Low-haze heat-resistant bope film, preparation method and application thereof

Abstract

The application discloses a low-haze heat-resistant BOPE film and a preparation method and application thereof, and belongs to the technical field of film preparation. Through optimization of material ratio and precise control of production process parameters, the application reduces the haze and the heat shrinkage rate at the same time, so that the prepared BOPE film has both low haze and heat resistance, and the requirements for the low haze and heat resistance of the BOPE film in the printing and bag making processes are solved.

Description

Technical Field

[0001] This application relates to the field of thin film preparation technology, and in particular to a low-haze heat-resistant BOPE thin film, its preparation method and application. Background Technology

[0002] Biaxially oriented polyethylene (BOPE) film is a high-performance polymer film material produced using special linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) as main raw materials, through a flat film process and biaxially oriented step-by-step stretching technology. BOPE film features high longitudinal and transverse tensile strength and excellent puncture resistance, and is widely used in various packaging fields such as food packaging, daily chemical packaging, and e-commerce logistics.

[0003] However, due to the low melting point and easy shrinkage of BOPE itself, BOPE film is prone to misregistration during printing and deformation and poor flatness during bag heat sealing. Increasing the proportion of HDPE can improve heat resistance to some extent, but it will increase haze, which limits the application of BOPE as a printing layer.

[0004] Chinese invention patent with publication number CN117261387A introduces a biaxially oriented polyethylene film material and a high-temperature resistant and deformation-resistant biaxially oriented polyethylene film. However, the patent mainly focuses on improving haze, but cannot prove that it has high-temperature resistance and deformation resistance.

[0005] Chinese invention patent CN119795716A discloses a low heat shrinkage biaxially oriented polyethylene film, its preparation method and application. The film body is composed of an upper corona layer, a sub-surface layer, an intermediate layer, a sub-inner layer and a lower corona layer connected in sequence. However, its heat shrinkage rate is relatively large, with the lowest longitudinal shrinkage rate being 3.2, and its thermal stability is still poor.

[0006] Therefore, there is an urgent need in this field to develop a low-haze, heat-resistant BOPE film to solve the problem of insufficient optical and heat resistance properties of BOPE film in the printing and bag making processes. Summary of the Invention

[0007] To solve at least one of the above-mentioned technical problems, the technical solution adopted in this application is as follows.

[0008] The first aspect of this application provides a method for preparing a low-haze heat-resistant BOPE film, wherein the BOPE film sequentially comprises a surface layer, a sub-surface layer, a core layer, a sub-inner layer, and an inner layer, and the preparation method includes the following steps: Prepare materials for each layer. Surface and inner layers: 80%~90% w / w high-density polyethylene, 9.5%~19.5% w / w linear low-density polyethylene, 0.5%~3.5% w / w anti-sticking agent. Secondary surface and secondary inner layers: 80%~90% w / w high-density polyethylene, 9.5%~19.5% w / w linear low-density polyethylene, 0.5%~1.5% w / w antistatic agent. Core layer: 75%~90% w / w high-density polyethylene, 9.5%~19.5% w / w linear low-density polyethylene, 0.5%~1.5% w / w antistatic agent; The materials for the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer are fed into five extruders for heating, melting, and extrusion. The five melts are co-extruded to form a cast sheet on a chilling roll, which is then biaxially stretched.

[0009] In this application, the high-density polyethylene is composed of polyethylene with different molecular weights, specifically including low molecular weight (0-4.5) polyethylene, medium molecular weight (4.5-5.5) polyethylene, and high molecular weight (5.5-10) polyethylene. In some embodiments of this application, the high-density polyethylene contains 10-30% low molecular weight polyethylene, 5-15% high molecular weight polyethylene, and 55-85% medium molecular weight polyethylene.

[0010] In this application, the linear low-density polyethylene has a melt index ≥2 g / 10 min and a density ≤0.918 g / cm³. 3 .

[0011] In some embodiments of this application, the biaxial stretching step is as follows: The casting is preheated at a longitudinal stretching preheating temperature and stretched at a longitudinal stretching temperature. After being stretched to a predetermined longitudinal stretching ratio, it is shaped at a longitudinal stretching shaping temperature. The film, after being stretched longitudinally, is preheated at a transverse stretching preheating temperature and stretched at a transverse stretching temperature. After being stretched to a predetermined transverse stretching ratio, it is then set at a transverse stretching setting temperature.

