Damp-heat-resistant polylactic acid transparent film and preparation method thereof

Abstract

The invention discloses a damp-heat-resistant polylactic acid transparent film and a preparation method thereof, and relates to the technical field of polymer packaging materials. According to the preparation method of the damp-heat-resistant polylactic acid transparent film, the nucleating agent, the anti-hydrolysis agent, the compatilizer and the polylactic acid resin are subjected to blending granulation and then subjected to tape casting processing, and a film blank is obtained; stretching the thin film blank at a preset temperature, then shaping the thin film blank, heating the thin film blank to 150 DEG C or above in a shaping state, keeping the temperature for 10-15 minutes, then cooling the thin film blank to a preset stretching temperature, and repeating the stretching-heating shaping-cooling process for 2-6 times to obtain the damp-heat-resistant polylactic acid transparent film product. The nucleating agent, the anti-hydrolysis agent, the compatilizer and the polylactic acid resin are compounded and matched with a multi-time stretching process, so that a large number of microcrystals are formed in the polylactic acid, the heat-resistant temperature of the polylactic acid film is increased, and the toughness and transparency of the polylactic acid film are kept.

Description

Technical Field

[0001] The invention relates to the technical field of polymer packaging materials, and in particular to a moisture-heat resistant polylactic acid transparent film and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA) resin is a biodegradable polyester polymer obtained by polymerization of lactic acid as the main raw material. Polylactic acid is currently the biodegradable polymer material with the largest production capacity and the most extensive application. Polylactic acid can be prepared into products for different purposes through various processing techniques such as injection molding, casting, spinning, etc. In addition to biodegradability, the obtained products also have good biocompatibility, mechanical properties, transparency and texture.

[0003] In the processing of PLA, the crystallization speed of PLA is very slow and almost no crystallization occurs during the processing. Therefore, the obtained products are often amorphous PLA, so its heat resistance is poor, and the heat deformation temperature is generally only 55-60 degrees. Once this temperature is exceeded, PLA will lose its original performance due to heat deformation. This shortcoming greatly limits the use of PLA in some daily life. Improving the thermal stability of PLA is also a major research hotspot in the current research on the heat resistance of PLA.

[0004] Patent CN102977563A discloses a heat-resistant polylactic acid / polyhydroxyalkanoate copolymer film and a preparation method thereof, wherein the heat deformation temperature of the composite material system is increased by blending and adding 5-40 parts of polyhydroxyalkanoic acid; Sun Chuangchuang et al. improved the thermal stability of polylactic acid composite materials by adding 20% ​​polybutylene succinate (PBS) and 20% talcum powder filler to polylactic acid. This type of research essentially increases and improves the heat deformation temperature of polylactic acid by adding polymers or fillers with higher heat deformation temperatures. However, the addition of such high-content heterogeneous polymer materials sacrifices some of the advantages of the polylactic acid material itself in exchange for improved thermal stability. While improving thermal stability, the transparency of polylactic acid and mechanical properties such as tensile modulus will be greatly reduced.

[0005] Patent CN108117728A discloses a heat-resistant polylactic acid resin composition for degradable film and its preparation method, which uses L-polylactic acid as the resin matrix, adds 5-30% of a cross-linked copolymer with a core-shell structure and L-polylactic acid for secondary cross-linking to improve the heat resistance temperature, and the core-shell polymer is a cross-linked product of D-polylactic acid and acrylate compounds condensed into glycidyl ester, and then adds polyols and isocyanate chain extenders for secondary cross-linking to obtain a twice cross-linked product with a core-shell structure, which is added to the matrix L-polylactic acid, thereby improving the thermal stability of the composite material. However, in this method, the isocyanate substance used is an important intermediate in organic synthesis, which can be used to prepare a series of pesticides, fungicides, and herbicides. It generally has a strong irritating taste and strong chemical activity, and is not suitable for use in occasions with high safety requirements; in addition, this method requires an intermediate grafting process, and the process is relatively complicated.

