High-barrier composite packaging film and preparation process thereof

Abstract

The application discloses a high-barrier composite packaging film and a preparation process thereof, and belongs to the technical field of degradable composite materials. The composite film is composed of an outer layer, a core layer and an inner layer, and is characterized in that the core layer is a semi-aromatic carbon dioxide-based copolymer film, and the outer layer and the inner layer are modified PLA films; the semi-aromatic carbon dioxide-based copolymer film comprises 90-100 parts of semi-aromatic carbon dioxide-based copolymer and 0-10 parts of toughening agent in terms of weight composition; and the modified PLA film comprises 1-40 parts of polycarbonate-lactide copolymer and 60-99 parts of PLA in terms of weight composition. The modification of the PLA in the core layer is cancelled, the barrier property of the semi-aromatic carbon dioxide-based copolymer is ensured not to be damaged, and the barrier property of the composite packaging film is ensured.

Description

TECHNICAL FIELD

[0001] The application relates to a high-barrier composite packaging film and a preparation process thereof. BACKGROUND

[0002] Multilayer composite packaging films with high barrier properties are known for their excellent gas and water vapor barrier properties. This packaging material is composed of multiple layers of thin films with different properties, effectively preventing the penetration of external gas and moisture, providing excellent protection to ensure the freshness and quality of packaged goods. Its structure is complex, usually containing various functional film layers such as polyethylene (PE), polypropylene (PP), nylon (PA), EVOH (ethylene-vinyl alcohol copolymer), etc., each layer plays a specific role, such as providing mechanical strength, moisture resistance and gas barrier, etc. Through multilayer stacking and compounding, this packaging film not only maintains the integrity of the packaged goods, but also maximizes the shelf life. Multilayer composite packaging films with high barrier properties are widely used in food, medicine, cosmetics and other fields, and are particularly suitable for products that require gas and water vapor barrier properties.

[0003] In patent CN116021850A, a biodegradable cigarette packaging film with barrier properties is disclosed, which is composed of an outer layer, a core layer and an inner layer to form a composite film. The core layer is a semi-aromatic carbon dioxide-based copolymer film, and the outer layer and the inner layer are PLA films. In this patent, in order to make the semi-aromatic carbon dioxide-based copolymer film have better compatibility with the PLA film and form good mutual penetration, an appropriate amount of PLA material is added to modify the semi-aromatic carbon dioxide-based copolymer film. However, in the actual application process later, it was found that due to the addition of PLA material, penetration points would be formed in the core layer, resulting in a decrease in the barrier properties of the semi-aromatic carbon dioxide-based copolymer film in the core layer. For example, in Example 6 of the patent, although high-barrier PPCP modification was added to the PLA film of the outer layer and the inner layer, the barrier properties of the core layer were damaged, and the overall barrier properties of the material did not improve compared with other examples. This limits the application of the packaging film in some fields with higher barrier performance requirements. SUMMARY

[0004] The technical problem to be solved by the application is to overcome the shortcomings of the prior art and provide a high-barrier composite packaging film and a preparation process thereof.

[0005] The technical scheme adopted by the present application to solve its technical problems is: the high-barrier composite packaging film is composed of an outer layer, a core layer and an inner layer, the core layer is a semi-aromatic carbon dioxide-based copolymer film, and the outer layer and the inner layer are modified PLA films; the composition of the semi-aromatic carbon dioxide-based copolymer film includes 90-100 parts of semi-aromatic carbon dioxide-based copolymer and 0-10 parts of toughening agent; and the composition of the modified PLA film includes 1-70 parts of polycarbonate-lactide copolymer and 30-99 parts of PLA.

[0006] In the present application, the semi-aromatic carbon dioxide-based copolymer with high barrier performance is still used as the main material in the core layer, but the modification of PLA is cancelled to ensure that the barrier performance of the semi-aromatic carbon dioxide-based copolymer is not destroyed and the barrier performance of the composite packaging film is ensured. In order to solve the compatibility of each layer, the PLA film of the outer layer is modified by polycarbonate-lactide copolymer, which can not only improve the barrier performance of the PLA film, but also contains similar segments of semi-aromatic carbon dioxide-based copolymer and PLA material, and has good compatibility with both of them. After modification, good mutual penetration is formed between the layers to ensure the peel strength of the packaging film.

[0007] Preferably, the composition of the modified PLA film includes 1-40 parts of polycarbonate-lactide copolymer and 60-99 parts of PLA. Preferably, the components of the modified PLA film are mainly PLA, and the obtained composite packaging film has higher temperature resistance and strength.

