Easily tearable heat-sealable film and process for its production

Abstract

The present application relates to the technical field of packaging film, in particular to an easy-to-tear heat-seal film and a preparation process thereof. The easy-to-tear heat-seal film comprises a surface layer, a first transition layer, an easy-to-tear layer, a second transition layer and a heat-seal layer arranged in sequence. The easy-to-tear heat-seal film is extruded and blown into a 5-layer film, so that each layer is thinner, and the planar trend of the single-layer resin is better. The content of homopolymer PP in each layer of raw materials is changed in gradient, and the raw material of the easy-to-tear layer adopts incompatible homopolymer PP and PE. The thickness of each layer of the easy-to-tear heat-seal film and the temperature of the screw extruder are set, so that the easy-to-tear heat-seal film has excellent easy-to-tear performance and relatively high peel strength.

Description

Technical Field

[0001] This invention relates to the field of packaging film technology, specifically to an easy-tear heat-sealable film and its preparation process. Background Technology

[0002] Easy-tear heat-sealable film is commonly used as the inner layer of packaging for coffee, probiotics, pharmaceuticals, facial masks, daily chemical products, and food. Compared to ordinary packaging bags, bags with easy-tear heat-sealable film are easier for consumers to open. During the opening process, the force is stable, the opening is smooth, and the contents or liquids inside the bag are less likely to spill out, providing consumers with a better user experience.

[0003] Most easy-tear heat-sealable films on the market are made by adding easy-tear materials to low-density polyethylene. The main components of easy-tear materials are ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, or cyclic polyethylene. Most of these materials are imported resins, resulting in long procurement cycles, high costs, and supply chains that are heavily influenced by the international environment. Summary of the Invention

[0004] In order to improve the existing easy-tear heat-sealable film, which is made by adding easy-tear raw materials to low-density polyethylene, most of which are imported, resulting in long procurement cycles, high costs, and significant supply chain disruptions due to international factors, this application provides an easy-tear heat-sealable film and its preparation process.

[0005] In the first aspect, this application provides an easy-tear heat-sealing film, which adopts the following technical solution: An easy-tear heat-sealable film includes a surface layer, an easy-tear layer, and a heat-sealable layer arranged sequentially, wherein the surface layer, easy-tear layer, and heat-sealable layer are prepared by an extrusion blown film process to obtain the easy-tear heat-sealable film; The surface layer, by weight, comprises 20-40 parts of LDPE and 60-80 parts of LLDPE. The easy-tear layer, by weight, comprises 10-30 parts of LDPE, 30-50 parts of LLDPE and 30-60 parts of homopolymer PP. The heat-sealing layer, by weight, comprises 5-15 parts of LDPE, 50-60 parts of LLDPE, 30-50 parts of MLLDPE, 1.5-3.5 parts of opening agent and 1.5-3.5 parts of slip agent. The thickness of the easy-tear layer is 16-26 μm.

[0006] By adopting the above technical solution, the easy-tear layer is made of PE and homopolymer PP mixed blown film. By utilizing the incompatibility of PE and homopolymer PP, an easy-tear film with low tensile strength and low elongation at break is obtained.

[0007] The surface material includes LDPE and LLDPE, giving it a smooth film surface. The combination of LLDPE and LDPE also gives the easy-tear heat-sealable film certain mechanical properties and good processability.

[0008] The heat-sealing layer uses a combination of LDPE, LLDPE, MLLDPE, opening agent, and slip agent, which gives the easy-tear heat-sealing film a low-temperature heat-sealing capability and high heat-sealing strength.

[0009] The combination of opening agent and slip agent gives the easy-tear heat-sealable film a relatively stable coefficient of friction, while effectively preventing the easy-tear heat-sealable film from sticking together when unwinding.

[0010] If the easy-tear layer is too thin, the easy-tear effect will not be ideal; if it is too thick, the synergy between the easy-tear layer and the surface layer and the heat-sealing layer may change, which will reduce the peel strength of the easy-tear heat-sealing film and make it easy for delamination to occur.

[0011] The use of incompatible homopolymer PP and PE in the easy-tear layer, along with the controlled thickness of the easy-tear layer, gives the easy-tear heat-sealable film both excellent tearability and peel strength.

