A highly shrinkable and degradable composite film and its preparation method

Abstract

The present invention belongs to the technical field of thin film packaging, and particularly relates to a highly shrinkable and biodegradable composite film and a preparation method thereof. The film layer structure of the highly shrinkable and biodegradable composite film sequentially includes a first heat-sealing layer, a first barrier layer, a core layer, a second barrier layer, and a second heat-sealing layer from top to bottom; the first heat-sealing layer and the second heat-sealing layer are polylactic acid film layers; the components of the first barrier layer and the second barrier layer include polyhydroxyalkanoates, toughening agents, nano-active oxides, plasticizers, and antistatic agents; the components of the core layer include poly-L-lactic acid, amorphous oligomers, and nano-active oxides. The composite film has biodegradability, excellent and stable heat-sealing performance, and excellent barrier performance. At the same time, the thermal shrinkage rates in the longitudinal and transverse directions of the composite film can be controlled, solving the problems of poor barrier performance and uncontrollable longitudinal and transverse shrinkage rates of existing ordinary biaxially oriented polylactic acid films.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film packaging, and particularly relates to a high-shrinkage degradable composite film and a preparation method thereof. Background Art

[0002] Cigarettes are both a popular consumer product and a high-end commodity. As the outermost packaging of cigarettes, cigarette films play a more prominent role in brand positioning. In addition to meeting the storage protection needs of cigarettes, special attention is paid to their market image effects. Therefore, on the basis of meeting the mechanical properties, stiffness, slipperiness and other properties, cigarette biaxially oriented polypropylene (BOPP) films are required to have lower haze, higher gloss, higher shrinkage rate and other high requirements. With the increasingly severe environmental protection situation, it is an inevitable trend in the future to adopt more new environmentally friendly films to replace traditional BOPP cigarette films.

[0003] Polylactic acid (PLA) is one of the more mature degradable plastics in research and application. Its raw materials come from renewable plant fibers, corn, agricultural by-products, etc., and it has good biodegradability. PLA has excellent mechanical properties, similar to polypropylene plastics, and can replace PP and PET plastics in some fields to alleviate the increasingly severe "white pollution" problem.

[0004] Biaxially oriented polylactic acid (BOPLA) film has excellent characteristics such as high transparency, high gloss, easy printing, heat sealability, and coatability, and is suitable for food packaging, fresh food packaging, paper-plastic composite packaging, consumer electronics packaging, tapes, labels and other fields, and is an ideal green packaging material. However, for the demanding cigarette film packaging field, the existing biaxially oriented polylactic acid (BOPLA) films have performance defects such as poor water barrier performance and uncontrollable longitudinal and transverse heat shrinkage, and it is difficult to meet the requirements of the cigarette film packaging field. Summary of the Invention

[0005] In order to solve the deficiencies of the prior art mentioned in the above background art, the present invention provides a high-shrinkage degradable composite film, and its technical solution is as follows:

[0006] The high-shrinkage degradable composite film has a film layer structure that sequentially includes a first heat-sealing layer, a first barrier layer, a core layer, a second barrier layer, and a second heat-sealing layer from top to bottom; the first heat-sealing layer and the second heat-sealing layer are polylactic acid film layers; the components of the first barrier layer and the second barrier layer include polyhydroxyalkanoates, toughening agents, nano-active oxides, plasticizers, and antistatic agents; the components of the core layer include L-polylactic acid, amorphous oligomers, and nano-active oxides.

[0007] In one embodiment, by weight, the components of the first heat-sealing layer and the second heat-sealing layer include 99.9 to 99.98 parts of a polylactic acid copolymer, 0.01 to 0.05 parts of an antiblocking agent, and 0.01 to 0.05 parts of a slip agent; the components of the first barrier layer and the second barrier layer include 69.4 to 89.35 parts of a polyhydroxyalkanoate, 10 to 25 parts of a toughening agent, 0.5 to 1.5 parts of a nano-active oxide, 0.1 to 1 part of a plasticizer, and 0.05 to 0.1 part of an antistatic agent; the components of the core layer include 83.5 to 89.5 parts of L-polylactic acid, 10 to 15 parts of an amorphous oligomer, and 0.5 to 1.5 parts of a nano-active oxide.

[0008] In one embodiment, it is a five-layer co-extruded biaxially oriented composite film composed of a first heat-sealing layer, a first barrier layer, a core layer, a second barrier layer, and a second heat-sealing layer from top to bottom in sequence.

[0009] In one embodiment, the polyhydroxyalkanoate is one or a combination of more than one of poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0010] In one embodiment, the toughening agent is one or a combination of more than one of polybutylene succinate, polybutylene succinate / adipate copolymer, and polycaprolactone; the nano-active oxide is one or a combination of more than one of nano-active magnesium oxide, nano-active aluminum oxide, and nano-active zinc oxide.

