Highly transparent low-strength tearable film and method for making same

Abstract

The application relates to the field of high polymer materials, and particularly discloses a high-transparency low-strength easy-tear film and a preparation method thereof. The high-transparency low-strength easy-tear film comprises an inner layer, a middle layer and an outer layer, the raw materials of the inner layer are 38-50 parts of LDPE, 50-70 parts of type I LLDPE, 1.5-2.5 parts of an opening agent, 2-2.8 parts of a slip agent, 0.3-0.5 parts of an antioxidant and 0.3-0.5 parts of a PPA additive, the raw materials of the middle layer are 25-35 parts of No. 1 LDPE, 25-35 parts of type I-No. 1 LLDPE, 8-12 parts of HDPE, 15-25 parts of a butadiene-styrene block copolymer, 0.6-1 part of a plasticizer, 0.2-0.4 parts of an antioxidant and 8-12 parts of a filling master batch, and the raw materials of the outer layer are 25-35 parts of No. 1 LDPE, 60-80 parts of type II LLDPE, an antioxidant and a plasticizer. The easy-tear film has the advantages of easy tearing in the longitudinal and transverse directions, high transparency and low haze.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and more specifically, it relates to a highly transparent, low-strength, easy-tear film and its preparation method. Background Technology

[0002] With the development of science and technology and the improvement of living standards, people have put forward various new requirements for packaging materials. People are no longer satisfied with the simple functions of food packaging, such as protecting food and extending its shelf life. They are increasingly demanding ease of use in actual use, especially in the food industry, for example, for rice or cat food. A well-known problem with these bags is their opening mechanism. Often, without tools (such as knives and scissors), the bags can only be opened with effort at predetermined serrations (or small holes or cuts). Another problem is that opening the bag by hand produces curved slits instead of straight ones, increasing the risk of unintentional leakage of the contents. Therefore, there is a need to develop films for bags that can be easily opened by hand at the cuts and produce straight slits inside the bag.

[0003] In the prior art, Chinese invention patent application document with application number 2019104629104 discloses an easy-tear PE film material, its preparation method and application. The easy-tear PE film material has a layered structure and contains a film composed of the following components by weight percentage: 55-70% polyethylene; 30-40% ethylene cyclic olefin copolymer; and 0-5% processing aids.

[0004] The aforementioned easy-tear PE film material is modified by cyclic olefin copolymer (COC), but it has high haze, low light transmittance, and poor transparency, which affects the appearance quality of the product in terms of shape, color, and freshness. It also has poor mechanical properties (including low tensile strength and low impact resistance), and its straight-line easy-tear performance is generally poor. It needs to be used in combination with other easy-tear materials such as BOPET and aluminum foil to achieve the easy-tear effect by making tearing holes or serrated lines. However, due to the poor tear guidance of tearing holes or serrated lines, it often leads to poor tearing or uneven tear edges, causing the contents to spill out. Moreover, the combined use of these materials still affects the transparency of the easy-tear PE film.

[0005] Regarding the aforementioned technologies, the inventors discovered that the transparency of current easy-tear PE films needs improvement. Summary of the Invention

[0006] In order to simultaneously improve the linear tearability and transparency of PE film, this application provides a high-transparency, low-strength tearable film and its preparation method.

[0007] In a first aspect, this application provides a highly transparent, low-strength, easy-tear film, employing the following technical solution:

[0008] A highly transparent, low-strength, easy-tear film includes an inner layer, a middle layer, and an outer layer. The inner layer comprises the following raw materials in parts by weight: 38-50 parts LDPE, 50-70 parts Class I LLDPE, 1.5-2.5 parts opening agent, 2-2.8 parts slip agent, 0.3-0.5 parts antioxidant, and 0.3-0.5 parts PPA additive.

