A biaxially stretched polylactic acid functional film and a preparation method thereof

Abstract

The application belongs to the technical field of film packaging, and particularly discloses a biaxial stretching polylactic acid functional film and a preparation method thereof, wherein the biaxial stretching polylactic acid functional film comprises, from top to bottom, a first surface layer, a core layer and a second surface layer; the first surface layer comprises, according to mass fraction, 0.01-10 parts of a matting agent, 20-50 parts of a hydroxyl fatty acid ester and 40-79.99 parts of polylactic acid; the core layer comprises, according to mass fraction, 0-0.5 parts of a photoinitiator, 20-40 parts of the hydroxyl fatty acid ester and 59.5-80 parts of the polylactic acid; and the second surface layer comprises, according to mass fraction, 0.01-0.05 parts of an opening agent, 0.01-0.05 parts of a slip agent, 20-50 parts of the hydroxyl fatty acid ester and 49.95-79.98 parts of the polylactic acid. The biaxial stretching polylactic acid functional film has the characteristics of good flexibility, high haze, low gloss and excellent mechanical properties, and has excellent antibacterial performance, meets the requirement of household composting degradation, expands the application field of the polylactic acid film, improves the flexible texture of the polylactic acid film, widens the degradation range of the polylactic acid film, and has a wide application prospect.

Description

Technical Field

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

[0002] Polylactic acid (PLA) is one of the most studied biodegradable materials both domestically and internationally, with medical, packaging, and fiber applications being its three major hot application areas. PLA uses naturally derived lactic acid as its main raw material, exhibiting excellent biodegradability and biocompatibility. Its environmental impact over its life cycle is significantly lower than that of petroleum-based materials, making it considered one of the most promising green packaging materials. Biaxially oriented polylactic acid film (BOPLA) possesses good transparency and gloss, with performance comparable to cellophane and PET, and has already been applied in food, airline tableware, flower packaging, and tapes. However, BOPLA film has several drawbacks, such as: ① high rigidity but poor flexibility, resulting in significant vibration noise and a inferior texture compared to traditional biaxially oriented polypropylene film (BOPP); ② degradation performance requires industrial composting conditions, and the degradation environment needs further improvement; ③ while it has some antibacterial properties, it does not meet the antibacterial requirements for food packaging; ④ currently, there is no mature technical solution for high-grade matte BOPLA, indicating significant room for further development.

[0003] It is essential to develop a matte biaxially oriented polylactic acid (PLA) film with good flexibility, high haze, low gloss, and excellent mechanical properties. This would enhance the flexible and high-end texture of the PLA film, while also providing excellent antibacterial properties to meet the requirements for home composting and degradation, thus expanding the application range of PLA films. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the existing technology and provide a biaxially oriented polylactic acid functional film and its preparation method.

[0005] To achieve the above objectives, one of the technical solutions of the present invention is: a biaxially oriented polylactic acid functional film, which comprises, from top to bottom, a first surface layer, a core layer, and a second surface layer; the first surface layer comprises, by weight, 0.01-10 parts of a matting agent, 20-50 parts of hydroxyl fatty acid ester, and 40-79.99 parts of polylactic acid; the core layer comprises, by weight, 0-0.5 parts of a photoinitiator, 20-40 parts of hydroxyl fatty acid ester, and 59.5-80 parts of polylactic acid; the second surface layer comprises, by weight percentage, 0.01-0.05 parts of an opening agent, 0.01-0.05 parts of a slip agent, 20-50 parts of hydroxyl fatty acid ester, and 49.95-79.98 parts of polylactic acid.

[0006] In a preferred embodiment of the present invention, the opening agent is one or a combination of several of the following: PMMA crosslinked particles, organosilicon crosslinked particles, talc, calcium carbonate, mica powder, and silicon dioxide.

[0007] In a preferred embodiment of the present invention, the slip agent is one or a combination of several of erucamide, oleamide, polyethylene wax, polypropylene wax, and ethylene bis-stearamide.

[0008] In a preferred embodiment of the present invention, the hydroxy fatty acid ester (PHA) is one or a combination of several of the following: poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB).

