BOPE (Biaxially Oriented Polyethylene) film and preparation method thereof

Abstract

The invention discloses a BOPE film and a preparation method thereof, and relates to the technical field of films. The high-density polyethylene and a small amount of high-molecular-weight linear polyethylene are compounded to serve as raw materials to prepare the BOPE film, the production conditions of a two-way stretching technology can be met, precipitates do not exist in the processing process, the BOPE film with HDPE as the main raw material is prepared, the elongation at break, tensile strength, transparency and other properties of the film are improved, and the film is suitable for large-scale production. The prepared film has excellent barrier property, impermeability, transparency and mechanical property.

Description

Technical Field

[0001] The present invention relates to the technical field of films, and in particular to a BOPE film and a preparation method thereof. Background Art

[0002] Biaxially oriented polyethylene (BOPE) film is considered the most valuable single recyclable material. However, low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) are currently commonly used as raw materials for BOPE products. This is due to the high crystallinity and temperature responsiveness of high-density polyethylene (HDPE). Consequently, BOPE films made primarily from HDPE have a narrow processing temperature range during production, making them extremely difficult to process. Because HDPE offers advantages over LDPE and LLDPE in terms of barrier properties, impermeability, and tensile strength, developing BOPE films made primarily from HDPE can significantly improve the film's key properties and holds great research and application value. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a BOPE film and a preparation method thereof.

[0004] The present invention provides a BOPE film comprising the following raw materials in percentage by mass: 85-99% high-density polyethylene and 1-15% linear polyethylene;

[0005] The high-density polyethylene has a melt index of 0.1 to 8 g / 10 min at 190° C. and 2.16 kg;

[0006] The molecular weight of the linear polyethylene is ≥500,000, and the melt index is ≤0.01 at 190° C. and 2.16 kg.

[0007] In the present invention, high-density polyethylene and a small amount of high-molecular-weight linear polyethylene are compounded as raw materials to prepare BOPE film. The high-molecular-weight linear polyethylene and high-density polyethylene have the same molecular structure and good compatibility. By controlling the high molecular weight of the linear polyethylene, the temperature responsiveness, processing range and processing viscosity of the high-density polyethylene can be regulated, the flow rate of the melt can be reduced, and the stability of the melt can be improved, thereby meeting the conditions for biaxial stretching production. In addition, no precipitates are produced during the processing, and a BOPE film with HDPE as the main raw material is obtained, so that the film's properties such as elongation at break, tensile strength, and transparency are improved. The obtained film has excellent barrier properties, anti-permeability properties, transparency and mechanical properties.

[0008] The mass percentage of high-density polyethylene may be, for example, 1%, 2%, 5%, 10%, or 15%; the mass percentage of linear polyethylene may be, for example, 99%, 98%, 95%, 90%, or 85%.

[0009] Preferably, in the present invention, the density of high-density polyethylene is 0.941 to 0.976 g / cm 3 For example, ExxonMobil HMA 025 has a melt index of 8 g / 10 min and a density of 0.964 g / cm3 at 190°C and 2.16 kg; Secco HD5502FA has a melt index of 5 g / 10 min and a density of 0.953 g / cm3 at 190°C and 2.16 kg; Yangzi Petrochemical HDPE has a melt index of 1 g / 10 min and a density of 0.951 g / cm3 at 190°C and 2.16 kg; ExxonMobil BA53-035 has a melt index of 0.1 g / 10 min and a density of 0.953 g / cm3 at 190°C and 2.16 kg.

[0010] Preferably, the BOPE film comprises the following raw materials in the following weight percentages: 85-95% high-density polyethylene and 5-15% linear polyethylene. In the biaxially oriented film production process, since the melt extrusion of the raw materials is carried out within a temperature range, the stability of the melt index within this temperature range has a crucial impact on the biaxial stretching process. The inventors have found that the melt formed from the above raw materials can maintain a highly stable melt index within a processing temperature range of 190-250°C, indicating that the melt stability is very good. Therefore, a very high biaxial stretch ratio can be achieved, thereby further obtaining a biaxially oriented polyethylene film with high mechanical strength, high barrier properties, and anti-permeability properties.