[0009] The inner layer contains LDPE of type 1 and type 2 in a mass ratio of 10:1-1.5. LDPE type 1 has a melt index of 1.9-2 g / 10 min and a density of 0.924-0.925 g / cm³. 3 The melt index of LDPE No. 2 is 4-5 g / 10 min, and its density is 0.923-0.925 g / cm³. 3 ;

[0010] The inner layer contains type I LLDPE, including LLDPE I-1 and LLDPE I-2 in a mass ratio of 1.5-2:1. LLDPE I-1 has a melt index of 2 g / 10 min and a density of 0.918-0.92 g / cm³. 3 The melt index of LLDPE No. I-2 is 4-10 g / 10 min;

[0011] The intermediate layer comprises the following raw materials in parts by weight: 25-35 parts of No. 1 LDPE, 25-35 parts of No. 1-1 LLDPE, 8-12 parts of HDPE, 15-25 parts of styrene-butadiene block copolymer, 0.6-1 parts of plasticizer, 0.2-0.4 parts of antioxidant, and 8-12 parts of filler masterbatch.

[0012] The outer layer comprises the following raw materials in parts by weight: 25-35 parts No. 1 LDPE, 60-80 parts Class II LLDPE, 0.3-0.5 parts antioxidant, and 0.6-1 parts plasticizer.

[0013] By adopting the above technical solution, the inner layer uses No. 2 LDPE with a high melt index, which has high transparency and excellent processability and ductility. In addition, when used in combination with No. 1 LDPE, it not only gives the plastic film a good longitudinal and transverse straight tear effect, but also good transparency. At the same time, the addition of Class I LLDPE, which uses two types of LLDPE with different melt indices, can be evenly dispersed in the inner layer, which not only enhances the straight tearability, but also has good low-temperature heat-sealing properties. The opening agent can reduce the surface friction coefficient of the film, giving the easy-tear film good opening performance, and the slip agent can reduce the surface friction coefficient, making the easy-tear film flow smoother.

[0014] The intermediate layer uses No. 1 LDPE and No. I-1 LLDPE. No. I-1 LLDPE has a high melt index, making it suitable for casting production. It has excellent dimensional stability, impact resistance, and stiffness. Moreover, the mixture of the two resins can produce a film with good stiffness and transparency, further improving tearability. In addition, the addition of styrene-butadiene block copolymer in the intermediate layer provides high rigidity, good heat-sealing properties, high gloss and clarity, and good toughness, which can improve the transparency and tearability of the film.

[0015] The outer layer uses No. 1 LDPE and another type of LLDPE. No. 1 LDPE has high fluidity, better processing performance, and is suitable for casting production. Moreover, after casting, it has high gloss and transparency, low haze, high impact resistance, and is easy to tear in both longitudinal and transverse directions.

[0016] The easy-tear film made from the above materials has high transparency and low haze, and is easier to tear both horizontally and vertically. Furthermore, it is less likely to be difficult to cut or to produce burrs or uneven edges when hot-cut.

[0017] Optionally, the outer layer comprises type II LLDPE, including type II-1 LLDPE and type II-2 LLDPE in a mass ratio of 2:4-5, wherein the density of type II-1 LLDPE is 0.924-0.925 g / cm³. 3 The melt flow index is 20 g / 10 min, and the density of II-2 LLDPE is 0.915-0.921 g / cm³. 3 The melt flow index is 1.6-2.4 g / 10 min.

[0018] By adopting the above technical solution, the outer layer uses II-1 LLDPE (ExxonMobil, grade 6101XR, melt index 20 g / 10 min, density 0.924 g / cm³) with a high melt index. 3 It has good fluidity, excellent thermal stability and stiffness, strong resistance to environmental stress cracking, and can effectively improve the transverse and longitudinal tearing effect of easy-tear film. II-2 LLDPE also has good melt fluidity and high tensile strength, puncture resistance and impact resistance.

[0019] Optionally, the density of HDPE in the intermediate layer is 0.95-0.9554 g / cm³. 3 The melt flow index is 0.17-0.2 g / 10 min.

[0020] By adopting the above technical solution, HDPE with this density and melt index has high strength and hardness, which can improve the stiffness of easy-tear film and reduce costs.

[0021] Optionally, the density of the styrene-butadiene block copolymer is 1.01 g / cm³. 3The melt flow index is 7.5 g / 10 min.

[0022] By adopting the above technical solution, at a certain temperature, the thermal motion of the styrene-butadiene block copolymer and various polyethylene molecules in the intermediate layer increases, thereby promoting mutual solubility. This allows the styrene-butadiene block copolymer to be dispersed in the polymer, forming a uniform two-phase structure. This disrupts the original forces between polyethylene molecules, causing the molecules to realign and improving the tearability of the polyethylene film.