[0009] In a preferred embodiment of the present invention, the polylactic acid is one or a combination of several of polylactic acid (PLLA), polylactic acid (PDLA), and racemic polylactic acid (PDLLA).

[0010] In a preferred embodiment of the present invention, the matting agent is silicon dioxide, and the silicon dioxide particle size is 2.5-3.5 μm.

[0011] In a preferred embodiment of the present invention, the photoinitiator is one or a combination of several of 1-hydroxycyclohexylbenzophenone (184), 2-hydroxy-2-methyl-1-phenylpropanone (1173), benzophenone (BP), and α,α'-benzopyroxyl ketal.

[0012] In a preferred embodiment of the present invention, the total thickness of the polylactic acid functional film layer is 15-30 μm, and the thickness of the first surface layer and the second surface layer is 1-5 μm.

[0013] To achieve the above objectives, the second technical solution of the present invention is: a method for preparing a biaxially oriented polylactic acid functional film, comprising the following preparation steps:

[0014] (1) Mix the components of the first surface layer, core layer and second surface layer evenly in a high-speed mixer according to the mass fraction, extrude and granulate through a twin-screw extruder, dry the moisture and then package; the extruder temperature is 110~170℃, the drying temperature is 60~80℃, and the particle moisture content is ≤500ppm.

[0015] (2) The components of the first surface layer, core layer and second surface layer are fed by a feeder according to the mass fraction, melted by their respective extruders, and then uniformly flowed out through the T-die and cooled on the cold roller to form an unstretched sheet; the extruder temperature is 110~205℃, the cold roller temperature is 25~40℃, and the thickness of the unstretched sheet is 120~400um;

[0016] (3) Stretch the unstretched sheet under heating; the stretching temperature is 50-90℃, and the stretching ratio is 2.0*2.0-6.0*6.0;

[0017] (4) The stretched film is heat-set to obtain a polylactic acid functional film with a thickness of 10-60 μm; the heat-setting temperature is 90-120℃ and the setting time is 4-60 s.

[0018] In a preferred embodiment of the present invention, the biaxially oriented polylactic acid functional film is further subjected to ultraviolet light treatment.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The biaxially oriented polylactic acid (PLA) functional film provided by this invention has the characteristics of good flexibility, high haze, low gloss and excellent mechanical properties. At the same time, it has excellent antibacterial properties, meets the requirements of household composting degradation, expands the application field of PLA film, improves the flexible texture of PLA film, broadens the degradation range of PLA film, and has broad application prospects.

[0021] 2. In this invention, PHA is a natural high-molecular biomaterial that can be quickly decomposed into carbon dioxide and water by bacteria in the natural environment, and is a natural biodegradable material; the combination of PHA and PLA is beneficial to both reducing the carbon footprint of PLA and expanding the degradation environment of PLA.

[0022] 3. In this invention, PHA is a fast-crystallizing material and PLA is a slow-crystallizing material. PHA and PLA are different types of polyesters and cannot form a homogeneous phase after blending. Such a resin system is prone to producing a high-haze, low-gloss matte effect after biaxial stretching. PHA is a flexible material that can improve the rigidity of polylactic acid and reduce vibration noise. At the same time, PHA is also an antibacterial material. When blended with PLA, it has a synergistic antibacterial effect and can improve antibacterial performance.

[0023] 4. In this invention, the refractive index of silica is similar to that of polylactic acid, which can improve the haze of polylactic acid film and reduce the refractive index. With proper concentration control, the whitening problem that occurs with other materials can be avoided.

[0024] 5. The addition of photoinitiators and ultraviolet light treatment to the film of the present invention can destroy the chain structure of polylactic acid, accelerate the hydrolysis of ester groups, and synergistically improve the flexibility and degradation performance of the film material. Attached Figure Description

[0025] Figure 1 for Figure 1 The diagram shows the layer structure of the biaxially oriented polylactic acid functional films in Examples 1-4.

[0026] Among them, 10 is the first surface layer, 20 is the core layer, and 30 is the second surface layer. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to these embodiments. The same reference numerals throughout the text always represent the same elements, and similar reference numerals represent similar elements.

