Low-density single barrier film and preparation method thereof

Abstract

The invention discloses a low-density single barrier film and a preparation method thereof, the film comprises a five-layer structure formed by a film blowing co-extrusion process, and the five-layer structure sequentially comprises a first heat sealing layer, a first heat-resistant layer, a barrier layer, a second heat-resistant layer and a second heat sealing layer. The first heat sealing layer and the second heat sealing layer comprise mLLDPE and a microporous foaming agent, and a micron-sized pore structure is formed through a microporous foaming technology; the first heat-resistant layer and the second heat-resistant layer adopt HDPE to provide heat-resistant support; the barrier layer comprises PEC, LLDPE and a compatilizer, and the PEC is utilized to realize low oxygen permeability. Through material innovation and structure optimization, on the premise of ensuring single recoverability, the density of the thin film is remarkably reduced, meanwhile, the thin film has the advantages of high strength, high barrier property and low cost, and the thin film is suitable for light-weight packaging requirements in the fields of food, medicine, electronics and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional films, and particularly relates to a low-density single-barrier film and a preparation method thereof. Background Art

[0002] Barrier films are widely used in the fields of food, medicine, electronics, etc. At present, the barrier films on the market mainly include the following categories: polyethylene (PE) / nylon (PA) co-extruded films, polyethylene / nylon / ethylene-vinyl alcohol copolymer (EVOH) co-extruded films, and polyethylene / aluminum foil (Al) composite films, etc. The above-mentioned barrier films significantly improve the comprehensive performance compared with single materials through the compound superposition of different materials.

[0003] However, traditional composite material barrier films generally adopt multi-material co-extrusion or composite processes. For example, polar polymers such as PA / EVOH need to be combined with the PE substrate through adhesives, while aluminum foil relies on adhesives or hot pressing processes to achieve interlayer composite. Although this multi-layer structure endows the film with excellent physical barrier functions, it leads to the complication of material components and a relatively large film density, restricting its application in the field of lightweight packaging. In addition, the interfaces of different materials are difficult to effectively separate during the recycling process, especially for composite materials containing nylon and aluminum foil, which can basically only be incinerated and cannot be recycled for secondary use. On the one hand, during the incineration process, the aluminum foil residues are likely to cause ash accumulation and corrosion in the incinerator, and the pyrolysis products of nitrogen-containing polymers such as nylon will further exacerbate air pollution and cause environmental damage; on the other hand, it causes waste of resources and does not conform to the green concept of sustainable development. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a low-density single-barrier film and a preparation method thereof, which have excellent performance while ensuring the single recyclability of the material.

[0005] In order to achieve the above purposes, the technical solution of the present invention is as follows:

[0006] A low-density single-barrier film, which includes a five-layer structure formed by blown film co-extrusion. The five-layer structure sequentially includes a first heat-sealing layer, a first heat-resistant layer, a barrier layer, a second heat-resistant layer, and a second heat-sealing layer. Among them, the components of the first heat-sealing layer and the second heat-sealing layer include mLLDPE and a microcellular foaming agent, the components of the first heat-resistant layer and the second heat-resistant layer include HDPE, and the components of the barrier layer include PEC, LLDPE, and a compatibilizer. The PEC is poly(ethylene carbonate); wherein the first heat-sealing layer and the second heat-sealing layer form a microcellular foaming structure through the microcellular foaming agent, and the microcells are micron-sized pores.

[0007] Optionally, in the five-layer structure, the thickness proportion of the first heat-sealing layer is 25%-30%, the thickness proportion of the first heat-resistant layer is 20-25%, the thickness proportion of the barrier layer is 15-20%, the thickness proportion of the second heat-resistant layer is 20-25%, and the thickness proportion of the second heat-sealing layer is 10-15%.

