A multilayer polyethylene film

Abstract

The present application relates to a kind of multilayer polyethylene film, including outer layer, middle layer and inner layer, the raw material of the outer layer includes component A, component B and component D, the raw material of the middle layer includes component A and component C, the raw material of the inner layer includes component B or component C, the content of component A in the middle layer is 1.1~1.3 times of the content in the outer layer;Component A is high-density polyethylene, component B is linear low-density polyethylene, component C is another linear low-density polyethylene, and component D is polypropylene.The multilayer composite polyethylene film provided in the present application has excellent tensile strength, tensile yield stress and puncture resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polyolefins, and particularly relates to a multi-layer composite high-strength polyethylene film. BACKGROUND

[0002] Polyethylene film is the most widely used film with the largest amount of use and the widest range of use, which has excellent characteristics such as easy processing, easy forming, good mechanical properties, wide temperature range, etc. It not only plays a role in the fields of agriculture and construction, but also has very wide application in packaging fields such as food packaging, heavy packaging, composite packaging, etc. In recent years, with the rapid development of fast-moving consumer goods industry, the demand and requirements of the consumer market for packaging materials are increasing day by day, and composite film materials with high strength can meet the high requirements in packaging, transportation and use, and have become a demand hotspot.

[0003] Single-layer polyethylene film has excellent characteristics such as simple preparation, low cost, light weight and environmental protection, but often has disadvantages such as poor strength and easy breakage, especially in the transportation process, which is easy to cause loss and inconvenience.

[0004] CN 111100364 A discloses a polyethylene composition and a preparation method thereof and a blow-molded packaging product. In the first aspect, the polyethylene composition is characterized in that it is composed of four components (1)-(4), and based on the total weight of the four components, component (1) is 10-80wt% of polyethylene A component, component (2) is 10-60wt% of polyethylene B component, component (3) is 10-40wt% of polyethylene C component, and component (4) is 0.01-3wt% of organic volatile molecules V. In the second aspect, a preparation method of the above polyethylene composition is provided, which comprises stirring and mixing the components, melt blending extrusion, cooling and granulation. In the third aspect, a blow-molded packaging product is provided, which is made of the above polyethylene composition, and the method for making the packaging product can use various conventional process methods in the art. The obtained blow-molded packaging product has about 10 times higher barrier performance to volatile organic small molecules than traditional low-density polyethylene blow-molded products. However, the polyethylene film involved in this technology is a single-layer polyethylene film, and does not involve a multi-layer composite polyethylene film.

[0005] CN108608696A discloses a puncture-resistant, high-barrier plastic composite film and a packaging bag made of the film, which is mainly composed of linear low-density polyethylene 65 parts, low-density polyethylene 25 parts, metallocene polyethylene 2-8 parts, and elastomer 2-8 parts. After a certain degree of proportioning, a polyethylene film with better performance is obtained. The polyethylene film is used as a puncture-resistant layer, and a biaxially stretched nylon film, an aluminum foil, and a biaxially stretched ethylene terephthalate are used as a stretching layer, a barrier layer, and a printing layer, respectively. The use of a multi-layer composite film structure including the puncture-resistant layer, the stretching layer, the barrier layer, and the printing layer achieves the effects of sealing, puncture resistance, and high barrier. The composite polyethylene film disclosed in the technology has the characteristics of sealing, puncture resistance, and high barrier function, and does not involve high-strength mechanical properties.

