and plasticized by their respective extruders at a temperature of 175°C and extruded through a T-die.

[0084] S3C: A low-pressure air knife is used to attach the melt onto a cold drum to form a thick sheet, wherein the thickness of the sheet is 300μm and the temperature of the cold drum is 8℃.

[0085] S4C. Pre-treat the thick sheet by immersing it in a 40°C water bath.

[0086] S5C: After heating the thick sheet, the polylactic acid film is simultaneously biaxially stretched using a Bruckner magnetic levitation synchronous biaxial stretching device, wherein the stretching temperature is 120℃ and the stretching ratio is 3*3.

[0087] S6C. The stretched film undergoes heat setting at 150℃ for 40 seconds. The film is then cooled and subjected to corona treatment at a power of 9 W / min / m. 2 And collect the roll;

[0088] S7C. The wound biaxially oriented polylactic acid film is cut as required to obtain the biaxially oriented polylactic acid film with good toughness and a film thickness of 20 μm.

[0089] Example 3

[0090] A biaxially oriented polylactic acid (PLA) film with good toughness is provided, comprising an upper surface layer 30, an intermediate layer 20, and a lower surface layer 10. By mass parts, the intermediate layer 20 is composed of 48 parts of PLA, 12 parts of a silicon-containing epoxidized cashew nut shell polymer (CHP-Glyceryl methacrylate), and 40 parts of a PLA block copolymer. Both the upper surface layer 30 and the lower surface layer 10 are composed of 40 parts of PLA, 12 parts of a silicon-containing epoxidized cashew nut shell polymer (CHP-Glyceryl methacrylate), 40 parts of a PLA block copolymer, and 8 parts of a functional masterbatch.

[0091] The specific preparation method of the silicon-containing epoxidized cashew nut phenol-glycidyl methacrylate polymer is as follows:

[0092] S1A. Dissolve 180 parts by weight of cashew phenol in 500 parts by weight of chlorobenzene, then add 90 parts by weight of oxalic acid, followed by adding 100 parts by weight of 35% hydrogen peroxide aqueous solution in multiple portions, raise the temperature to 70°C, and react for 10 hours under chlorobenzene reflux conditions.

[0093] S2A: Separate the organic matter, wash it 4 times with alkaline saturated aqueous solution, then wash it 5 times with distilled water, remove the solvent by reduced pressure in a rotary evaporator, and dry the obtained product under vacuum at 75°C for 4 hours to obtain epoxidized cashew phenol.

[0094] S3A. 180 parts by mass of epoxidized cashew nut shell, 90 parts by mass of 2-bromo-1-butene and 350 parts by mass of magnesium hydroxide were added to a reactor and reacted at 75°C for 25 hours. Then, alkylated epoxidized cashew nut shell was obtained by filtration, separation, purification and drying.

[0095] S4A. 280 parts by weight of alkylated epoxy cashew phenol, 3 parts by weight of hexachloroplatinic acid, 70 parts by weight of phenyltriethoxysilane and 8 parts by weight of glycidyl methacrylate were reacted at 75°C for 14 hours to obtain a silicon-containing epoxy cashew phenol-glycidyl methacrylate polymer.

[0096] The specific preparation method of the polylactic acid block copolymer is as follows:

[0097] S1B. Add 180 parts by mass of lactic acid and 450 parts by mass of cyclohexane to a distillation flask, control the temperature at 145°C, and distill for 18 hours to obtain distillate A, and make its water content less than 0.5 wt%.

[0098] S2B: Add 96.6 parts by mass of distillate A, 0.9 parts by mass of catalyst, and 2.5 parts by mass of stabilizer to the reactor, introduce N2 or inert gas and circulate it 5 times, while turning on the agitator and controlling the stirring speed at 220 r / min, raise the temperature to 200℃, and melt polycondense under a pressure of 500 Pa for 28 hours to obtain prepolymer B;

[0099] S3B, add 37 parts by weight of prepolymer B, 45 parts by weight of 6-caprolactone and 18 parts by weight of hydroxyethyl methacrylate to the reactor, introduce N2 or inert gas and circulate it 5 times, at the same time turn on the agitator and control the stirring speed at 320 r / min, raise the temperature to 180℃, and react for 50 hours under a pressure of 300 Pa to obtain block prepolymer C;

[0100] S4B. Block prepolymer C was dissolved in acetone, precipitated and washed with ethanol, and washed with distilled water in sequence. It was then vacuum dried at 55°C to obtain a white powdered polylactic acid block copolymer.