[0028] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "horizontal", "vertical", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the perspective view in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] A biaxially oriented polylactic acid (PLA) functional film, comprising, from top to bottom, a first surface layer, a core layer, and a second surface layer; the first surface layer comprises, by weight, 0.01-10 parts of a matting agent, 20-50 parts of hydroxyl fatty acid esters, and 40-79.99 parts of PLA; the core layer comprises, by weight, 0-0.5 parts of a photoinitiator, 20-40 parts of hydroxyl fatty acid esters, and 59.5-80 parts of PLA; the second surface layer comprises, by weight percentage, 0.01-0.05 parts of an opening agent, 0.01-0.05 parts of a slip agent, 20-50 parts of hydroxyl fatty acid esters, and 49.95-79.98 parts of PLA.

[0030] The opening agent is one or a combination of PMMA cross-linked particles, organosilicon cross-linked particles, talc, calcium carbonate, mica powder, and silica.

[0031] The slip agent is one or a combination of several of the following: erucamide, oleamide, polyethylene wax, polypropylene wax, and ethylene bis-stearamide.

[0032] The hydroxy fatty acid ester (PHA) is one or a combination of several of the following: poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB).

[0033] The polylactic acid is one or a combination of polylactic acid (PLLA), polylactic acid (PDLA), and racemic polylactic acid (PDLLA).

[0034] The matting agent is silicon dioxide, and the silicon dioxide particle size is 2.5-3.5 μm.

[0035] The photoinitiator is one or a combination of 1-hydroxycyclohexylbenzophenone (184), 2-hydroxy-2-methyl-1-phenylpropanone (1173), benzophenone (BP), and α,α'-benzopyroxyl ketal.

[0036] The total thickness of the polylactic acid functional film is 15-30 μm, and the thickness of the first and second surface layers is 1-5 μm.

[0037] A method for preparing a biaxially oriented polylactic acid functional film includes the following preparation steps:

[0038] (1) Mix the components of the first surface layer, core layer and second surface layer evenly in a high-speed mixer according to the mass fraction, extrude and granulate through a twin-screw extruder, dry the moisture and then package.

[0039] (2) The components of the first surface layer, core layer and second surface layer are fed by a feeder according to the mass fraction, melted by their respective extruders, and then uniformly flowed out through the T-die and cooled on the cold roller to form an unstretched sheet.

[0040] (3) Stretch the unstretched sheet while it is heated;

[0041] (4) The stretched film is heat-set to obtain a polylactic acid functional film with a thickness of 10-60 μm.

[0042] In step (1), the extruder temperature is 110-170℃, the drying temperature is 60-80℃, and the particle moisture content is ≤500ppm.

[0043] In step (2), the extruder temperature is 110-205°C, the cold roll temperature is 25-40°C, and the thickness of the unstretched sheet is 120-400 μm.

[0044] In step (3), the stretching temperature is 50-90℃ and the stretching ratio is 2.0*2.0-6.0*6.0.

[0045] In step (4), the setting temperature is 90-120℃ and the setting time is 4-60s.

[0046] It also includes ultraviolet light treatment of biaxially oriented polylactic acid functional films.

[0047] It should be noted that, where no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this field or the product instructions shall be followed. If the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be obtained commercially.

[0048] Example 1

[0049] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer, by weight, comprises: 0.03 parts silica, 30 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 69.97 parts L-polylactic acid (PLLA) with 98% optical purity. The core layer, by weight, comprises: 0.05 parts 1-hydroxycyclohexylbenzophenone (184), 30 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 69.95 parts L-polylactic acid (PLLA) with 98% optical purity. The second surface layer, by weight, comprises: 0.03 parts silica, 0.03 parts erucamide, 30 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 98% L-polylactic acid (PLLA). 69.94 copies.

[0050] It was prepared by the following method:

[0051] Step 1: Mix the components of the first surface layer, core layer, and second surface layer evenly in a high-speed mixer according to the mass ratio, extrude and granulate through a twin-screw extruder, dry the moisture and then package; the extruder temperature is 165℃, the water temperature in the water tank is 35℃, the oven temperature is 80℃, and the particle moisture content is ≤500ppm.