[0006] CN 108359170 A discloses a multi-layer co-extrusion polyethylene film and a preparation method thereof. The multi-layer co-extrusion polyethylene film comprises a composite intermediate layer and a heat-sealing layer from top to bottom. The preparation raw materials of the composite layer include LLDPE, LDPE, and processing aids. The preparation raw materials of the intermediate layer include LLDPE and LDPE. The preparation raw materials of the heat-sealing layer include LDPE, elastomer, opening agent, and slip agent. The weight ratio of LLDPE to LDPE in the composite layer and the intermediate layer is 2-4:1, and the processing aids account for 1% of the total weight of the polyethylene film. The weight ratio of LDPE to elastomer used in the heat-sealing layer is 1:1 to 17:3, and the opening agent and the slip agent account for 1% of the total weight of the multi-layer co-extrusion polyethylene film, respectively. The weight ratio of LDPE to elastomer used in the heat-sealing layer is 7:3 or 4:1. The processing aids are lubricants, and the elastomer is a poly-alpha-olefin elastomer with a melt index of 1.2 g / 10 min and a density of 885 kg / m 3 . The disclosed preparation method comprises weighing and mixing the LLDPE, LDPE, and processing aids used to prepare the composite layer to form a composite layer mixture; weighing and mixing the LLDPE and LDPE used to prepare the intermediate layer to form an intermediate layer mixture; weighing and mixing the LDPE, elastomer, opening agent, and slip agent used to prepare the heat-sealing layer to form a heat-sealing layer mixture; feeding the composite layer mixture, the intermediate layer mixture, and the heat-sealing layer mixture into three different feeding ports, respectively, and then extruding through an extruder; and blowing film forming to obtain a multi-layer co-extrusion polyethylene film. The obtained polyethylene film has ultra-low temperature heat-sealing function and can meet the needs of multi-layer co-extrusion processing. However, the multi-layer co-extrusion polyethylene film disclosed in the technology has the characteristics of ultra-low temperature heat-sealing function, and does not involve the high-strength and puncture-resistant mechanical properties of the multi-layer polyethylene film. SUMMARY

[0007] Based on the above, the present application aims to provide a multi-layer composite high-strength polyethylene film, which has excellent tensile strength and puncture resistance and can be used in the field of plastic packaging.

[0008] To this end, the present application provides a multi-layer polyethylene film, which comprises an outer layer, a middle layer and an inner layer, characterized in that the raw material of the outer layer comprises component A, component B and component D, the raw material of the middle layer comprises component A and component C, and the raw material of the inner layer comprises component B or component C, the content of component A in the middle layer is 1.1-1.3 times that in the outer layer; component A is high-density polyethylene, component B is linear low-density polyethylene, component C is another linear low-density polyethylene, and component D is polypropylene.

[0009] Specifically, in the multi-layer composite polyethylene film of the present application, the outer layer, the middle layer and the inner layer are each composed of one or more of component A, component B, component C and component D in specific amounts, and the multi-layer composite polyethylene film with good tensile strength and puncture resistance can be prepared by combining these raw materials through multi-layer co-extrusion blow molding.

[0010] In the multi-layer polyethylene film of the present application, preferably, each layer comprises 20-40 parts of component A, 50-70 parts of component B and 3-12 parts of component D, based on the total mass of the raw material of each layer being 100 parts; the middle layer comprises 25-45 parts of component A and 50-75 parts of component C; and the inner layer comprises 100 parts of component B or 100 parts of component C.

[0011] In the multi-layer polyethylene film of the present application, preferably, each layer comprises 24-35 parts of component A, 56-68 parts of component B and 5-10 parts of component D, based on the total mass of the raw material of each layer being 100 parts; the middle layer comprises 30-40 parts of component A and 60-72 parts of component C.

[0012] In the multi-layer polyethylene film of the present application, preferably, the high-density polyethylene has a density ρA of 0.942-0.956 g / cm 3 , and a melt flow rate MA of 8-18 g / 10 min at a temperature of 190℃ and a load of 21.6 kg.

[0013] In the multi-layer polyethylene film of the present application, preferably, the high-density polyethylene has a density ρA of 0.946-0.952 g / cm 3 , and a melt flow rate MA of 10-16 g / 10 min at a temperature of 190℃ and a load of 21.6 kg.

[0014] The multilayer polyethylene film according to the present application, wherein preferably the linear low density polyethylene corresponding to component B has a density ρB of 0.912 to 0.922 g / cm 3 The melt flow rate MB at a temperature of 190°C under a load of 2.16 kg is 0.2 to 4.0 g / 10 min.

[0015] The multilayer polyethylene film according to the present application, wherein preferably the linear low density polyethylene corresponding to component B has a density ρB of 0.914 to 0.920 g / cm 3 The melt flow rate MB at a temperature of 190°C under a load of 2.16 kg is 0.8 to 2.4 g / 10 min.

