High-transparency polyethylene film and preparation method thereof

Abstract

The invention belongs to the technical field of film materials, and particularly relates to a high-transparency polyethylene film and a preparation method thereof.The preparation method of the high-transparency polyethylene film comprises the steps that 1, a chelating agent is added into a calcium chloride solution to be evenly mixed, and a CaCl2 / chelating agent solution is formed; (2) adding polyethylene resin master batches into the CaCl2 / chelating agent solution to form a suspension; (3) heating the suspension to dissolve polyethylene in the suspension so as to obtain a film-forming solution; and (4) covering the film forming solution in the mold and curing to form the film. The calcium chloride ion solution is mixed with the polyethylene resin, so that the crystal structure and molecular arrangement of polyethylene can be effectively improved, and the light transmittance of the film is improved. Meanwhile, sufficient strength, toughness and tensile property are kept, the problems of embrittlement and strength reduction of the film in the transparency improving process are solved, and the film is suitable for high-end application occasions requiring the dual properties of mechanical strength and transparency.

Description

Technical Field

[0001] The invention belongs to the technical field of film materials, and particularly relates to a highly transparent polyethylene film and a preparation method thereof. Background Art

[0002] Polyethylene (PE) is a widely used thermoplastic. Due to its excellent chemical stability, good mechanical properties, and low cost, it is one of the most commonly used plastics in industrial production. Polyethylene film is widely used in a variety of fields, including food packaging, pharmaceutical packaging, optical films, and electronic products. However, due to its molecular structure, the transparency of polyethylene film is poor, limiting its use in applications requiring high transparency, such as high-end packaging, optical displays, and transparent electronic screens. Therefore, improving the transparency of polyethylene film has become an important research direction in materials science and engineering.

[0003] Transparency is an important performance indicator of polyethylene film during use, which directly affects the appearance and functionality of the film. For example, in the packaging industry, transparent films enable consumers to see the appearance of the product more clearly, increasing the market appeal of the product; in electronic products, transparent films can ensure the optical performance. Therefore, how to improve the transparency of polyethylene film has become a key challenge in polyethylene film technology. At present, there are mainly the following methods to improve the transparency of polyethylene film: chemical modification and blending modification. The chemical modification method improves the transparency of the film by introducing other polymer substances, cross-linking agents or plasticizers, but may affect the mechanical properties and processing properties of the film to a certain extent; and the blending modification method achieves the effect of improving transparency by mixing polyethylene with other materials such as polypropylene, polystyrene, etc., but such methods often require more complex process steps and cost investment. Summary of the Invention

[0004] In order to solve the shortcoming of insufficient transparency of polyethylene films in the prior art, the present invention provides a highly transparent polyethylene film and a preparation method thereof.

[0005] The technical solution adopted by the present invention is: a method for preparing a highly transparent polyethylene film, comprising:

[0006] (1) adding a chelating agent to a calcium chloride solution and mixing the mixture to form a CaCl2 / chelating agent solution;

[0007] (2) adding polyethylene resin masterbatch to the CaCl2 / chelating agent solution to form a suspension;

[0008] (3) heating the suspension to dissolve the polyethylene therein to obtain a film-forming solution;

[0009] (4) The film-forming solution is covered in the mold and solidified to form a thin film.

[0010] Furthermore, the concentration of the calcium chloride solution is 0.5 mol / L to 1 mol / L.

[0011] Specifically, the average molecular weight of the polyethylene resin masterbatch is 100,000.

[0012] Preferably, the chelating agent is EDTA or a salt thereof, preferably EDTA in its sodium salt form (Na2EDTA), and the chelating agent is prepared into a solution and added to the calcium chloride solution, wherein the concentration of the chelating agent solution is 0.5 mol / L to 1 mol / L.

[0013] Preferably, the molar ratio of the chelating agent to the calcium chloride is 1:1.

[0014] Furthermore, the mass ratio of the polyethylene resin masterbatch to calcium chloride is 100:1-5.

[0015] Preferably, the heating in step (3) is carried out under ultrasonic conditions.

[0016] Preferably, the heating temperature is 160-220° C., and the heating time is 15 minutes.

[0017] Furthermore, the method for covering the mold with the film-forming solution is spin coating or spray coating.