[0008] Optionally, the components of the first heat-sealing layer and the second heat-sealing layer respectively include, by weight: 25-45 parts of first mLLDPE, 50-70 parts of second mLLDPE, 1-2 parts of microcellular foaming agent, 1-2 parts of antiblocking and slip agent, and 1-2 parts of rheological agent; the density of the first mLLDPE is 0.90-0.91 g / cm 3 , the melt index is 1-1.5 g / 10 min, and the softening temperature is 90-100 °C; the density of the second mLLDPE is 0.925-0.93 g / cm 3 , the melt index is 0.8-1.2 g / 10 min, the tensile strength > 30 Mpa, and the softening temperature > 105 °C.

[0009] Optionally, the microcellular foaming agent includes, by weight: 5-10 parts of hemicellulose, 89-94 parts of polyethylene wax, and 0.5-2% parts of antioxidant; the relative molecular weight of the polyethylene wax is 3000-5000.

[0010] Optionally, the antiblocking and slip agent includes, by weight: 3-8 parts of erucamide, 8-10 parts of talcum powder, 3-8 parts of silicone powder, and 75-85 parts of LDPE.

[0011] Optionally, the size of the micropores is 0.1-0.5 μm.

[0012] Optionally, the components of the first heat-resistant layer and the second heat-resistant layer respectively include, by weight: 98-99.5 parts of HDPE and 0.5-2 parts of rheological agent; the density of the HDPE is 0.95-0.96 g / cm 3 , the melt index is 0.03-0.04 g / 10 min, the softening temperature is 120-126 °C, and the tensile strength > 30 Mpa.

[0013] Optionally, the components of the barrier layer include, by weight: 20-25 parts of PEC, 20-25 parts of compatibilizer, and 50-60 parts of LLDPE; the softening point of the PEC is 20-25 °C, the melt index is 1-2 g / 10 min, and the density is 1.35-1.48 g / cm 3 ; the melt index of the LLDPE is 1.8-3 g / 10 min, and the density is 0.915-0.925 g / cm 3 .

[0014] Optionally, the oxygen transmission rate of the PEC < 5 cm 3 / (m 2 ·24H·0.1MPa).

[0015] The preparation method of the above-mentioned low-density single-barrier film comprises the following steps:

[0016] 1) Provide the components of the first heat-sealing layer, the first heat-resistant layer, the barrier layer, the second heat-resistant layer and the second heat-sealing layer, wherein the components of the first heat-sealing layer and the second heat-sealing layer include mLLDPE and a microcellular foaming agent, the components of the first heat-resistant layer and the second heat-resistant layer include HDPE, and the components of the barrier layer include PEC, LLDPE and a compatibilizer;

[0017] 2) Using the components of the first heat-sealing layer, the first heat-resistant layer, the barrier layer, the second heat-resistant layer and the second heat-sealing layer as raw materials, perform multilayer coextrusion blown film to obtain the low-density single-barrier film.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. 100% recyclable with a single material, avoiding the recycling problems caused by traditional multi-layer composite films containing different materials such as aluminum foil and nylon, which conforms to the development trend of green packaging;

[0020] 2. The barrier layer is compounded with PEC, LLDPE and a compatibilizer, and the oxygen barrier performance is improved by 200-400 times compared with traditional PE materials. At the same time, through the coordinated setting of the HDPE heat-resistant layer and the heat-sealing layer, the appearance and mechanical properties of the film are ensured, taking into account the advantages of high strength, high barrier and low cost;

[0021] 3. The heat-sealing layer with microcellular foaming is formed through the microcellular foaming process, reducing the density of the material and expanding the application in the field of lightweight packaging;

[0022] 4. High process compatibility, suitable for actual production applications.

[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. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the interlayer structure of the low-density single-barrier film for the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] The following further explains the present invention with reference to the accompanying drawings and specific embodiments. The drawings of the present invention are only schematic for easier understanding of the present invention, and the specific proportions can be adjusted according to design requirements.

[0026] In the present invention, mLLDPE refers to metallocene linear low density polyethylene, which is a polymer prepared by ethylene polymerization reaction using a metallocene coordination compound as a catalyst.

[0027] In the present invention, HDPE refers to high density polyethylene. Ethylene gas is polymerized through a catalyst under high temperature and high pressure, and the molecular chain is basically linear, so there are no or very few branches on its main chain.