[0011] In one embodiment, the plasticizer is one or a combination of more than one of polyethylene glycol, glycerol, neopentyl glycol, and mannitol; the antistatic agent is one or a combination of more than one of stearate, alkyl phosphate, and alkyl sulfate.

[0012] In one embodiment, the amorphous oligomer is one or a combination of more than one of racemic polylactic acid, polybutylene terephthalate / adipate copolymer, and carbon dioxide-propylene oxide copolymer.

[0013] In one embodiment, the number-average molecular weight Mn of the amorphous oligomer is 500 to 150,000.

[0014] In one embodiment, the total thickness of the film layers of the degradable composite film is 15 μm to 35 μm, the thicknesses of the first heat-sealing layer and the second heat-sealing layer are 1 μm to 3 μm respectively, and the thicknesses of the first barrier layer and the second barrier layer are 2 μm to 5 μm respectively.

[0015] The present invention also provides a preparation method of the high-shrinkage degradable composite film as described above, which includes the following steps:

[0016] S100. According to the formula ratio, put the components in the first heat-sealing layer and the second heat-sealing layer into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first heat-sealing layer and the masterbatch for the second heat-sealing layer;

[0017] S200. According to the formula ratio, put the components in the first barrier layer and the second barrier layer into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first barrier layer and the masterbatch for the second barrier layer;

[0018] S300. According to the formula ratio, put the components in the core layer into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the core layer;

[0019] S400. Respectively put the masterbatch for the first heat-sealing layer, the masterbatch for the first barrier layer, the masterbatch for the core layer, the masterbatch for the second barrier layer, and the masterbatch for the second heat-sealing layer into different extruders for melting, extrusion, and converging at the same T-die head, and the melt flows out of the die head; wherein, the melting temperatures of the extruder for the first heat-sealing layer, the extruder for the second heat-sealing layer, the extruder for the first barrier layer, and the extruder for the second barrier layer are 165°C to 200°C, and the melting temperature of the extruder for the core layer and the temperature of the T-die head are 165°C to 220°C;

[0020] S500. Adopt the step-by-step stretching method to rapidly cool and cast the melt flowing out of each film layer, and then perform biaxial stretching treatment to obtain a high-shrinkage degradable composite film.

[0021] Based on the above, compared with the prior art, the high-shrinkage degradable composite film provided by the present invention has the following beneficial effects:

[0022] The high-shrinkage degradable composite film provided by the present invention has biodegradability, excellent and stable heat-sealing performance, and excellent barrier performance. At the same time, the thermal shrinkage rates in the longitudinal direction (MD) and the transverse direction (TD) of the composite film can be controlled, solving the problems of poor barrier performance and uncontrollable longitudinal and transverse shrinkage rates of the existing ordinary biaxially stretched polylactic acid film.

[0023] Other features and beneficial effects of the present invention will be described in the subsequent specification, and part of them will become obvious from the specification or be understood by implementing the present invention. The objectives and other beneficial effects of the present invention can be achieved and obtained through the structures specifically pointed out in the specification, claims, and drawings. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings; in the following description of the positional relationship of the accompanying drawings, unless otherwise specified, the directions shown by the components in the drawings are used as the reference.

[0025] Figure 1 It is a schematic diagram of the film layer structure of the high-shrinkage degradable composite film in Embodiment 1 provided by the present invention.

[0026] Reference numerals: 10 - first heat-sealing layer, 20 - first barrier layer, 30 - core layer, 40 - second barrier layer, 50 - second heat-sealing layer. Detailed implementation manners

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention; the technical features designed in different implementation manners of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0028] In the description of the present invention, it should be noted that all terms (including technical terms and scientific terms) used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the technical field to which the present invention belongs, and should not be construed as a limitation to the present invention; it should be further understood that the terms used in the present invention should be understood as having meanings consistent with their meanings in the context of this specification and the relevant technical fields, and should not be understood in an idealized or overly formal sense, unless clearly defined as such in the present invention.

[0029] The present invention provides a high-shrinkage degradable composite film, and its solution is as follows:

[0030] The film layer structure of the high-shrinkage degradable composite film sequentially includes a first heat-sealing layer 10, a first barrier layer 20, a core layer 30, a second barrier layer 40, and a second heat-sealing layer 50 from top to bottom; the first heat-sealing layer 10 and the second heat-sealing layer 50 are polylactic acid film layers; the components of the first barrier layer 20 and the second barrier layer 40 include polyhydroxyalkanoates, toughening agents, nano-active oxides, plasticizers, and antistatic agents; the components of the core layer 30 include poly-L-lactic acid, amorphous oligomers, and nano-active oxides.