[0008] Preferably, in the above high-barrier composite packaging film, the comonomer of the semi-aromatic carbon dioxide-based copolymer is alkylene oxide, carbon dioxide, aromatic anhydride and optional lactide, and the aromatic anhydride is phthalic anhydride or naphthalic anhydride. The semi-aromatic carbon dioxide-based copolymer itself is a degradable material, and the addition of aromatic anhydride not only improves the temperature resistance of the material, but also forms a planar effect to improve the barrier performance of the material.

[0009] Preferably, the high-barrier composite packaging film, the semi-aromatic carbon dioxide-based copolymer comprises randomly or block arranged polycarbonate segments, polyether segments, PE segments and optional polylactic acid segments, wherein the polycarbonate segments are copolymerization segments of an epoxy compound and carbon dioxide, the polyether segments are self-polymerization segments of an epoxy compound and / or copolymerization segments between epoxy compounds, the PE segments are copolymerization segments of an epoxy compound and a cyclic anhydride, and the polylactic acid segments are self-polymerization segments of lactide. The polycarbonate segments ensure good biodegradability of the material, the polyether segments maintain a certain toughness of the material, and the PE segments formed by the epoxy compound and the cyclic anhydride can ensure the barrier property of the material. If the semi-aromatic carbon dioxide-based copolymer contains a certain amount of polylactic acid segments, the core layer film has better dimensional stability, and the compatibility between the core layer and the inner and outer layers is improved, and the interlayer bonding strength is increased.

[0010] Preferably, the high-barrier composite packaging film, the semi-aromatic carbon dioxide-based copolymer is one or more of PPCP, PPCCP, PPCPLA and PECPLA. The semi-aromatic carbon dioxide-based copolymer has better strength and barrier property. More preferably, the semi-aromatic carbon dioxide-based copolymer is PPCPLA or / and PECPLA. PPCPLA and PECPLA not only have better transparency, strength and barrier property, but also contain polylactic acid segments in the molecular chain, which can make the core layer film have better dimensional stability, and improve the compatibility between the core layer and the inner and outer layers, and increase the interlayer bonding strength.

[0011] Preferably, the high-barrier composite packaging film, the toughening agent is one or more of PBAT, PCL, PBS and PECP. The toughening agent can enhance the toughness of the core layer and has little effect on the barrier property.

[0012] Preferably, the high-barrier composite packaging film, the comonomer of the polycarbonate-lactide copolymer is an alkylene oxide, carbon dioxide, lactide and optional aromatic anhydride, and the aromatic anhydride is phthalic anhydride or naphthalene anhydride. The polycarbonate-lactide copolymer has good biodegradability, and after adding lactide monomers, polylactic acid chain ends are formed to modify the PLA material, have better compatibility, and can better promote the interlayer bonding strength.

[0013] Preferably, the high-barrier composite packaging film, the polycarbonate lactide copolymer comprises polycarbonate segments, polylactic acid segments, optional PE segments and optional polyether segments arranged randomly or in blocks, wherein the polycarbonate segments are copolymerization segments of an epoxy compound and carbon dioxide, the polylactic acid segments are self-polymerization segments of lactide, the PE segments are copolymerization segments of an epoxy compound and a cyclic anhydride, and the polyether segments are self-polymerization segments and / or copolymerization segments of an epoxy compound. The polycarbonate segments ensure good biodegradability of the material, the polylactic acid segments can promote the compatibility of the material with PLA and promote the fusion of the layers during the forming process, thereby ensuring the interlayer bonding strength. When necessary, the polyether segments can be used to increase the toughness of the material, and the PE segments can be used to further improve the barrier property of the material.

[0014] Preferably, the high-barrier composite packaging film, the polycarbonate lactide copolymer is one or more of PECLA, PECPLA, PPCLA and PPCPLA. The preparation method of PECLA, PECPLA and PPCPLA can refer to CN116375989A, and the preparation process of PPCLA can also refer to the invention, and only the copolymerization monomer of PECLA is replaced by propylene oxide. Preferably, the polycarbonate lactide copolymer can be well miscible with the PLA material, the transparency of the material is high, the barrier properties of the inner and outer layers are improved, the compatibility of the modified PLA film with the core layer of the semi-aromatic carbon dioxide-based copolymer film is ensured, and the peel strength of the composite packaging film is improved.