[0028] In the present invention, LLDPE refers to linear low density polyethylene, and its molecular chain is linearly arranged with a small number of short branches.

[0029] In the present invention, PEC (Poly Ethylene Carbonate) refers to poly (ethylene carbonate), which is a barrier polymer synthesized by copolymerization of carbon dioxide (CO2) and ethylene oxide (EO), and the carbon dioxide content is not less than 45%.

[0030] In the present invention, LDPE refers to low density polyethylene, and its molecular chain is highly branched.

[0031] The performance test standards adopted in the present invention are as follows:

[0032] Project Test Standard Tensile Strength Astm D882 Density Astm D792 Melt Index Astm D1238 (190℃, 2.16kg) Vicat Softening Temperature Astm D1525 Oxygen Transmission Rate ASTM D1434 - 82

[0033] Reference Figure 1 , the low density single barrier film of the embodiment includes a five-layer structure, which is, in order, a first heat-sealing layer A, a first heat-resistant layer B, a barrier layer C, a second heat-resistant layer D and a second heat-sealing layer E. The thickness ratios of each layer are as follows:

[0034] Interlayer Ratio Layer A (Inner Layer, First Heat - sealing Layer) 25％-30％ Layer B (Sub - inner Layer, First Heat - resistant Layer) 20-25％ Layer C (Middle Layer, Barrier Layer) 15-20％ Layer D (Sub - outer Layer, Second Heat - resistant Layer) 20-25％ Layer E (Outer Layer, Second Heat - sealing Layer) 10-15％

[0035] Among them, the first heat-sealing layer A and the second heat-sealing layer E are formed of the same material, and the first heat-resistant layer B and the second heat-resistant layer D are formed of the same material. The component contents described below all refer to parts by mass.

[0036] Layers A and E (inner and outer layers) - the material components of the heat-sealing layer are 25-45% first mLLDPE, 50-70% second mLLDPE, 1-2% microcellular foaming agent, 1-2% opening and slipping agent, and 1-2% rheological agent.

[0037] The density of the first mLLDPE (low density special metallocene mLLDPE) is 0.90-0.91 g / cm 3 , the melt index is 1-1.5 g / 10 min, and the softening temperature is 90-100 °C. The specific model adopted in the embodiment is Dow 59999.

[0038] The density of the second mLLDPE (high strength special metallocene mLLDPE) is 0.925-0.93 g / cm3 , with a melt index of 0.8 - 1.2 g / 10 min, a tensile strength > 30 Mpa, a softening temperature > 105 °C, and the specific model used in the example is Dow ST100.

[0039] The components of the opening and slip agent are: 5% erucamide, 10% talc powder, 5% silicone powder, and 80% LDPE 2420D.

[0040] The components of the microcellular foaming agent are: 5 - 10% hemicellulose (manufacturer: Wuhan Kemike Biology), 89 - 94% polyethylene wax (relative molecular weight 3000 - 5000), and 1% antioxidant 1010. The manufacturer of polyethylene wax is Kayin Chemical Industry, and the manufacturer of antioxidant is BASF 1010.

[0041] Rheological agent: A conventional rheological agent on the market can be used, such as Xiamen Meinawei 2080.

[0042] Using the first mLLDPE can reduce the unsealing temperature of the material. The unsealing temperature of the low-density special metallocene mLLDPE is around 98 - 102 °C. As the heat-sealing surface layer, it needs to have heat-sealing performance. At the same time, the middle layer material uses a PEC barrier material, and its heat resistance is poor. In order to ensure that there are no problems such as scalding and deformation during the heat-sealing of the material to make bags, it is necessary to reduce the heat-sealing temperature of the inner and outer layers to create a temperature difference with the melting point of the heat-resistant layer. At the same time, it has good production and processing performance and can be effectively mixed with high-strength metallocene to improve the screw plasticization problem of high-strength metallocene blown film.

