Anti-pollution heat-sealing film, anti-pollution inner film, composite film and preparation method thereof

Abstract

The present invention discloses an anti-pollution heat-sealing film, an anti-pollution inner film, a composite film and a preparation method thereof, and relates to the field of packaging films. The raw materials for preparing the anti-pollution heat-sealing film include, by weight percentage: 20% to 35% of metallocene linear low-density polyethylene resin, 14% to 45.5% of linear low-density polyethylene resin, 10% to 20% of low-density polyethylene resin, 20% to 35% of polyolefin elastomer, 1% to 2% of lubricant, 1% to 2% of opening agent, and 1% to 2% of fluorine-containing processing aid. The anti-pollution heat-sealing film is prepared by using components with good heat-sealing properties, and still maintains good heat-sealing properties when the surface is contaminated by food juice.

Description

Technical Field

[0001] The invention relates to the field of packaging films, and in particular to an anti-pollution heat-sealing film, an anti-pollution inner layer film, a composite film and a preparation method thereof. Background Art

[0002] Vacuum plastic bags are often used in the food packaging industry. After the internal gas is evacuated, the vacuum plastic bags are heat-sealed to create a low oxygen or oxygen-deficient state inside the bag, inhibiting the reproduction and growth of most bacteria and fungi, and effectively extending the shelf life of food.

[0003] During food packaging, the sealing of plastic bags often has contents or other contaminants, such as food juice, adhering to them. The presence of these contaminants often results in poor heat sealing or even failure to heat seal. Among them, various additives, salt, sugar, edible oil, etc. contained in the juice will affect the heat sealing effect.

[0004] In automated production packaging, failure to effectively seal the bag opening may cause leakage of the bag contents, or air leakage in the bag during transportation and storage may shorten the shelf life of the food.

[0005] It can be seen that the existing technology still needs to be improved and enhanced. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide an anti-pollution heat-sealing film, an anti-pollution inner layer film, a composite film and a preparation method thereof, aiming to solve the technical problem in the prior art that the opening of the packaging bag is difficult or impossible to heat-seal after being contaminated.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The invention discloses an anti-pollution heat-sealing film, wherein the raw materials for preparing the film include, by weight percentage, 20% to 35% of metallocene linear low-density polyethylene resin, 14% to 45.5% of linear low-density polyethylene resin, 10% to 20% of low-density polyethylene resin, 20% to 35% of polyolefin elastomer, 1% to 2% of lubricant, 1% to 2% of opening agent and 1% to 2% of fluorine-containing processing aid.

[0009] The anti-pollution heat-sealing film, wherein the metallocene linear low-density polyethylene resin has a melting point of 106°C and a density of 0.908 g / cm 3 .

[0010] The anti-pollution heat-sealing film, wherein the melting point of the polyolefin elastomer is 100°C and the density is 0.904 g / cm 3 .

[0011] An anti-pollution inner layer film comprises a corona layer, a barrier layer and an anti-pollution heat-sealing layer which are stacked, and the anti-pollution heat-sealing layer is the anti-pollution heat-sealing film as described above.

[0012] The anti-pollution inner film, wherein the raw materials for preparing the barrier layer include, by weight percentage: 20% to 60% of metallocene linear medium-density polyethylene resin and 40% to 80% of linear low-density polyethylene resin.

[0013] The anti-pollution inner layer film, wherein the melting point of the metallocene linear medium density polyethylene resin is 123°C and the density is 0.935 g / cm 3 .

[0014] The anti-pollution inner layer film, wherein the melt index of the metallocene linear medium density polyethylene resin at 190° C. and 2.16 kg pressure is 0.5 to 2.0 g / 10 min.

[0015] The anti-pollution inner film, wherein the raw materials for preparing the corona layer include, by weight percentage, 10% to 50% of low-density polyethylene resin and 50% to 90% of linear low-density polyethylene resin.

[0016] A composite film comprises a surface layer, an adhesive layer and an inner layer which are stacked in sequence, wherein the inner layer is the anti-pollution inner film as described above; the surface layer is a polyamide film; and the adhesive layer is a two-component polyurethane adhesive layer.