[0018] The present invention also provides a highly transparent polyethylene film, which is prepared by the above preparation method.

[0019] The beneficial effects of the present invention are as follows: by mixing calcium chloride ion solution and chelating agent solution with polyethylene resin, the crystal structure and molecular arrangement of polyethylene can be effectively improved. 2+ The introduction of amorphous regions can reduce crystal defects in polyethylene films and increase the proportion of amorphous regions, thereby reducing light scattering and improving the film's light transmittance. Compared to traditional transparency enhancement methods, this method ensures that while improving transparency, the film maintains sufficient strength, toughness, and tensile strength, avoiding film embrittlement and strength loss during the transparency enhancement process. It is suitable for high-end applications requiring both mechanical strength and transparency.

[0020] Compared to the use of expensive additives, complex chemical modifiers or high-cost multiple processing techniques in the prior art, the present invention uses calcium chloride solution as a modifier, and calcium chloride is cheap and easy to obtain, simple to operate and low in cost. In addition, the process flow of the present invention is relatively simple, avoids tedious chemical reactions or complex equipment requirements, and has strong industrial production potential. Calcium chloride, as an inorganic salt, has good environmental characteristics, does not contain toxic ingredients, and meets the requirements of green environmental protection. The polyethylene film prepared using this method, while meeting the transparency and mechanical property requirements, will not bring about the release of harmful substances, and is particularly suitable for food packaging, medical packaging and other fields closely related to human health.

[0021] Calcium chloride can increase the surface energy of polyethylene films, changing their wettability and hydrophilicity, thereby improving their adhesion and surface finish. This property is particularly important for specialized applications (such as optical films and coating films), as it can enhance the film's performance during subsequent processing and improve the quality and functionality of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Contact angle test results of the films prepared in various examples;

[0023] Figure 2 The transparency comparison chart of the films prepared in each embodiment and comparative example, in which (a) is the film prepared in Example 1, (b) is the film prepared in Example 2, (c) is the film prepared in Example 3, (d) is the film prepared in Comparative Example 1, (e) is the film prepared in Comparative Example 2, and (f) is the film prepared in Comparative Example 3. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but is not limited thereto. Any improvement or substitution based on the basic spirit of the embodiments of the present invention still falls within the scope of protection of the present invention.

[0025] Material selection: Polyethylene resin masterbatch: brand 2426H, purchased from Yangzi Petrochemical-BASF Co., Ltd.; calcium chloride: purchased from Shanghai Myrrel Biochemical Technology Co., Ltd.; Na2EDTA: purchased from Jiangsu Aikon Biopharmaceutical Research and Development Co., Ltd.

[0026] Example 1

[0027] (1) A 0.5 mol / L chelating agent Na2EDTA solution was added to a 0.5 mol / L calcium chloride solution and mixed evenly to form a CaCl2 / chelating agent solution, wherein the molar ratio of Na2EDTA to calcium chloride was 1:1.

[0028] (2) Add polyethylene resin masterbatch (average molecular weight of 100,000) to the CaCl2 / chelating agent solution to form a suspension; wherein the mass ratio of polyethylene resin masterbatch to calcium chloride is 100:5.

[0029] (3) Heating the suspension at 160°C for 15 min under ultrasonic conditions to form a film-forming solution;

[0030] (4) The film-forming solution is evenly coated on the mold surface by spin coating. After cooling and solidification, a thin film is formed with a thickness of 20 μm.

[0031] Example 2

[0032] (1) A 0.8 mol / L chelating agent Na2EDTA solution was added to a 0.8 mol / L calcium chloride solution and mixed evenly to form a CaCl2 / chelating agent solution, wherein the molar ratio of Na2EDTA to calcium chloride was 1:1.

[0033] (2) Add polyethylene resin masterbatch (average molecular weight of 100,000) to the CaCl2 / chelating agent solution to form a suspension; wherein the mass ratio of polyethylene resin masterbatch to calcium chloride is 100:3.

[0034] (3) Heating the suspension at 200°C for 15 min under ultrasonic conditions to form a film-forming solution;

[0035] (4) The film-forming solution is evenly coated on the mold surface by spin coating. After cooling and solidification, a thin film is formed with a thickness of 20 μm.