[0006] Patent No. CN113427867A discloses a multi-layer heat-resistant, highly transparent, biodegradable polylactic acid-based film, specifically a multi-layer polylactic acid film comprising an outer layer / adhesive layer / barrier layer / adhesive layer / outer layer, wherein the adhesive layer is a copolymer of EVOH-polylactic acid, the barrier layer comprises EVOH and EVA resin, and the outer layer is a high molecular weight polylactic acid copolymer prepared from a polylactic acid-based copolymer and a chain extender. The process of this method also requires an independent chain extension preparation process, which is relatively complicated, and the chain extension process also requires the use of isocyanate, acyl chloride chain extenders and other chain extenders with certain irritation.

[0007] In summary, there is currently no safe and effective method that can improve the heat resistance of polylactic acid materials without affecting their transparency and mechanical properties such as tensile modulus. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a transparent and heat-resistant polylactic acid film and a preparation method thereof, which can effectively solve the disadvantage of poor heat resistance of polylactic acid materials and take into account the transparency and tensile modulus of the material.

[0009] In order to solve the above problems, the present invention proposes the following technical solutions:

[0010] A method for preparing a heat-and-humidity resistant polylactic acid transparent film comprises the following steps:

[0011] S1, blending and granulating a nucleating agent, an anti-hydrolysis agent, a compatibilizer and a polylactic acid resin to obtain a composite resin masterbatch;

[0012] S2, performing tape casting on the composite resin masterbatch to obtain a film body;

[0013] S3. The film blank is stretched and shaped within a preset temperature. While maintaining the shaped state, the temperature is increased to above 150° C., maintained for 10 to 15 minutes, and then cooled to the preset stretching temperature. The stretching-heating-shaping-cooling process is repeated 2 to 6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

[0014] A further technical solution is that the nucleating agent includes one or more of silicon dioxide, calcium carbonate, mica, talc, hydrotalcite, ethylene bisstearamide (vinyl bisstearamide), sebacic acid diphenyl dihydrazide, suberic acid dibenzohydrazide, zinc citrate, and copper citrate.

[0015] A further technical solution is that the anti-hydrolysis agent includes one or more of titanium dioxide, polycarbodiimide, N,N'-diisopropylcarbodiimide, bis(2,6-diisopropylbenzene)carbodiimide, N,N'-dicyclohexylcarbodiimide, N,N-di-tert-butylcarbodiimide, N,N'-bis(2,4,6-trimethylphenyl)ethanediimide, N,N'-di(tridecyl)-3,4,9,10-perylenetetracarboxylic acid diimide, 3,4,9,10-tetracarboxylic acid diimide, and 1,3-diimidoisoindoline.

[0016] A further technical solution is that the compatibilizer includes one or more of sorbitol, epoxidized soybean oil and maleic anhydride.

[0017] A further technical solution is that the polylactic acid resin is any commercially available polylactic acid resin product or a mixture thereof. The present invention does not limit the optical rotation properties of the polylactic acid product, and includes any proportion of a mixture of L-polylactic acid resin, D-polylactic acid resin or LD-polylactic acid resin.

[0018] It should be noted that the polylactic acid resin raw material needs to be dried before use. The drying method is a conventional technical means and the present invention does not limit this.

[0019] A further technical solution is that in step S3, the elongation of each stretching is 1-20%, for example, 4%, 7%, 10%, 13%, 16%, 18%, 20%.

[0020] A further technical solution is that in step S3, the time for each stretching is 5-30 s, for example, 5 s, 8 s, 10 s, 15 s, 20 s, 25 s, or 30 s.

[0021] A further technical solution is that in step S3, the preset temperature is 90-130°C, for example, 90°C, 100°C, 110°C, 120°C, 130°C.