[0031] Among them, preferably, by weight parts, the components of the first heat-sealing layer 10 and the second heat-sealing layer 50 include 99.9 to 99.98 parts of polylactic acid copolymer, 0.01 to 0.05 parts of an antiblocking agent, and 0.01 to 0.05 parts of a slip agent; the components of the first barrier layer 20 and the second barrier layer 40 include 69.4 to 89.35 parts of polyhydroxyalkanoate, 10 to 25 parts of a toughening agent, 0.5 to 1.5 parts of a nano-active oxide, 0.1 to 1 part of a plasticizer, and 0.05 to 0.1 part of an antistatic agent; the components of the core layer 30 include 83.5 to 89.5 parts of L-polylactic acid, 10 to 15 parts of an amorphous oligomer, and 0.5 to 1.5 parts of a nano-active oxide.

[0032] For the film layer size: the total thickness of the degradable composite film layer is 15 μm to 35 μm, and the thicknesses of the first heat-sealing layer 10 and the second heat-sealing layer 50 are 1 μm to 3 μm respectively, and the thicknesses of the first barrier layer 20 and the second barrier layer 40 are 2 μm to 5 μm respectively.

[0033] Specifically, the present invention also provides a method for preparing the high-shrinkage degradable composite film, and the steps are as follows:

[0034] Step 1: According to the formula ratio, put the components in the first heat-sealing layer 10 and the second heat-sealing layer 50 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first heat-sealing layer 10 and the masterbatch for the second heat-sealing layer 50;

[0035] Step 2: According to the formula ratio, put the components in the first barrier layer 20 and the second barrier layer 40 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first barrier layer 20 and the masterbatch for the second barrier layer 40;

[0036] Step 3: According to the formula ratio, put the components in the core layer 30 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the core layer 30;

[0037] Step 4: Melt and extrude the masterbatch for the first heat-sealing layer 10, the masterbatch for the first barrier layer 20, the masterbatch for the core layer 30, the masterbatch for the second barrier layer 40, and the masterbatch for the second heat-sealing layer 50 from different extruders and converge them at the same T-die head, and the melt flows out of the die head; among them, the melting temperatures of the extruder for the first heat-sealing layer 10, the extruder for the second heat-sealing layer 50, the extruder for the first barrier layer 20, and the extruder for the second barrier layer 40 are 165°C to 200°C, and the melting temperature of the extruder for the core layer 30 and the temperature of the T-die head are 165°C to 220°C;

[0038] Specifically, the masterbatch for the first heat-sealing layer 10 and the masterbatch for the second heat-sealing layer 50 are respectively fed into the extruder for the first heat-sealing layer 10 and the extruder for the second heat-sealing layer 50 to produce the first heat-sealing layer 10 and the second heat-sealing layer 50; the masterbatch for the first barrier layer 20 and the masterbatch for the second barrier layer 40 are respectively fed into the extruder for the first barrier layer 20 and the extruder for the second barrier layer 40 to produce the first barrier layer 20 and the second barrier layer 40; the masterbatch for the core layer 30 is fed into the extruder for the core layer 30 to produce the core layer 30;

[0039] Step 5: Adopt the step-by-step stretching method to rapidly cool and cast the melt flowing out of each film layer, and then perform biaxial stretching treatment to obtain a high-shrinkage degradable composite film. Among them, the longitudinal stretching temperature is 70°C to 85°C, the transverse stretching temperature is 95°C to 115°C, the setting temperature is 110°C to 130°C, and the stretching ratio is (3.0×3.0) to (3.8×3.8).

[0040] The present invention also provides the following examples and comparative examples:

[0041] Example 1

[0042] The film layer structure of the high-shrinkage degradable composite film is as Figure 1 shown, which includes a 5-layer structure, from top to bottom in sequence are the first heat-sealing layer 10, the first barrier layer 20, the core layer 30, the second barrier layer 40, and the second heat-sealing layer 50;

[0043] The film layer size is:

[0044] The total thickness of the film layers of the degradable composite film is 21 μm, the thicknesses of the first heat-sealing layer 10 and the second heat-sealing layer 50 are respectively 2 μm, and the thicknesses of the first barrier layer 20 and the second barrier layer 40 are respectively 3 μm.

[0045] The raw material component formulations of each film layer are:

[0046] The components of the first heat-sealing layer 10 and the second heat-sealing layer 50 include 99.96 parts of PLLA-CO-PDLA polylactic acid copolymer, 0.02 parts of silicon dioxide, and 0.02 parts of erucic acid amide;

[0047] The components of the first barrier layer 20 and the second barrier layer 40 include 83.42 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 15 parts of polycaprolactone, 1 part of nano-active magnesium oxide, 0.5 part of polyglycerol, and 0.08 part of alkyl sulfate;

[0048] The components of the core layer 30 include 87 parts of L-polylactic acid, 12 parts of carbon dioxide-propylene oxide copolymer, and 1 part of nano-active magnesium oxide. Among them, the number-average molecular weight Mn of the carbon dioxide-propylene oxide copolymer is 15000.