[0101] The catalyst in step S2B is glutaric anhydride.

[0102] The stabilizer in step S2B is phosphorous acid.

[0103] The functional masterbatch comprises, by weight, 1 part lubricant, 9 parts opening agent, 4 parts antioxidant and 86 parts polylactic acid; the lubricant is erucamide; the opening agent is silica; the antioxidant is a 1:1 mixture of antioxidant 1010 and antioxidant 168; the functional masterbatch is obtained by melt extrusion, stranding, cooling, pelletizing and drying at 195°C using a twin-screw extruder.

[0104] The thickness of the biaxially oriented polylactic acid film with good toughness is 30 μm; wherein the thickness of the upper surface layer 30 and the lower surface layer 10 are 2.5 μm and the thickness of the intermediate layer 20 is 25 μm.

[0105] A method for preparing a biaxially oriented polylactic acid film with good toughness specifically includes the following steps:

[0106] S1C. Dry the raw materials to control the moisture content of the raw materials to below 100 ppm;

[0107] S2C: The raw materials of the upper surface layer 30, the middle layer 20 and the lower surface layer 10 are mixed according to the formula ratio and dispersed evenly by a high-speed mixer. Then, they are melted and plasticized by their respective extruders at a temperature of 195°C and extruded through a T-die.

[0108] S3C: A low-pressure air knife is used to attach the melt onto a cold drum to form a thick sheet, wherein the thickness of the sheet is 400μm and the temperature of the cold drum is 12℃.

[0109] S4C. Pre-treat the thick sheet by immersing it in a 60°C water bath.

[0110] S5C: After heating the thick sheet, the polylactic acid film is simultaneously biaxially stretched using a Bruckner magnetic levitation synchronous biaxial stretching device, wherein the stretching temperature is 135℃ and the stretching ratio is 3.2*3.2.

[0111] S6C. The stretched film undergoes heat setting at 160℃ for 30 seconds. The film is then cooled and subjected to corona treatment at a power of 10 W / min / m. 2 And collect the roll;

[0112] S7C. The wound biaxially oriented polylactic acid film is cut as required to obtain the biaxially oriented polylactic acid film with good toughness and a film thickness of 30 μm.

[0113] Comparative Example 1

[0114] A biaxially oriented polylactic acid (PLA) film with good toughness and its preparation method are disclosed. The PLA film with good toughness comprises a three-layer structure, wherein the three layers are, from top to bottom, an upper surface layer, an intermediate layer, and a lower surface layer. By mass parts, the upper surface layer comprises 95 parts of PLA and 5 parts of functional masterbatch; the intermediate layer comprises 100 parts of PLA; and the lower surface layer comprises 95 parts of PLA and 5 parts of functional masterbatch.

[0115] The functional masterbatch is composed of lubricant, opening agent, antioxidant and polylactic acid;

[0116] The formulation ratio, components and processing method of the functional masterbatch are the same as those in Example 1;

[0117] The thickness of the biaxially oriented polylactic acid film with good toughness is 25 μm; wherein the thickness of the upper and lower surface layers is 2 μm; and the thickness of the intermediate layer is 21 μm.

[0118] The preparation method of the biaxially oriented polylactic acid film with good toughness provided in Comparative Example 1 is the same as that in Example 1.

[0119] Comparative Example 2

[0120] A biaxially oriented polylactic acid (PLA) film with good toughness and its preparation method are disclosed. The PLA film with good toughness comprises a three-layer structure, wherein the three layers are, from top to bottom, an upper layer, an intermediate layer, and a lower layer. By mass parts, the upper layer comprises 85 parts of PLA, 10 parts of a silicon-containing epoxidized cashew nut shell polymer (CHP-Glyceryl methacrylate), and 5 parts of functional masterbatch; the intermediate layer comprises 90 parts of PLA and 10 parts of a silicon-containing epoxidized cashew nut shell polymer (CHP-Glyceryl methacrylate); and the lower layer comprises 85 parts of PLA, 10 parts of a silicon-containing epoxidized cashew nut shell polymer (CHP-Glyceryl methacrylate), and 5 parts of functional masterbatch.