[0017] A method for preparing a composite film, for preparing the composite film as described above, comprising the following steps:

[0018] S1. Applying an adhesive to the polyamide film and drying it to form the adhesive layer;

[0019] S2. The polyamide film coated with an adhesive is hot-pressed with the anti-pollution inner film, and the adhesive layer is laminated with the corona layer of the anti-pollution inner film;

[0020] S3. Ripening treatment to obtain the finished product.

[0021] Beneficial effects:

[0022] The invention provides an anti-pollution heat-sealing film, which can still have good heat-sealing performance after being contaminated by soup used to soak fish fillets by combining metallocene linear low-density polyethylene resin, linear low-density polyethylene resin, low-density polyethylene resin and polyolefin elastomer.

[0023] The present invention also provides an anti-pollution inner layer film, including a corona layer, a barrier layer and an anti-pollution heat-sealing layer. The combination of the barrier layer and the anti-pollution heat-sealing layer can make the film have good barrier properties, toughness and heat-sealing properties, make the film not easily punctured, and have better processing performance.

[0024] The present invention also provides a composite film and a preparation method thereof. The composite film is formed by composite processing of a polyamide film with good comprehensive performance and an anti-pollution inner layer film. The polyamide film gives the surface of the composite film good printing performance, barrier properties and toughness, and the anti-pollution inner layer film gives the inner side of the composite film good heat sealing properties, barrier properties and toughness, so that the composite film is not easily punctured from the inside. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of the anti-pollution inner layer film provided by the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of the composite membrane provided by the present invention.

[0027] Explanation of the main component symbols: 11 - corona layer, 12 - barrier layer, 13 - anti-pollution heat sealing layer, 1 - anti-pollution inner film, 2 - two-component polyurethane adhesive layer, 3 - polyamide film. DETAILED DESCRIPTION

[0028] The present invention provides an anti-pollution heat-sealing film, an anti-pollution inner layer film, a composite film and a preparation method thereof. To make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the following examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The invention provides an anti-pollution heat-sealing film, and the raw materials for its preparation include, by weight percentage: 20% to 35% of metallocene linear low-density polyethylene resin, 14% to 45.5% of linear low-density polyethylene resin, 10% to 20% of low-density polyethylene resin, 20% to 35% of polyolefin elastomer, 1% to 2% of lubricant, 1% to 2% of opening agent, and 1% to 2% of fluorine-containing processing aid. Among them, the metallocene linear low-density polyethylene resin and the linear low-density polyethylene resin both have good hot viscosity and heat-sealing strength. The low-density polyethylene resin has good fluidity and foam stability. The polyolefin elastomer has excellent anti-pollution heat-sealing property and low-temperature heat-sealing property. The opening agent and the lubricant have excellent opening property and are used to improve the lubricity of the film surface. The fluorine-containing processing aid is beneficial for the plastic film to have good plasticizing performance and dispersibility in production.

[0030] Preferably, the metallocene linear low-density polyethylene resin has a melting point of 106°C and a density of 0.908 g / cm 3The melting point of the metallocene linear low-density polyethylene resin is 106°C, which is more suitable for film blowing production and helps save processing energy. In addition, the density of the metallocene linear low-density polyethylene resin is 0.908g / cm 3 , which is of great help to the low temperature heat sealing performance of the material. Density greater or less is not conducive to production and processing.

[0031] Preferably, the polyolefin elastomer has a melting point of 100°C and a density of 0.904 g / cm 3 The melting point of this elastomer is 100°C, which is suitable for heat sealing at a lower temperature and helps to avoid interference from foreign matter during heat sealing. The density of polyolefin elastomer is 0.904g / cm 3 , which is of great help to the low temperature heat sealing performance of the material. Higher or lower density is inconvenient for production and processing.

[0032] See also Figure 1 The present invention also provides an anti-pollution inner layer film, comprising a stacked corona layer 11, a barrier layer 12 and an anti-pollution heat-sealing layer 13, wherein the anti-pollution heat-sealing layer is the anti-pollution heat-sealing film as described above.