[0043] Using the second mLLDPE can improve the overall strength of the film. The proportion of the AE layer material accounts for about 40% of the total material. The tensile performance of the special metallocene is more than twice that of ordinary LLDPE materials, enabling the material to maintain good performance.

[0044] In the microcellular foaming agent, hemicellulose will decompose into trace gases such as carbon dioxide and methane when heated above 180 °C, forming uniform bubbles with a size of 0.1 - 0.5 μm inside the material, thereby reducing the density of the material without affecting its performance; polyethylene wax serves as the carrier and dispersant of hemicellulose, enabling the foaming components to be effectively and evenly dispersed in the material; polyethylene wax with a molecular weight of 3000 - 5000 is selected. If the molecular weight is too large, it becomes brittle and is not easy to granulate. If the molecular weight is too small, it is too soft and not easy to cut into granules.

[0045] The synthesis method of the microcellular foaming agent is as follows:

[0046] ① Add a quantitative amount of hemicellulose, polyethylene wax, and antioxidant to a high-speed mixer and stir at 2000 - 2500 revolutions per minute at room temperature for 10 - 15 minutes.

[0047] ② Add the well - stirred mixture into a single - screw extruder. The length of the screw is no more than 1.2 m, the temperature is set at 50 °C, and low - temperature cold cutting granulation is carried out. The finished product is bagged for standby.

[0048] Since the main material of the heat - seal layer is mLLDPE and mucosal problems are likely to occur, the anti - blocking and slip agent used needs to be specially configured. By adding a certain proportion of silicone powder, the anti - blocking effect of the material can be good, and the film surface will not stick back after aging and baking at 60 °C for 15 days. However, if the addition amount of silicone powder is too large, the film surface will become rough, the friction force will increase, which is not conducive to the later inflation of the product. If the addition amount is small, there will be no effect.

[0049] Layer B and D - The material components of the heat - resistant layer are: 99% HDPE and 1% rheological agent. The density of HDPE is 0.95 - 0.96 g / cm 3 , the melt index is 0.03 - 0.04 g / 10 min, the softening temperature is 120 - 126 °C, the tensile strength is > 30 Mpa, and the specific model used in the example is Lotte 7000f. Among them, HDPE mainly plays the role of heat resistance and improving the film strength. The softening temperature of HDPE is more than 20 °C higher than that of the metallocene in the outer and inner layers, and it will not burn through the film itself during the bag - making process while ensuring good heat - sealing of the film. Because the viscosity of HDPE material is relatively large, an appropriate amount of rheological agent needs to be heated to avoid the material burning and caking on the surface of the screw. The rheological agent can coat an anti - sticking film on the surface of the screw.

[0050] Layer C - The material components of the barrier layer are: 20 - 25% PEC, 20 - 25% compatibilizer, and 50 - 60% LLDPE. The softening point of PEC is 20 - 25 °C, the melt index is: 1 - 2 g / 10 min, the oxygen permeability rate is < 5 cm 3 / (m 2 ·24H·0.1 MPa), the density is 1.35 - 1.48 g / cm 3 , and the specific manufacturer model used in the example is the LG Ethylene Oxide series. The compatibilizer is LDPE / graft - maleic anhydride, and the graft - maleic anhydride content is 0.8 - 1%, and the specific manufacturer model used in the example is Lushan ef8. The melt index of LLDPE is 1.8 - 3 g / 10 min, the density is: 0.915 - 0.925 g / cm 3 , and the specific manufacturer model used in the example is ExxonMobil 1002ay.

[0051] PEC has good oxygen barrier properties, which are 200 - 400 times that of ordinary PE materials of the same thickness. However, the material has a relatively low softening point, average compatibility with PE, and cannot be used independently as the middle layer. There are also problems such as insufficient blown film strength and poor bubble stability. To avoid delamination from the HDPE material of the heat-resistant layer, it needs to be mixed and blown with a compatibilizer and LLDPE. The compatibilizer should be a material with a maleic anhydride grafting content of 0.8 - 1%, because if the grafting rate is too low, the compatibility is poor, and if the grafting rate is too high, overreaction will cause crystal point problems. LLDPE should be a material with a relatively large melt index and good fluidity, which is convenient for blending with PEC and the compatibilizer in the blown film screw.