[0052] Step 2: The components of the first surface layer, core layer, and second surface layer are fed by a feeder according to their respective mass proportions and melted through their respective extruders. They are then uniformly discharged through a T-die and cooled on a cold roller to form an unstretched sheet. The extruder temperature is 165℃, the cold roller temperature is 30℃, and the thickness of the unstretched sheet is 230um.

[0053] Step 3: Stretch the unstretched sheet under heating conditions, where the stretching temperature is 80℃ and the stretching ratio is 3.4*3.4.

[0054] Step 4: Heat set the stretched film at a temperature of 115°C for 10 seconds to obtain the polylactic acid functional film with a thickness of 20 μm.

[0055] The fifth step is to subject the prepared biaxially oriented polylactic acid functional film to ultraviolet light irradiation treatment.

[0056] Example 2

[0057] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer comprises, by weight, 0.01 parts silica, 40 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 59.99 parts L-polylactic acid (PLLA) with 98% optical purity. The core layer comprises, by weight, 40 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX) and 60 parts L-polylactic acid (PLLA) with 98% optical purity. The second surface layer comprises, by weight, 0.05 parts PMMA crosslinked particles, 0.05 parts polyethylene wax, 40 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 59.9 parts L-polylactic acid (PLLA) with 98% optical purity.

[0058] The preparation method is the same as in Example 1, except that the obtained film was not subjected to ultraviolet light treatment in this example.

[0059] Example 3

[0060] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer comprises, by weight, 5 parts silica, 20 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 75 parts L-polylactic acid (PLLA) with 98% optical purity. The core layer comprises, by weight, 0.5 parts 1-hydroxycyclohexylbenzophenone (184), 20 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 79.5 parts L-polylactic acid (PLLA) with 98% optical purity. The second surface layer comprises, by weight, 0.01 parts talc, 0.01 parts ethylene bis-stearamide, 20 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and L-polylactic acid (PLLA) with 98% optical purity. 79.98 copies.

[0061] The preparation method is the same as in Example 1.

[0062] Example 4

[0063] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer comprises, by weight, 0.03 parts silica, 30 parts poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), and 69.97 parts L-polylactic acid (PLLA) with 98% optical purity. The core layer comprises, by weight, 0.05 parts 2-hydroxy-2-methyl-1-phenylpropanone (1173) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0064] (P34HB) 30 parts, L-polylactic acid PLLA with 98% optical purity 69.95 parts; the second surface layer components include, by mass parts: calcium carbonate 0.03 parts, oleic acid amide 0.03 parts, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX) 30 parts, L-polylactic acid PLLA with 98% optical purity 69.94 parts.

[0065] The preparation method is the same as in Example 1.

[0066] Comparative Example 1

[0067] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer comprises, by weight, 0.03 parts silica, 0.03 parts erucamide, and 99.96 parts L-PLLA with 98% optical purity. The core layer comprises, by weight, 100 parts L-PLLA with 98% optical purity. The second surface layer comprises, by weight, 0.03 parts silica, 0.03 parts erucamide, and 99.96 parts L-PLLA with 98% optical purity.

[0068] The difference between the preparation method and Example 1 is that the film was not subjected to ultraviolet light treatment.

[0069] Comparative Example 2

[0070] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer comprises, by weight, 0.03 parts silica, 0.03 parts erucamide, and 99.96 parts L-PLLA with 98% optical purity. The core layer comprises, by weight, 0.05 parts 1-hydroxycyclohexylbenzophenone (184) and 99.95 parts L-PLLA with 98% optical purity. The second surface layer comprises, by weight, 0.03 parts silica, 0.03 parts erucamide, and 99.96 parts L-PLLA with 98% optical purity.

[0071] The preparation method is the same as in Example 1.

[0072] Comparative Example 3

[0073] A biaxially oriented polylactic acid (PLLA) functional film comprises a three-layer structure, consisting of a first surface layer, a core layer, and a second surface layer from top to bottom. The first surface layer comprises, by weight, 0.01 parts silica, 20 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 79.99 parts L-polylactic acid (PLLA) with 98% optical purity. The core layer comprises, by weight, 20 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 80 parts L-polylactic acid (PLLA) with 98% optical purity. The second surface layer comprises, by weight, 0.01 parts silica, 0.01 parts erucamide, 20 parts poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHX), and 79.98 parts L-polylactic acid (PLLA) with 98% optical purity.