[0012] Preferably, an easy-tear heat-sealable film further includes a first transition layer and a second transition layer, wherein the first transition layer is located between the connecting surface layer and the easy-tear layer, and the second transition layer is located between the connecting easy-tear layer and the heat-sealable layer; The surface layer, first transition layer, easy-tear layer, second transition layer, and heat-sealing layer are prepared into an easy-tear heat-sealing film by an extrusion blown film process; the first transition layer, by weight, comprises 5-15 parts of LDPE, 50-80 parts of LLDPE, and 10-40 parts of homopolymer PP. The second transition layer, by weight, comprises 5-15 parts of LDPE, 50-80 parts of LLDPE and 10-40 parts of homopolymer PP.

[0013] Through the above technical solution, the first transition layer and the second transition layer use a large amount of PE and a small amount of homopolymer PP, so that the homopolymer PP content in the formulation of the surface layer, the first transition layer and the easy-tear layer varies in a gradient, so that the surface layer, the first transition layer and the easy-tear layer have high bonding strength, and the easy-tear heat-sealable film has good tearability, peel strength and heat-seal strength at the same time.

[0014] The easy-tear heat-sealable film is made by extruding and blowing a 5-layer film, making each layer thinner and the planarity of the single-layer resin better. The easy-tear layer uses incompatible homopolymer PP and PE, and the homopolymer PP content in the formulation of each layer is varied. The easy-tear heat-sealable film has low tensile strength and low elongation at break, which makes the easy-tear heat-sealable film have good tearability, peel strength and heat-sealing strength at the same time.

[0015] Preferably, the thickness of the surface layer is 6-14 μm, the thickness of the first transition layer is 10-21 μm, the thickness of the second transition layer is 10-21 μm, and the thickness of the heat-sealing layer is 5-14 μm.

[0016] By using the above technical solutions, and by selecting appropriate thicknesses for the surface layer, the first transition layer, the easy-tear layer, the second transition layer, and the heat-sealing layer, the easy-tear heat-sealing film can simultaneously possess good tearability and peel strength.

[0017] Preferably, the opening agent is at least one of oleamide, erucamide, and synthetic silica powder; the slip agent is at least one of paraffin wax, polyethylene, zinc stearate, calcium stearate, lead stearate, oleamide, and lauric acid.

[0018] Through the above technical solutions, the opening agent and slip agent enable the easy-tear heat-sealable film to have a stable coefficient of friction, while effectively preventing the easy-tear heat-sealable film from sticking together when unwinding.

[0019] Preferably, the easy-tear layer further comprises, by weight, 4-8 parts of nano-titanium dioxide and 2-4 parts of nano-calcium carbonate.

[0020] By adding nano-titanium dioxide to the easy-tear layer, the weak interfacial bonding strength between nano-titanium dioxide and the homopolymer PP and PE resin in the easy-tear layer is utilized to further improve the easy-tear heat-sealable film's tearability. At the same time, the high surface energy of nano-titanium dioxide further enhances the bonding strength between the easy-tear layer and other composite layers, thereby improving the easy-tear heat-sealable film's tearability, peel strength, and heat-seal strength.

[0021] Nano-calcium carbonate enhances the toughness of easy-tear heat-sealable films. However, adding nano-titanium dioxide to easy-tear heat-sealable films may lead to poor synergy between the easy-tear heat-sealable film and other film layers, resulting in unsatisfactory effects of nano-titanium dioxide in enhancing the bonding strength between the easy-tear layer and other composite layers. By using nano-titanium dioxide in combination with nano-calcium carbonate, the easy-tear properties of the easy-tear heat-sealable film, as well as the bonding strength and heat-sealing strength between the easy-tear layer and other composite layers, can be further enhanced.

[0022] Preferably, the nano-titanium dioxide has a particle size of 30-100 nm, and the nano-calcium carbonate has a particle size of 50-100 nm.

[0023] By optimizing the particle size of nano-titanium dioxide and nano-calcium carbonate through the above technical solution, the nano-titanium dioxide and nano-calcium carbonate are more evenly dispersed, resulting in better synergistic effect between the nano-titanium dioxide and nano-calcium carbonate, further enhancing the tearability of the easy-tear heat-sealable film and the bonding strength and heat-sealing strength between the easy-tear layer and other composite layers.