[0049] The preparation method of the high-shrinkage degradable composite film comprises the following steps:

[0050] Step 1: According to the formula ratio, put the components in the first heat-sealing layer 10 and the second heat-sealing layer 50 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first heat-sealing layer 10 and the masterbatch for the second heat-sealing layer 50; the melt extrusion temperature is 170°C.

[0051] Step 2: According to the formula ratio, put the components in the first barrier layer 20 and the second barrier layer 40 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first barrier layer 20 and the masterbatch for the second barrier layer 40; the melt extrusion temperature is 170°C.

[0052] Step 3: According to the formula ratio, put the components in the core layer 30 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the core layer 30; the melt extrusion temperature is 170°C.

[0053] Step 4: Melt and extrude the masterbatch for the first heat-sealing layer 10, the masterbatch for the first barrier layer 20, the masterbatch for the core layer 30, the masterbatch for the second barrier layer 40, and the masterbatch for the second heat-sealing layer 50 respectively from different extruders, and converge the extruded melts at the same T-die head, and the melt flows out of the die head; among them, the melting temperatures of the extruder for the first heat-sealing layer 10, the extruder for the second heat-sealing layer 50, the extruder for the first barrier layer 20, and the extruder for the second barrier layer 40 are 185°C, and the melting temperature of the extruder for the core layer 30 and the temperature of the T-die head are 205°C;

[0054] Step 5: Adopt the step-by-step stretching method to quickly cool and cast the melt flowing out of each film layer, the cooling temperature is 35°C, and then carry out biaxial stretching treatment to obtain the high-shrinkage degradable composite film. Among them, the longitudinal stretching temperature is 80°C, the transverse stretching temperature is 95°C, the setting temperature is 120°C, and the stretching ratio is 3.1×3.3.

[0055] Example 2

[0056] The film layer structure of the high-shrinkage degradable composite film: it includes a 5-layer structure, which are, from top to bottom, the first heat-sealing layer 10, the first barrier layer 20, the core layer 30, the second barrier layer 40, and the second heat-sealing layer 50;

[0057] The film layer size is:

[0058] The total thickness of the film layer of the degradable composite film is 21μm, the thicknesses of the first heat-sealing layer 10 and the second heat-sealing layer 50 are 2μm respectively, and the thicknesses of the first barrier layer 20 and the second barrier layer 40 are 3μm respectively.

[0059] The raw material component formula of each film layer is:

[0060] The components of the first heat-sealing layer 10 and the second heat-sealing layer 50 include 99.9 parts of PLLA-CO-PDLA polylactic acid copolymer, 0.05 parts of silica, and 0.05 parts of erucic acid amide;

[0061] The components of the first barrier layer 20 and the second barrier layer 40 include 69.4 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 25 parts of polycaprolactone, 1.5 parts of nano-active magnesium oxide, 1 part of polyglycerol, and 0.1 part of alkyl sulfate;

[0062] The components of the core layer 30 include 83.5-89.5 parts of L-polylactic acid, 15 parts of carbon dioxide-propylene oxide copolymer, and 1.5 parts of nano-active magnesium oxide. Among them, the number-average molecular weight Mn of the carbon dioxide-propylene oxide copolymer is 50000.

[0063] The preparation method of the high-shrinkage degradable composite film includes the following steps:

[0064] Step 1: According to the formula ratio, put the components in the first heat-sealing layer 10 and the second heat-sealing layer 50 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first heat-sealing layer 10 and the masterbatch for the second heat-sealing layer 50; the melt extrusion temperature is 170 °C.

[0065] Step 2: According to the formula ratio, put the components in the first barrier layer 20 and the second barrier layer 40 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first barrier layer 20 and the masterbatch for the second barrier layer 40; the melt extrusion temperature is 170 °C.

[0066] Step 3: According to the formula ratio, put the components in the core layer 30 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the core layer 30; the melt extrusion temperature is 170 °C.

