Process for the production of biaxially oriented high density polyethylene film by the wet process

Abstract

The application discloses a preparation method of a biaxially stretched high-density polyethylene film prepared by a wet process, and relates to the field of polyolefin film materials, and comprises the following steps: S1, mixing HDPE resin and a diluent according to a proportion, and preparing a casting wafer by mixing the materials; S2, stretching the casting wafer; S3, extracting the stretched casting wafer; and S4, drying and winding after the extraction is completed, so that the preparation of the biaxially stretched high-density polyethylene film is completed. The prepared film wafer is arranged closely, the wafer size distribution is narrowed, and the film wafer has excellent optical performance.

Description

Technical Field

[0001] This invention relates to the field of polyolefin film materials, specifically to a method for preparing biaxially oriented high-density polyethylene film using a wet process. Background Technology

[0002] The statements in this section are provided only as background information in connection with this disclosure and may not constitute prior art.

[0003] Biaxially oriented polyethylene film (BOPE film) boasts advantages such as high tensile strength and excellent optical properties, making it widely used in food and express packaging. Compared to PE films prepared by traditional blown film methods, BOPE films exhibit twice the impact strength, three times the puncture strength, and three times the tensile strength of ordinary PE films, while reducing material usage by 2-3 times, making it a more sustainable and environmentally friendly solution. However, because the biaxial stretching process is carried out below the melting point of PE, higher crystallinity makes the film more prone to breakage. Therefore, currently developed BOPE films typically use low-density polyethylene (LDPE) with lower crystallinity and a small amount of medium-density polyethylene (MDPE) as the substrate. Preparing BOPE films using high-density polyethylene (HDPE), which has superior mechanical properties, as the substrate remains an unsolved industry challenge. This is mainly because HDPE crystallizes extremely quickly and has high crystallinity, making it highly susceptible to cavitation during biaxial stretching, leading to film breakage.

[0004] Studies have found that when extruded and cast PE is immersed in a low molecular weight solvent, the solvent penetrates into the amorphous region and fills its internal defects. During stretching, this suppresses cavitation and significantly improves the elongation at break of the material (Rozanski A, Galeski A. Macromolecules, 2011, 44: 7273-7287). On the other hand, the wet process of blending ultra-high molecular weight polyethylene and white oil, followed by melt extrusion and biaxial stretching, has been widely used in the preparation of lithium battery separators. White oil fills the defects in the amorphous region of PE, thus significantly improving its stretching film stability. However, due to the high amount of white oil added (>70%), a large amount of white oil agglomerates between the spherulites, resulting in a film with a large number of micropores. Traditional wet processes cannot yet produce dense, homogeneous films. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a method for preparing biaxially oriented high-density polyethylene film using a wet process. This new technology for preparing polyethylene film fills a market gap and provides mechanical and optical properties superior to traditional packaging films, thereby solving the aforementioned problems.

[0006] The technical solution of the present invention is as follows:

[0007] A wet process for preparing biaxially oriented high-density polyethylene film includes:

[0008] Step S1: Mix HDPE resin and diluent in a certain proportion, and prepare the mixed material into a cast sheet;

[0009] Step S2: Stretch the cast sheet;

[0010] Step S3: Extract the stretched cast sheet;

[0011] Step S4: After extraction, dry and roll up the film to complete the preparation of biaxially oriented high-density polyethylene film.

[0012] Further, step S1 includes:

[0013] Step S11: Mix HDPE resin and diluent evenly; wherein the content of HDPE resin is 80-95% and the content of diluent is 5-20%;

[0014] Step S12: The mixed material is fed into a twin-screw extruder, extruded through a single-layer or multi-layer co-extrusion die, and then cooled to form a cast sheet.

[0015] Furthermore, the melt extrusion temperature of the twin-screw extruder is 160-230℃;

[0016] The temperature of the cooling roller is 15-40℃.

[0017] Furthermore, the HDPE resin is selected from at least one of Dow Chemical's DMDH-6400NT 7, DMDA-6200NT 7, Mitsui Chemicals' 6200BX, and Basel's ACP 9255PLUS.

[0018] Furthermore, the diluent is at least one of dioctyl phthalate, soybean oil, decahydronaphthalene, chloroform, solid paraffin, and liquid paraffin.

[0019] Further, step S2 includes:

[0020] Step S21: Longitudinally stretch the cast sheet;

[0021] Step S22: Perform lateral stretching and heat setting.