[0023] Optionally, the filler masterbatch comprises the following raw materials in parts by weight: 0.3-0.4 parts filler, 4-5 parts HDPE, 0.03-0.04 parts diaminosilane coupling agent, 1-1.5 parts EVOH, and 0.15-0.2 parts maleic anhydride-grafted HDPE.

[0024] By adopting the above technical solution, the filler masterbatch is placed in the middle layer, and the filler masterbatch is made of raw materials such as HDPE and diaminosilane coupling agent. EVOH is a copolymer of ethylene and vinyl acetate. Its interaction with polyethylene may restrict the movement of polyethylene molecular chains, hinder the crystallization of PE, and reduce its crystallization rate. Moreover, using maleic anhydride-grafted HDPE as a compatibilizer can form a chemical reaction with EVOH. This compatibility effect may make heterogeneous nucleation more obvious, affecting the normal crystallization of polyethylene, slowing down its grain growth rate, and to a certain extent refining the grains, blurring the intercrystalline interface, making it easier for light beams to pass through, and reducing haze. The diaminosilane coupling agent can improve the compatibility of the filler with HDPE and EVOH. The filler masterbatch makes the heterogeneous nucleation effect of polyethylene gradually more significant during the crystallization process, further increasing the density of crystal nuclei, improving the dispersion of crystal nuclei, making the internal grains of the material significantly refined, reducing spherulites, reducing the amount of light reflection and light scattering on the film surface, thereby reducing the haze of the film and increasing its transparency.

[0025] Optionally, the method for preparing the filler masterbatch is as follows:

[0026] The filler and the diaminosilane coupling agent are mixed and stirred at 5000-6000 rpm for 20-30 minutes at 60-70℃ to obtain the pretreated filler.

[0027] The pretreated filler is mixed with HDPE, EVOH and maleic anhydride-grafted HDPE, and then melted, extruded and granulated.

[0028] By adopting the above technical solution, the filler is first surface modified with a diaminosilane coupling agent to increase its compatibility with EVOH and HDPE and improve its dispersion uniformity. The filler masterbatch is then obtained through blending and granulation.

[0029] Optionally, the filler is selected from at least one of barium sulfate, calcium carbonate, silica and talc.

[0030] By adopting the above technical solutions, barium sulfate has high transparency and has little impact on the transparency of plastic film, thus obtaining an easy-tear film with high gloss and transparency. Calcium carbonate can reduce costs, increase production efficiency, reduce deformation caused by tearing, and obtain a better straight-line easy-tear effect. Talc can improve dimensional stability and surface scratch resistance, enhance dimensional stability, and improve product quality. Silica can increase weather resistance, improve melt flowability, improve thermal stability, and make it easier to tear.

[0031] Optionally, the thickness ratio of the inner layer, middle layer and outer layer is 1:2-3:1-2.

[0032] By adopting the above technical solution, the thickness of the middle and outer layers is relatively high, which can increase the hot air performance of the easy-tear film, ensure its easy-tear effect, and improve the barrier performance of the film.

[0033] Optionally, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, antioxidant 1076 and antioxidant 1098;

[0034] The plasticizer is selected from at least one of dioctyl phthalate, dibutyl phthalate, epoxidized soybean oil, and epoxidized fatty acid butyl ester.

[0035] By adopting the above technical solution, the oxidant can prevent the plastic film from degrading and oxidizing due to factors such as heat, light and oxygen during processing, storage and use, thus avoiding changes in color and performance of the plastic film due to oxidation and maintaining its original performance and appearance.

[0036] Plasticizers can increase the fluidity of various polyethylene molecules, lower the glass transition temperature, and improve the flexibility, extensibility, plasticity, and processability of polyethylene.

[0037] Secondly, this application provides a method for preparing a highly transparent, low-strength, easy-tear film, employing the following technical solution:

[0038] A method for preparing a highly transparent, low-strength, easy-tear film includes the following steps:

[0039] Ingredients: Mix the raw materials for the inner layer, middle layer, and outer layer evenly to obtain the inner layer material, middle layer material, and outer layer material;

[0040] Heating: Heat the outer layer main unit to 195-230℃, the middle layer main unit to 195-230℃, the inner layer main unit to 195-230℃, and the mold head temperature to 195-205℃;

[0041] Blow molding: The inner layer material, middle layer material and outer layer material are placed into the corresponding main machine, and the film bubble is obtained through hot melting, casting, film casting, blowing and pulling.