[0015] A preparation process of the high-barrier composite packaging film, the process steps are as follows:

[0016] 1) Co-extrusion casting: the formulations of the layers are respectively placed in a double screw machine, plasticized and melted at high temperature, and then pressed through the nip between two rollers arranged horizontally and rotating relative to each other to form a sheet, thereby forming a composite film, and the composite film is wound to obtain the composite film;

[0017] 2) Biaxial stretching: the composite film is cut into a sheet, placed in a high-temperature double-line stretching machine, stretched in the longitudinal direction after preheating, and then stretched in the transverse direction after preheating, and then cooled and shaped; after the corona treatment, winding, aging and slitting, a biaxially stretched film is obtained.

[0018] The composite packaging film of the present application is first co-extrusion cast into a composite film by a modified PLA film and a semi-aromatic carbon dioxide-based copolymer film, and then biaxially stretched to form a composite film. The three-layer film is combined together at high strength after co-extrusion casting, and the composite film is biaxially stretched to the required thickness.

[0019] When the core layer adopts the main material of PPCPLA and PECPLA, the size shrinkage ratio of the inner layer and the outer layer to the core layer is closer, the layers of the film have better synchronous stretching ratio in the biaxial stretching process, the interlayer peeling does not occur in the forming process when the composite film is prepared by using the co-extrusion casting process, and the interlayer peeling strength of the composite packaging film is more easily ensured.

[0020] Preferably, in the preparation process of the high-barrier composite packaging film, in step 1) co-extrusion casting, the melting temperature of the double screw machine of the modified PLA film is 150-200 DEG C, the melting temperature of the double screw machine of the semi-aromatic carbon dioxide-based copolymer film is 150-180 DEG C, and the head co-extrusion temperature is 150-200 DEG C; in step 2) biaxial stretching, the longitudinal and transverse stretching ratios are both 2-6 times, the longitudinal and transverse stretching temperatures are both 50-100 DEG C, and the longitudinal and transverse stretching rates are both 20-80 mm / s. Preferably, the temperature setting of the double screw machine can make the softening state of each layer of the film reach a better combined state, so that the penetration between the layers of the film is not too much, and the bonding strength is ensured.

[0021] The thickness of the biaxial stretching film is preferably 20-30 microns.

[0022] Compared with the prior art, the high-barrier composite packaging film and the preparation process thereof have the following beneficial effects: the composite film of the application is a PLA film and a semi-aromatic carbon dioxide-based copolymer film, the glass transition temperature of the PLA film is relatively high, and the tensile strength is large, so that the temperature resistance and mechanical strength of the product are ensured, after the polycarbonate lactide copolymer is modified, the PLA film itself has good barrier properties, and has better compatibility with the semi-aromatic carbon dioxide-based copolymer film, can form good interlayer mutual penetration, and ensure the peeling strength of the packaging film. The semi-aromatic carbon dioxide-based copolymer film in the core layer has high barrier properties, the modification of the PLA is cancelled, the barrier properties of the semi-aromatic carbon dioxide-based copolymer are not destroyed, and the overall barrier properties of the composite packaging film are ensured. DETAILED DESCRIPTION

[0023] The application will be specifically described below by examples. The semi-aromatic carbon dioxide-based copolymer materials used in the examples are all self-made products, and other raw materials are commercially available. In order to facilitate the performance comparison between the examples, the thickness of the packaging film samples prepared in each example is controlled to be 21.5 microns, and other thicknesses do not affect the implementation of the application. In order to facilitate the performance comparison between the examples, no functional additives such as anti-blocking agent, antistatic agent, stiffening agent, and slip agent are added in each example, which can be added as appropriate in actual application in each field.

[0024] Example 1

[0025] Each layer is prepared by weight parts:

[0026] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the following weight parts: PPCPLA 98 parts, PEC 2 parts.

[0027] The modified PLA film is prepared according to the following weight parts: PEC PLA 10 parts, PLA 90 parts.

[0028] Preparation of the composite packaging film:

[0029] 1) Co-extrusion casting: the formulations of each layer are respectively placed in a double screw machine, and high temperature plasticization and melting are carried out through the nip between the two rollers which are relatively rotated and horizontally arranged, to press a sheet, wherein the melting temperature of the double screw machine for the modified PLA film of the inner and outer layers is set to 185°C, the melting temperature of the double screw machine for the semi-aromatic carbon dioxide-based copolymer film of the core layer is set to 170°C, and the co-extrusion temperature of the die head is 190°C; the composite film is prepared, and the composite film is obtained by winding.