[0012] In some embodiments of this application, the proportions of the materials in each layer are as follows: Outer and inner layers: 80% w / w high-density polyethylene, 17.5% w / w linear low-density polyethylene, 2.5% w / w anti-sticking agent. Secondary surface and secondary inner layers: 80% w / w high-density polyethylene, 19.5% w / w linear low-density polyethylene, 0.5% w / w antistatic agent. Core layer: 80% w / w high-density polyethylene, 19.5% w / w linear low-density polyethylene, 0.5% w / w antistatic agent.

[0013] In some embodiments of this application, the longitudinal stretching preheating temperature is 100℃~120℃, the longitudinal stretching temperature is 95℃~110℃, and the longitudinal stretching setting temperature is 105℃~115℃; the transverse stretching preheating temperature is 125℃~140℃, the transverse stretching temperature is 115℃~130℃, and the transverse stretching setting temperature is 120℃~135℃.

[0014] In some specific embodiments of this application, the longitudinal stretching preheating temperature is 115°C, the longitudinal stretching temperature is 105°C, and the longitudinal stretching setting temperature is 110°C; the transverse stretching preheating temperature is 135°C, the transverse stretching temperature is 125°C, and the transverse stretching setting temperature is 130°C.

[0015] In some embodiments of this application, the longitudinal stretch ratio is 4 to 5, and the transverse stretch ratio is 8 to 9.

[0016] In some embodiments of this application, the temperature of the cooling roller is 50°C to 80°C.

[0017] In some embodiments of this application, the anti-adhesive includes one or more of silicates, silica, and glass microspheres.

[0018] In some embodiments of this application, the antistatic agent includes one or more of ethoxylated lauramide, ethoxylated stearamide, glyceryl monostearate, and alkyl sulfonates.

[0019] The second aspect of this application provides a BOPE film prepared using any of the preparation methods described in the first aspect of this application.

[0020] The third aspect of this application provides the use of the BOPE film described in the second aspect of this application in the preparation of product packaging.

[0021] In some embodiments of this application, the product packaging is flexible packaging, composed of two or more layers of materials, including a printed layer, a barrier layer, and a hot air layer. In some embodiments of this application, the BOPE film serves as the printed layer.

[0022] In some embodiments of this application, the products include, but are not limited to, food, daily chemical products, electronic products, electronic components, and batteries. Further, the food includes, but is not limited to, frozen food, pet food, coffee beans, and rice / grains; the daily chemical products include, but are not limited to, laundry detergent, cosmetics, shampoo, and shower gel.

[0023] Compared with the prior art, this application has the following advantages: This application optimizes material ratios and precisely controls production process parameters to reduce both haze and heat shrinkage, resulting in a BOPE film that combines low haze and heat resistance. This solves the requirements for low haze and heat resistance in BOPE films during printing and bag making.

[0024] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this application, nor is it intended to limit the scope of this application. Other features of this application will become readily apparent from the following description. Attached Figure Description

[0025] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of this application are illustrated in the drawings by way of example and not limitation, wherein: Figure 1 The properties of the BOPE film prepared in Example 2 of this application are shown. Detailed Implementation

[0026] Unless otherwise stated, implied from the context, or as is customary in the art, all parts and percentages in this application are based on weight, and all testing and characterization methods used are concurrent with the filing date of this application. Where applicable, any patent, patent application, or disclosure relating to this application is incorporated herein by reference in its entirety, and its equivalent patent families are also incorporated herein by reference, particularly the definitions of relevant terms in the art disclosed in such documents. If any definition of a specific term disclosed in the prior art is inconsistent with any definition provided in this application, the definition provided in this application shall prevail.

[0027] The numerical ranges used in this application are approximate values ​​and therefore may include values ​​outside the range unless otherwise stated. The numerical range includes all values ​​from the lower limit to the upper limit, increasing by one unit, provided that there is an interval of at least two units between any lower and any higher value. For ranges containing values ​​less than 1 or fractions greater than 1 (e.g., 1.1, 1.5, etc.), one unit is appropriately considered as 0.0001, 0.001, 0.01, or 0.1. For ranges containing single digits less than 10 (e.g., 1 to 5), one unit is generally considered as 0.1. These are merely specific examples of what is intended to be expressed, and all possible combinations of values ​​between the listed lowest and highest values ​​are considered to be clearly described in this application.