[0052] Example 1

[0053] Self-made anti-blocking and slip agent: Add 5% erucamide, 10% talcum powder, 5% silicone powder, and 80% LDPE 2420D to a high-speed mixer and mix for 5 minutes. Then, use a twin-screw extruder to draw, air-cool, pelletize, and bag for later use. The set temperature of the extruder is as follows:

[0054] Feeding Section Heating Section 1 Heating Section 2 Heating Section 3 Heating Section 4 Extrusion Section Die 110℃ 120-130℃ 120-130℃ 120-130℃ 120-130℃ 120-130℃ 130-140℃

[0055] Self-made microcellular foaming agent: Add 5% hemicellulose (manufacturer: Wuhan Kemike Biology), 91% polyethylene wax (relative molecular weight 3000 - 5000), and 1% antioxidant 1010 to a high-speed mixer and mix for 5 minutes. Then, use a twin-screw extruder to draw, water-cool, pelletize, and bag for later use. The set temperature of the extruder is as follows:

[0056] Feeding Section Heating Section 1 Heating Section 2 Heating Section 3 Heating Section 4 Extrusion Section Die 50℃ 60-65℃ 60-65℃ 60-65℃ 60-65℃ 60-65℃ 60-65℃

[0057] Pour the materials into a blender according to the ratio, stir for 1 hour to mix evenly, and then suck them into the abcde five-layer screw hopper for later use. The specific ratio is as follows:

[0058]

[0059] Set the extrusion ratio of each layer. The set temperature of each layer of the screw is as follows, with a temperature deviation of ±5°C:

[0060] Interlayer Feeding Section Heating Section 1 Heating Section 2 Heating Section 3 Heating Section 4 Extrusion Section Die Layer A 140℃ 190℃ 190℃ 190℃ 190℃ 190℃ 190℃ Layer B 160℃ 200℃ 200℃ 200℃ 200℃ 200℃ 200℃ Layer C 140℃ 220℃ 220℃ 220℃ 220℃ 220℃ 220℃ Layer D 140℃ 190℃ 190℃ 190℃ 190℃ 190℃ 190℃ Layer E 160℃ 200℃ 200℃ 200℃ 200℃ 200℃ 200℃

[0061] Set the film thickness to 5C and the width to 1 meter.

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is that the first mLLDPE in the AE layer uses Fushun F331, with a density of 0.918 g / cm 3 , a melt index of 1 g / 10 min, a softening temperature of 110°C, an unsealing temperature of 103°C, and a tensile strength of 20 Mpa. Compared with the low-density special metallocene in Example 1, the unsealing temperature has increased by more than 10°C.

[0064] Comparative Example 2

[0065] The difference between Comparative Example 2 and Example 1 is that the second mLLDPE of the AE layer uses Fujian Refining F331. Compared with the high-strength special metallocene of Example 1, the tensile strength decreases by more than 40%.

[0066] Perform performance tests on the films referred to in Example 1 and Comparative Examples 1 and 2, as shown in the following table:

[0067] Tensile Strength TD Heat - sealing Strength TD at 120℃ Elongation at Break TD Example 1 53Mpa 43Mpa 538％ Comparative Example 1 56Mpa 18Mpa 220％ Comparative Example 2 22Mpa 21Mpa 300％

[0068] The heat-sealing strength of Example 1 is greatly improved compared with that of Comparative Example 1, and the tensile strength of Example 1 has a difference of nearly 1 time compared with that of Comparative Example 2.

[0069] Comparative Example 3

[0070] The difference between Comparative Example 3 and Example 1 is that the self-made microcellular foaming agent is changed to Yanbang Chemical AC foaming agent.

[0071] Comparative Example 4

[0072] The difference between Comparative Example 4 and Example 1 is that the self-made microcellular foaming agent is changed to expanded microspheres, and the manufacturer is American Borikem.