[0011] Preferably, the thickness of the film is 10 to 80 μm.

[0012] The present invention also proposes a method for preparing the BOPE film, comprising the following steps:

[0013] S1, adding the raw materials of the film into a twin-screw extruder, and performing melt blending and granulation to obtain pellets;

[0014] S2. Add the pellets into a single-screw extruder, melt them, and then perform casting, biaxial stretching, and shaping to obtain a BOPE film.

[0015] Preferably, in S1, the temperature of melt blending is 210-250°C.

[0016] Preferably, in S2, the melting temperature is 210-250°C.

[0017] Preferably, in S2, the biaxial stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching ratio is 3 to 7 times, and the transverse stretching ratio is 3 to 10 times. For example, the longitudinal stretching ratio is 3 times, 4 times, 5 times, 6 times, or 7 times, and the transverse stretching ratio is 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, or 10 times.

[0018] Preferably, the temperature for longitudinal stretching is 105-120°C, and the temperature for transverse stretching is 125-140°C.

[0019] The beneficial effects of the present invention are as follows:

[0020] In the present invention, high-density polyethylene and a small amount of high-molecular-weight linear polyethylene are compounded as raw materials to prepare BOPE film, which can meet the conditions of biaxial stretching production and no precipitates are produced during the processing. The BOPE film with HDPE as the main raw material is obtained, and the properties of the film such as elongation at break, tensile strength, and transparency are improved. The obtained film has excellent barrier properties, anti-permeability, transparency and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the melt index of the raw materials of the films of Examples 3 to 4 of the present invention and Comparative Examples 1 to 2 when melt blended at different temperatures. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is described in detail below through specific embodiments.

[0023] In the following examples and comparative examples:

[0024] PE1: High-density polyethylene, with a melt index of 5g / 10min at 190°C and 2.16kg, and a density of 0.953g / cm 3 , brand name is SECCO HD5502FA;

[0025] PE2: linear polyethylene, molecular weight ≥ 500,000, melt index 0.01 g / 10 min at 190°C and 2.16 kg, brand Yingchuang HD 7000F;

[0026] PE3: linear polyethylene, with a melt index of 0.1 g / 10 min at 190°C and 2.16 kg, and the brand is Lotte Datan MF1461.

[0027] Example 1

[0028] A BOPE film comprises the following raw materials in percentage by mass: 99% high-density polyethylene (PE1) and 1% linear polyethylene (PE2).

[0029] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0030] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0031] S2. Add the pellets into a single-screw extruder, melt them at 210-230°C, and then cast, biaxially stretch, and shape to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 4 times, the stretching temperature is 105-120°C, and the transverse stretching ratio is 4 times, and the stretching temperature is 125-140°C.

[0032] Example 2

[0033] A BOPE film comprises the following raw materials in percentage by mass: 98% high-density polyethylene (PE1) and 2% linear polyethylene (PE2).

[0034] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0035] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0036] S2. Add the pellets into a single-screw extruder, melt them at 210-230°C, and then cast, biaxially stretch, and shape to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 4 times, the stretching temperature is 105-120°C, and the transverse stretching ratio is 4 times, and the stretching temperature is 125-140°C.

[0037] Example 3

[0038] A BOPE film comprises the following raw materials in percentage by mass: 95% high-density polyethylene (PE1) and 5% linear polyethylene (PE2).

[0039] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0040] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0041] S2. Add the pellets into a single-screw extruder, melt them at 210-230°C, and then cast, biaxially stretch, and shape to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 6 times, the stretching temperature is 105-120°C, and the transverse stretching ratio is 6 times, and the stretching temperature is 125-140°C.

[0042] Example 4

[0043] A BOPE film comprises the following raw materials in percentage by mass: 90% high-density polyethylene (PE1) and 10% linear polyethylene (PE2).