[0016] The multilayer polyethylene film according to the present application, wherein preferably the linear low density polyethylene corresponding to component C has a density ρC of 0.914 to 0.926 g / cm 3 The melt flow rate MC at a temperature of 190°C under a load of 2.16 kg is 0.2 to 4.0 g / 10 min.

[0017] The multilayer polyethylene film according to the present application, wherein preferably the linear low density polyethylene corresponding to component C has a density ρC of 0.916 to 0.922 g / cm 3 The melt flow rate MC at a temperature of 190°C under a load of 2.16 kg is 0.8 to 2.4 g / 10 min.

[0018] The multilayer polyethylene film according to the present application, wherein preferably the polypropylene has a melt flow rate MD at a temperature of 190°C under a load of 2.16 kg of 1 to 6 g / 10 min, further preferably 2 to 5 g / 10 min.

[0019] To this end, the present application further provides a method for preparing the multilayer polyethylene film, wherein each component in the outer layer, the middle layer and the inner layer is mixed uniformly by a high-speed mixer in a certain proportion, and then is added to a three-layer co-extrusion film blowing machine to blow the film, and the prepared film has a thickness of 150 to 180 μm.

[0020] The present application has the following advantages:

[0021] (1) The multilayer composite polyethylene film provided by the present application has excellent tensile properties. In the specific embodiment, the difference between Example 2 and Comparative Examples 1 and 2 is that, in the case where the raw materials of the outer layer, the middle layer and the inner layer are all linear low-density polyethylene, the outer layer and the middle layer of Example 1 are added with high-density polyethylene in corresponding proportions, and the content of high-density polyethylene in the middle layer is 1.1-1.3 times that in the outer layer. This technical means makes the tensile strength of Example 2 higher than that of Comparative Example 2 by about 15 MPa, and higher than that of Comparative Example 3 by about 8 MPa; the tensile yield stress is higher than that of Comparative Example 2 by about 3 MPa, and higher than that of Comparative Example 3 by about 2 MPa. It can be seen from this that the combination of the layers of the present application improves the tensile properties of the multilayer composite polyethylene film. This is because the branched chain structure of high-density polyethylene is shorter than that of linear low-density polyethylene. When high-density polyethylene is melt-blended with linear low-density polyethylene, the entanglement degree and crystallization of the molecular chains of the two are changed. The high-density polyethylene with short branched chains plays a role in increasing the entanglement points in the linear low-density polyethylene, so that the density of the entanglement points is increased and the distance between the entanglement points is shortened. This change in the molecular chain structure makes it more difficult for the molecular chains to disentangle, thereby enhancing the mechanical properties such as the tensile strength and the tensile yield stress of the film.

[0022] (2) The multilayer composite polyethylene film provided by the present application has excellent puncture resistance. In the specific embodiment, the difference between Example 3 and Comparative Example 3 is that polypropylene is added to the outer layer of the polyethylene film in Example 3. This technical means makes the puncture force of Example 3 higher than that of Comparative Example 3 by 1.75 N. This is because the addition of a small amount of polypropylene affects the crystallization of the polyethylene system, reduces the crystallinity and enhances the toughness of the film, resulting in an increase in the puncture resistance.

[0023] (3) The multilayer composite polyethylene film provided by the present application has excellent tensile strength, tensile yield stress and puncture resistance. The longitudinal tensile strength is > 62 MPa, the transverse tensile strength is > 60 MPa, the longitudinal tensile yield stress is > 16 MPa, the transverse tensile yield stress is > 15 MPa, and the puncture force is > 5 N. When the content of high-density polyethylene in the middle layer of the multilayer composite polyethylene film is 1.1-1.3 times that in the outer layer, the tensile strength and the tensile yield stress of the film are improved in Examples 1-5 compared with Comparative Examples 1-3. DETAILED DESCRIPTION

[0024] The examples of the present application are described in detail as follows: The present examples are implemented on the premise of the technical solution of the present application, and detailed implementation methods and processes are given, but the protection scope of the present application is not limited to the following examples. The experimental methods not specified in the following examples are usually carried out under conventional conditions, and the % not specified is the weight %.