[0022] The further technical solution is that the specific operation of step S3 is: heating the film body to a preset temperature within 2-8 seconds, stretching and shaping, and after the stretching is completed, the temperature is raised to above 150°C and maintained for 10-15 minutes while maintaining the shaping state, and then cooled to the preset stretching temperature within 2-8 seconds; preferably, heating the film body to a preset temperature within 3-6 seconds, stretching and shaping, and after the stretching is completed, the temperature is raised to above 150°C and maintained for 10-15 minutes while maintaining the shaping state, and then cooled to the preset stretching temperature within 3-6 seconds;

[0023] The above-mentioned heating-stretching-cooling operation is repeated 2-6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

[0024] A further technical solution is that in the step S1, the usage ratio of the nucleating agent, the anti-hydrolysis agent, the compatibilizer and the polylactic acid resin is: 0.01-0.2: 0.2-3: 0.05-0.5: 100.

[0025] The present invention also provides a moisture-heat resistant polylactic acid transparent film, which is prepared by the moisture-heat resistant polylactic acid transparent film preparation method described above.

[0026] Compared with the prior art, the technical effects achieved by the present invention include:

[0027] The preparation method of the heat-resistant polylactic acid transparent film provided by the present invention comprises the following steps: a nucleating agent, an anti-hydrolysis agent, a compatibilizer and a polylactic acid resin are blended and granulated, and then a film blank is obtained; the film blank is stretched within a preset temperature and then shaped, and while maintaining the shaped state, the temperature is raised to above 150°C, maintained for 10 to 15 minutes, and then cooled to the preset stretching temperature, and the stretching-setting-cooling process is repeated 2 to 6 times to obtain a heat-resistant polylactic acid transparent film product. The present invention forms a large number of microcrystals inside the polylactic acid by compounding the nucleating agent, the anti-hydrolysis agent, the compatibilizer and the polylactic acid resin, and combining the process of multiple stretching, thereby improving the heat-resistant temperature of the polylactic acid film and maintaining the toughness and transparency of the polylactic acid film. The preparation method of the present invention is simple, environmentally friendly, low-cost, and has excellent product performance.

[0028] The moisture-heat resistant polylactic acid transparent film provided by the invention has high transparency and excellent heat resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0030] Figure 1 This is a photo of the film blank prepared in Example 1 of the present invention.

[0031] Figure 2 This is a photo of the heat and moisture resistant polylactic acid transparent film prepared in Example 1 of the present invention.

[0032] Figure 3 The results of the heat resistance test at 90° C. of the film blank and the moisture-heat resistant polylactic acid transparent film prepared in Example 1 of the present invention are shown.

[0033] Figure 4 The results of the heat resistance test at 100° C. of the film blank and the moisture-heat resistant polylactic acid transparent film prepared in Example 4 of the present invention are shown.

[0034] Figure 5 These are the XRD characterization results of the film blank and the moisture-heat resistant polylactic acid transparent film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0037] It should also be understood that the terms used in this description of the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present invention. As used in the description of the embodiments of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms of "a", "an" and "the" are intended to include plural forms.

[0038] The embodiment of the present invention provides a method for preparing a moisture-heat resistant polylactic acid transparent film, comprising the following steps:

[0039] S1. Blending and granulating a nucleating agent, an anti-hydrolysis agent, a compatibilizer and a polylactic acid resin in a mass ratio of 0.01-0.2:0.2-3:0.05-0.5:100 to obtain a composite resin masterbatch;

[0040] S2, performing tape casting on the composite resin masterbatch to obtain a film body;

[0041] S3, stretching the film body within a preset temperature and then shaping it. While maintaining the shaping state, raising the temperature to above 150°C, maintaining it for 10 to 15 minutes, and then cooling it to the preset stretching temperature. Repeat the stretching-shaping-cooling process 2 to 6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

[0042] In a preferred embodiment, step S3 is as follows: heating the film blank to a preset temperature within 2-8 seconds, stretching and shaping it, and after stretching, while maintaining the shaping state, raising the temperature to above 150°C, maintaining it for 10 to 15 minutes, and then cooling it to the preset stretching temperature within 2-8 seconds, repeating the above stretching-heating and shaping-cooling operations 2-6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