[0121] The preparation method of the silicon-containing epoxidized cashew phenol-glycidyl methacrylate polymer is the same as that in Example 1;

[0122] The formulation ratio, components and processing method of the functional masterbatch are the same as those in Example 1;

[0123] The thickness of the biaxially oriented polylactic acid film with good toughness is 25 μm; wherein the thickness of the upper and lower surface layers is 2 μm; and the thickness of the intermediate layer is 21 μm.

[0124] The preparation method of the biaxially oriented polylactic acid film with good toughness provided in Comparative Example 2 is the same as that in Example 1.

[0125] Comparative Example 3

[0126] A biaxially oriented polylactic acid (PLA) film with good toughness and its preparation method are disclosed. The PLA film with good toughness comprises a three-layer structure, wherein the three layers are, from top to bottom, an upper surface layer, an intermediate layer, and a lower surface layer. By mass parts, the upper surface layer comprises 65 parts of PLA, 30 parts of PLA block copolymer, and 5 parts of functional masterbatch; the intermediate layer comprises 70 parts of PLA and 30 parts of PLA block copolymer; and the lower surface layer comprises 65 parts of PLA, 30 parts of PLA block copolymer, and 5 parts of functional masterbatch.

[0127] The polylactic acid block copolymer is prepared in the same way as in Example 1;

[0128] The formulation ratio, components and processing method of the functional masterbatch are the same as those in Example 1;

[0129] The thickness of the biaxially oriented polylactic acid film with good toughness is 25 μm; wherein the thickness of the upper and lower surface layers is 2 μm; and the thickness of the intermediate layer is 21 μm.

[0130] The preparation method of the biaxially oriented polylactic acid film with good toughness provided in Comparative Example 3 is the same as that in Example 1.

[0131] Comparative Example 4

[0132] A biaxially oriented polylactic acid (PLA) film with good toughness and its preparation method are disclosed. The PLA film with good toughness comprises a three-layer structure, wherein the three layers are, from top to bottom, an upper layer, an intermediate layer, and a lower layer. By mass parts, the upper layer comprises 55 parts of PLA, 10 parts of POE-g-glycidyl methacrylate, 30 parts of PLA block copolymer, and 5 parts of functional masterbatch; the intermediate layer comprises 60 parts of PLA, 10 parts of POE-glycidyl methacrylate, and 30 parts of PLA block copolymer; and the lower layer comprises 55 parts of PLA, 10 parts of POE-glycidyl methacrylate, 30 parts of PLA block copolymer, and 5 parts of functional masterbatch.

[0133] The POE-g-glycidyl methacrylate is Coais's W5D;

[0134] The polylactic acid block copolymer is prepared in the same way as in Example 1;

[0135] The formulation ratio, components and processing method of the functional masterbatch are the same as those in Example 1;

[0136] The thickness of the biaxially oriented polylactic acid film with good toughness is 25 μm; wherein the thickness of the upper and lower surface layers is 2 μm; and the thickness of the intermediate layer is 21 μm.

[0137] The preparation method of the biaxially oriented polylactic acid film with good toughness provided in Comparative Example 4 is the same as that in Example 1.

[0138] Comparative Example 5

[0139] A biaxially oriented polylactic acid (PLA) film with good toughness and its preparation method are disclosed. The PLA film with good toughness comprises a three-layer structure, wherein the three layers are, from top to bottom, an upper layer, an intermediate layer, and a lower layer. By mass parts, the upper layer comprises 55 parts of PLA, 10 parts of a silicon-containing epoxidized cashew nut shell polymer (CPMP-Glyceryl methacrylate), 30 parts of PLA / PBAT copolymer, and 5 parts of functional masterbatch; the intermediate layer comprises 60 parts of PLA, 10 parts of a CPMP-CCPMP-Glyceryl methacrylate polymer (CPMP-Glyceryl methacrylate), and 30 parts of PLA / PBAT copolymer; the lower layer comprises 55 parts of PLA, 10 parts of a CPMP-CCPMP-Glyceryl methacrylate polymer (CPMP-Glyceryl methacrylate), 30 parts of PLA / PBAT copolymer, and 5 parts of functional masterbatch.