[0044] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0045] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0046] S2. Add the pellets into a single-screw extruder, melt them at 210-230°C, and then cast, biaxially stretch, and shape to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 6 times, the stretching temperature is 105-120°C, and the transverse stretching ratio is 6 times, and the stretching temperature is 125-140°C.

[0047] Example 5

[0048] A BOPE film comprises the following raw materials in percentage by mass: 85% high-density polyethylene (PE1) and 15% linear polyethylene (PE2).

[0049] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0050] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0051] S2. Add the pellets into a single-screw extruder, melt them at 210-230°C, and then cast, biaxially stretch, and shape to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 6 times, the stretching temperature is 105-120°C, and the transverse stretching ratio is 6 times, and the stretching temperature is 125-140°C.

[0052] Comparative Example 1

[0053] A BOPE film comprises the following raw materials in percentage by mass: 80% high-density polyethylene (PE1) and 20% linear polyethylene (PE2).

[0054] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0055] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0056] S2. Add the pellets into a single-screw extruder, melt them at 210-230° C., and then cast, biaxially stretch, and shape them to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching temperature is 105-120° C., and the transverse stretching temperature is 125-140° C.

[0057] Comparative Example 2

[0058] A BOPE film comprises the following raw materials in percentage by mass: 100% high-density polyethylene (PE1).

[0059] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0060] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0061] S2. The pellets are fed into a single-screw extruder and melted at 210-230°C. The film is then cast, biaxially stretched, and shaped to obtain a BOPE film. The biaxial stretching process includes longitudinal stretching and transverse stretching at a temperature of 105-120°C and a transverse stretching temperature of 125-140°C.

[0062] Comparative Example 3

[0063] A BOPE film comprises the following raw materials in percentage by mass: 90% high-density polyethylene (PE1) and 10% linear polyethylene (PE3).

[0064] The preparation method of the above-mentioned BOPE film comprises the following steps:

[0065] S1. Add the raw materials of the film into a twin-screw extruder, melt-blend at 210-230° C., and then granulate to obtain pellets;

[0066] S2. Add the pellets into a single-screw extruder, melt them at 210-230° C., and then cast, biaxially stretch, and shape them to obtain a BOPE film; wherein the biaxial stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching temperature is 105-120° C., and the transverse stretching temperature is 125-140° C.

[0067] The raw material components of Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1:

[0068] Table 1

[0069] PE1 PE2 PE3 Example 1 99 1 Example 2 98 2 Example 3 95 5 Example 4 90 10 Example 5 85 15 Comparative Example 1 80 20 Comparative Example 2 100 0 Comparative Example 3 90 10

[0070] Test example

[0071] The melt index of the raw materials of the films of Examples 3 to 4 and Comparative Examples 1 to 2 was measured when melt blended at different temperatures. The results are shown in Tables 2 and Figure 1 shown. Figure 1 , the curves from top to bottom are Comparative Example 2, Example 3, Example 4, and Comparative Example 1.

[0072] Table 2

[0073] Average melt index and variance at 190-250℃ Example 3 3.28±0.74g / 10min Example 4 1.11±0.27g / 10min Comparative Example 1 0.18±0.029g / 10min Comparative Example 2 7.11±2.26g / 10min

[0074] Table 2 and Figure 1 The test data of Comparative Example 2 is melt-processed using only high-density polyethylene as the raw material. It can be seen that the melt obtained is not only too fluid, making it difficult to form a biaxial stretch film, but also has a melt index that increases significantly with increasing temperature within the temperature range of 190-250°C, indicating that the melt obtained by melt-processing using only high-density polyethylene as the raw material is very unstable and does not meet the requirements of biaxial stretching. The inventors have discovered that by adding an appropriate amount of high-molecular-weight linear polyethylene to the high-density polyethylene for compounding, the resulting melt not only has a suitable melt index that meets the requirements of biaxial stretching, but also has a melt index that varies very little at different temperatures within the temperature range of 190-250°C, indicating that the melt is very stable within this temperature range, enabling the production of BOPE film with a large stretch ratio, thereby obtaining a BOPE film with significantly improved performance in various aspects. As shown in the experimental results of Examples 3 and 4, the amount of high-molecular-weight linear polyethylene in the raw material of Comparative Example 1 is relatively high. Although the resulting melt is also highly stable, its fluidity is too low, which can cause the clamp to fall off and prevent biaxial stretching.