[0025] The multilayer polyethylene film comprises an outer layer, a middle layer and an inner layer, the raw material of the outer layer comprises component A, component B and component D, the raw material of the middle layer comprises component A and component C, the raw material of the inner layer comprises component B or component C, the content of component A in the middle layer is 1.1-1.3 times of the content in the outer layer; component A is high-density polyethylene, component B is linear low-density polyethylene, component C is another linear low-density polyethylene, and component D is polypropylene.

[0026] Specifically, the outer layer, the middle layer and the inner layer of the multilayer composite polyethylene film in the application each comprise one or more of component A, component B, component C and component D in a specific content, and the multilayer composite polyethylene film with good tensile strength and puncture resistance can be prepared by combining the raw materials through a multilayer co-extrusion blow molding method.

[0027] In some embodiments, preferably, according to the total mass of the raw material of each layer as 100 parts, the outer layer comprises 20-40 parts of component A, 50-70 parts of component B and 3-12 parts of component D; the middle layer comprises 25-45 parts of component A and 50-75 parts of component C; and the inner layer comprises 100 parts of component B or 100 parts of component C.

[0028] In some embodiments, preferably, according to the total mass of the raw material of each layer as 100 parts, the outer layer comprises 24-35 parts of component A, 56-68 parts of component B and 5-10 parts of component D; the middle layer comprises 30-40 parts of component A and 60-72 parts of component C.

[0029] In some embodiments, preferably, the density ρA of the high-density polyethylene is 0.942-0.956 g / cm 3 , the melt flow rate MA under the condition of a temperature of 190 DEG C and a load of 21.6 kg is 8-18 g / 10 min.

[0030] In some embodiments, preferably, the density ρA of the high-density polyethylene is 0.946-0.952 g / cm 3 , the melt flow rate MA under the condition of a temperature of 190 DEG C and a load of 21.6 kg is 10-16 g / 10 min.

[0031] In some embodiments, preferably, the density ρB of the linear low-density polyethylene corresponding to component B is 0.912-0.922 g / cm 3 , the melt flow rate MB under the condition of a temperature of 190 DEG C and a load of 2.16 kg is 0.2-4.0 g / 10 min.

[0032] In some embodiments, preferably, the linear low density polyethylene corresponding to component B has a density ρB of 0.914-0.920 g / cm 3 , a melt flow rate MB of 0.8-2.4 g / 10 min at a temperature of 190℃ and a load of 2.16 kg.

[0033] In some embodiments, preferably, the linear low density polyethylene corresponding to component C has a density ρC of 0.914-0.926 g / cm 3 , a melt flow rate MC of 0.2-4.0 g / 10 min at a temperature of 190℃ and a load of 2.16 kg.

[0034] In some embodiments, preferably, the linear low density polyethylene corresponding to component C has a density ρC of 0.916-0.922 g / cm 3 , a melt flow rate MC of 0.8-2.4 g / 10 min at a temperature of 190℃ and a load of 2.16 kg.

[0035] In some embodiments, preferably, the polypropylene has a melt flow rate MD of 1-6 g / 10 min, further preferably 2-5 g / 10 min, at a temperature of 190℃ and a load of 2.16 kg.

[0036] The method for preparing the multilayer polyethylene film provided by the present application comprises the following steps: mixing each component in the outer layer, the middle layer and the inner layer according to the proportion respectively by using a high-speed mixer, and then adding the mixture into a three-layer co-extrusion film blowing machine to blow the film into a film with a thickness of 150-180 μm.

[0037] Raw material or equipment source:

[0038] The component A high-density polyethylene, the component B linear low density polyethylene, the component C linear low density polyethylene and the component D polypropylene described in the present application are all commercially available polyethylene raw materials. The high-density polyethylene is DGDB6097 produced by Daqing Petrochemical. The linear low density polyethylene includes DFDA7042 produced by Daqing Petrochemical, DFDA7047 produced by Daqing Petrochemical, 1018HA produced by Dushanz Petrochemical and DFDA9047 produced by Daqing Petrochemical. The polypropylene includes T30S produced by Fushun Petrochemical and L5E89 produced by Fushun Petrochemical.

[0039] The three-layer co-extrusion film blowing equipment is SJ-45*25-FM600 manufactured by Dalian Rubber and Plastic Machinery Factory.