[0033] Preferably, the raw materials for preparing the barrier layer include, by weight percentage: 20% to 60% of metallocene linear medium density polyethylene resin and 40% to 80% of linear low density polyethylene resin. Metallocene linear medium density polyethylene resin has a higher density and a more regular linear molecular structure, which is beneficial to prevent the contents from penetrating the composite glue layer during or after heat sealing, and plays a greater role in protecting the overall structural integrity of the bag. At the same time, a certain proportion of linear low density polyethylene is beneficial to the processing of blown film production.

[0034] Preferably, the metallocene linear medium density polyethylene resin has a melting point of 123°C and a density of 0.935 g / cm 3 ;

[0035] Preferably, the melt index of the metallocene linear medium density polyethylene resin and the linear low density polyethylene resin at 190° C. and a pressure of 2.16 kg are both 0.5 to 2.0 g / 10 min.

[0036] Preferably, the raw materials for preparing the corona layer include, by weight percentage: 10% to 50% low-density polyethylene resin and 50% to 90% linear low-density polyethylene resin; the melt index of the linear low-density polyethylene resin and the low-density polyethylene resin at 190°C and 2.16kg pressure is 1.0 to 4.0g / 10min. The density of the low-density polyethylene resin is 0.918 to 0.922g / cm 3 .

[0037] Preferably, the thickness of the corona layer accounts for 25% to 35% of the total thickness of the anti-pollution inner film, the thickness of the barrier layer accounts for 35% to 45% of the total thickness of the anti-pollution inner film, and the thickness of the anti-pollution heat seal layer accounts for 28% to 32% of the total thickness of the anti-pollution inner film.

[0038] A method for preparing an anti-pollution inner layer film, which is used to prepare the anti-pollution inner layer film as described above, comprises the following steps: S11. putting raw materials for preparing a corona layer, a barrier layer and an anti-pollution heat-sealing layer into an extruder according to a ratio for plasticization; S12. extruding the three layers of raw materials in a molten state, and then continuing to plasticize them through a three-layer co-extrusion film blowing machine; S13. co-extruding through a circular die to form a tubular film; S14. The tubular film is blown with compressed air for transverse stretching, and at the same time, an annular wind ring is used to blow out cold air for shaping, and an upper traction clamp is used for longitudinal stretching, and after upper rotary traction, the corona layer is subjected to corona treatment, cut, and rolled to obtain a finished product.

[0039] See also Figure 2 The present invention also provides a composite film, comprising a surface layer, an adhesive layer and an inner layer stacked in sequence, wherein the inner layer is the anti-pollution inner film 1 as described above; the surface layer is a polyamide film 3; and the adhesive layer is a two-component polyurethane adhesive layer 2. Polyamide film is an excellent barrier material, which has good heat resistance, cold resistance, barrier properties, wear resistance and puncture resistance, and has a soft texture and excellent printability. Graphic information can be transferred to the polyamide film by printing as needed, so that the packaging has rich color patterns and relevant text information of the product. The anti-pollution inner film has excellent water barrier properties and heat sealing properties, and the adhesive layer helps to increase the water and gas barrier properties. This structural design can achieve a good vacuum effect.

[0040] Preferably, the thickness of the surface layer is 12 to 25 μm, the thickness of the adhesive layer is 1 to 3 μm, and the thickness of the anti-pollution inner film is 40 to 130 μm.

[0041] The method for preparing the composite film comprises the following steps:

[0042] S1. Applying an adhesive to the polyamide film and drying it to form the adhesive layer;

[0043] Specifically, the polyamide film enters the glue coating device through the guide roller, and the mesh roller in the glue coating device scrapes off the adhesive outside the mesh cells under the action of the scraper. Under the pressure of the glue pressure roller and the mesh roller, the adhesive in the mesh cells in the mesh roller is transferred to the polyamide film to form an adhesive layer. The polyamide film enters the drying device of the oven after passing through the glue roller under the tension of the oven. Under the action of the oven temperature, the solvent in the adhesive layer of the polyamide film evaporates rapidly;

[0044] Among them, the pressure of the glue roller and the wire roller is 0.3-0.4Mpa, and the oven has four groups of drying temperature sections, which are stepped temperatures from low to high. The first group of temperature sections is 45-50℃, the second group of temperature sections is 50-55℃, the third group of temperature sections is 60-65℃, and the fourth group of temperature sections is 70-75℃.