[0030] 2) Biaxial stretching: the above composite film sheet is cut into a size of 10 cm x 10 cm, and is placed in a film high temperature double line stretching machine, and is preheated to 80°C, and then is stretched longitudinally by 4 times at a stretching rate of 50 mm / s, and is cooled and shaped; and then is preheated to 80°C, and is stretched transversely by 4 times at a stretching rate of 50 mm / s, and is cooled and shaped. After being treated by corona discharge, wound, aged, and slit, a biaxially stretched film with a thickness of 21.5 μm is prepared.

[0031] Example 2

[0032] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the following weight parts: PPCPLA 100 parts.

[0033] The modified PLA film is prepared according to the following weight parts: PEC LA 40 parts, PLA 60 parts.

[0034] The preparation process of the composite packaging film is the same as that in Example 1.

[0035] Example 3

[0036] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the following weight parts: PECPLA 95 parts, PBATP 5 parts.

[0037] The modified PLA film is prepared according to the following weight parts: PPCPLA 1 part, PLA 99 parts.

[0038] The preparation process of the composite packaging film is the same as that in Example 1.

[0039] Example 4

[0040] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the following weight parts: PPC 90 parts, PEC 10 parts.

[0041] The modified PLA film is prepared according to the following weight parts: PEC LA 10 parts, PLA 90 parts.

[0042] The preparation process of the composite packaging film is the same as that of Example 1.

[0043] Example 5

[0044] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the weight parts of PPCP 93 parts, PBS 3 parts, and PECP 4 parts.

[0045] The modified PLA film is prepared according to the weight parts of PECPLA 10 parts and PLA 90 parts.

[0046] The preparation process of the composite packaging film is the same as that of Example 1.

[0047] Example 6

[0048] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the weight parts of PECLA 97 parts and PCL 3 parts.

[0049] The modified PLA film is prepared according to the weight parts of PECPLA 20 parts and PLA 80 parts.

[0050] Preparation of the composite packaging film:

[0051] 1) Co-extrusion casting: place each layer formula in a double screw machine, melt and co-extrude through the nip between the two rollers set horizontally by relative rotation, and press into a sheet, wherein the melt temperature of the double screw machine for the modified PLA film of the inner and outer layers is set to 150°C, the melt temperature of the double screw machine for the semi-aromatic carbon dioxide-based copolymer film of the core layer is set to 150°C, and the co-extrusion temperature of the die head is 150°C; the composite film is prepared, and the composite film is obtained by winding.

[0052] 2) Biaxial stretching: cut the above-mentioned composite film sheet into a size of 10 cm x 10 cm, place it in a film high-temperature double-line stretching machine, preheat to 50°C, and then stretch longitudinally at a stretching rate of 80 mm / s for 4 times, and cool and set; preheat to 50°C again, and then stretch transversely at a stretching rate of 80 mm / s for 4 times, and cool and set. After corona treatment, winding, aging, and slitting, a biaxially stretched film with a thickness of 21.5 μm is prepared.

[0053] Example 7

[0054] The semi-aromatic carbon dioxide-based copolymer film is prepared according to the weight parts of PPCP 93 parts, PBS 3 parts, and PECP 4 parts.

[0055] The modified PLA film is prepared according to the weight parts of PECPLA 10 parts and PLA 90 parts.

[0056] Preparation of the composite packaging film:

[0057] 1) Co-extrusion casting: Put each layer formula into the twin-screw machine respectively, melt and plasticize at high temperature, and extrude through the nip between the two rollers arranged horizontally and rotating relatively to press into a sheet, wherein the melt temperature of the twin-screw machine for the modified PLA film of the inner and outer layers is set to 200℃, the melt temperature of the twin-screw machine for the semi-aromatic carbon dioxide-based copolymer film of the core layer is set to 180℃, and the co-extrusion temperature of the head is 200℃; the composite film is prepared, and the composite film is obtained by winding.

[0058] 2) Biaxial stretching: cut the above composite film sheet into a size of 10cm x 10cm, place it in a film high-temperature double-line stretching machine, preheat to 100℃, then stretch longitudinally 4 times at a stretching rate of 20mm / s, and cool and set; preheat to 100℃ again, then stretch transversely 4 times at a stretching rate of 20mm / s, and cool and set. After corona treatment, winding, aging, and slitting, a biaxially stretched film with a thickness of 21.5μm is prepared.

[0059] Example 8

[0060] The semi-aromatic carbon dioxide-based copolymer film is prepared by 100 parts of PPCPLA by weight.

[0061] The modified PLA film is prepared by 70 parts of PPCLA and 30 parts of PLA by weight.