[0024] Secondly, this application provides a process for preparing an easy-tear heat-sealing film.

[0025] A process for preparing an easy-tear heat-sealable film includes the following preparation steps: S1: The raw materials for the surface layer, easy-tear layer and heat-sealing layer are fed, mixed, melted and extruded separately using independent screws. After extrusion, the molten resins of the surface layer, easy-tear layer and heat-sealing layer are stacked in sequence. S2: Stacked resins are blown laterally and stretched longitudinally to achieve the required thickness range for the easy-tear heat-sealable film. After cooling, the easy-tear heat-sealable film is obtained. S3: Cut and rewind.

[0026] By adopting the above technical solution and using extrusion blown film technology, each layer of the multi-layer easy-tear heat-sealable film is thinner, and the planarity of the single-layer resin is better, resulting in a better easy-tear effect for the easy-tear heat-sealable film.

[0027] Preferably, the easy-tear heat-sealing film further includes a first transition layer and a second transition layer. In S1, the raw materials of the surface layer, the first transition layer, the easy-tear layer, the second transition layer and the heat-sealing layer are fed, mixed, melted and extruded by independent screws respectively. The molten resin of the surface layer, the first transition layer, the easy-tear layer, the second transition layer and the heat-sealing layer after extrusion is stacked in sequence. Before S3 cutting and winding, the surface is subjected to corona treatment to make the surface tension of the surface layer ≥40dyn.

[0028] By adopting the above technical solution, an easy-tear heat-sealable film is produced by extrusion blown film technology from the surface layer, the first transition layer, the easy-tear layer, the second transition layer, and the heat-sealable layer. The easy-tear heat-sealable film has excellent tear-off effect, interlayer bonding strength, and heat-sealable performance.

[0029] Corona treatment makes the surface tension of the surface layer ≥40dyn, making the easy-tear heat-sealable film easier to laminate with other packaging composite bags.

[0030] Preferably, in step S1, the temperature of the screw extruder in the surface layer is 150-160℃ in zone one, 170-180℃ in zone two, 170-180℃ in zone three, 170-180℃ in zone four, 165-180℃ in zone five, and the die temperature is 180-200℃. The temperature of the screw extruder in the first transition layer is 165℃ in zone one, 180-195℃ in zone two, 180-195℃ in zone three, 180-195℃ in zone four, 175-195℃ in zone five, 175-190℃ in zone six, and the die temperature is 180-195℃. The temperature of the screw extruder for the easy-tear layer is 165℃ in zone one, 180-195℃ in zone two, 185-195℃ in zone three, 180-200℃ in zone four, 175-195℃ in zone five, 175-190℃ in zone six, 175-190℃ in zone seven, and the die temperature of the die head is 180-195℃. The temperature of the screw extruder in the second transition layer is 160-165℃ in zone one, 180-195℃ in zone two, 180-200℃ in zone three, 180-200℃ in zone four, 175-190℃ in zone five, 175-190℃ in zone six, and the die opening temperature is 180-195℃. The temperature of the screw extruder for the heat-sealing layer is 150-160℃ in zone one, 170-180℃ in zone two, 170-180℃ in zone three, 170-180℃ in zone four, 165-175℃ in zone five, and the die temperature is 180-200℃.

[0031] By adopting the above technical solution, the raw materials of the surface layer, the first transition layer, the easy-tear layer, the second transition layer and the heat-sealing layer are matched with each other, and the extrusion temperature of the screw extruder for the surface layer, the first transition layer, the easy-tear layer, the second transition layer and the heat-sealing layer is set so that the adjacent layers of the tear-and-seal film have high bonding strength and heat-sealing strength, thereby making the prepared easy-tear heat-sealing film have excellent peel strength and heat-sealing strength.

[0032] In summary, this application has the following beneficial effects: 1. An easy-tear heat-sealable film, comprising a surface layer, an easy-tear layer, and a heat-sealable layer, wherein the surface layer, the easy-tear layer, and the heat-sealable layer are prepared by an extrusion blown film process to obtain the easy-tear heat-sealable film; The easy-tear layer uses incompatible homopolymer PP and PE, and the thickness of each layer of the easy-tear heat-sealable film and the temperature of the screw extruder are set to give the easy-tear heat-sealable film excellent tear-resistant properties.