[0045] S2. The polyamide film coated with a two-component polyurethane adhesive is hot-pressed with the anti-pollution inner film, and the adhesive layer is laminated with the corona layer of the anti-pollution inner film;

[0046] The anti-pollution inner film and the dried polyamide film enter the composite device, and the adhesive layer on the polyamide film and the corona layer of the anti-pollution inner film are hot-pressed and laminated under the composite steel roller and rubber roller;

[0047] Among them, the temperature of the composite steel roller is 55-65°C, the composite pressure is 0.4Mpa, and the composite speed is 100-150m / min;

[0048] S3. The laminated composite film is placed in a curing chamber for curing treatment. The temperature of the curing chamber is 45°C and the curing time is ≥24h to obtain a finished product.

[0049] The present invention is further described with reference to the following examples.

[0050] Example 1

[0051] A composite film, the preparation method of which comprises the following steps:

[0052] S1. The polyamide film is passed through a guide roller into a glue coating device, and a two-component polyurethane adhesive is coated on the film. After the mesh roller in the glue coating device scrapes off the adhesive outside the mesh cells under the action of a scraper, the adhesive in the mesh cells in the mesh roller is transferred to the polyamide film under the pressure of the glue pressure roller and the mesh roller to form an adhesive layer. The polyamide film is pulled by the tension of the oven and then passes through the glue roller into the drying device of the oven. Under the action of the oven temperature, the solvent in the adhesive layer of the polyamide film evaporates rapidly;

[0053] Among them, the pressure of the glue roller and the wire roller is 0.4Mpa, and the oven has four groups of drying temperature sections, which are stepped temperatures from low to high. The first temperature section is 45℃, the second temperature section is 55℃, the third temperature section is 65℃, and the fourth temperature section is 75℃.

[0054] S2. The anti-pollution inner film and the dried polyamide film enter the composite device, and the adhesive layer on the polyamide film and the corona layer of the anti-pollution inner film are hot-pressed and laminated under the composite steel roller and rubber roller; wherein the composite steel roller temperature is 60°C, the composite pressure is 0.4Mpa, and the composite speed is 130m / min;

[0055] S3. The laminated composite film is placed in a curing chamber for curing treatment. The temperature of the curing chamber is 45°C and the curing time is 24h to obtain a finished product.

[0056] In the composite film, the thickness of the surface layer is 15 μm, the thickness of the adhesive layer is 2 μm, and the thickness of the anti-pollution inner film is 80 μm;

[0057] In the anti-pollution inner film:

[0058] The raw materials for preparing the corona layer include, by weight percentage: 20% low-density polyethylene resin and 80% linear low-density polyethylene resin; the melt index of the linear low-density polyethylene resin and the low-density polyethylene resin at 190° C. and 2.16 kg pressure is 2.0 g / 10 min;

[0059] The raw materials for preparing the barrier layer include, by weight percentage: 25% of metallocene linear medium density polyethylene resin and 75% of linear low density polyethylene resin; the melting point of the metallocene linear medium density polyethylene resin is 123°C and the density is 0.935 g / cm 3 The melt index of the metallocene linear medium density polyethylene resin and the linear low density polyethylene resin at 190°C and 2.16kg pressure is 1.0g / 10min;

[0060] The formula of the anti-pollution heat-sealing film is shown in Table 1. In the anti-pollution heat-sealing film, the melting point of the metallocene linear low-density polyethylene resin is 106° C. and the density is 0.908 g / cm 3 The melting point of the polyolefin elastomer is 100°C and the density is 0.904 g / cm 3 .

[0061] Example 2

[0062] A composite film, which is different from Example 1 in that the formula of the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film in this example is shown in Table 1.

[0063] Example 3

[0064] A composite film, which is different from Example 1 in that the formula of the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film in this example is shown in Table 1.

[0065] Example 4

[0066] A composite film, which is different from Example 1 in that the formula of the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film in this example is shown in Table 1.

[0067] Example 5

[0068] A composite film, which is different from Example 1 in that the formula of the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film in this example is shown in Table 1.

[0069] Example 6

[0070] A composite film, which is different from Example 1 in that the formula of the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film in this example is shown in Table 1.