[0040] Evaluation and analysis method:

[0041] The melt mass flow rate is tested according to the method specified in GB / T 3682-2000.

[0042] Density was tested according to the method specified in GB / T 1033.

[0043] The tensile properties of the film were tested according to the method specified in GB 13022.

[0044] The puncture resistance of the film was tested according to the method specified in ASTM F1306-90. DETAILED DESCRIPTION

[0046] The preparation method of the multilayer composite polyethylene film in the present application is as follows: each component in the outer layer, the middle layer and the inner layer is mixed uniformly according to the proportion by using a high-speed mixer, and then is added to a three-layer co-extrusion film blowing machine to blow into a film, and the film prepared has a thickness of 180 μm.

[0047] Example 1

[0048] The density of the high-density polyethylene in component A is ρA=0.949 g / cm 3 , the melt flow rate under the condition of a temperature of 190 ℃ and a load of 21.6 kg is MA=11 g / 10 min (DGDB6097); the density of the linear low-density polyethylene in component B is ρB=0.918 g / cm 3 , the melt flow rate under the condition of a temperature of 190 ℃ and a load of 2.16 kg is MB=2.0 g / 10 min (DFDA7042); the density of the linear low-density polyethylene in component C is ρC=0.918 g / cm 3 , the melt flow rate under the condition of a temperature of 190 ℃ and a load of 2.16 kg is MC=1.0 g / 10 min (1018HA); the melt flow rate of the polypropylene in component D under the condition of a temperature of 190 ℃ and a load of 2.16 kg is MD=3.0 g / 10 min (T30S).

[0049] According to the total mass of the raw materials of each layer being 100 parts, the number of parts of component A in the outer layer is 24, the number of parts of component B is 68, and the number of parts of component D is 8; the number of parts of component A in the middle layer is 30, and the number of parts of component C is 70; the number of parts of component B in the inner layer is 100.

[0050] The content of component A in the middle layer is 1.25 times the content of component A in the outer layer.

[0051] The multilayer composite polyethylene film is prepared according to the above preparation method, and the tensile properties and puncture resistance of the film are tested, and the results are shown in Table 1.

[0052] Example 2

[0053] The density of the high-density polyethylene in component A is ρA=0.949 g / cm 3The melt flow rate MA at 190°C under a load of 21.6 kg is 11 g / 10 min (DGDB6097); the density pB of the linear low density polyethylene of component B is 0.917 g / cm 3 The melt flow rate MB at 190°C under a load of 2.16 kg is 0.8 g / 10 min (DFDA9047); the density pC of the linear low density polyethylene of component C is 0.918 g / cm 3 The melt flow rate MC at 190°C under a load of 2.16 kg is 1.0 g / 10 min (1018HA); the melt flow rate MD at 190°C under a load of 2.16 kg of the polypropylene of component D is 3.5 g / 10 min (L5E89).

[0054] The proportions of the components A, B and D in the outer layer are 30 parts, 64 parts and 6 parts, respectively, based on the total mass of the raw materials of the outer layer being 100 parts; the proportions of the components A and C in the middle layer are 35 parts and 65 parts, respectively; the proportion of the component B in the inner layer is 100 parts.

[0055] The content of the component A in the middle layer is 1.17 times the content of the component A in the outer layer.

[0056] The multi-layer composite polyethylene film is prepared according to the above preparation method, and the tensile properties and puncture resistance of the film are tested, and the results are shown in Table 1.

[0057] Example 3

[0058] The density pA of the high density polyethylene of component A is 0.949 g / cm 3 The melt flow rate MA at 190°C under a load of 21.6 kg is 11 g / 10 min (DGDB6097); the density pB of the linear low density polyethylene of component B is 0.918 g / cm 3 The melt flow rate MB at 190°C under a load of 2.16 kg is 1.0 g / 10 min (1018HA); the density pC of the linear low density polyethylene of component C is 0.918 g / cm 3 The melt flow rate MC at 190°C under a load of 2.16 kg is 2.0 g / 10 min (DFDA7042); the melt flow rate MD at 190°C under a load of 2.16 kg of the polypropylene of component D is 3.0 g / 10 min (T30S).

