Method for preparing biaxially stretched high-density polyethylene film by semi-dry semi-wet process

Abstract

The application discloses a preparation method of a biaxially stretched high-density polyethylene film prepared by a semi-dry semi-wet process, and relates to the field of polyolefin film materials, and specifically comprises the following steps: S1, preparing a flow casting sheet from pure HDPE resin; S2, soaking the flow casting sheet in a solvent; and S3, stretching and extracting the soaked flow casting sheet, and winding after heat setting to complete the preparation of the biaxially stretched high-density polyethylene film. The application greatly reduces the production cost, and the prepared film has good optical performance and mechanical performance, thereby providing a new film material solution for film processing enterprises.

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 semi-dry, semi-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 current technology by providing a method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-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 method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process includes:

[0008] Step S1: Prepare cast sheets from pure HDPE resin;

[0009] Step S2: Immerse the cast sheet in solvent;

[0010] Step S3: Stretch and extract the soaked cast film, heat-set it, and then roll it up to complete the preparation of biaxially oriented high-density polyethylene film.

[0011] Further, step S1 includes:

[0012] Pure HDPE resin is fed into a twin-screw extruder, extruded through a single-layer or multi-layer co-extrusion die, and then cooled to form cast sheets.

[0013] Furthermore, the melt extrusion temperature of the twin-screw extruder is 160-230℃;

[0014] The temperature of the cooling roller is 15-40℃.

[0015] Furthermore, the pure 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.

[0016] Furthermore, the solvent is a low molecular weight solvent;

[0017] The soaking time is 0.5 hours.

[0018] Furthermore, the solvent is a diluent;

[0019] The diluent is at least one of petroleum ether, acetone, ethyl acetate, and butanone.

[0020] Further, step S3 includes:

[0021] Step S31: Longitudinally stretch the immersed cast sheet;

[0022] Step S32: Perform lateral stretching again;

[0023] Step S33: Extract the cast film after longitudinal stretching and transverse stretching;

[0024] Step S34: After heat setting, the film is wound up to obtain a biaxially oriented high-density polyethylene film.

[0025] Furthermore, the longitudinal stretching temperature is 105-120℃, and the longitudinal stretching ratio is 5 times;

[0026] The temperature for the transverse stretching is 110-120℃, and the transverse stretching ratio is 4 times.

[0027] Furthermore, the extraction solvent is dichloromethane, and the extraction time is 30 min.

[0028] Furthermore, the heat setting temperature is 110-120℃.

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

[0030] A semi-dry, semi-wet process method for preparing biaxially oriented high-density polyethylene (HDPE) film includes: step S1: preparing pure HDPE resin into a cast film; step S2: immersing the cast film in a solvent; step S3: stretching and extracting the immersed cast film, heat-setting it, and then winding it up to complete the preparation of the biaxially oriented high-density polyethylene (HDPE) film. This method significantly reduces production costs, and the resulting film exhibits excellent optical and mechanical properties, providing a new film material solution for film processing companies. Attached Figure Description

[0031] Figure 1 A flowchart of a method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process. 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 1 A method for preparing biaxially oriented high-density polyethylene (HDPE) film using a semi-dry, semi-wet process is described. This method utilizes a diluent to improve the stretchability of HDPE, suppress cavitation, and enhance film-forming stability. The specific steps include:

[0036] Step S1: Prepare cast sheets from pure HDPE resin;

[0037] Step S2: Immerse the cast sheet in solvent;

[0038] Step S3: Stretch and extract the soaked cast film, heat-set it, and then roll it up to complete the preparation of biaxially oriented high-density polyethylene film.

[0039] In this embodiment, specifically, step S1 includes:

[0040] Pure HDPE resin is fed into a twin-screw extruder, extruded through a single-layer or multi-layer co-extrusion die, and then cooled to form cast sheets.

[0041] In this embodiment, specifically, the melt extrusion temperature of the twin-screw extruder is 160-230℃;

[0042] The temperature of the cooling roller is 15-40℃.

[0043] In this embodiment, specifically, the pure 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.

[0044] In this embodiment, specifically, the solvent is a low molecular weight solvent;

[0045] The soaking time is 0.5 hours.

[0046] In this embodiment, specifically, the solvent is a diluent;

[0047] The diluent is at least one of petroleum ether, acetone, ethyl acetate, and butanone.