[0071] The composite films prepared in Examples 1-6 were used to prepare vacuum plastic bags, and then the heat sealing properties of the vacuum plastic bags were tested.

[0072] The preparation method of the vacuum plastic bag is as follows: the aged composite film is placed in the unwinding device, the composite film enters the forming stage under the traction tension, the composite film is accurately cut in half under the control of the deviation correction electric eye to form composite film 1 and composite film 2, and composite film 1 and composite film 2 are superimposed on each other by the former and enter the heat sealing stage. The horizontal and vertical heat sealing knives press the superimposed composite film at the set temperature and pressure, cool and shape after heat sealing, punch and tear the heat sealing edge after heat sealing, and finally send out the position under the control of the photoelectric system, and cut the continuous bag material sent out by the cutter device into individual bags.

[0073] One of the four sides of the vacuum plastic bag prepared above is left unsealed.

[0074] The test method for heat sealing performance is as follows: Take the vacuum plastic bag to be heat sealed, and use a cotton swab to evenly apply cooking oil and fish fillet soaking soup on the heat-sealed area, with a coating amount of 5g / m 2 Then, the heat sealing temperature was tested at 150℃, 160℃, 170℃ and 180℃, the heat sealing time was 2s, and the pressure was 0.38Mpa. After heat sealing, the anti-pollution heat sealing strength was tested according to the QB / T 2358-1998 test method. The anti-pollution strength is the value measured at the moment of opening.

[0075] The above-mentioned soup for soaking fish fillets used for testing is prepared from fish fillets, water, edible salt, white sugar, egg white, edible flavoring and other various additives.

[0076] The corresponding test data results are shown in Table 2.

[0077] Table 1

[0078]

[0079] Table 2

[0080]

[0081] It can be seen from the test results in Table 2 that when the seal of the vacuum plastic bag is contaminated by edible oil, its anti-contamination heat seal strength is not much different from the conventional ordinary heat seal strength. For this degree of contamination, Examples 1 to 6 have good anti-contamination properties.

[0082] Since the soup for soaking fish fillets contains sodium pyrophosphate and other food additives, it is easy to adhere to the surface of the heat-sealing layer of the heat-sealed bag, which has a great impact on the surface performance of the heat-sealing layer and the heat-sealing temperature. In view of this situation, the present invention designs an anti-pollution heat-sealing film and an anti-pollution inner film that can improve the surface anti-pollution and low-temperature heat-sealing properties. In the example, when the seals of Examples 1 to 6 were contaminated by the soup for soaking fish fillets, the anti-pollution properties of the vacuum plastic bags prepared in Examples 1 to 2 were obviously insufficient. When the heat-sealing temperature was increased to 180°C, it still could not be heat-sealed or the heat-sealing strength was too low. The anti-pollution properties of Examples 3 to 6 have been greatly improved. At 170°C, they have a certain heat-sealing ability but the strength is low. When the heat-sealing temperature is increased to 180°C, they can all be heat-sealed and the heat-sealing strength is good, but the anti-pollution strength of Examples 4 to 6 is higher than that of Example 3.

[0083] Compared with Example 4, Example 5 uses a larger amount of polyolefin elastomer, but the anti-pollution performance is similar. With the increase of polyolefin elastomer, the film has greater viscosity and difficulty in operation during the production process, and the production cost is greatly increased.

[0084] Comparative Example 1

[0085] A composite film, which differs from Example 1 in that the density and melting point of the polyolefin elastomer are different. In this comparative example, the density of the polyolefin elastomer is 0.908 g / cm 3 , melting point is 108℃;

[0086] The addition amount of polyolefin elastomer in the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film is shown in Table 3.

[0087] Comparative Example 2

[0088] A composite film, which differs from Comparative Example 1 in that the amount of polyolefin elastomer added to the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film is shown in Table 3.

[0089] Comparative Example 3

[0090] A composite film, which differs from Comparative Example 1 in that the amount of polyolefin elastomer added to the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film is shown in Table 3.

[0091] Comparative Example 4

[0092] A composite film, which differs from Example 1 in that the density and melting point of the polyolefin elastomer are different. In this comparative example, the density of the polyolefin elastomer is 0.85 g / cm 3 , melting point is 80℃;

[0093] The addition amount of polyolefin elastomer in the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film is shown in Table 3.