[0042] Rewinding: After corona treatment, the film bubble is cut, rewound, and packaged.

[0043] By adopting the above technical solution, the temperature of each layer of the host is controlled at 195-230℃. By precisely controlling the temperature stability of each zone, the plasticization of LDPE resin is maximized to prevent the resin from decomposing due to high temperature, and to prevent the resin from being poorly plasticized due to low temperature, which would reduce the surface gloss and transparency of the PE film, thereby improving the processing performance.

[0044] In summary, this application has the following beneficial effects:

[0045] 1. Because this application uses specific amounts of LDPE (containing No. 1 LDPE and No. 2 LDPE) and LLDPE (containing No. I-1 LLDPE and No. I-2 LLDPE), and the melt index of No. 2 LDPE and No. I-2 LLDPE is relatively high, HDPE and filler masterbatch are used in the middle layer, and No. 1 LDPE and Type II LLDPE are used in the outer layer, the resulting easy-tear film has low haze, strong transparency and gloss, and good tearability in both longitudinal and transverse directions, with smooth cuts and less burr generation.

[0046] 2. In this application, it is preferred to use filler, bis(aminosilane) coupling agent, HDPE, EVOH and maleic anhydride grafted HDPE to prepare filler masterbatch, which can effectively reduce the grain refinement of polyethylene, reduce haze and improve transparency.

[0047] 3. The method of this application improves longitudinal and transverse tensile strength by controlling the processing temperature of the extruder, which maintains good stiffness and tearability, while increasing transparency and reducing haze. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of a straight-line tear test method for highly transparent, low-strength, easy-tear films. Detailed Implementation

[0049] The following embodiments provide a further detailed description of this application.

[0050] Preparation Examples of Filler Masterbatch 1-4

[0051] In the preparation example, the density of HDPE was 0.9554 g / cm³. 3The melt index (190℃, 2.16kg) is 0.17g / 10min, selected from Zhenhai Refining & Chemical, model ZH5502H; the diaminosilane coupling agent is selected from Dow Corning OFS-6020; the EVOH is selected from Kuraray, Japan, model H171B; and the maleic anhydride-grafted HDPE is selected from Arkema, France, model 18410P.

[0052] Preparation Example 1: 0.4 kg of filler and 0.04 kg of bisaminosilane coupling agent were mixed and stirred at 5000 rpm for 30 min at 60 °C to obtain a pretreated filler, which was barium sulfate.

[0053] The pretreated filler was mixed with 4 kg HDPE, 1 kg EVOH and 0.15 kg maleic anhydride-grafted HDPE, heated to 200°C, and extruded and granulated at a speed of 50 rpm.

[0054] Preparation Example 2: 0.3 kg of filler and 0.03 kg of bisaminosilane coupling agent were mixed and stirred at 6000 rpm for 20 min at 70 °C to obtain a pretreated filler, which was barium sulfate.

[0055] The pretreated filler was mixed with 5 kg HDPE, 1.5 kg EVOH and 0.2 kg maleic anhydride-grafted HDPE, heated to 200°C, and extruded and granulated at a speed of 50 rpm.

[0056] Preparation Example 3: The difference from Preparation Example 1 is that an equal amount of HDPE was used instead of EVOH.

[0057] Preparation Example 4: The difference from Preparation Example 1 is that an equal amount of HDPE was used instead of maleic anhydride-grafted HDPE. Example

[0058] The sources of each raw material in the following examples are shown in Table 1.