[0074] The preparation method is the same as in Example 1, except that the film is not subjected to ultraviolet light treatment.

[0075] The films prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests. The test items and test standards are shown in Table 1, and the test evaluation results are shown in Table 2.

[0076] Table 1 Test Items

[0077]

[0078]

[0079] Table 2 Test Evaluation Results

[0080]

[0081] As can be seen from Examples 1-4 and Comparative Examples 1-3 in Table 1, the biaxially oriented polylactic acid functional films prepared in Examples 1-4 have the characteristics of good flexibility, high haze, and low gloss, and also have excellent antibacterial properties, meeting the requirements for household composting degradation.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A biaxially oriented polylactic acid functional film, characterized in that, From top to bottom, it comprises a first surface layer, a core layer, and a second surface layer; the first surface layer comprises, by weight, 0.01-10 parts of matting agent, 20-50 parts of polyhydroxyalkanoate, and 40-79.99 parts of polylactic acid; the core layer comprises, by weight, 0-0.5 parts of photoinitiator, 20-40 parts of polyhydroxyalkanoate, and 59.5-80 parts of polylactic acid; The second surface layer component comprises, by weight, 0.01-0.05 parts of an opening agent, 0.01-0.05 parts of a slip agent, 20-50 parts of polyhydroxy fatty acid ester, and 49.95-79.98 parts of polylactic acid; the polyhydroxy fatty acid ester is one or a combination of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the matting agent is silica with a particle size of 2.5-3.5 μm; the photoinitiator is 1-hydroxycyclohexylbenzophenone, 2-hydroxy-2-methyl-1-phenylpropanone, benzophenone, α,α ， - One or more combinations of benzoyl ketal.

2. The biaxially oriented polylactic acid functional film as described in claim 1, characterized in that, The opening agent is one or a combination of PMMA cross-linked particles, organosilicon cross-linked particles, talc, calcium carbonate, mica powder, and silica.

3. The biaxially oriented polylactic acid functional film as described in claim 1, characterized in that, The slip agent is one or a combination of several of the following: erucamide, oleamide, polyethylene wax, polypropylene wax, and ethylene bis-stearamide.

4. The biaxially oriented polylactic acid functional film as described in claim 1, characterized in that, The polylactic acid is one or a combination of L-polylactic acid, D-polylactic acid, and racemic polylactic acid.

5. The biaxially oriented polylactic acid functional film as described in claim 1, characterized in that, The total thickness of the polylactic acid functional film is 15-30 μm, and the thickness of the first and second surface layers is 1-5 μm.

6. A method for preparing a biaxially oriented polylactic acid functional film as described in any one of claims 1-5, characterized in that, The preparation steps include the following: (1) Mix the components of the first surface layer, core layer and second surface layer evenly in a high-speed mixer according to the mass fraction, extrude and granulate through a twin-screw extruder, dry the moisture and package to obtain the masterbatch of each layer; the extruder temperature is 110~170℃, the drying temperature is 60~80℃, and the particle moisture content is ≤500ppm. (2) The masterbatch of the first surface layer, core layer and second surface layer is fed by a feeder and melted through their respective extruders. After being uniformly discharged through the T-die, it is cooled on the cold roller to form an unstretched sheet. The extruder temperature is 110-205℃, the cold roller temperature is 25-40℃, and the thickness of the unstretched sheet is 120-400um. (3) Stretch the unstretched sheet under heating; the stretching temperature is 50-90℃, and the stretching ratio is 2.0*2.0-6.0*6.0; (4) The stretched film is heat-set to obtain a polylactic acid functional film with a thickness of 15-30 μm; the heat-setting temperature is 90-120℃ and the setting time is 4-60s.

7. The preparation method according to claim 6, characterized in that, It also includes ultraviolet light treatment of biaxially oriented polylactic acid functional films.

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