[0062] The composite packaging film is prepared by the same process as in Example 1.

[0063] The performance indicators of Examples 1-8 are shown in Table 1: the data of performance tests are determined according to relevant national standards.

[0064] Table 1

[0065] .

[0066] The above is only the preferred embodiment of the present application, and is not intended to limit the other forms of the present application. Any person skilled in the art can modify or change the above disclosed technical content to obtain equivalent embodiments. However, any simple modification, equivalent change and modification of the above embodiments made without departing from the technical solution of the present application, and in accordance with the technical essence of the present application, still fall within the protection scope of the present application.

Claims

1. A high barrier composite packaging film, which is composed of an outer layer, a core layer, and an inner layer to form a composite film, characterized in that, The core layer is a semi-aromatic carbon dioxide-based copolymer film, and the outer layer and the inner layer are modified PLA films; the semi-aromatic carbon dioxide-based copolymer film comprises 90-100 parts of semi-aromatic carbon dioxide-based copolymer and 0-10 parts of toughening agent; the modified PLA film comprises 1-70 parts of polycarbonate-lactide copolymer and 30-99 parts of PLA; the comonomer of the polycarbonate-lactide copolymer is alkylene oxide, carbon dioxide, lactide and optional aromatic anhydride, and the aromatic anhydride is phthalic anhydride or naphthalic anhydride; and the core layer does not contain PLA. The comonomer of the semi-aromatic carbon dioxide-based copolymer is alkylene oxide, carbon dioxide, aromatic anhydride and optional lactide, and the aromatic anhydride is phthalic anhydride or naphthalic anhydride.

2. The high barrier composite packaging film according to claim 1, characterized in that: The semi-aromatic carbon dioxide-based copolymer comprises randomly or block arranged polycarbonate segments, polyether segments, PE segments and optional polylactic acid segments, wherein the polycarbonate segments are copolymerization segments of an epoxy compound and carbon dioxide, the polyether segments are self-polymerization segments and / or copolymerization segments of epoxy compounds, the PE segments are copolymerization segments of an epoxy compound and a cyclic anhydride, and the polylactic acid segments are self-polymerization segments of lactide.

3. The high barrier composite packaging film according to claim 1, characterized in that: The semi-aromatic carbon dioxide-based copolymer is one or more of PPCP, PPCCP, PPCPLA and PECPLA.

4. The high barrier composite packaging film according to claim 1, characterized in that: The toughening agent is one or more of PBAT, PCL, PBS and PECP.

5. The high barrier composite packaging film according to claim 1, characterized in that: The polycarbonate-lactide copolymer comprises randomly or block arranged polycarbonate segments, polylactic acid segments, optional PE segments and optional polyether segments, wherein the polycarbonate segments are copolymerization segments of an epoxy compound and carbon dioxide, the polylactic acid segments are self-polymerization segments of lactide, the PE segments are copolymerization segments of an epoxy compound and a cyclic anhydride, and the polyether segments are self-polymerization segments and / or copolymerization segments of epoxy compounds.

6. The high barrier composite packaging film according to claim 1, characterized in that: The polycarbonate-lactide copolymer is one or more of PECLA, PPCLA, PECPLA and PPCPLA.

7. A process for the preparation of a high barrier composite packaging film according to any one of claims 1 to 6, characterized in that, The process steps are as follows: 1) Co-extrusion casting: the formulations of the respective layers are respectively placed in a double screw machine, melted and plasticized at high temperature, extruded through the nip between two relatively rotating and horizontally arranged rollers, pressed into a sheet to form a composite film, and wound to obtain the composite film; 2) Two-way stretching: the composite film is cut into a sheet, placed in a high-temperature double-line stretching machine, stretched longitudinally after preheating, cooled and shaped, stretched transversely after preheating, cooled and shaped, subjected to corona treatment, wound, aged, and cut to obtain a two-way stretched film.

8. The process for the preparation of a high barrier composite packaging film according to claim 7, characterized in that: In step 1) co-extrusion casting, the melting temperature of the double screw machine for the modified PLA film is 150-200℃, and the melting temperature of the double screw machine for the semi-aromatic carbon dioxide-based copolymer film is 150-180℃, and the co-extrusion temperature of the die head is 150-200℃; In step 2) two-way stretching, the longitudinal and transverse stretching ratios are both 2-6 times, the longitudinal and transverse stretching temperatures are both 50-100℃, and the longitudinal and transverse stretching rates are both 20-80 mm / s.