[0073] Comparative Example 5

[0074] The difference between Comparative Example 5 and Example 1 is that the molecular weight of the polyethylene wax in the self-made microcellular foaming agent is changed from 3000 - 5000 to 1000 - 2000.

[0075] Comparative Example 6

[0076] The difference between Comparative Example 6 and Example 1 is that the molecular weight of the polyethylene wax in the self-made microcellular foaming agent is changed from 3000 - 5000 to 6000 - 7000.

[0077] Comparative Example 7

[0078] The difference between Comparative Example 7 and Example 1 is that the self-made microcellular foaming agent is not added to layers A and E.

[0079] Perform performance tests on the films obtained in Example 1 and Comparative Examples 3 - 7, and the results are as follows:

[0080]

[0081] As can be seen from Example 1 and Comparative Examples 3 to 4, when using AC and expandable microbeads as foaming agents, the foam cells of the material are too large to form micron-sized pores, which affects the appearance and performance. The hemicellulose thermal decomposition foaming solution is more suitable for foaming buffer packaging films. As can be seen from Example 1 and Comparative Examples 5 to 6, when using polyethylene wax with a molecular weight of 3000 - 5000, the molecular weight is too small to granulate. When using polyethylene wax with a molecular weight of 6000 - 7000, the molecular weight is relatively large, the brittleness is high, and the particles form a mixture of uneven powder particles. The dispersion during film blowing is not good, the hemicellulose accumulates locally and agglomerates, and large bubble holes appear locally. As can be seen from Example 1 and Comparative Example 7, when adding the self-made microcellular foaming agent, the film performance ratio does not change significantly, and the density is reduced by about 16%.

[0082] Comparative Example 8

[0083] The difference between Comparative Example 8 and Example 1 is that the self-made opening and slip agent in the AE layer is replaced with the silicone-free powder amide opening and slip agent Xiamen Taisong 2100.

[0084] Comparative Example 9

[0085] The difference between Comparative Example 9 and Example 1 is that the silicone powder content in the self-made opening and slip agent in the AE layer is changed from 5% to 10%.

[0086] Comparative Example 10

[0087] The difference between Comparative Example 10 and Example 1 is that the silicone powder content in the self-made opening and slip agent in the AE layer is changed from 5% to 2%.

[0088] Perform performance tests on the films prepared in Example 1 and Comparative Examples 8 to 10. Method for measuring the anti-sticking on the film surface: Test conditions: 80°C × 48H, pressure on the film: 10 kg.

[0089] Case Whether It Returns to Stickiness Whether the 20mm - diameter Inflatable Tube Gets Jammed at an Inflation Speed of 20m / min Example 1 No No Comparative Example 8 Yes Yes Comparative Example 9 No Yes Comparative Example 10 Yes Yes

[0090] As can be seen from Example 1 and Comparative Example 8, the ordinary amide opening and slip agent without silicone powder cannot play an anti-sticking role; as can be seen from Example 1 and Comparative Example 9, although adding an excessive amount of silicone powder can play an anti-sticking role, the film surface is too rough, the friction is too large, and the film is prone to jamming during inflation; as can be seen from Example 1 and Comparative Example 10, when the silicone powder content is too small, there is no effect.

[0091] Comparative Example 11

[0092] The difference between Comparative Example 11 and Example 1 is that LLDPE is used instead of HDPE in layers B and D. LLDPE manufacturer model: ExxonMobil 1002ay.

[0093] Comparative Example 12

[0094] The difference between Comparative Example 12 and Example 1 is that mLLDPE is used instead of HDPE in layers B and D. The manufacturer model of mLLDPE is Fushun Refining f331.

[0095] Case Tensile Strength TD Heat - sealing Strength TD at 120℃ Heat - sealing Strength TD at 130℃ Example 1 53Mpa 43Mpa 38Mpa Comparative Example 11 34Mpa 24Mpa 0 Hot - cut Comparative Example 12 46Mpa 40Mpa 0 Hot - cut

[0096] As can be seen from Example 1 and Comparative Example 11, when LLDPE is used instead of HDPE, both the heat resistance and strength decrease; as can be seen from Example 1 and Comparative Example 12, when mLLDPE is used instead of HDPE, the heat resistance significantly decreases.