[0043] In a more preferred embodiment, step S3 is: heating the film blank to a preset temperature within 3-6 seconds, stretching and shaping, and after stretching, while maintaining the shaping state, raising the temperature to above 150°C, maintaining it for 10 to 15 minutes, and then cooling it to the preset stretching temperature within 3-6 seconds, repeating the above stretching-shaping-cooling operation 2-6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

[0044] In a specific embodiment, the nucleating agent is selected from one or more of silicon dioxide, calcium carbonate, mica, talc, hydrotalcite, ethylene bisstearamide (vinyl bisstearamide), sebacic acid diphenyl dihydrazide, suberic acid dibenzohydrazide, zinc citrate, and copper citrate.

[0045] In a specific embodiment, the anti-hydrolysis agent is selected from one or more of titanium dioxide, polycarbodiimide, N,N'-diisopropylcarbodiimide, bis(2,6-diisopropylbenzene)carbodiimide, N,N'-dicyclohexylcarbodiimide, N,N-di-tert-butylcarbodiimide, N,N'-bis(2,4,6-trimethylphenyl)ethanediimide, N,N'-di(tridecyl)-3,4,9,10-perylenetetracarboxylic acid diimide, 3,4,9,10-tetracarboxylic acid diimide, and 1,3-diimidoisoindoline.

[0046] In a specific embodiment, the compatibilizer is selected from one or more of sorbitol, epoxidized soybean oil, and maleic anhydride.

[0047] It should be noted that the present invention does not limit the optical rotation properties of the polylactic acid resin, that is, the polylactic acid resin described in the embodiments of the present invention is any commercially available polylactic acid resin product or a mixture thereof, including a mixture of any proportion of L-polylactic acid resin, D-polylactic acid resin or LD-polylactic acid resin.

[0048] It should be noted that the polylactic acid resin raw material needs to be dried before use. The drying method is a conventional technical means and the present invention does not limit this.

[0049] The present invention is further described below with reference to the embodiments.

[0050] Example 1

[0051] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0052] 0.2 g of calcium carbonate, 10 g of polycarbodiimide, 1 g of epoxy soybean oil and 1000 g of polylactic acid were simply stirred and mixed evenly, and then extruded and granulated by a twin-screw extruder to obtain a resin masterbatch.

[0053] The obtained resin masterbatch is cast into a uniform film blank using a casting machine. The film blank picture of this embodiment is shown in Figure 1 , has good transparency, and the light transmittance reaches 94.5%.

[0054] The obtained film blank is stretched and shaped, and the specific operation is as follows: the above film blank is placed in a 100°C oven for 3 seconds to heat the film blank to 100°C, and then stretched and shaped within 5 seconds with an elongation of 5%. While maintaining the shaping state, the film temperature is increased to 150°C and maintained for 15 minutes, and then the shaped film is quickly taken out and cooled to 100°C within 3 seconds; the above stretching-heating and shaping-cooling operation is repeated 5 times to obtain the final moisture-heat resistant polylactic acid transparent film product.

[0055] The final heat-resistant polylactic acid transparent film product obtained in this embodiment is as follows Figure 2 It can be seen that after stretching, the polylactic acid film still maintains a high degree of transparency. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product is 50 μm , the light transmittance reaches 93.2%.

[0056] Heat resistance test

[0057] The film blank of this embodiment and the stretched heat-resistant polylactic acid transparent film product were respectively coated on the surface of the vial and placed in a 90°C oven for 2 hours. Figure 3 .

[0058] The film blank that was not stretched shrank and deformed, while the moisture-heat resistant polylactic acid transparent film product finally obtained in this embodiment was obtained by stretching the film blank multiple times and had no obvious deformation after being placed at 90°C for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0059] The film blank of this embodiment and the stretched heat-resistant polylactic acid transparent film were subjected to XRD analysis. The results are shown in Figure 5 .