[0140] The preparation method of the silicon-containing epoxidized cashew phenol-glycidyl methacrylate polymer is the same as that in Example 1;

[0141] The polylactic acid block copolymer is prepared using the method described in Yuan Hua and Yang Junwei's "Preparation of PLA / PBAT Multiblock Copolymer by Melt Chain Extension Reaction";

[0142] The formulation ratio, components and processing method of the functional masterbatch are the same as those in Example 1;

[0143] The thickness of the biaxially oriented polylactic acid film with good toughness is 25 μm; wherein the thickness of the upper and lower surface layers is 2 μm; and the thickness of the intermediate layer is 21 μm.

[0144] The preparation method of the biaxially oriented polylactic acid film with good toughness provided in Comparative Example 5 is the same as that in Example 1.

[0145] The biaxially oriented polylactic acid films prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests, and the results are shown in Table 1.

[0146] Table 1 Performance test results for Examples 1-3 and Comparative Examples 1-5

[0147]

[0148] The testing methods used are as follows:

[0149] (1) Tensile strength and elongation at break performance test: The test shall be conducted in accordance with the requirements of GB / T 1040.3 "Determination of tensile properties of plastics (Part 3: Test conditions for films and sheets)".

[0150] (2) Elongation at break test: Refer to the test standard for tensile strength.

[0151] (3) Dart impact strength test: The test shall be conducted in accordance with the requirements of GB / T 9639.1 "Test method for impact resistance of plastic films and sheets (free fall method Part 1: step method)".

[0152] (4) Thickness performance test: The test shall be conducted in accordance with the requirements of GB / T 6672 "Determination of thickness of plastic film and sheet: mechanical measurement method".

[0153] (5) In the table, the symbol “◎” indicates excellent, the symbol “□” indicates good, the symbol “△” indicates average, and the symbol “×” indicates poor.

[0154] As shown in Table 1, compared with the biaxially oriented polylactic acid (BOA) film produced by traditional methods, the BOA film with good toughness prepared by the present invention not only has good toughness but is also completely biodegradable, which can meet the needs of packaging markets in different fields.

[0155] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A biaxially-stretched polylactic acid film having good toughness, characterized by: The bi-directional stretch polylactic acid film with good toughness comprises an upper surface layer (30), a middle layer (20) and a lower surface layer (10); the middle layer (20) is composed of 25-89 parts by mass of polylactic acid, 1-15 parts by mass of a silicon-containing epoxidized cardanol-glycidyl methacrylate polymer and 10-60 parts by mass of a polylactic acid block copolymer; and the upper surface layer (30) and the lower surface layer (10) are each composed of 25-88 parts by mass of polylactic acid, 1-15 parts by mass of the silicon-containing epoxidized cardanol-glycidyl methacrylate polymer, 10-50 parts by mass of the polylactic acid block copolymer and 1-10 parts by mass of a functional master batch; The specific preparation method of the silicon-containing epoxidized cardanol-glycidyl methacrylate polymer is as follows: S1A, 100-200 parts by mass of cardanol is dissolved in 100-600 parts of chlorobenzene, then 50-100 parts of oxalic acid is added, followed by the addition of 20-120 parts of 20-40% hydrogen peroxide aqueous solution in multiple portions, the temperature is raised to 40-80°C, and the reaction is carried out under chlorobenzene reflux for 2-12 hours; S2A, the organic matter is separated, first washed with an alkaline saturated aqueous solution for 1-5 times, then washed with distilled water for 1-6 times, the solvent is removed by reduced pressure in a rotary evaporator, and the obtained product is dried under vacuum at 50-80°C for 1-5 hours to obtain epoxidized cardanol; S3A, 100-200 parts by mass of epoxidized cardanol, 10-100 parts of 2-bromo-1-butene and 50-400 parts of magnesium hydroxide are added into a reactor, and the reaction is carried out at a temperature of 20-80°C for 6-30 hours, followed by filtration, separation, purification and drying to obtain alkylated epoxidized cardanol; S4A, 100-300 parts by mass of alkylated epoxidized cardanol, 0.1-5 parts of hexachloroplatinic acid, 10-80 parts of phenyltriethoxysilane and 1-10 parts of glycidyl methacrylate are reacted at 50-80°C for 1-16 hours to obtain the silicon-containing epoxidized cardanol-glycidyl methacrylate polymer; The specific preparation method of the polylactic acid block copolymer is as follows: S1B, 100-200 parts by mass of lactic acid and 10-500 parts of cyclohexane are added into a distillation flask, the temperature is controlled at 100-150°C, and the distillate A is obtained by distillation for 2-20 hours, and the water content of the distillate A is controlled to be less than 3wt%; S2B, 96-99.98 parts by mass of the distillate A, 0.01-1 parts of a catalyst and 0.01-3 parts of a stabilizer are added into a reactor, N2 or inert gas is introduced, and the circulation is carried out for 2-6 times, while the stirring paddle is started, the stirring speed is controlled at 50-250r / min, the temperature is raised to 150-210°C, and the melt polycondensation is carried out under a pressure of 1-1500Pa for 5-30 hours to obtain a prepolymer B; S3B, the prepolymers B of 30-79 parts by mass, 6-hexalactone of 20-50 parts by mass and hydroxyethyl methacrylate of 1-20 parts by mass are added into a reaction kettle, N2 or inert gas is introduced and circulated for 2-6 times, the stirring paddle is started, the stirring speed is controlled at 50-350 r / min, the temperature is raised to 130-185℃, the reaction is carried out under the pressure of 1-800 Pa for 10-60 hours to obtain the block prepolymers C; S4B, the block prepolymers C are sequentially dissolved with acetone, washed with ethanol precipitation and distilled water, and dried at 30-60℃ under vacuum to obtain the white powdery polylactic acid block copolymer.