[0033] 2. An easy-tear heat-sealable film further includes a first transition layer and a second transition layer. The first transition layer is located between the connecting surface layer and the easy-tear layer, and the second transition layer is located between the connecting easy-tear layer and the heat-sealable layer. The easy-tear heat-sealable film is made of 5-layer film extrusion blown film, which makes each layer thinner and the planarity of the single-layer resin better. The easy-tear layer uses incompatible homopolymer PP and PE, and the gradient change of homopolymer PP content in each layer is matched, so that the easy-tear heat-sealable film has excellent tear performance, peel strength and heat-seal strength at the same time.

[0034] 3. An easy-tear heat-sealable film, wherein the easy-tear layer is made of nano-titanium dioxide and nano-calcium carbonate. By using nano-titanium dioxide and nano-calcium carbonate in combination, the easy-tear heat-sealable film's tearability, peel strength, and heat-sealing strength are further enhanced. Detailed Implementation

[0035] Example of preparation of raw materials and / or intermediates: Raw materials: silica powder (average particle size: 2.5±1μm), paraffin wax (molecular weight 360-540), microcrystalline wax (molecular weight 250-450), polyethylene wax (average molecular weight 2000-3000). Example

[0036] Example 1 An easy-tear heat-sealable film includes a surface layer, a first transition layer, an easy-tear layer, a second transition layer, and a heat-sealable layer arranged sequentially. The easy-tear heat-sealable film is prepared using the following steps. The raw materials for the surface layer, the first transition layer, the easy-tear layer, the second transition layer, and the heat-sealable layer are shown in Table 1.

[0037] S1: The surface layer, first transition layer, easy-tear layer, second transition layer and heat-sealing layer are fed, mixed and melted by independent screws and extruded from the die head. After extrusion, the molten resin of the surface layer, first transition layer, easy-tear layer, second transition layer and heat-sealing layer are stacked in sequence.

[0038] The surface layer screw extruder has a zone temperature of 150℃, a zone temperature of 170℃, a zone temperature of 170℃, a zone temperature of 170℃, a zone temperature of 170℃, a zone temperature of 165℃, and a die head temperature of 180℃.

[0039] The temperature of the screw extruder in the first transition layer is 165℃ in zone one, 180℃ in zone two, 180℃ in zone three, 180℃ in zone four, 175℃ in zone five, 175℃ in zone six, and 180℃ at the die opening.

[0040] The temperature of the screw extruder with the easy-tear layer is 165℃ in zone 1, 180℃ in zone 2, 185℃ in zone 3, 180℃ in zone 4, 175℃ in zone 5, 175℃ in zone 6, 175℃ in zone 7, and the die temperature is 180℃.

[0041] The temperature of the screw extruder in the second transition layer is 160℃ in zone one, 180℃ in zone two, 180℃ in zone three, 180℃ in zone four, 175℃ in zone five, 175℃ in zone six, and 180℃ at the die opening.

[0042] The temperature of the screw extruder for the heat-sealing layer is 150℃ in zone 1, 170℃ in zone 2, 170℃ in zone 3, 170℃ in zone 4, 165℃ in zone 5, and the die temperature is 180℃.

[0043] S2: The stacked resin is blown laterally and stretched longitudinally to make the thickness of the easy-tear heat-sealable film reach the required range. At the same time, an internal circulation cooling and an external blowing cooling system are used for cooling. After cooling, the surface layer is corona treated by an online corona machine to make the surface tension of the surface layer ≥40dyn, thus preparing the easy-tear heat-sealable film.

[0044] S3: Cut to the required width and roll up.

[0045] Among them, the LDPE for the surface layer, the first transition layer, and the easy-tear layer is grade 2420H, and the LLDPE is grade FL201XV; the LDPE for the second transition layer and the heat-sealing layer is grade 2426H, and the LLDPE is grade FL201KI; the homopolymer PP for the first transition layer, the easy-tear layer, and the second transition layer is grade T30S; the MLLDPE grades are SP1520 and SP0510H, and the mass ratio of SP1520 to SP0510H is 1:2; the synthetic silica powder is grade POIYBATCH AB5; and the polyethylene is grade Shulman Plastics FSU-105-E.