[0067] Step 4: Melt and extrude the masterbatch for the first heat-sealing layer 10, the masterbatch for the first barrier layer 20, the masterbatch for the core layer 30, the masterbatch for the second barrier layer 40, and the masterbatch for the second heat-sealing layer 50 from different extruders and converge them at the same T-die head, and the melt flows out of the die head; among them, the melting temperatures of the extruder for the first heat-sealing layer 10, the extruder for the second heat-sealing layer 50, the extruder for the first barrier layer 20, and the extruder for the second barrier layer 40 are 185 °C, and the melting temperature of the extruder for the core layer 30 and the temperature of the T-die head are 205 °C;

[0068] Step 5: Adopt the step-by-step stretching method to rapidly cool and cast the melt flowing out of each film layer, the cooling temperature is 35 °C, and then carry out biaxial stretching treatment to obtain the high-shrinkage degradable composite film. Among them, the longitudinal stretching temperature is 80 °C, the transverse stretching temperature is 95 °C, the setting temperature is 120 °C, and the stretching ratio is 3.1×3.3.

[0069] Example 3

[0070] The film layer structure of the highly shrinkable degradable composite film: It includes a 5-layer structure, which are, from top to bottom, the first heat-sealing layer 10, the first barrier layer 20, the core layer 30, the second barrier layer 40, and the second heat-sealing layer 50;

[0071] The film layer size is:

[0072] The total thickness of the film layer of the degradable composite film is 21 μm. The thicknesses of the first heat-sealing layer 10 and the second heat-sealing layer 50 are 2 μm respectively, and the thicknesses of the first barrier layer 20 and the second barrier layer 40 are 3 μm respectively.

[0073] The raw material component formulations of each film layer are:

[0074] The components of the first heat-sealing layer 10 and the second heat-sealing layer 50 include 99.98 parts of PLLA~CO~PDLA polylactic acid copolymer, 0.01 part of acrylic acid, and 0.01 part of ethylene bisstearamide;

[0075] The components of the first barrier layer 20 and the second barrier layer 40 include 89.35 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 10 parts of polycaprolactone, 0.5 part of nano-active magnesium oxide, 0.1 part of polyglycerol, and 0.05 part of alkyl sulfate;

[0076] The components of the core layer 30 include 89.5 parts of L-polylactic acid, 10 parts of carbon dioxide-propylene oxide copolymer, and 0.5 part of nano-active magnesium oxide. Among them, the number-average molecular weight Mn of the carbon dioxide-propylene oxide copolymer is 1000.

[0077] The preparation method of the highly shrinkable degradable composite film includes the following steps:

[0078] Step 1: According to the formula ratio, put the components in the first heat-sealing layer 10 and the second heat-sealing layer 50 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first heat-sealing layer 10 and the masterbatch for the second heat-sealing layer 50; the melt extrusion temperature is 170 °C.

[0079] Step 2: According to the formula ratio, put the components in the first barrier layer 20 and the second barrier layer 40 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first barrier layer 20 and the masterbatch for the second barrier layer 40; the melt extrusion temperature is 170 °C.

[0080] Step 3: According to the formula ratio, put the components in the core layer 30 into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the core layer 30; the melt extrusion temperature is 170 °C.

[0081] Step 4: Melt and extrude the masterbatch for the first heat-sealing layer 10, the masterbatch for the first barrier layer 20, the masterbatch for the core layer 30, the masterbatch for the second barrier layer 40, and the masterbatch for the second heat-sealing layer 50 respectively from different extruders, and then converge and flow out the melt from the same T-die. Among them, the melting temperature of the extruder for the first heat-sealing layer 10, the extruder for the second heat-sealing layer 50, the extruder for the first barrier layer 20, and the extruder for the second barrier layer 40 is 185°C, and the melting temperature of the extruder for the core layer 30 and the temperature of the T-die are 205°C;

[0082] Step 5: Adopt the step-by-step stretching method to rapidly cool and cast the melt flowing out of each film layer, and then perform biaxial stretching treatment to obtain a high-shrinkage degradable composite film. Among them, the longitudinal stretching temperature is 35°C, the transverse stretching temperature is 80°C, the setting temperature is 95°C, and the stretching ratio is 3.1×3.3.

[0083] Example 4

[0084] The film layer structure of the high-shrinkage degradable composite film: It includes a 5-layer structure, which are, from top to bottom, the first heat-sealing layer 10, the first barrier layer 20, the core layer 30, the second barrier layer 40, and the second heat-sealing layer 50;

[0085] The film layer size is:

[0086] The total thickness of the film layer of the degradable composite film is 21μm, the thicknesses of the first heat-sealing layer 10 and the second heat-sealing layer 50 are 2μm respectively, and the thicknesses of the first barrier layer 20 and the second barrier layer 40 are 3μm respectively.