[0059] Table 1. Sources of raw materials in high-transparency, low-strength, easy-tear film

[0060]

[0061] Example 1: A high-transparency, low-strength, easy-tear film comprising an inner layer, a middle layer, and an outer layer interconnected thereto, with a thickness ratio of 1:3:1. The raw material amounts for each layer are shown in Table 2. The LDPE in the inner layer comprises LDPE No. 1 and LDPE No. 2 in a mass ratio of 10:1, with LDPE No. 1 having a density of 0.924 g / cm³. 3 The melt index (190℃, 2.16kg) is 1.9g / 10min, and the density of LDPE No. 2 is 0.923 g / cm³. 3The melt flow index (190℃, 2.16kg) is 4g / 10min; Class I LLDPE includes I-1 LLDPE and I-2 LLDPE with a mass ratio of 2:1. The density of I-1 LLDPE is 0.918g / cm³. 3 The melt index (190℃, 2.16kg) is 2g / 10min, and the melt index of LLDPE I-2 is 4g / 10min;

[0062] The melt flow index (190℃, 2.16kg) of HDPE in the intermediate layer is 0.17g / 10min, and the density is 0.9554g / cm³. 3 The melt index (200℃, 5kg) of the styrene-butadiene block copolymer is 7.5g / 10min, and the density is 1.01g / cm³. 3 ;

[0063] The outer layer of Class II LLDPE includes LLDPE II-1 and LLDPE II-2 in a mass ratio of 2:5. The density of LLDPE II-1 is 0.924 g / cm³. 3 The melt flow index is 20 g / 10 min, and the density of II-2 LLDPE is 0.918 g / cm³. 3 The melt flow index is 1.9 g / 10 min;

[0064] The antioxidants in the inner, middle, and outer layers are all antioxidant 1010. The plasticizers in the middle and outer layers are all epoxidized soybean oil. The masterbatch filling the middle layer is selected from Dongguan Changping Sanlong Plastic Products Co., Ltd., model T60.

[0065] The preparation method of the above-mentioned high-transparency, low-strength, easy-tear film includes the following steps:

[0066] S1. Ingredients: Weigh the raw materials according to the amount of each layer in Table 2 and mix them evenly to obtain the inner layer material, the middle layer material and the outer layer material;

[0067] S2. Heating: The blown film unit is continuously heated in zones. The temperatures of each zone of the die head are: Zone 1 195℃, Zone 2 200℃, Zone 3 205℃, Zone 4 205℃. The temperatures of each zone of the outer layer main unit are: Zone 1 195℃, Zone 2 220℃, Zone 3 225℃, Zone 4 230℃, Zone 5 230℃, Zone 6 225℃. The temperatures of each layer of the middle layer main unit are: Zone 1 195℃, Zone 2 220℃, Zone 3 225℃, Zone 4 230℃, Zone 5 230℃, Zone 6 225℃. The temperatures of each zone of the inner layer main unit are: Zone 1 195℃, Zone 2 220℃, Zone 3 225℃, Zone 4 230℃, Zone 5 230℃, Zone 6 225℃. After heating is completed, the unit is kept at the desired temperature for 20 minutes. The machine is then started sequentially in the order of outer layer, middle layer, and inner layer, with a 2-minute interval between starts.

[0068] S3, Blow Molding: The inner layer material, middle layer material and outer layer material are placed into the corresponding main machine. The outer layer main machine speed is 50r / min, the middle layer main machine speed is 150r / min, and the inner layer main machine speed is 50r / min. The air inlet temperature is 20℃. After hot melting, the molten plastic is pulled upward and quickly kneaded. Compressed air is injected into the die head. The blow-up ratio is 3. The film bubble is pulled up at a uniform speed. The traction speed is 19m / min and the traction ratio is 6.

[0069] S4. Winding: The membrane bubble is corona treated to make the surface tension of the membrane 40mN / m, cut into two pieces, and then wound up and packaged.

[0070] Table 2. Raw material consumption of high-transparency, low-strength, easy-tear films in Examples 1-8

[0071]

[0072] Examples 2-3: A highly transparent, low-strength, easy-tear film, which differs from Example 1 in that the amount of raw materials used in each layer is shown in Table 2.

[0073] Example 4: A high-transparency, low-strength, easy-tear film, which differs from Example 1 in that the mass ratio of II-1 LLDPE and II-2 LLDPE in the outer layer is 2:4.

[0074] Example 5: A high-transparency, low-strength, easy-tear film, which differs from Example 1 in that II-2 LLDPE is used instead of II-1 LLDPE in the outer layer.

[0075] Example 6: A high-transparency, low-strength, easy-tear film, which differs from Example 1 in that II-1 LLDPE is used instead of II-2 LLDPE in the outer layer.