[0046] Examples 2-4 A type of easy-tear heat-sealable film differs from Example 1 in that the raw material weights and thicknesses of the surface layer, first transition layer, easy-tear layer, easy-tear layer, and heat-sealable layer are different, as are the types and settings of the opening agent and slip agent, and the parameter settings of the screw extruder, as shown in Tables 1-2.

[0047] Table 1 lists the raw material weights and thicknesses of the surface layer, first transition layer, easy-tear layer, easy-tear layer, and heat-sealable layer of the easy-tear heat-sealable film in Examples 1-4, as well as the types and configurations of the opening agent and slip agent. Table 2 lists the parameter settings for the screw extruder of the surface layer, first transition layer, easy-tear layer, easy-tear layer, and heat-sealing layer of the easy-tear heat-sealable film in Examples 1-4. Examples 5-8 An easy-tear heat-sealable film differs from Example 1 in that the raw material weight, thickness, and percentage content of homopolymer PP in the easy-tear layer are set differently, as detailed in Table 3.

[0048] Table 3 lists the raw material weight, thickness, and percentage of homopolymer PP content in the easy-tear layer of Examples 5-8 and Example 1. Examples 9-16 An easy-tear heat-sealing film differs from Example 1 in that the raw material weight, thickness, and percentage content of homopolymer PP in the first and second transition layers are set differently, as detailed in Table 4.

[0049] Table 4 lists the raw material weight, thickness, and percentage of homopolymer PP content in the first and second transition layers of Examples 9-16 and Example 1. Example 17 An easy-tear heat-sealable film, which differs from Example 1 in that it does not employ a first transition layer and a second transition layer.

[0050] Example 18 An easy-tear heat-sealable film differs from Example 1 in that it does not employ a first transition layer and a second transition layer, and the surface of the easy-tear heat-sealable film is not subjected to corona treatment before cutting and winding in S3.

[0051] Examples 19-20 The difference between this easy-tear heat-sealable film and Example 18 is that the screw extruder parameters for the surface layer, first transition layer, easy-tear layer, easy-tear layer, and heat-sealable layer of the easy-tear heat-sealable film are set differently, as shown in Table 5.

[0052] Table 5 lists the parameter settings for the screw extruder of the surface layer, first transition layer, easy-tear layer, easy-tear layer, and heat-sealing layer of the easy-tear heat-sealable film in Examples 19-20. Examples 21-23 An easy-tear heat-sealable film differs from Example 18 in that the raw material of the easy-tear layer also includes nano-titanium dioxide and nano-calcium carbonate. The difference between Examples 21-23 lies in the different weight and particle size settings of nano-titanium dioxide and nano-calcium carbonate, as shown in Table 6.

[0053] Table 6. Weight and particle size settings of nano-titanium dioxide and nano-calcium carbonate in Examples 21-23. Example 24 An easy-tear heat-sealable film, which differs from Example 21 in that it does not use nano-calcium carbonate.

[0054] Comparative Example Comparative Example 1 An easy-tear heat-sealable film, which differs from Example 18 in that it does not have an easy-tear layer.

[0055] Comparative Example 2 An easy-tear heat-sealable film, which differs from Example 18 in that the easy-tear layer uses 70 kg of homopolymer PP, 5 kg of LDPE and 20 kg of LLDPE.

[0056] Comparative Example 3 An easy-tear heat-sealable film, which differs from Example 18 in that the easy-tear layer uses 40 kg of LDPE, 60 kg of LLDPE and 20 kg of homopolymer PP.

[0057] Comparative Example 4 An easy-tear heat-sealable film, which differs from Example 18 in that the thickness of the easy-tear layer is 12 μm, the surface layer does not use LLDPE, and the heat-sealable layer does not use LLDPE.

[0058] Comparative Example 5 An easy-tear heat-sealable film, which differs from Example 18 in that the thickness of the easy-tear layer is 12 μm and the surface layer is not made of LLDPE.