[0059] The outer layer contains 30 parts of component A, 60 parts of component B and 10 parts of component D; the middle layer contains 39 parts of component A and 61 parts of component C; and the inner layer contains 100 parts of component B.

[0060] The content of component A in the middle layer is 1.3 times the content of component A in the outer layer.

[0061] The multilayer composite polyethylene film is prepared according to the above preparation method, and the tensile property and puncture resistance of the film are tested, and the results are shown in Table 1.

[0062] Example 4

[0063] The density of component A, high-density polyethylene, is ρA=0.949 g / cm 3 , and the melt flow rate MA under the conditions of a temperature of 190°C and a load of 21.6 kg is 11 g / 10 min (DGDB6097); the density of component B, linear low-density polyethylene, is ρB=0.920 g / cm 3 , and the melt flow rate MB under the conditions of a temperature of 190°C and a load of 2.16 kg is 1.0 g / 10 min (DFDA7047); the density of component C, linear low-density polyethylene, is ρC=0.918 g / cm 3 , and the melt flow rate MC under the conditions of a temperature of 190°C and a load of 2.16 kg is 2.0 g / 10 min (DFDA7042); and the melt flow rate MD of component D, polypropylene, under the conditions of a temperature of 190°C and a load of 2.16 kg is 3.5 g / 10 min (L5E89).

[0064] The outer layer contains 32 parts of component A, 63 parts of component B and 5 parts of component D; the middle layer contains 36 parts of component A and 64 parts of component C; and the inner layer contains 100 parts of component B.

[0065] The content of component A in the middle layer is 1.13 times the content of component A in the outer layer.

[0066] The multilayer composite polyethylene film is prepared according to the above preparation method, and the tensile property and puncture resistance of the film are tested, and the results are shown in Table 1.

[0067] Example 5

[0068] The density of component A, high-density polyethylene, is ρA=0.949 g / cm 3The melt flow rate MA at a temperature of 190°C under a load of 21.6 kg is 11 g / 10 min (DGDB6097); the density pB of the linear low density polyethylene of component B is 0.920 g / cm 3 The melt flow rate MB at a temperature of 190°C under a load of 2.16 kg is 1.0 g / 10 min (DFDA7047); the density pC of the linear low density polyethylene of component C is 0.918 g / cm 3 The melt flow rate MC at a temperature of 190°C under a load of 2.16 kg is 1.0 g / 10 min (1018HA); the melt flow rate MD of the polypropylene of component D at a temperature of 190°C under a load of 2.16 kg is 3.0 g / 10 min (T30S).

[0069] The proportions of the components in each layer are as follows: in the outer layer, the proportion of component A is 33 parts, the proportion of component B is 58 parts, and the proportion of component D is 9 parts; in the middle layer, the proportion of component A is 40 parts, and the proportion of component C is 60 parts; in the inner layer, the proportion of component B is 100 parts.

[0070] The content of component A in the middle layer is 1.2 times the content of component A in the outer layer.

[0071] A multi-layer composite polyethylene film was prepared according to the above preparation method, and the tensile properties and puncture resistance of the film were tested, and the results are shown in Table 1.

[0072] Comparative Example 1

[0073] This comparative example does not include component A high density polyethylene compared with Example 1.

[0074] The density pB of the linear low density polyethylene of component B is 0.918 g / cm 3 The melt flow rate MB at a temperature of 190°C under a load of 2.16 kg is 2.0 g / 10 min (DFDA7042); the density pC of the linear low density polyethylene of component C is 0.918 g / cm 3 The melt flow rate MC at a temperature of 190°C under a load of 2.16 kg is 1.0 g / 10 min (1018HA); the melt flow rate MD of the polypropylene of component D at a temperature of 190°C under a load of 2.16 kg is 3.0 g / 10 min (T30S).

[0075] The proportions of the components in each layer are as follows: in the outer layer, the proportion of component B is 92 parts, and the proportion of component D is 8 parts; in the middle layer, the proportion of component C is 100 parts; in the inner layer, the proportion of component B is 100 parts.

[0076] The multilayer composite polyethylene film was prepared according to the above preparation method, and the tensile property and puncture resistance of the film were tested, and the results are shown in Table 1.