[0076] Example 7: A high-transparency, low-strength, easy-tear film, which differs from Example 1 in that the mass ratio of II-1 LLDPE and II-2 LLDPE in the outer layer is 1:6.

[0077] Example 8: A high-transparency, low-strength, easy-tear film, which differs from Example 1 in that the mass ratio of II-1 LLDPE and II-2 LLDPE in the outer layer is 3:4.

[0078] Example 9: A highly transparent, low-strength, easy-tear film, differing from Example 1 in that the styrene-butadiene block copolymer is selected from INEOS Styrolux 693D, with a density of 1.01 g / cm³. 3 The melt flow index (200℃, 5kg) is 12.5cm. 3 / 10min

[0079] Example 10: A highly transparent, low-strength, easy-tear film, which differs from Example 1 in that the intermediate layer is filled with masterbatch made from Preparation Example 1.

[0080] Example 11: A highly transparent, low-strength, easy-tear film, which differs from Example 1 in that the filler masterbatch is made from Preparation Example 2.

[0081] Example 12: A highly transparent, low-strength, easy-tear film, which differs from Example 10 in that the filler masterbatch is made from Preparation Example 3.

[0082] Example 13: A highly transparent, low-strength, easy-tear film, which differs from Example 10 in that the filler masterbatch is made from Preparation Example 4.

[0083] Comparative Example

[0084] Comparative Examples 1-8: A high-transparency, low-strength, easy-tear film. The raw material amounts are shown in Table 3. Compared with Example 1, in Comparative Example 1, an equal amount of No. 1 LDPE was used to replace No. 2 LDPE in the inner layer; in Comparative Example 2, the mass ratio of No. 1 LDPE to No. 2 LDPE in the inner layer was 7:1; in Comparative Example 3, the mass ratio of No. 1 LDPE to No. 2 LDPE in the inner layer was 12:1; in Comparative Example 4, an equal amount of No. I-1 LDPE was used to replace No. I-2 LLDPE in the inner layer; in Comparative Example 5, the mass ratio of No. I-1 LDPE to No. I-2 LLDPE in the inner layer was 1:1; in Comparative Example 6, the mass ratio of No. I-1 LDPE to No. I-2 LLDPE in the inner layer was 3:1; in Comparative Example 7, the amount of HDPE in the intermediate layer was doubled; and in Comparative Example 8, no styrene-butadiene block copolymer was added to the intermediate layer.

[0085] Table 3 Raw material usage of high-transparency, low-strength, easy-tear films in Comparative Examples 1-8

[0086]

[0087] Performance testing

[0088] A highly transparent, low-strength, easy-tear film with a thickness of 20 μm was prepared according to the raw materials and methods in the examples and comparative examples, and its performance was tested according to the following methods. The test results are recorded in Table 4.

[0089] 1. Tensile strength at break and elongation at break: Tested in accordance with GB / T13022-1991 "Test Method for Tensile Properties of Plastic Films".

[0090] 2. Tear strength: Tested in accordance with GB / T16578-1996 "Test method for tear resistance of plastic films and sheets".

[0091] 3. Light transmittance and haze: Tested according to GB / T2410-2008 "Test Method for Light Transmittance and Haze of Transparent Plastics";

[0092] 4. Straight-line tear resistance: Cut the film into rectangles with a width (W1) of 4 cm and a length of 20 cm. Then, make a slit in the middle of the width direction and tear along a straight line. Measure the width of the other end (W2) of the sample. Figure 1 As shown. The tear deviation α is calculated by the following formula. The lower the value of α, the better the straight tear resistance of the film. α=[(1 / 2W1)-W2] / (1 / 2W1)×100%.

[0093] Table 4 Performance test results of high transparency, low strength, easy-tear film

[0094]

[0095] As can be seen from the data in Table 1, in Examples 1-4, using No. 1 LDPE and No. 2 LDPE at a mass ratio of 10:1, No. I-1 LLDPE and No. I-2 LLDPE at a mass ratio of 2:1, and using low-addition HDPE in the middle layer and No. II-1 LLDPE and No. II-2 LLDPE at a mass ratio of 2:5 in the outer layer, the resulting easy-tear film has a light transmittance of over 93%, a haze of less than 5%, and a tear deviation of less than 7%, exhibiting good straight-line tear performance. In addition, the measured values ​​of tensile strength at break, elongation at break, and tear strength are low, indicating a good easy-tear effect.