[0022] Furthermore, the longitudinal stretching temperature is 105-120℃, and the longitudinal stretching ratio is 6 times;

[0023] The temperature for the transverse stretching is 110-120℃, and the transverse stretching ratio is 5 times.

[0024] Furthermore, the heat setting temperature is 110-120℃.

[0025] Further, step S3 includes:

[0026] The extraction solvent was dichloromethane, and the extraction time was 30 min.

[0027] Further, step S4 includes:

[0028] The drying temperature is 40℃.

[0029] Compared with existing technologies, the advantages of this invention are:

[0030] A wet process for preparing biaxially oriented high-density polyethylene (HDPE) film includes: Step S1: mixing HDPE resin and diluent in a certain proportion, and preparing the mixed material into a cast film; Step S2: stretching the cast film; Step S3: extracting the stretched cast film; Step S4: after extraction, drying and winding to complete the preparation of biaxially oriented high-density polyethylene film; the prepared film has a densely packed wafer arrangement, a narrowed wafer size distribution, and excellent optical properties. Attached Figure Description

[0031] Figure 1 A flowchart of a wet process for preparing biaxially oriented high-density polyethylene film. Detailed Implementation

[0032] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0033] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0034] Example 1

[0035] Please see Figure 1A wet process for preparing biaxially oriented high-density polyethylene (HDPE) film utilizes a diluent to improve the stretchability of HDPE, suppress cavitation, and enhance film-forming stability. The specific steps include:

[0036] Step S1: Mix HDPE resin and diluent in a certain proportion, and prepare the mixed material into a cast sheet;

[0037] Step S2: Stretch the cast sheet;

[0038] Step S3: Extract the stretched cast sheet;

[0039] Step S4: After extraction, dry and roll up the film to complete the preparation of biaxially oriented high-density polyethylene film.

[0040] In this embodiment, specifically, step S1 includes:

[0041] Step S11: Mix HDPE resin and diluent evenly; wherein the content of HDPE resin is 80-95% and the content of diluent is 5-20%;

[0042] Step S12: The mixed material is fed into a twin-screw extruder, extruded through a single-layer or multi-layer co-extrusion die, and then cooled to form a cast sheet.

[0043] In this embodiment, specifically, the melt extrusion temperature of the twin-screw extruder is 160-230℃;

[0044] The temperature of the cooling roller is 15-40℃.

[0045] In this embodiment, specifically, the HDPE resin is selected from at least one of Dow Chemical's DMDH-6400NT 7, DMDA-6200NT7, Mitsui Chemicals' 6200BX, and Basel's ACP 9255PLUS.

[0046] In this embodiment, specifically, the diluent is at least one of dioctyl phthalate, soybean oil, decahydronaphthalene, chloroform, solid paraffin, and liquid paraffin (LP). It should be noted that the purpose of step S3 is to extract the diluent. Therefore, when solid paraffin is used as the diluent, step S3 can be skipped, and the process can proceed directly to step S4.

[0047] In this embodiment, specifically, step S2 includes:

[0048] Step S21: Longitudinally stretch the cast sheet;

[0049] Step S22: Perform lateral stretching and heat setting.

[0050] In this embodiment, specifically, the longitudinal stretching temperature is 105-120℃, and the longitudinal stretching ratio is 6 times;

[0051] The temperature for the transverse stretching is 110-120℃, and the transverse stretching ratio is 5 times.

[0052] In this embodiment, specifically, the heat setting temperature is 110-120℃.

[0053] In this implementation, specifically, step S3 includes:

[0054] The extraction solvent was dichloromethane, and the extraction time was 30 min.

[0055] In this implementation, specifically, step S4 includes:

[0056] The drying temperature is 40℃.

[0057] Example 2

[0058] Example 2 is a comparative experiment of the preparation method of biaxially oriented high-density polyethylene film using the wet process proposed in Example 1.

[0059] Experimental group 1:

[0060] The HDPE resin used was Hostalen ACP 9255PLUS from LyondellBasell, with a weight-average molecular weight of 300,000 g / mol.

[0061] The diluent is liquid paraffin (LP), manufactured by SK Lubricants, brand name PHAZOL-18, with a density of 0.84 g / cm3 (20℃) and a viscosity of 35.5 mm2 / s (40℃).