[0075] The performance tests of the films prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were performed, and the results are shown in Table 3:

[0076] Table 3

[0077]

[0078] The film thickness is 40 μm.

[0079] The test results in Table 3 show that Examples 1 to 5, by using high-density polyethylene and a small amount of high-molecular-weight linear polyethylene as raw materials to prepare BOPE films, can meet the conditions for biaxial stretching production, and no precipitates are produced during the processing. The BOPE films produced with HDPE as the main raw material have improved properties such as elongation at break, tensile strength, and transparency. In Comparative Example 1, the amount of high-molecular-weight linear polyethylene in the raw material is relatively high. Although the resulting melt is highly stable, its fluidity is too low, requiring a large stretching force during the stretching process, which can cause the clamp to fall off, and thus it is very easy to come off, making biaxial stretching impossible. In Comparative Example 2, only high-density polyethylene is used as the raw material for melt processing. The resulting melt cannot meet the requirements of biaxial stretching and cannot be biaxially stretched into a film. In Comparative Example 3, the linear polyethylene used for compounding with high-density polyethylene has a relatively large melt index and a relatively low molecular weight. The resulting melt also cannot meet the requirements of biaxial stretching and cannot be biaxially stretched into a film.

[0080] In particular, by comparing Examples 1 to 2 with Examples 3 to 5, it can be seen that in Examples 3 to 5, when the high molecular weight linear polyethylene compound is used and the dosage ratio of the high molecular weight linear polyethylene is appropriate, the melt obtained by melting has a high stability in the temperature range of 190 to 250°C, and can be used to produce BOPE films with a very high stretching ratio, thereby further obtaining a biaxially oriented polyethylene film with high mechanical strength, high barrier properties and anti-permeability properties; while in Examples 1 to 2, the dosage of high molecular weight linear polyethylene is relatively low, and although the melt index is suitable for biaxial stretching production, the melt is not stable enough within the temperature range, and can only be used to produce low-ratio BOPE films.

[0081] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A BOPE film, characterized in that: The raw materials include the following mass percentages: 85-99% high-density polyethylene and 1-15% linear polyethylene; The high-density polyethylene has a melt index of 0.1 to 8 g / 10 min at 190° C. and 2.16 kg; The molecular weight of the linear polyethylene is ≥500,000, and the melt index is ≤0.01 g / 10 min at 190° C. and 2.16 kg.

2. The BOPE film according to claim 1, characterized in that: The invention comprises the following raw materials in percentage by mass: 85-95% of high-density polyethylene and 5-15% of linear polyethylene.

3. The BOPE film according to claim 1, characterized in that: The density of the high-density polyethylene is 0.941-0.976 g / cm 3 .

4. The BOPE film according to claim 1, characterized in that: The thickness of the film is 10-80 μm.

5. A method for preparing a BOPE film as claimed in claim 1, characterized in that: The steps include: S1, adding the raw materials of the film into a twin-screw extruder, and performing melt blending and granulation to obtain pellets; S2, adding the pellets into a single screw extruder, and after melting, casting, biaxial stretching, and shaping are performed to obtain a BOPE film.

6. The method for preparing the BOPE film according to claim 5, characterized in that: In S1, the temperature of melt blending is 210 to 250°C.

7. The method for preparing the BOPE film according to claim 5, characterized in that: In S2, the melting temperature is 210 to 250°C.

8. The method for preparing the BOPE film according to claim 5, characterized in that: In S2, the biaxial stretching includes longitudinal stretching and transverse stretching, wherein the ratio of the longitudinal stretching is 3 to 7 times, and the ratio of the transverse stretching is 3 to 10 times.

9. The method for preparing a BOPE film according to claim 8, characterized in that: The temperature of the longitudinal stretching is 105-120°C, and the temperature of the transverse stretching is 125-140°C.

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