2. The bidirectional-stretchable polylactic acid film with good tenacity according to claim 1, characterized by: The catalyst in step S2B is any one or a mixture of at least two of Zn(NO3)2, Zn(ClO4)2, Zn(BF4)2, malonic acid, azelaic acid, nonadecane acid, phthalic acid, isophthalic acid and glutaric anhydride in any ratio.

3. The biaxially-stretched polylactic acid film having good toughness according to claim 1, wherein: the polylactic acid film has a thickness of 10 to 50 μm. The stabilizer in step S2B is phosphorous acid.

4. The biaxially-stretched polylactic acid film having good toughness according to claim 1, wherein: The functional master batch comprises 0.5-8 parts by mass of a lubricant, 3-10 parts by mass of an opening agent, 0.5-5 parts by mass of an antioxidant and 77-96 parts by mass of polylactic acid; the lubricant is one or both of erucic acid amide and oleic acid amide; the opening agent is one or more of silica, calcium carbonate, diatomite and talc powder; the antioxidant is a mixture of one or more of phosphite esters and phenols; and the functional master batch is obtained by melt extrusion, drawing, cooling, pelletizing and drying of the functional master batch through a twin-screw extruder at a temperature of 145-200℃.

5. The biaxially-stretched polylactic acid film with good toughness according to claim 1, characterized by: The biaxially stretched polylactic acid film with good toughness has a thickness of 15-60 μm; wherein the thicknesses of the upper surface layer (30) and the lower surface layer (10) are 1-3 μm respectively, and the thickness of the intermediate layer (20) is 9-58 μm.

6. A process for producing a biaxially-stretched polylactic acid film having good toughness according to any one of claims 1 to 5, characterized by, Specifically comprising the following steps: S1C, drying the raw materials to control the water content of the raw materials below 100 ppm; S2C, mixing the raw materials of the upper surface layer (30), the intermediate layer (20) and the lower surface layer (10) according to the formula proportion, uniformly dispersing through a high-speed stirrer, and then melt plasticizing extruding through respective extruders at a temperature of 145-200℃; S3C, using a low-pressure air knife to attach the melt on a cold drum to form a thick sheet, wherein the thickness of the thick sheet is 120-550 μm, and the temperature of the cold drum is 6-30℃; S4C, immersing the thick sheet into a water tank at 15-90℃ for pretreatment; S5C, heating the thick sheet and then using a Bruckner magnetic suspension synchronous biaxial stretching equipment to perform synchronous biaxial stretching of the polylactic acid film, wherein the stretching temperature is 90-185℃, and the stretching ratio is 2.5*2.5-3.8*3.8; S6C, performing heat setting treatment of the stretched film, wherein the setting temperature is 140-195℃, and the setting time is 5-50 s, then the film is cooled and treated by corona discharge, the power of the corona discharge treatment is 8-18 Wmin / m², and the film is wound up. S7C, the biaxially oriented polylactic acid film after winding is slit according to requirements, and finally the biaxially oriented polylactic acid film with good toughness is obtained, and the film thickness is 15-60 μm.

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