[0060] It was found that the unstretched polylactic acid film had almost no crystallization peak, while the polylactic acid film that had been stretched multiple times had a sharp crystallization peak, which proved that the stretching process of the present invention can make the polylactic acid crystallize, thereby improving the heat resistance temperature of the polylactic acid.

[0061] Example 2

[0062] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0063] 0.2 g of silica, 0.3 g of mica, 30 g of N,N-di-tert-butylcarbodiimide, 5 g of sorbitol and 1000 g of polylactic acid were simply stirred and mixed uniformly, and then extruded and granulated using a twin-screw extruder to obtain a resin masterbatch.

[0064] The obtained resin masterbatch is cast into a uniform film body using a casting machine.

[0065] The obtained film blank was stretched and shaped. The specific operation is as follows: the film blank was placed in a 110°C oven for 5 seconds to raise the temperature of the film blank to 110°C, and then stretched and shaped within 10 seconds with an elongation of 10%. While maintaining the shaped state, the film temperature was raised to 160°C and maintained for 15 minutes. Then the shaped film was quickly taken out and cooled to 110°C within 5 seconds. The above stretching-heating-setting-cooling operation was repeated 3 times to obtain the final heat-resistant polylactic acid transparent film product. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 91.7%.

[0066] After testing, the finally obtained moisture-heat resistant polylactic acid transparent film product in this embodiment has no obvious deformation after being placed at 90° C. for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0067] Example 3

[0068] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0069] 0.5 g of talc, 15 g of N,N'-diisopropylcarbodiimide, 2 g of maleic anhydride and 1000 g of polylactic acid were simply stirred and mixed uniformly, and then extruded and granulated using a twin-screw extruder to obtain a resin masterbatch.

[0070] The obtained resin masterbatch is cast into a uniform film body using a casting machine.

[0071] The obtained film blank was stretched and shaped. The specific operation is as follows: the above film blank was placed in a 130℃ oven for 10 seconds to raise the temperature of the film blank to 130℃, and then stretched and shaped within 20 seconds, with an elongation of 20%. While maintaining the shaping state, the film temperature was raised to 160℃ and maintained for 10 minutes, and then the shaped film was quickly taken out and cooled to 130℃ within 10 seconds; the above stretching-heating shaping-cooling operation was repeated 3 times to obtain the final heat and moisture resistant polylactic acid transparent film product. After measurement, the thickness of the final heat and moisture resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 92.6%.

[0072] After testing, the finally obtained moisture-heat resistant polylactic acid transparent film product in this embodiment has no obvious deformation after being placed at 90° C. for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0073] Example 4

[0074] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0075] 1 g of zinc citrate, 20 g of N,N-di-tert-butylcarbodiimide, 3 g of maleic anhydride and 1000 g of polylactic acid were simply stirred and mixed uniformly, and then extruded and granulated through a twin-screw extruder to obtain a resin masterbatch.

[0076] The obtained resin masterbatch is cast into a uniform film body using a casting machine.

[0077] The obtained film blank was stretched and shaped. The specific operation was as follows: the film blank was placed in a 120°C oven for 5 seconds to raise the temperature of the film blank to 120°C, and then stretched and shaped within 5 seconds with an elongation of 10%. While maintaining the shaped state, the film temperature was raised to 155°C and maintained for 15 minutes. Then the shaped film was quickly taken out and cooled to 120°C within 3 seconds. The above stretching-heating-setting-cooling operation was repeated 3 times to obtain the final heat-resistant polylactic acid transparent film product. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 93.1%.

[0078] The film blank of this embodiment and the stretched heat-resistant polylactic acid transparent film product were respectively coated on the surface of the vial and placed in an oven at 100°C for 2 hours. Figure 4 .

[0079] The film blank that was not stretched shrank and deformed, while the moisture-heat resistant polylactic acid transparent film product finally obtained in this embodiment was obtained by stretching the film blank multiple times and had no obvious deformation after being placed at 100°C for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0080] Meanwhile, the heat and moisture resistant polylactic acid transparent film of this embodiment has high transparency.