[0059] Comparative Example 6 An easy-tear heat-sealable film, which differs from Example 18 in that the easy-tear layer is composed of 80 parts LLDPE, 10 parts LDPE and 10 parts HDPE.

[0060] Comparative Example 7 An easy-tear heat-sealable film, which differs from Example 18 in that the easy-tear layer is made of polyethylene, polyethylene-vinyl acrylate and polyethylene-acrylic resin in a mass ratio of 1:1:1.

[0061] Performance testing Test 1: Tensile strength test method: The test shall be conducted in accordance with GB / T13022-1991 "Test method for tensile properties of plastic films".

[0062] Test 2: Elongation at break test method: The test shall be conducted in accordance with GB / T13022-1991 "Test method for tensile properties of plastic films".

[0063] Test 3: Peel Strength Test method: in accordance with GB / T2792-2014 "Test method for peel strength of adhesive tape".

[0064] Test 4: Heat seal strength test method: The heat seal strength between heat seal layers is tested according to QB / T2358-1998 "Test method for heat seal strength of plastic film packaging bags".

[0065] Test samples: The easy-tear heat-sealing films of Examples 1-24 were used as test samples, and the easy-tear heat-sealing films of Comparative Examples 1-7 were used as control samples.

[0066] Test results: The tensile strength, elongation at break, peel strength and heat seal strength of the easy-tear heat-sealable films of Examples 1-24 and Comparative Examples 1-7 are shown in Table 7.

[0067] Table 7 lists the test results of tensile strength, elongation at break, peel strength, and heat seal strength of the easy-tear heat-sealable films of Examples 1-24 and Comparative Examples 1-7. Combining Examples 1-24 and Comparative Examples 1-7 with Table 7, it can be seen that: The tensile strength and elongation at break of Examples 1-24 were significantly lower than those of Comparative Examples 1-7, indicating that by setting an easy-tear layer in the easy-tear heat-sealable film, and by using incompatible homopolymers PP and PE in the easy-tear layer, and by setting the thickness of each layer of the easy-tear heat-sealable film and the temperature of the screw extruder, the easy-tear heat-sealable film has excellent tearability. Furthermore, the raw materials of the easy-tear layer also include nano-titanium dioxide and nano-calcium carbonate. By using nano-titanium dioxide and nano-calcium carbonate in combination, the tearability and peel strength of the easy-tear heat-sealable film are further enhanced.

[0068] Compared with Examples 17-18, Examples 1-16 and 19-24 show significantly better peel strength than Examples 17-18. This indicates that by setting a first transition layer and a second transition layer in the easy-tear heat-sealable film, the easy-tear heat-sealable film has low tensile strength and low elongation at break, while also exhibiting excellent peel strength and heat-seal strength. This may be because the easy-tear heat-sealable film is made by extruding and blowing a 5-layer film, resulting in thinner layers and better planarity of the single-layer resin. The easy-tear layer uses incompatible homopolymer PP and PE, with a gradient change in the content of homopolymer PP between each layer, which makes the easy-tear heat-sealable film have low tensile strength and low elongation at break, while also exhibiting excellent peel strength and heat-seal strength.

[0069] Although Comparative Example 1 has higher peel strength and heat seal strength, its tensile strength and elongation at break are significantly higher than those of the embodiments in this application, and its tear resistance is poor.

[0070] Compared with Example 1, in Examples 5-6, when the homopolymer PP content in the easy-tear layer of Example 1 is 50%, the tensile strength and elongation at break of the easy-tear heat-sealable film are the lowest. This may be because when the homopolymer PP content in the easy-tear layer is 50%, the interaction force between homopolymer PP and PE in the easy-tear layer is the lowest due to the incompatibility of homopolymer PP and PE, resulting in the best easy-tear effect of the easy-tear heat-sealable film. As the homopolymer PP content in the easy-tear layer changes, when the homopolymer PP content in the easy-tear layer is the lowest and the PE content is higher, the force of the easy-tear layer on the first transition layer is greater, which reduces the toughness of the first transition layer and makes it easier to peel off from the surface layer, thus reducing the peel strength of the easy-tear heat-sealable film.