[0096] Compared with Example 1, Comparative Example 5 did not add LLDPE II-1 to the outer layer and used LLDPE II-2 instead of LLDPE II-1. Example 6 used LLDPE II-1 instead of LLDPE II-2 in the outer layer. The melt index of LLDPE II-1 was 20 g / 10 min, while the melt index of LLDPE II-2 was 1.9 g / 10 min. As can be seen from the data in Table 4, the tensile strength at break, elongation at break, and tear strength of the easy-tear films prepared in Examples 5 and 6 were increased, while the light transmittance decreased, the haze increased, the tear deviation increased, and the straight tear effect deteriorated.

[0097] Compared with Example 1, the ratios of LLDPE II-1 and LLDPE II-2 used in Examples 7 and 8 were 1:6 and 3:4, respectively. As shown in Table 4, the mechanical properties of the easy-tear films prepared in Examples 7 and 8 increased, but the easy-tear effect decreased and the transparency weakened.

[0098] In Example 9, a styrene-butadiene block copolymer with an increased melt index was used, and it was observed that the transparency of the resulting easy-tear film decreased and the easy-tear effect was weakened.

[0099] Compared with Example 1, Examples 10 and 11 used filler masterbatches prepared in Preparation Example 1 and Preparation Example 2, respectively. The data in Table 4 shows that the elongation at break, tensile strength at break, and tear strength of the easy-tear films prepared in Examples 10 and 11 all increased. Moreover, the light transmittance increased, the transparency improved, the tearing deviation decreased, and the straight-line easy-tear effect increased.

[0100] In Example 12, the filler masterbatch prepared in Preparation Example 3 was used. Compared with Example 10, HDPE was used to replace EVOH in the filler masterbatch prepared in Preparation Example 3. In Example 13, the filler masterbatch prepared in Preparation Example 4 was used. Compared with Example 10, an equal amount of HDPE was used to replace maleic anhydride-grafted HDPE in Preparation Example 4. As can be seen from the data in Table 4, the mechanical strength of the easy-tear films prepared in Examples 12 and 13 increased, the easy-tear effect deteriorated, and the straight tear performance weakened.

[0101] Compared with Example 1, Comparative Example 1 uses HDPE No. 1 to replace LDPE No. 2 in the inner layer. It can be seen that the mechanical strength of the easy-tear film made in Comparative Example 1 is increased, the easy-tear effect is weakened, the transparency is also reduced, and the straight tear effect is worse.

[0102] Compared with Example 1, the mass ratios of LDPE No. 1 and LDPE No. 2 in Comparative Examples 2 and 3 were 7:1 and 13:1, respectively. The easy-tear films prepared in Comparative Examples 2 and 3 showed increased mechanical strengths compared with Example 1, but were improved compared with Comparative Example 1.

[0103] In Comparative Example 4, an equal amount of I-1 LDPE was used to replace I-2 LLDPE. In Comparative Examples 5 and 6, the mass ratios of I-1 LDPE and I-2 LLDPE were 1:1 and 3:1, respectively. It can be seen that compared with Example 1, the mechanical strength of the easy-tear films prepared in Comparative Examples 4-6 increased, while the increase in Comparative Examples 5 and 6 was smaller than that in Comparative Example 4. This indicates that the ratio of I-1 LDPE to I-2 LLDPE has a significant impact on the easy-tear effect of the film.

[0104] Compared with Example 1, Comparative Example 7 increased the amount of HDPE in the intermediate layer. Compared with Example 1, Comparative Example 8 did not add styrene-butadiene block copolymer in the intermediate layer. The easy-tear films prepared by Comparative Examples 7 and 8 had increased mechanical strength, decreased straight tear performance, and decreased transparency.

[0105] 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. A highly transparent, low-strength, easy-tear film, characterized in that, It includes an inner layer, a middle layer and an outer layer, wherein the inner layer comprises the following raw materials in parts by weight: 38-50 parts LDPE, 50-70 parts Class I LLDPE, 1.5-2.5 parts opening agent, 2-2.8 parts slip agent, 0.3-0.5 parts antioxidant, and 0.3-0.5 parts PPA additive; The inner layer contains LDPE of type 1 and type 2 in a mass ratio of 10:1-1.