[0081] Example 5

[0082] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0083] 1 g of diphenyl dihydrazide sebacic acid, 1 g of dibenzoyl hydrazide suberic acid, 2 g of polycarbodiimide, 0.5 g of epoxy soybean oil and 1000 g of polylactic acid were simply stirred and mixed uniformly, and then extruded and granulated through a twin-screw extruder to obtain a resin masterbatch.

[0084] The obtained resin masterbatch is cast into a uniform film body using a casting machine.

[0085] The obtained film blank was stretched and shaped. The specific operation is as follows: the film blank was placed in a 105°C oven for 3 seconds to raise the temperature of the film blank to 105°C, and then stretched and shaped within 30 seconds with an elongation of 10%. While maintaining the shaped state, the film temperature was raised to 160°C and maintained for 10 minutes. Then the shaped film was quickly taken out and cooled to 105°C within 2 seconds. The above stretching-heating-setting-cooling operation was repeated 5 times to obtain the final heat-resistant polylactic acid transparent film product. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 93.3%.

[0086] After testing, the finally obtained moisture-heat resistant polylactic acid transparent film product in this embodiment has no obvious deformation after being placed at 90° C. for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0087] Example 6

[0088] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0089] 0.8 g of ethylenebisstearamide, 0.2 g of hydrotalcite, 5 g of N,N'-bis(2,4,6-trimethylphenyl)ethanediimide, 1 g of epoxy soybean oil and 1000 g of polylactic acid were simply stirred and blended, and then extruded and granulated using a twin-screw extruder to obtain a resin masterbatch.

[0090] The obtained resin masterbatch was cast into a uniform film using a casting machine.

[0091] The obtained film blank was stretched and shaped. The specific operation was as follows: the film blank was placed in a 90°C oven for 3 seconds to raise the temperature of the film blank to 90°C, and then stretched and shaped within 5 seconds with an elongation of 1%. While maintaining the shaped state, the film temperature was raised to 165°C and maintained for 10 minutes. Then the shaped film was quickly taken out and cooled to 90°C within 6 seconds. The above stretching-heating-setting-cooling operation was repeated 5 times to obtain the final heat-resistant polylactic acid transparent film product. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 92.6%.

[0092] After testing, the finally obtained moisture-heat resistant polylactic acid transparent film product in this embodiment has no obvious deformation after being placed at 90° C. for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0093] Example 7

[0094] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0095] 0.2 g of diphenyl dihydrazide sebacic acid, 0.5 g of hydrotalcite, 10 g of polycarbodiimide, 5 g of 3,4,9,10-tetracarboxamide diimide, 0.8 g of epoxy soybean oil and 1000 g of polylactic acid were simply stirred and mixed uniformly, and then extruded and granulated by a twin-screw extruder to obtain a resin masterbatch.

[0096] The obtained resin masterbatch is cast into a uniform film body using a casting machine.

[0097] The obtained film blank was stretched and shaped. The specific operation is as follows: the film blank was placed in a 115°C oven for 5 seconds to raise the temperature of the film blank to 115°C, and then stretched and shaped within 20 seconds with an elongation of 10%. While maintaining the shaped state, the film temperature was raised to 168°C and maintained for 10 minutes. Then the shaped film was quickly taken out and cooled to 115°C within 3 seconds. The above stretching-heating-setting-cooling operation was repeated 6 times to obtain the final heat-resistant polylactic acid transparent film product. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 90.8%.

[0098] After testing, the finally obtained moisture-heat resistant polylactic acid transparent film product in this embodiment has no obvious deformation after being placed at 90° C. for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0099] Example 8

[0100] This embodiment provides a heat and moisture resistant polylactic acid transparent film, the preparation process of which is as follows:

[0101] 0.2 g of copper citrate, 0.3 g of talc, 15 g of polycarbodiimide, 0.5 g of epoxy soybean oil and 1000 g of polylactic acid were simply stirred and mixed uniformly, and then extruded and granulated through a twin-screw extruder to obtain a resin masterbatch.