[0071] Compared to Example 1, in Examples 7-8, when the content of PE and homopolymer PP in the easy-tear layer remains constant, the tensile strength and elongation at break of the easy-tear layer decrease with increasing thickness, indicating that the easy-tear heat-sealable film exhibits excellent tearability. However, when the thickness of the easy-tear layer is 26 μm, the peel strength of Example 8 is significantly lower than that of Examples 1 and 7. This may be because when the easy-tear layer is too thick, the difference in strain performance between the easy-tear layer and the first transition layer increases under external force, resulting in a decrease in the peel strength of the easy-tear heat-sealable film.

[0072] The peel strength test results from Examples 9-12 and Example 1 show that in the first and second transition layers, the homopolymer PP content is in the range of 8%-48%. As the homopolymer PP content increases, the peel strength first increases and then decreases. The peel strength is the highest when the homopolymer PP content is 21%. This may be because when the homopolymer PP content of the first transition layer is 21%, the homopolymer PP content of the surface layer, the first transition layer, and the easy-tear layer shows a gradient increase, which makes the first transition layer have good adhesion to both the surface layer and the easy-tear layer, resulting in good peel strength and heat-sealing strength of the easy-tear heat-sealable film.

[0073] The test results of tensile strength and elongation at break of Examples 9-12 and Example 1 show that in the first transition layer and the second transition layer, the homopolymer PP content is in the range of 8%-48%. As the homopolymer PP content increases, the tensile strength and elongation at break of the easy-tear heat-sealable film show a decreasing trend.

[0074] The peel strength test results from Examples 13-16 and Example 1 show that, within the thickness range of 5-26 μm for the first and second transition layers, the peel strength and heat-sealing strength of the easy-tear heat-sealing film first increase and then decrease as the thickness of the first and second transition layers increases. This may be because when the thickness of the first transition layer is thin, it is insufficient to withstand the force exerted on it by the surface layer and the easy-tear layer, resulting in lower peel strength and heat-sealing strength of the easy-tear heat-sealing film. When the thickness of the first transition layer is thick, the synergistic effect between the first transition layer and the surface layer and the easy-tear layer is poor when the easy-tear heat-sealing film is subjected to external force, resulting in lower peel strength of the easy-tear heat-sealing film.

[0075] The test results of tensile strength and elongation at break of Examples 13-16 and Example 1 show that: The thickness of the first and second transition layers is in the range of 5-26 μm. As the thickness of the first and second transition layers increases, the tensile strength and elongation at break of the easy-tear heat-sealable film show an increasing trend. This may be because the homopolymer PP content in the transition layer is relatively low, while PE accounts for the majority. The first and second transition layers have a reinforcing effect on the tensile strength and elongation at break of the easy-tear heat-sealable film.

[0076] Test 5: Friction coefficient test method: The surface of the easy-tear heat-sealable film was tested according to GB10006 "Determination of friction coefficient of plastic film and sheet".

[0077] Experiment 6: Corona Value Test method: The surface of the easy-tear heat-sealing film was tested using a 38-dyne pen.

[0078] Test samples: The easy-tear heat-sealing films of Examples 1-4 and Example 18 were used as test samples.

[0079] Test results: The coefficient of friction and corona value of the easy-tear heat-sealing film of Examples 1-4 and Example 18 are shown in Table 8.

[0080] Table 8 lists the test results of the friction coefficient and corona value of the easy-tear heat-sealing film in Examples 1-4 and Example 18. In Table 8, the curing conditions for the easy-tear heat-sealing film are 45℃ / 30min.

[0081] A comparison of the coefficient of friction and corona value of the easy-tear heat-sealable film in Examples 1-4 and Example 18 shows that the coefficient of friction of the surface layer of the easy-tear heat-sealable film increases after corona treatment.