[0094] Comparative Example 5

[0095] A composite film, which differs from Comparative Example 4 in that the amount of polyolefin elastomer added to the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film is shown in Table 3.

[0096] Comparative Example 6

[0097] A composite film, which differs from Comparative Example 4 in that the amount of polyolefin elastomer added to the anti-pollution heat-sealing film is different. The formula of the anti-pollution heat-sealing film is shown in Table 3.

[0098] Table 3

[0099]

[0100] The processing performance and heat sealing performance of the composite films of Comparative Examples 1-6 were measured, using the soup of soaked fish fillets as the pollutant, the heat sealing temperature was 180° C., the heat sealing time was 2 s, and compared with the results of Examples 3-5. The corresponding test results are shown in Table 4.

[0101] Table 4

[0102]

[0103] Comparative Examples 1-6 used polyolefin elastomers with different densities and melting points as the test objects. From the results in Table 4, it can be seen that in Comparative Examples 1-3, a polyolefin elastomer with a density of 0.908 g / cm 3 The polyolefin elastomer with a melting point of 108°C has a certain heat sealability when the addition amount of the polyolefin elastomer is 20% and 30%, but the heat seal strength is significantly lower than that of Example 4 and Example 5; In Comparative Examples 4-6, a density of 0.85 g / cm 3 The polyolefin elastomer with a melting point of 80°C has good processing performance only when the addition amount is 10%, but the heat sealing strength of the composite film obtained is obviously insufficient. When the addition amount is increased to more than 20%, the material cannot form a film due to poor temperature resistance and excessive viscosity, resulting in the inability to produce.

[0104] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. An anti-pollution heat-sealing film, characterized in that: The raw materials for its preparation include, by weight percentage: 20% to 35% of metallocene linear low-density polyethylene resin, 14% to 35.5% of linear low-density polyethylene resin, 10% to 20% of low-density polyethylene resin, 20% to 35% of polyolefin elastomer, 1% to 2% of lubricant, 1% to 2% of anti-blocking agent, and 1% to 2% of fluorine-containing processing aid; the melting point of the metallocene linear low-density polyethylene resin is 106°C, and the density is 0.908 g / cm 3 The melting point of the polyolefin elastomer is 100°C and the density is 0.904 g / cm 3 .

2. An anti-pollution inner layer film, characterized in that: The invention comprises a corona layer, a barrier layer and an anti-pollution heat-sealing layer which are stacked, and the anti-pollution heat-sealing layer is the anti-pollution heat-sealing film according to claim 1.

3. The anti-pollution inner layer film according to claim 2, characterized in that: The raw materials for preparing the barrier layer include, by weight percentage, 20% to 60% of metallocene linear medium-density polyethylene resin and 40% to 80% of linear low-density polyethylene resin.

4. The anti-pollution inner layer film according to claim 3, characterized in that: The melting point of the metallocene linear medium density polyethylene resin is 123°C and the density is 0.935 g / cm 3 .

5. The anti-pollution inner layer film according to claim 4, characterized in that: The metallocene linear medium density polyethylene resin has a melt index of 0.5 to 2.0 g / 10 min at 190° C. and a pressure of 2.16 kg.

6. The anti-pollution inner layer film according to claim 2, characterized in that: The raw materials for preparing the corona layer include, by weight percentage, 10% to 50% of low-density polyethylene resin and 50% to 90% of linear low-density polyethylene resin.

7. A composite membrane, characterized in that It comprises a surface layer, an adhesive layer and an inner layer which are stacked in sequence, wherein the inner layer is the anti-pollution inner layer film according to any one of claims 2 to 6; the surface layer is a polyamide film; and the adhesive layer is a two-component polyurethane adhesive layer.

8. A method for preparing a composite membrane, for preparing the composite membrane according to claim 7, characterized in that: The following steps are involved: S1. Applying an adhesive to the polyamide film and drying it to form the adhesive layer; S2. The polyamide film coated with an adhesive is hot-pressed with the anti-pollution inner film, and the adhesive layer is laminated with the corona layer of the anti-pollution inner film; S3. Ripening treatment to obtain the finished product.

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