[0097] Comparative Example 13

[0098] The difference between Comparative Example 13 and Example 1 is that pure PEC is used in layer C.

[0099] Comparative Example 14

[0100] The difference between Comparative Example 14 and Example 1 is that layer C uses 25% PEC and 75% LLDPE.

[0101] Comparative Example 15

[0102] The difference between Comparative Example 15 and Example 1 is that layer C uses 25% PEC and 75% compatibilizer.

[0103] Comparative Example 16

[0104] The difference between Comparative Example 16 and Example 1 is that the PEC in layer C is replaced with PA6, and the manufacturer model is BASF b40.

[0105] Comparative Example 17

[0106] The difference between Comparative Example 17 and Example 1 is that the compatibilizer used in layer C is a material with a graft content of 0.6%, and the manufacturer model is Xiamen Meinawei A6.

[0107] Comparative Example 18

[0108] The difference between Comparative Example 18 and Example 1 is that the compatibilizer used in layer C is a material with a graft content of 1.2%, and the manufacturer model is Xiamen Meinawei A12.

[0109] The performance tests were carried out on the films prepared in Example 1 and Comparative Examples 11 - 18, and the results are as follows:

[0110]

[0111] In Comparative Example 13, compared with Example 1, the oxygen barrier performance was improved, but the film showed delamination, and the heat resistance and mechanical properties decreased to varying degrees; in Comparative Example 14, compared with Example 1, without a compatibilizer between LLDPE and PEC, the compatibilization effect was poor and film formation was impossible; in Comparative Example 15, compared with Example 1, when PEC was mixed with an excessive amount of compatibilizer, it was prone to overreaction and crystal points appeared, resulting in a decrease in film properties and air leakage on the surface, and the oxygen transmission rate could not be measured; in Comparative Example 16, compared with Example 1, when PA6 was used to replace PEC, since the processing temperature of nylon was 100 °C higher than that of PE, plasticization and molding were impossible and film formation was impossible; in Comparative Example 17, compared with Example 1, the maleic anhydride grafting rate of the compatibilizer in layer C was too low, the compatibility was poor, there were crystal points in the material, which affected the performance, and air leakage appeared on the surface, and the oxygen transmission rate could not be measured; in Comparative Example 18, compared with Example 1, the maleic anhydride grafting rate of the compatibilizer in layer C was too high, overreaction occurred and crystal points appeared, resulting in a decrease in film properties and air leakage on the surface, and the oxygen transmission rate could not be measured.

[0112] In summary, for the low-density single-barrier film of the embodiment of the present invention, using carbon dioxide-polymerized cyclic polyethylene, i.e., PEC material, to replace the traditional PE material, while ensuring the single recyclability of the material, greatly improves the oxygen barrier performance of the PE material itself. At the same time, through the microcellular foaming process, a cellular pore structure is formed inside the material. Through these cellular pore structures, the film density is greatly reduced by 15-30%, while not affecting the appearance and mechanical properties of the material itself, obtaining a low-density single-barrier film with good application performance and processing performance, which is suitable for fields such as inflatable filling air cushions, liquid filling, and food packaging. It can be recycled by means of crushing and granulation.

[0113] The above embodiments are only used to further illustrate a low-density single-barrier film and its preparation method of the present invention, but the present invention is not limited to the embodiments. Any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention all fall within the protection scope of the technical solution of the present invention.