[0082] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An easy-tear heat-sealable film, characterized in that, The film comprises a surface layer, a first transition layer, an easy-tear layer, a second transition layer, and a heat-sealing layer arranged sequentially. The surface layer, the first transition layer, the easy-tear layer, the second transition layer, and the heat-sealing layer are prepared by an extrusion blown film process to obtain an easy-tear heat-sealing film. The surface layer, by weight, comprises 20-40 parts of LDPE and 60-80 parts of LLDPE. The easy-tear layer, by weight, comprises 10-30 parts of LDPE, 30-50 parts of LLDPE, 30-60 parts of homopolymer PP, 4-8 parts of nano titanium dioxide and 2-4 parts of nano calcium carbonate. The heat-sealing layer, by weight, comprises 5-15 parts of LDPE, 50-60 parts of LLDPE, 25-35 parts of MLLDPE, 1.5-3.5 parts of opening agent and 1.5-3.5 parts of slip agent. The first transition layer, by weight, comprises 5-15 parts of LDPE, 50-80 parts of LLDPE and 10-40 parts of homopolymer PP. The second transition layer, by weight, comprises 5-15 parts of LDPE, 50-80 parts of LLDPE and 10-40 parts of homopolymer PP. The thickness of the easy-tear layer is 16-26 μm; the thickness of the surface layer is 6-14 μm; the thickness of the first transition layer is 10-21 μm; the thickness of the second transition layer is 10-21 μm; and the thickness of the heat-sealing layer is 5-14 μm. The homopolymer PP content of the surface layer, the first transition layer, and the easy-tear layer increases in a gradient, as does the homopolymer PP content of the heat-sealing layer, the second transition layer, and the easy-tear layer.

2. The easy-tear heat-sealing film according to claim 1, characterized in that: The thickness of the first transition layer is 15 μm, the thickness of the easy-tear layer is 21 μm, and the thickness of the second transition layer is 15 μm.

3. The easy-tear heat-sealing film according to claim 1, characterized in that: The opening agent is at least one of oleamide, erucamide, and synthetic silica powder; the slip agent is at least one of paraffin wax, polyethylene, zinc stearate, calcium stearate, lead stearate, oleamide, and lauric acid.

4. The easy-tear heat-sealing film according to claim 1, characterized in that: The nano-titanium dioxide has a particle size of 30-100 nm, and the nano-calcium carbonate has a particle size of 50-100 nm.

5. The preparation process of an easy-tear heat-sealing film according to any one of claims 1-4, characterized in that: The preparation steps include the following: S1: The raw materials for the surface layer, first transition layer, easy-tear layer, second transition layer and heat-sealing layer are fed, mixed, melted and extruded separately using independent screw extruders. The molten resins of the surface layer, first transition layer, easy-tear layer, second transition layer and heat-sealing layer after extrusion are stacked in sequence. S2: Stacked resins are blown laterally and stretched longitudinally to achieve the required thickness range for the easy-tear heat-sealable film. After cooling, the easy-tear heat-sealable film is obtained. S3: Cut and rewind.

6. The preparation process of an easy-tear heat-sealing film according to claim 5, characterized in that: Before S3 cutting and winding, the surface of the surface layer is subjected to corona treatment to make the surface tension of the surface layer ≥40dyn.

7. The preparation process of an easy-tear heat-sealing film according to claim 6, characterized in that: In step S1, the temperature of the screw extruder in the surface layer is 150-160℃ in zone one, 170-180℃ in zone two, 170-180℃ in zone three, 170-180℃ in zone four, 165-180℃ in zone five, and the die temperature of the die head is 180-200℃. The temperature of the screw extruder in the first transition layer is 165℃ in zone one, 180-195℃ in zone two, 180-195℃ in zone three, 180-195℃ in zone four, 175-195℃ in zone five, 175-190℃ in zone six, and the die temperature is 180-195℃. The temperature of the screw extruder for the easy-tear layer is 165℃ in zone one, 180-195℃ in zone two, 185-195℃ in zone three, 180-200℃ in zone four, 175-195℃ in zone five, 175-190℃ in zone six, 175-190℃ in zone seven, and the die temperature of the die head is 180-195℃. The temperature of the screw extruder in the second transition layer is 160-165℃ in zone one, 180-195℃ in zone two, 180-200℃ in zone three, 180-200℃ in zone four, 175-190℃ in zone five, 175-190℃ in zone six, and the die opening temperature is 180-195℃. The temperature of the screw extruder for the heat-sealing layer is 150-160℃ in zone one, 170-180℃ in zone two, 170-180℃ in zone three, 170-180℃ in zone four, 165-175℃ in zone five, and the die temperature is 180-200℃.

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