[0036] Example 3

[0037] (1) A 1 mol / L chelating agent Na2EDTA solution was added to a 1 mol / L calcium chloride solution and mixed evenly to form a CaCl2 / chelating agent solution, wherein the molar ratio of Na2EDTA to calcium chloride was 1:1.

[0038] (2) Add polyethylene resin masterbatch (average molecular weight of 100,000) to the CaCl2 / chelating agent solution to form a suspension; wherein the mass ratio of polyethylene resin masterbatch to calcium chloride is 100:1.

[0039] (3) Heating the suspension at 220°C for 15 min under ultrasonic conditions to form a film-forming solution;

[0040] (4) The film-forming solution is evenly coated on the mold surface by spin coating. After cooling and solidification, a thin film is formed with a thickness of 20 μm.

[0041] Comparative Example 1

[0042] (1) Prepare 1 mol / L calcium chloride solution.

[0043] (2) Polyethylene resin masterbatch (average molecular weight 100,000) ) Add to calcium chloride solution to form a suspension; the mass ratio of polyethylene resin masterbatch to calcium chloride is 100:1.

[0044] (3) Heating the suspension at 220°C for 15 min under ultrasonic conditions to form a film-forming solution;

[0045] (4) The film-forming solution is evenly coated on the mold surface by spin coating. After cooling and solidification, a thin film is formed with a thickness of 20 μm.

[0046] Comparative Example 2

[0047] (1) A 0.5 mol / L chelating agent Na2EDTA solution was added to a 0.5 mol / L calcium chloride solution and mixed evenly to form a CaCl2 / chelating agent solution, wherein the molar ratio of Na2EDTA to calcium chloride was 1:1.

[0048] (2) Add polyethylene resin masterbatch (average molecular weight of 100,000) to the CaCl2 / chelating agent solution to form a suspension; wherein the mass ratio of polyethylene resin masterbatch to calcium chloride is 100:6.

[0049] (3) Heating the suspension at 160°C for 15 min under ultrasonic conditions to form a film-forming solution;

[0050] (4) The film-forming solution is evenly coated on the mold surface by spin coating. After cooling and solidification, a thin film is formed with a thickness of 20 μm.

[0051] Comparative Example 3

[0052] (1) A 1 mol / L chelating agent Na2EDTA solution was added to a 1 mol / L calcium chloride solution and mixed evenly to form a CaCl2 / chelating agent solution, wherein the molar ratio of Na2EDTA to calcium chloride was 1:1.

[0053] (2) Add polyethylene resin masterbatch (average molecular weight of 100,000) to the CaCl2 / chelating agent solution to form a suspension; wherein the mass ratio of polyethylene resin masterbatch to calcium chloride is 100:0.5.

[0054] (3) Heating the suspension at 220°C for 15 min under ultrasonic conditions to form a film-forming solution;

[0055] (4) The film-forming solution is evenly coated on the mold surface by spin coating. After cooling and solidification, a thin film is formed with a thickness of 20 μm.

[0056] The performance of the membrane materials prepared in the above embodiments and comparative examples was tested, and the test results are shown in the following table:

[0057]

[0058] The mechanical properties test used a specimen measuring 20.01mm long, 5.22mm wide, and 0.02mm thick. The tensile rate was set at 4mm / min, allowing for the determination of tensile strength and elongation at break. Based on the measured stress-strain curve, the corresponding toughness can be determined by integrating the stress-strain curves of different materials. The impact strength test used a specimen measuring 63.5mm x 12.7mm x 0.02mm. An Izod impact tester was used, with the specimen notched. The impact energy was recorded to assess the impact strength.

[0059] From the above data, it can be seen that the mechanical properties of the PE films prepared by adding calcium chloride and a chelating agent in Examples 1 to 3 are significantly improved compared with those prepared in Comparative Examples 1 to 3.