[0062] The melt extrusion raw materials consist of 95% HDPE resin and 5% LP.

[0063] Step 1: Weigh the materials according to the above proportions and mix them evenly. Put the evenly mixed materials into a twin-screw extruder. After melt blending, the materials pass through the extrusion die and cooling rollers to form a cast sheet, resulting in a uniform sample. The extrusion temperature is 200℃, and the temperature of the cast rollers is maintained at 20℃.

[0064] Step 2: The cast film is fed into a synchronous biaxial stretching device at a stretching temperature of 110°C to form a biaxial film with a stretching ratio of 6*5. Then it is heat-set at a heat-setting temperature of 110°C. After passing through a traction device, it is fed into an extraction tank and extracted in dichloromethane for 30 minutes. Then it is dried at a temperature of 40°C.

[0065] Experimental group 2:

[0066] The difference from Experimental Group 1 is that the melt extrusion raw materials consist of 90% HDPE resin and 10% LP.

[0067] Experimental group 3

[0068] The difference from Experimental Group 1 is that the melt extrusion raw materials consist of 85% HDPE resin and 15% LP.

[0069] Experimental group 4

[0070] The difference from Experimental Group 1 is that the melt extrusion raw materials consist of 80% HDPE resin and 20% LP.

[0071] Experimental group 5

[0072] The difference from Example 1 is that the melt extrusion raw material was pure HDPE resin, and the resin used was Hostalen ACP 9255PLUS from LyondellBasell; the film broke during the biaxial stretching process, and no finished film was obtained.

[0073] Table 1 compares the performance parameters of the finished products after the preparation process of experimental groups 1, 2, 3, 4, and 5.

[0074] Table 1. Comparison of performance parameters of finished products after preparation process in experimental groups 1, 2, 3, 4, and 5.

[0075]

[0076] As can be seen from experiments 1-5, the wet process method for preparing biaxially oriented high-density polyethylene film provided by this invention can successfully prepare biaxially oriented high-density polyethylene film, filling a market gap, and the film has excellent optical and mechanical properties.

[0077] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0078] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A method for preparing biaxially oriented high-density polyethylene film using a wet process, characterized in that, include: Step S1: Mix HDPE resin and diluent in a certain proportion, and prepare the mixed material into a cast sheet; Step S2: Stretch the cast sheet; Step S3: Extract the stretched cast sheet; Step S4: After extraction, dry and roll up the film to complete the preparation of biaxially oriented high-density polyethylene film; Step S1 includes: Step S11: Mix HDPE resin and diluent evenly; wherein the content of HDPE resin is 80-95% and the content of diluent is 5-20%; Step S12: The mixed material is fed into a twin-screw extruder, extruded through a single-layer or multi-layer co-extrusion die, and then cooled by rollers to form a cast sheet; Step S2 includes: Step S21: Longitudinally stretch the cast sheet; Step S22: Perform lateral stretching and heat setting; The longitudinal stretching temperature is 105-120℃, and the longitudinal stretching ratio is 6 times. The temperature for the transverse stretching is 110-120℃, and the transverse stretching ratio is 5 times.

2. The method for preparing biaxially oriented high-density polyethylene film using a wet process according to claim 1, characterized in that, The melt extrusion temperature of the twin-screw extruder is 160-230℃; The temperature of the cooling roller is 15-40℃.

3. The method for preparing biaxially oriented high-density polyethylene film using a wet process according to claim 1, characterized in that, The HDPE resin is selected from at least one of Dow Chemical's DMDH-6400 NT 7, DMDA-6200 NT 7, Mitsui Chemicals' 6200BX, and Basel's ACP 9255 PLUS.

4. The method for preparing biaxially oriented high-density polyethylene film using a wet process according to claim 1, characterized in that, The diluent is at least one of dioctyl phthalate, soybean oil, decahydronaphthalene, chloroform, solid paraffin, and liquid paraffin.

5. The method for preparing biaxially oriented high-density polyethylene film using a wet process according to claim 1, characterized in that, The heat setting temperature is 110-120℃.

6. The method for preparing biaxially oriented high-density polyethylene film using a wet process according to claim 1, characterized in that, Step S3 includes: The extraction solvent was dichloromethane, and the extraction time was 30 min.

7. The method for preparing biaxially oriented high-density polyethylene film using a wet process according to claim 1, characterized in that, Step S4 includes: The drying temperature is 40℃.

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