[0077] Comparative Example 2

[0078] The density of the high-density polyethylene of component A ρA was 0.949 g / cm 3 , the melt flow rate MA at a temperature of 190 ℃ and a load of 21.6 kg was 11 g / 10 min (DGDB6097); the density of the linear low-density polyethylene of component B ρB was 0.917 g / cm 3 , the melt flow rate MB at a temperature of 190 ℃ and a load of 2.16 kg was 0.8 g / 10 min (DFDA9047); the density of the linear low-density polyethylene of component C ρC was 0.918 g / cm 3 , the melt flow rate MC at a temperature of 190 ℃ and a load of 2.16 kg was 1.0 g / 10 min (1018HA); the melt flow rate MD of the polypropylene of component D at a temperature of 190 ℃ and a load of 2.16 kg was 3.5 g / 10 min (L5E89).

[0079] The proportions of component A, component B and component D in the outer layer were 30 parts, 64 parts and 6 parts respectively, based on 100 parts of the total mass of the raw materials of the outer layer; the proportions of component A and component C in the middle layer were 20 parts and 80 parts respectively; the proportion of component B in the inner layer was 100 parts.

[0080] The content of component A in the middle layer was 0.67 times the content of component A in the outer layer.

[0081] The multilayer composite polyethylene film was prepared according to the above preparation method, and the tensile property and puncture resistance of the film were tested, and the results are shown in Table 1.

[0082] Comparative Example 3

[0083] This comparative example was compared with Example 3, and no polypropylene of component D was added to the outer layer.

[0084] The density of the high-density polyethylene of component A ρA was 0.949 g / cm 3 , the melt flow rate MA at a temperature of 190 ℃ and a load of 21.6 kg was 11 g / 10 min (DGDB6097); the density of the linear low-density polyethylene of component B ρB was 0.918 g / cm 3 , the melt flow rate MB at a temperature of 190 ℃ and a load of 2.16 kg was 1.0 g / 10 min (1018HA); the density of the linear low-density polyethylene of component C ρC was 0.918 g / cm 3The melt flow rate MC at a temperature of 190°C under a load of 2.16 kg is 2.0 g / 10 min (DFDA 7042).

[0085] The content of component A in the outer layer is 30 parts, and the content of component B is 70 parts, based on 100 parts of the total mass of the raw materials of each layer; the content of component A in the middle layer is 39 parts, and the content of component C is 61 parts; and the content of component B in the inner layer is 100 parts.

[0086] The content of component A in the middle layer is 1.3 times the content of component A in the outer layer.

[0087] The multilayer composite polyethylene film prepared according to the above preparation method is tested for tensile properties and puncture resistance, and the results are shown in Table 1.

[0088] Table 1, film performance test results of examples 1-5 and comparative examples 1-3 in the present application

[0089]

[0090] From the performance test results of the films in the examples and comparative examples in Table 1, it can be seen that (1) the multilayer composite polyethylene film provided by the present application has excellent tensile properties. The difference between example 2 and comparative examples 1 and 2 is that in the case where the raw materials of the outer layer, the middle layer and the inner layer are all linear low density polyethylene, high density polyethylene is added in the outer layer and the middle layer of example 1 in corresponding proportions, and the content of high density polyethylene in the middle layer is 1.1-1.3 times the content in the outer layer. This technical means makes the tensile strength of example 2 higher than that of comparative example 2 by about 15 MPa, and higher than that of comparative example 3 by about 8 MPa; the tensile yield stress is higher than that of comparative example 2 by about 3 MPa, and higher than that of comparative example 3 by about 2 MPa. Therefore, the combination of layers in the present application improves the tensile properties of the multilayer composite polyethylene film. (2) The multilayer composite polyethylene film provided by the present application has excellent puncture resistance. The difference between example 3 and comparative example 3 is that polypropylene is added to the outer layer of the polyethylene film in example 3. This technical means makes the puncture force of example 3 higher than that of comparative example 3 by 1.75 N. (3) The multilayer composite polyethylene film provided by the present application has excellent tensile strength, tensile yield stress and puncture resistance. The longitudinal tensile strength is > 62 MPa, the transverse tensile strength is > 60 MPa, the longitudinal tensile yield stress is > 16 MPa, the transverse tensile yield stress is > 15 MPa, and the puncture force is > 5 N. When the content of high density polyethylene in the middle layer of the multilayer composite polyethylene film is 1.1-1.3 times the content in the outer layer, the tensile strength and tensile yield stress of the film of examples 1-5 are improved compared to comparative examples 1-3.