[0060] The hydrophilicity test of the membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was conducted, and the results were as follows: Figure 1 As shown, Figure 1 It can be explained that the PE film prepared by adding calcium chloride and a chelating agent in Examples 1 to 3 has better hydrophilicity than the PE film prepared in Comparative Examples 1 to 3. The improved hydrophilicity of the film means that the surface of the film can better interact with aqueous inks and coatings, thereby enhancing its surface adhesion. Especially in the packaging, labeling and printing industries, hydrophilicity helps to improve printing quality and durability. Aqueous coatings and inks usually have better adhesion on hydrophilic surfaces, so the durability and pattern quality of the printing or coating on the surface of the film can be effectively improved. The hydrophilic film surface is easy to combine well with glue, adhesives, etc. In the packaging industry, especially in food packaging, the adhesion of the film to other materials (such as aluminum foil, paper) is crucial. After improving the hydrophilicity, the adhesion between the PE film and these materials can be enhanced, and the overall performance of the packaging material can be improved. For composite film applications, hydrophilicity helps to enhance the adhesion between film layers and improve the durability of the composite film. However, adding too much or too little calcium chloride and chelating agent will affect the hydrophilic properties of the film.

[0061] The films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested for transparency. The results are as follows: Figure 2 As shown, from Figure 2 It can be seen that Figure 2 (b) shows that the transparency of the film is the best, and Example 1 ( Figure 2(a)) Due to the small amount of calcium chloride added, the transparency is not as good as that of Example 2, but it can still effectively improve the transparency of the PE film, while Example 3 ( Figure 2 (c)) The amount of calcium chloride added is relatively large, but the transparency is not as good as that of Example 2. This is because the addition of calcium chloride solution can affect the crystallization behavior of polyethylene to a certain extent, increase the proportion of its amorphous region, and thus improve transparency. However, excessive calcium ions may form tiny crystals on the surface or inside the membrane, thereby affecting the transparency of the membrane. The addition of a chelating agent can form a stable complex with calcium ions, preventing calcium ions from precipitating in the membrane or reacting with other components, avoiding the formation of crystals, and being more conducive to the positive effect of calcium ions on the properties of the PE membrane. At the same time, it helps to improve the physical stability of the PE membrane in long-term use, especially for membrane materials that need to be stored for a long time or exposed to specific environmental conditions. While Comparative Example 1 ( Figure 2 In (d)), since no chelating agent is added and only a small amount of calcium chloride is added, calcium chloride crystals will be precipitated, which will have a serious impact on the transparency of the film and cannot effectively improve the transparency of the film. Figure 2 In (e) and (f)), too much calcium chloride is added. Although a chelating agent is added, the transparency of the film cannot be effectively improved due to the precipitation of calcium chloride. Too little calcium chloride is added, which also cannot effectively improve the transparency of the film.

[0062] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a highly transparent polyethylene film, characterized in that: include (1) adding a chelating agent to a calcium chloride solution and mixing the mixture to form a CaCl2 / chelating agent solution; (2) adding polyethylene resin masterbatch to the CaCl2 / chelating agent solution to form a suspension; (3) heating the suspension to dissolve the polyethylene therein to obtain a film-forming solution; (4) The film-forming solution is covered in the mold and solidified to form a thin film.

2. The method for preparing a highly transparent polyethylene film according to claim 1, wherein: The concentration of the calcium chloride solution is 0.5 mol / L to 1 mol / L.

3. The method for preparing a highly transparent polyethylene film according to claim 1, wherein: The average molecular weight of the polyethylene resin masterbatch is 100,000.

4. The method for preparing a highly transparent polyethylene film according to claim 1, wherein: The chelating agent is EDTA or a salt thereof. The chelating agent is prepared into a solution and then added into the calcium chloride solution. The concentration of the chelating agent solution is 0.5 mol / L to 1 mol / L.

5. The method for preparing a highly transparent polyethylene film according to claim 1 or 4, wherein: The molar ratio of the chelating agent to the calcium chloride is 1:

1.

6. The method for preparing a highly transparent polyethylene film according to claim 1, wherein: The mass ratio of the polyethylene resin masterbatch to calcium chloride is 100:1-5.

7. The method for preparing a highly transparent polyethylene film according to claim 1, wherein: The heating in step (3) is carried out under ultrasonic conditions.

8. The method for preparing a highly transparent polyethylene film according to claim 1 or 7, wherein: The heating temperature is 160-220° C., and the heating time is 15 minutes.

9. The method for preparing a highly transparent polyethylene film according to claim 1, wherein: The method for covering the mold with the film-forming solution is a spin coating method or a spray coating method.

10. A highly transparent polyethylene film, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

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