[0087] The raw material component formulations of each film layer are:

[0088] The components of the first heat-sealing layer 10 and the second heat-sealing layer 50 include 99.96 parts of PLLA-CO-PDLA polylactic acid copolymer, 0.02 parts of silica, and 0.02 parts of erucic acid amide;

[0089] The components of the first barrier layer 20 and the second barrier layer 40 include 83.42 parts of poly-3-hydroxybutyrate, 15 parts of poly(butylene succinate / adipate) copolymer, 1 part of nano-active zinc oxide, 0.5 part of polyethylene glycol, and 0.08 part of stearate;

[0090] The components of the core layer 30 include 87 parts of L-polylactic acid, 12 parts of meso-polylactic acid, and 1 part of nano-active zinc oxide. Among them, the number-average molecular weight Mn of meso-polylactic acid is 15,000.

[0091] The preparation method of the high-shrinkage degradable composite film includes the following steps:

[0092] Step 1. According to the formulation ratio, put the components in the first heat-sealing layer 10 and the second heat-sealing layer 50 into a twin-screw extruder for melt blending and extrusion to obtain masterbatches for the first heat-sealing layer 10 and the second heat-sealing layer 50; the melt extrusion temperature is 170°C.

[0093] Step 2. According to the formulation ratio, put the components in the first barrier layer 20 and the second barrier layer 40 into a twin-screw extruder for melt blending and extrusion to obtain masterbatches for the first barrier layer 20 and the second barrier layer 40; the melt extrusion temperature is 170°C.

[0094] Step 3. According to the formulation ratio, put the components in the core layer 30 into a twin-screw extruder for melt blending and extrusion to obtain a masterbatch for the core layer 30; the melt extrusion temperature is 170°C.

[0095] Step 4. Melt and extrude the masterbatch for the first heat-sealing layer 10, the masterbatch for the first barrier layer 20, the masterbatch for the core layer 30, the masterbatch for the second barrier layer 40, and the masterbatch for the second heat-sealing layer 50 respectively from different extruders and converge the extruded melts at the same T-die head, and the melt flows out of the die head; among them, the melting temperatures of the extruder for the first heat-sealing layer 10, the extruder for the second heat-sealing layer 50, the extruder for the first barrier layer 20, and the extruder for the second barrier layer 40 are 185°C, and the melting temperature of the extruder for the core layer 30 and the temperature of the T-die head are 205°C;

[0096] Step 5. Adopt the step-by-step stretching method to rapidly cool and cast the melts flowing out of each film layer, the cooling temperature is 35°C, and then conduct biaxial stretching treatment to obtain a high-shrinkage degradable composite film. Among them, the longitudinal stretching temperature is 80°C, the transverse stretching temperature is 95°C, the setting temperature is 120°C, and the stretching ratio is 3.1×3.3.

[0097] Comparative Example 1

[0098] Compared with Example 1, the difference of this comparative example is that the components of the first heat-sealing layer 10 and the second heat-sealing layer 50 include 99.96 parts of L-lactic acid, 0.02 parts of silicon dioxide, and 0.02 parts of erucic acid amide; the components of the first barrier layer 20 and the second barrier layer 40 include 100 parts of L-lactic acid.

[0099] Except for the above differences, the raw material component ratios, raw material component types, and preparation processes of each film layer in this comparative example are the same as those in Example 1.

[0100] Comparative Example 2

[0101] Compared with Example 1, the difference of this comparative example is that the components of its first barrier layer 20 and the second barrier layer 40 include 83.42 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 1 part of nano-active magnesium oxide, 0.5 part of polyglycerol, and 0.08 part of alkyl sulfate.

[0102] Except for the above differences, the raw material component ratios, types of raw material components, and preparation processes of each film layer in this comparative example are the same as those in Example 1.

[0103] Comparative Example 3

[0104] Compared with Example 1, the difference in this comparative example is that the components of its core layer 30 include 87 parts of L-polylactic acid and 1 part of nano-active magnesium oxide.

[0105] Except for the above differences, the raw material component ratios, types of raw material components, and preparation processes of each film layer in this comparative example are the same as those in Example 1.

[0106] Comparative Example 4

[0107] Compared with Example 1, the difference in this comparative example is that the components of its first barrier layer 20 and second barrier layer 40 include 83.42 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 15 parts of polycaprolactone, 0.5 part of polyglycerol, and 0.08 part of alkyl sulfate; the components of its core layer 30 include 87 parts of L-polylactic acid and 12 parts of carbon dioxide-propylene oxide copolymer.

[0108] Except for the above differences, the raw material component ratios, types of raw material components, and preparation processes of each film layer in this comparative example are the same as those in Example 1.

[0109] The films prepared in the examples and comparative examples were subjected to performance tests. The test items and test standards are shown in Table 1, and the test results are shown in Table 2:

[0110] Table 1 Test Items

[0111]

[0112] Table 2 Test Results

[0113]

[0114] It can be concluded from the test results in Table 1 that:

[0115] Comparative Example 1 is an existing heat-sealable biaxially oriented polylactic acid film, which does not have a first barrier layer 20 and a second barrier layer 40. Compared with the example, its water and oxygen barrier properties become worse, its mechanical strength becomes worse, its heat-sealing performance becomes worse, and the longitudinal and transverse heat shrinkage differences become larger.