Claims

1. A low-density single-barrier film, characterized in that, It includes a five-layer structure formed by blown film coextrusion. The five-layer structure sequentially includes a first heat-sealing layer, a first heat-resistant layer, a barrier layer, a second heat-resistant layer, and a second heat-sealing layer. Among them, the components of the first heat-sealing layer and the second heat-sealing layer include mLLDPE and a microcellular foaming agent. The components of the first heat-resistant layer and the second heat-resistant layer include HDPE. The components of the barrier layer include PEC, LLDPE, and a compatibilizer. The PEC is poly(ethylene carbonate); wherein the first heat-sealing layer and the second heat-sealing layer form a microcellular foaming structure through the microcellular foaming agent, and the micropores are micron-sized pores.

2. The low-density single-barrier film according to claim 1, wherein: In the five-layer structure, the thickness ratio of the first heat-sealing layer is 25%-30%, the thickness ratio of the first heat-resistant layer is 20-25%, the thickness ratio of the barrier layer is 15-20%, the thickness ratio of the second heat-resistant layer is 20-25%, and the thickness ratio of the second heat-sealing layer is 10-15%.

3. The low-density single-barrier film according to claim 1, characterized in that: The size of the micropores is 0.1-0.5 μm.

4. The low-density single-barrier film according to claim 1, wherein: The components of the first heat-sealing layer and the second heat-sealing layer respectively include, by weight: 25-45 parts of first mLLDPE, 50-70 parts of second mLLDPE, 1-2 parts of microcellular foaming agent, 1-2 parts of antiblocking and slip agent, and 1-2 parts of rheological agent; the density of the first mLLDPE is 0.90-0.91 g / cm 3 , the melt index is 1-1.5 g / 10 min, and the softening temperature is 90-100 °C; the density of the second mLLDPE is 0.925-0.93 g / cm 3 , the melt index is 0.8-1.2 g / 10 min, the tensile strength > 30 Mpa, and the softening temperature > 105 °C.

5. The low-density single-barrier film according to claim 1 or 4, characterized in that: The microcellular foaming agent includes, by weight: 5-10 parts of hemicellulose, 89-94 parts of polyethylene wax, and 0.5-2 parts of antioxidant; the relative molecular weight of the polyethylene wax is 3000-5000.

6. The low-density single-barrier film according to claim 4, wherein: The anti-blocking and slip agent includes, by weight: 3-8 parts of erucamide, 8-10 parts of talc powder, 3-8 parts of silicone powder, and 75-85 parts of LDPE.

7. The low-density single-barrier film according to claim 1, wherein: The components of the first heat-resistant layer and the second heat-resistant layer respectively include, by weight: 98-99.5 parts of HDPE and 0.5-2 parts of rheological agent; the density of the HDPE is 0.95-0.96 g / cm 3 , the melt index is 0.03-0.04 g / 10 min, the softening temperature is 120-126 °C, and the tensile strength > 30 Mpa.

8. The low-density single-barrier film according to claim 1, characterized in that: The components of the barrier layer include, by weight: 20-25 parts of PEC, 20-25 parts of compatibilizer, and 50-60 parts of LLDPE; the softening point of the PEC is 20-25 °C, the melt index is 1-2 g / 10 min, and the density is 1.35-1.48 g / cm 3 ; the melt index of the LLDPE is 1.8-3 g / 10 min, and the density is 0.915-0.925 g / cm 3 .

9. The low-density single-barrier film according to claim 8, wherein: The oxygen transmission rate of the PEC < 5 cm 3 / (m 2 ·24H·0.1MPa).

10. A method for preparing the low-density single-barrier film according to any one of claims 1 to 9, characterized in that, It includes the following steps: 1) Provide the components of the first heat-sealing layer, the first heat-resistant layer, the barrier layer, the second heat-resistant layer, and the second heat-sealing layer. Among them, the components of the first heat-sealing layer and the second heat-sealing layer include mLLDPE and a microcellular foaming agent. The components of the first heat-resistant layer and the second heat-resistant layer include HDPE. The components of the barrier layer include PEC, LLDPE, and a compatibilizer; 2) Use the components of the first heat-sealing layer, the first heat-resistant layer, the barrier layer, the second heat-resistant layer, and the second heat-sealing layer as raw materials to perform multi-layer coextrusion blow molding to obtain the low-density single-barrier film.

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