[0102] The obtained resin masterbatch is cast into a uniform film body using a casting machine.

[0103] The obtained film blank was stretched and shaped. The specific operation is as follows: the film blank was placed in a 125°C oven for 6 seconds to raise the temperature of the film blank to 125°C, and then stretched and shaped within 30 seconds with an elongation of 10%. While maintaining the shaped state, the film temperature was raised to 158°C and maintained for 14 minutes. Then the shaped film was quickly taken out and cooled to 125°C within 5 seconds. The above stretching-heating-setting-cooling operation was repeated 3 times to obtain the final heat-resistant polylactic acid transparent film product. After measurement, the thickness of the final heat-resistant polylactic acid transparent film product was 50 μm , the light transmittance reaches 91.2%.

[0104] After testing, the moisture-heat resistant polylactic acid transparent film product finally obtained in this embodiment has no obvious deformation after being placed at 95° C. for 2 hours, indicating that the moisture-heat resistant polylactic acid transparent film obtained in this embodiment has good heat resistance.

[0105] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0106] The above is a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a heat-resistant polylactic acid transparent film, characterized in that: The following steps are involved: S1, blending and granulating a nucleating agent, an anti-hydrolysis agent, a compatibilizer and a polylactic acid resin to obtain a composite resin masterbatch; S2, performing tape casting on the composite resin masterbatch to obtain a film body; S3. The film blank is stretched and shaped within a preset temperature. While maintaining the shaped state, the temperature is increased to above 150° C., maintained for 10 to 15 minutes, and then cooled to the preset stretching temperature. The stretching-heating-shaping-cooling process is repeated 2 to 6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

2. The method for preparing the heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: The nucleating agent includes one or more of silicon dioxide, calcium carbonate, mica, talc, hydrotalcite, ethylene bisstearamide, sebacic acid diphenyl dihydrazide, suberic acid dibenzohydrazide, zinc citrate, and copper citrate.

3. The method for preparing the heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: The anti-hydrolysis agent includes one or more of titanium dioxide, polycarbodiimide, N,N'-diisopropylcarbodiimide, bis(2,6-diisopropylbenzene)carbodiimide, N,N'-dicyclohexylcarbodiimide, N,N-di-tert-butylcarbodiimide, N,N'-bis(2,4,6-trimethylphenyl)ethanediimide, N,N'-di(tridecyl)-3,4,9,10-perylenetetracarboxylic acid diimide, 3,4,9,10-tetracarboxylic acid diimide, and 1,3-diimidoisoindoline.

4. The method for preparing the heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: The compatibilizer includes one or more of sorbitol, epoxidized soybean oil and maleic anhydride.

5. The method for preparing the heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: In the step S3, the elongation of each stretching is 5-20%.

6. The method for preparing the heat-and-humidity resistant polylactic acid transparent film according to claim 5, characterized in that: In step S3, the time of each stretching is 5-30s.

7. The method for preparing a heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: In step S3, the preset temperature is 90-130°C.

8. The method for preparing a heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: The specific operation of step S3 is: heating the film blank to a preset temperature within 2-8 seconds, stretching and shaping, and after stretching, while maintaining the shaping state, raising the temperature to above 150°C for 10 to 15 minutes, and then cooling to the preset stretching temperature within 2-8 seconds, repeating the above stretching-heating and shaping-cooling operations 2-6 times to obtain a moisture-heat resistant polylactic acid transparent film product.

9. The method for preparing a heat-and-humidity resistant polylactic acid transparent film according to claim 1, characterized in that: In the step S1, the usage ratio of the nucleating agent, the anti-hydrolysis agent, the compatibilizer and the polylactic acid resin is: 0.01-0.2:0.2-3:0.05-0.5:

100.

10. A heat-and-humidity resistant polylactic acid transparent film, characterized in that: The film is prepared by the method for preparing the moisture-heat resistant polylactic acid transparent film according to any one of claims 1 to 9.

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