[0048] In this embodiment, specifically, step S3 includes:

[0049] Step S31: Longitudinally stretch the immersed cast sheet;

[0050] Step S32: Perform lateral stretching again;

[0051] Step S33: Extract the cast film after longitudinal stretching and transverse stretching;

[0052] Step S34: After heat setting, the film is wound up to obtain a biaxially oriented high-density polyethylene film.

[0053] In this embodiment, specifically, the longitudinal stretching temperature is 105-120℃, and the longitudinal stretching ratio is 5 times.

[0054] In this embodiment, specifically, the temperature for the transverse stretching is 110-120℃, and the transverse stretching ratio is 4 times.

[0055] In this embodiment, specifically, the extraction solvent is dichloromethane, and the extraction time is 30 min.

[0056] In this embodiment, specifically, the heat setting temperature is 110-120℃.

[0057] Example 2

[0058] Example 2 is a comparative experiment of the preparation method of biaxially oriented high-density polyethylene film using the semi-dry and semi-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] Step 1: Pure HDPE resin is fed into a twin-screw extruder, melt-blended, passed through an 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℃.

[0062] Step 2: The cast film was fed into a synchronous biaxial stretching device at a stretching temperature of 110°C to form a biaxial film with a stretching ratio of 5*4. It was then heat-set at a temperature of 110°C and then sent to an extraction tank via a traction device. It was extracted in dichloromethane for 10 minutes and then dried at 40°C. During the biaxial stretching process, the film broke and no finished film was obtained.

[0063] Experimental group 2:

[0064] The HDPE resin used was Hostalen ACP 9255PLUS from LyondellBasell, with a weight-average molecular weight of 300,000 g / mol.

[0065] The diluent used was petroleum ether (100), purchased from Tianjin Fuyu Chemical Co., Ltd., and the solvent soaking time was 0.5 hours.

[0066] Step 1: Pure HDPE resin is fed into a twin-screw extruder, melt-blended, passed through an 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℃.

[0067] Step 2: Soak the cast sheet in petroleum ether (100) for 0.5 hours.

[0068] Step 3: The above-mentioned soaked cast film is fed into a synchronous biaxial stretching device. The stretching temperature is 110℃, and biaxial stretching is performed to form a film with a stretching ratio of 5*5. Then, extraction and heat setting are performed. The extraction solvent is dichloromethane, and the extraction time is 30 min. The heat setting temperature is 110℃. The film is output through a traction device to obtain a biaxially stretched high-density polyethylene film.

[0069] Table 1 shows a comparison of the performance parameters of the finished products after the preparation process of experimental groups 1 and 2.

[0070] Table 1 Comparison of performance parameters of finished products after preparation process in Experimental Groups 1 and 2

[0071]

[0072] As shown in Table 1, the present invention provides a semi-dry, semi-wet process for successfully preparing biaxially oriented high-density polyethylene film, which greatly reduces production costs.

[0073] 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.

[0074] 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 semi-dry, semi-wet process, characterized in that, include: Step S1: Prepare cast sheets from pure HDPE resin; Step S2: Immerse the cast sheet in solvent; Step S3: Stretch and extract the soaked cast film, heat-set it, and then roll it up to complete the preparation of biaxially oriented high-density polyethylene film.

2. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 1, characterized in that, Step S1 includes: Pure HDPE resin is fed into a twin-screw extruder, extruded through a single-layer or multi-layer co-extrusion die, and then cooled to form cast sheets.

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

4. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 1, characterized in that, The pure 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.

5. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 1, characterized in that, The solvent is a low molecular weight solvent; The soaking time is 0.5 hours.

6. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 5, characterized in that, The solvent is a diluent; The diluent is at least one of petroleum ether, acetone, ethyl acetate, and butanone.

7. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 1, characterized in that, Step S3 includes: Step S31: Longitudinally stretch the immersed cast sheet; Step S32: Perform lateral stretching again; Step S33: Extract the cast film after longitudinal stretching and transverse stretching; Step S34: After heat setting, the film is wound up to obtain a biaxially oriented high-density polyethylene film.

8. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 7, characterized in that, The longitudinal stretching temperature is 105-120℃, and the longitudinal stretching ratio is 5 times. The temperature for the transverse stretching is 110-120℃, and the transverse stretching ratio is 4 times.

9. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 7, characterized in that, The extraction solvent was dichloromethane, and the extraction time was 30 min.

10. The method for preparing biaxially oriented high-density polyethylene film using a semi-dry, semi-wet process according to claim 7, characterized in that, The heat setting temperature is 110-120℃.

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