[0116] Compared with the example, in Comparative Example 2, the first barrier layer 20 and the second barrier layer 40 do not add the toughening agent polycaprolactone, and its water and oxygen barrier properties become worse, and its mechanical strength becomes worse.

[0117] Compared with the examples, the core layer 30 in Comparative Example 3 did not add the amorphous oligomer carbon dioxide - propylene oxide copolymer, resulting in worse water and oxygen barrier properties, worse mechanical strength, and a larger difference in thermal shrinkage between the longitudinal and transverse directions.

[0118] Compared with the examples, the first barrier layer 20, the second barrier layer 40, and the core layer 30 in Comparative Example 4 did not add the nano - active oxide nano - active magnesium oxide, resulting in worse water and oxygen barrier properties, worse mechanical strength, and a larger difference in thermal shrinkage between the longitudinal and transverse directions.

[0119] In summary, the high - shrinkage degradable composite film provided by the embodiments of the present invention has a high thermal shrinkage rate, a small difference in thermal shrinkage between the longitudinal and transverse directions, a greatly improved water and oxygen barrier property, high mechanical strength, a low haze, and good optical properties, and is suitable for cigarette film packaging.

[0120] Based on the above, the high - shrinkage degradable composite film provided by the present invention has at least the following principle of action, mechanism, and technical effects:

[0121] 1. The high - shrinkage degradable composite film of the present invention has stable heat - sealing performance. By introducing amorphous oligomers, the thermal shrinkage rates in the longitudinal (TD) and transverse (MD) directions are high, and the difference in shrinkage rates between the longitudinal and transverse directions is small, which can meet the requirements of high thermal shrinkage rate for cigarette films.

[0122] 2. The first barrier layer 20 and the second barrier layer 40 in the high - shrinkage degradable composite film of the present invention have excellent barrier properties, solving the problem of poor barrier properties of pure biaxially oriented polylactic acid films (BOPLA).

[0123] 3. By introducing nano - active particles (i.e., nano - active oxides) in the present invention, the nano - active particles added in the first barrier layer 20 and the second barrier layer 40 can react with hydroxyl or carboxyl groups to reduce the migration of small molecules and improve the barrier properties of the film; the nano - active particles added in the core layer 30 improve the dimensional stability of the film, and the introduced nano - active particles do not affect the optical properties of the film.

[0124] 4. The high - shrinkage degradable composite film of the present invention uses polylactic acid as the matrix, which has biodegradability.

[0125] In summary, the high - shrinkage degradable composite film provided by the present invention has biodegradability, excellent and stable heat - sealing performance, and excellent barrier properties. At the same time, the thermal shrinkage rates in the longitudinal (MD) and transverse (TD) directions of the composite film can be controlled, solving the problems of poor barrier properties and uncontrollable longitudinal and transverse shrinkage rates of existing ordinary biaxially oriented polylactic acid films.

[0126] It should be noted that:

[0127] In addition to the actual selections demonstrated in the above specific embodiments, the polyhydroxyalkanoate may preferably be one or more combinations of poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), including but not limited to the actual selections demonstrated in the above embodiments;

[0128] In addition to the actual selections demonstrated in the above specific embodiments, the toughener may preferably be one or more combinations of polybutylene succinate, poly(butylene succinate-co-butylene adipate) copolymer, polycaprolactone, including but not limited to the actual selections demonstrated in the above embodiments;

[0129] In addition to the actual selections demonstrated in the above specific embodiments, the nano-active oxide may preferably be one or more combinations of nano-active magnesium oxide, nano-active aluminum oxide, nano-active zinc oxide, including but not limited to the actual selections demonstrated in the above embodiments;

[0130] In addition to the actual selections demonstrated in the above specific embodiments, the plasticizer may preferably be one or more combinations of polyethylene glycol, glycerol, neopentyl glycol, mannitol, including but not limited to the actual selections demonstrated in the above embodiments;

[0131] In addition to the actual selections demonstrated in the above specific embodiments, the antistatic agent may preferably be one or more combinations of stearate, alkyl phosphate, alkyl sulfate, including but not limited to the actual selections demonstrated in the above embodiments;

[0132] In addition to the actual selections demonstrated in the above specific embodiments, the amorphous oligomer may preferably be one or more combinations of racemic polylactic acid, poly(butylene terephthalate-co-butylene adipate) (PBAT), carbon dioxide-propylene oxide copolymer. Among them, the number-average molecular weight Mn of the amorphous oligomer is preferably feasible within the range of 500 to 150,000, including but not limited to the actual selections demonstrated in the above embodiments;

[0133] In addition to the actual selections demonstrated in the above specific embodiments, the antiblocking agent and slip agent may be selected from commercially available antiblocking agents and slip agents, including but not limited to the actual selections demonstrated in the above embodiments.