5. LDPE type 1 has a melt index of 1.9-2 g / 10 min and a density of 0.924-0.925 g / cm³. 3 The melt index of LDPE No. 2 is 4-5 g / 10 min, and its density is 0.923-0.925 g / cm³. 3 ; The inner layer contains type I LLDPE, including LLDPE I-1 and LLDPE I-2 in a mass ratio of 1.5-2:

1. LLDPE I-1 has a melt index of 2 g / 10 min and a density of 0.918-0.92 g / cm³. 3 The melt index of LLDPE No. I-2 is 4-10 g / 10 min; The intermediate layer comprises the following raw materials in parts by weight: 25-35 parts of No. 1 LDPE, 25-35 parts of No. 1-1 LLDPE, 8-12 parts of HDPE, 15-25 parts of styrene-butadiene block copolymer, 0.6-1 parts of plasticizer, 0.2-0.4 parts of antioxidant, and 8-12 parts of filler masterbatch. The outer layer comprises the following raw materials in parts by weight: 25-35 parts No. 1 LDPE, 60-80 parts Class II LLDPE, 0.3-0.5 parts antioxidant, and 0.6-1 parts plasticizer; The outer layer comprises type II LLDPE, including type II-1 LLDPE and type II-2 LLDPE in a mass ratio of 2:4-5, with type II-1 LLDPE having a density of 0.924-0.925 g / cm³. 3 The melt flow index is 20 g / 10 min, and the density of II-2 LLDPE is 0.915-0.921 g / cm³. 3 The melt flow index is 1.6-2.4 g / 10 min; The density of HDPE in the intermediate layer is 0.95-0.9554 g / cm³. 3 The melt flow index is 0.17-0.2 g / 10 min; The density of the styrene-butadiene block copolymer is 1.01 g / cm³. 3 The melt flow index is 7.5 g / 10 min.

2. The high-transparency, low-strength, easy-tear film according to claim 1, characterized in that: The filler masterbatch comprises the following raw materials in parts by weight: 0.3-0.4 parts filler, 4-5 parts HDPE, 0.03-0.04 parts diaminosilane coupling agent, 1-1.5 parts EVOH, and 0.15-0.2 parts maleic anhydride-grafted HDPE.

3. The high-transparency, low-strength, easy-tear film according to claim 2, characterized in that: The method for preparing the filler masterbatch is as follows: The filler and the diaminosilane coupling agent are mixed and stirred at 5000-6000 rpm for 20-30 minutes at 60-70℃ to obtain the pretreated filler. The pretreated filler is mixed with HDPE, EVOH and maleic anhydride-grafted HDPE, and then melt-extruded and granulated.

4. The high-transparency, low-strength, easy-tear film according to claim 2, characterized in that: The filler is selected from at least one of barium sulfate, calcium carbonate, silicon dioxide, and talc.

5. The high-transparency, low-strength, easy-tear film according to claim 1, characterized in that: The thickness ratio of the inner layer, the middle layer and the outer layer is 1:2-3:1-2.

6. The high-transparency, low-strength, easy-tear film according to claim 1, characterized in that: The antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, antioxidant 1076 and antioxidant 1098; The plasticizer is selected from at least one of dioctyl phthalate, dibutyl phthalate, epoxidized soybean oil, and epoxidized fatty acid butyl ester.

7. The method for preparing the highly transparent, low-strength, easy-tear film according to any one of claims 1-6, characterized in that: Includes the following steps: Ingredients: Mix the raw materials for the inner layer, middle layer and outer layer evenly to obtain the inner layer material, middle layer material and outer layer material; Heating: Heat the outer layer main unit to 195-230℃, the middle layer main unit to 195-230℃, the inner layer main unit to 195-230℃, and the mold head temperature to 195-205℃; Blow molding: The inner layer material, middle layer material and outer layer material are placed into the corresponding main machine, and the film bubble is obtained through hot melting, casting, film casting, blowing and pulling. Rewinding: After corona treatment, the film bubble is cut, rewound, and packaged.

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