[0091] The multilayer composite polyethylene film relates to the present application, wherein the branched chain structure of high-density polyethylene is shorter than that of linear low-density polyethylene, and the molecular chain entanglement degree and crystallization of high-density polyethylene and linear low-density polyethylene are changed after melt blending. The high-density polyethylene with short branched chain increases the entanglement points in the linear low-density polyethylene, so that the entanglement point density is increased and the distance between the entanglement points is shortened. The change of the molecular chain structure increases the difficulty of molecular disentanglement, and further enhances the mechanical properties such as tensile strength and tensile yield stress of the film. The addition of a small amount of polypropylene affects the crystallization of the polyethylene system, reduces the crystallinity, enhances the toughness of the film, and increases the puncture resistance of the film.

[0092] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application. However, these corresponding changes and modifications should belong to the protection scope of the present application.​

Claims

1. A multi-layer polyethylene film comprising an outer layer, a middle layer and an inner layer, characterized in that, The raw material of the outer layer comprises component A, component B and component D, the raw material of the middle layer comprises component A and component C, the raw material of the inner layer comprises component B or component C, the content of the component A in the middle layer is 1.1-1.3 times of the content in the outer layer; The component A is a high-density polyethylene having a density pA of 0.942 to 0.956 g / cm3 3 a melt flow rate MA at a temperature of 190°C under a load of 21.6 kg of 8 to 18 g / 10 min; The component B is a linear low density polyethylene, the density pB of the linear low density polyethylene corresponding to the component B is 0.912~0.922 g / cm 3 The melt flow rate MB at a temperature of 190℃ and a load of 2.16 kg is 0.2~4.0 g / 10 min; Said component C is another linear low density polyethylene, the density of the linear low density polyethylene corresponding to said component C is 0.914~0.926g / cm 3 The melt flow rate MC at the temperature of 190℃ under the load of 2.16kg is 0.2~4.0g / 10min; The component D is polypropylene, the melt flow rate MD of the polypropylene at a temperature of 190 DEG C and a load of 2.16 kg is 1-6 g / 10 min; According to the total mass of the raw material of each layer being 100 parts, the outer layer comprises 20-40 parts of component A, 50-70 parts of component B and 3-12 parts of component D; the middle layer comprises 25-45 parts of component A and 50-75 parts of component C; and the inner layer is 100 parts of component B or 100 parts of component C.

2. The multi-layer polyethylene film according to claim 1, characterized in that, According to the total mass of the raw material of each layer being 100 parts, the outer layer comprises 24-35 parts of component A, 56-68 parts of component B and 5-10 parts of component D; the middle layer comprises 30-40 parts of component A and 60-72 parts of component C.

3. The multi-layer polyethylene film according to claim 1, wherein, The high-density polyethylene has a density ρA of 0.946 to 0.952 g / cm 3 a melt flow rate MA of 10 to 16 g / 10 min at a temperature of 190 °C under a load of 21.6 kg.

4. The multi-layer polyethylene film according to claim 1, wherein, The density pB of the linear low density polyethylene corresponding to the component B is 0.914 to 0.920 g / cm 3 The melt flow rate MB at a temperature of 190 °C under a load of 2.16 kg is 0.8 to 2.4 g / 10 min.

5. The multilayer polyethylene film according to claim 1, wherein The density pC of the linear low density polyethylene corresponding to the component C is 0.916 to 0.922 g / cm3 3 The melt flow rate MC at a temperature of 190 °C under a load of 2.16 kg is 0.8 to 2.4 g / 10 min.

6. The multilayer polyethylene film according to claim 1, wherein The melt flow rate MD of the polypropylene at a temperature of 190 DEG C and a load of 2.16 kg is 2-5 g / 10 min.

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