[0134] It should be noted that the specific parameters or some common reagents or raw materials in the above embodiments are specific embodiments or preferred embodiments under the concept of the present invention, rather than limitations thereto; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention.

[0135] In addition, unless otherwise specified, the raw materials used may also be conventional commercially available products in the art or prepared by conventional methods in the art.

[0136] In addition, those skilled in the art should understand that although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, and it is not necessary to solve all the technical problems listed in the prior art or the background art at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be regarded as a limitation to that claim.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements 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 high-shrinkage degradable composite film, characterized in that: It is a five-layer co-extruded biaxially oriented composite film composed of a first heat-sealing layer, a first barrier layer, a core layer, a second barrier layer, and a second heat-sealing layer from top to bottom in sequence; The total thickness of the film layers of the degradable composite film is 15 μm to 35 μm, the thicknesses of the first heat-sealing layer and the second heat-sealing layer are 1 μm to 3 μm respectively, and the thicknesses of the first barrier layer and the second barrier layer are 2 μm to 5 μm respectively; The first heat-sealing layer and the second heat-sealing layer are polylactic acid film layers; The components of the first barrier layer and the second barrier layer include polyhydroxyalkanoates, toughening agents, nano-active oxides, plasticizers, and antistatic agents; The components of the core layer include L-polylactic acid, amorphous oligomers, and nano-active oxides; Among them, by weight, the components of the first heat-sealing layer and the second heat-sealing layer include 99.9 to 99.98 parts of polylactic acid copolymer, 0.01 to 0.05 parts of antiblocking agent, and 0.01 to 0.05 parts of slip agent; The components of the first barrier layer and the second barrier layer include 69.4 to 89.35 parts of polyhydroxyalkanoates, 10 to 25 parts of toughening agent, 0.5 to 1.5 parts of nano-active oxide, 0.1 to 1 part of plasticizer, and 0.05 to 0.1 part of antistatic agent; The components of the core layer include 83.5 to 89.5 parts of L-polylactic acid, 10 to 15 parts of amorphous oligomers, and 0.5 to 1.5 parts of nano-active oxide; The polyhydroxyalkanoates are one or more combinations of poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate); The toughening agents are one or more combinations of polybutylene succinate, poly(butylene succinate / adipate) copolymer, and polycaprolactone; The nano-active oxides are one or more combinations of nano-active magnesium oxide, nano-active aluminum oxide, and nano-active zinc oxide; the plasticizers are one or more combinations of polyethylene glycol, glycerol, neopentyl glycol, and mannitol; The antistatic agents are one or more combinations of stearate, alkyl phosphate, and alkyl sulfate; the amorphous oligomers are one or more combinations of racemic polylactic acid, poly(butylene terephthalate / adipate) copolymer, and carbon dioxide-propylene oxide copolymer.

2. The high-shrinkage degradable composite film according to claim 1, wherein: The number-average molecular weight Mn of the amorphous oligomers is 500 to 150,000.

3. A method for preparing a highly shrinkable degradable composite film according to any one of claims 1 to 2, characterized in that, It includes the following steps: S100. According to the formula ratio, put the components in the first heat-sealing layer and the second heat-sealing layer into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first heat-sealing layer and the masterbatch for the second heat-sealing layer; S200. According to the formula ratio, put the components in the first barrier layer and the second barrier layer into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the first barrier layer and the masterbatch for the second barrier layer; S300. According to the formula ratio, put the components in the core layer into a twin-screw extruder for melt blending and extrusion to obtain the masterbatch for the core layer; S400. Respectively feed the masterbatch for the first heat-sealing layer, the masterbatch for the first barrier layer, the masterbatch for the core layer, the masterbatch for the second barrier layer, and the masterbatch for the second heat-sealing layer into different extruders for melting, extrusion, and then converge them at the same T-die head, and the melt flows out of the die head. Among them, the melting temperature of the extruder for the first heat-sealing layer, the extruder for the second heat-sealing layer, the extruder for the first barrier layer, and the extruder for the second barrier layer is 165°C to 200°C, and the melting temperature of the extruder for the core layer and the temperature of the T-die head are 165°C to 220°C; S500. Adopt the step-by-step stretching method to rapidly cool and cast the melt flowing out of each film layer, and then conduct biaxial stretching treatment to obtain a high-shrinkage degradable composite film.

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