[0028] The terms “comprising,” “including,” “having,” and their derivatives do not exclude the presence of any other components, steps, or processes, regardless of whether such other components, steps, or processes are disclosed in this application. To eliminate any doubt, unless expressly stated otherwise, all compositions using the terms “comprising,” “including,” or “having” in this application may contain any additional additives, excipients, or compounds. Conversely, except for those necessary for operational performance, the term “substantially constitutes…” excludes any other components, steps, or processes described below with respect to that term. The term “consisting of…” does not include any components, steps, or processes not specifically described or listed. Unless expressly stated otherwise, the term “or” refers to the individual members listed or any combination thereof.

[0029] To make the technical problems, technical solutions and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments.

[0030] The following examples are used to illustrate preferred embodiments of this application. Those skilled in the art will understand that the techniques disclosed in the examples represent technologies discovered by the inventors that can be used to implement this application, and therefore can be considered preferred embodiments of this application. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed herein, still yielding the same or similar results, without departing from the spirit or scope of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains, and all materials cited herein and referenced by them are incorporated herein by reference.

[0032] Those skilled in the art will recognize, or can learn through routine experimentation, many equivalents of the specific embodiments of the invention described herein. These equivalents will be included in the claims.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the instruments and equipment used in the following examples are all conventional laboratory instruments and equipment; unless otherwise specified, the experimental materials used in the following examples were all purchased from conventional biochemical reagent stores.

[0034] Example 1 1. Material Proportioning The BOPE film prepared in this embodiment adopts a five-layer co-extrusion structure, consisting of a surface layer, a sub-surface layer, a core layer, a sub-inner layer, and an inner layer. Each layer is made of high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and additives (anti-sticking agents or antistatic agents). By designing the formulation of each layer of the film, low haze and heat resistance are achieved while ensuring processing stability. The material composition of the BOPE film prepared in this embodiment is shown in Table 1. Table 1 ; in: HDPE is made of high-melting-point unimodal polyethylene with a melting point ≥132℃. It is composed of polyethylene with different molecular weights: low molecular weight (0-4.5, accounting for 20%), medium molecular weight (4.5-5.5, accounting for 70%), and high molecular weight (5.5-10, accounting for 10%).

[0035] LLDPE is made from bimodal polyethylene with high melt index, low density, and excellent extrusion flowability, with a melt index ≥2g / 10min and a density ≤0.918g / cm³. 3 .

[0036] The anti-adhesion agent selected is Shantou Best ABPE9305, which is a spherical anti-adhesion agent with silicate as the main component.

[0037] The antistatic agent selected is Shantou Best AS230PED, which is a compound of ethoxylated laurylamide and ethoxylated stearamide as the main components.

[0038] This embodiment achieves low haze and heat resistance by precisely controlling the combination of HDPE and LLDPE with different molecular weights, molecular weight distributions, densities, and melting points. Specifically, the combination of HDPE and LLDPE in the surface layer, sub-surface layer, sub-inner layer, and inner layer improves heat resistance while forming a smooth interface on the surface, reducing diffuse light reflection; the combination of HDPE and LLDPE in the core layer results in low extrusion pressure, stable extrusion, and combines processability, optical properties, and heat resistance.

[0039] 2. Extrusion process After the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer are prepared, they are respectively transported to five extruders for heating, melting, and extrusion. The extrusion processing temperature is 240℃.

[0040] Five melts (in a ratio of 5:5:80:5:5) are gathered into a die, extruded through the die, and then rapidly cooled onto a 70°C quenching roller using compressed air in cooling water (30°C) to form a cast sheet.

[0041] The casting is preheated at 115℃, then stretched longitudinally by 4.5 times at 105℃, and finally shaped at 110℃. The film, after longitudinal stretching, is preheated at 135°C, then stretched 8 times laterally at 125°C, and finally set at 130°C. After stretching, the product enters the traction system for single-sided corona treatment, edge trimming, automatic thickness measurement, and finally winding. Then it undergoes aging at a temperature of 30±2℃ before being slit by a slitting machine. After product inspection, it is packaged, weighed, and put into storage. The entire production speed is 220m / min.

[0042] The entire production process achieves low haze and low heat shrinkage (i.e., heat resistance) in the film through precise control of extrusion temperature, quench roll temperature, cooling water temperature, preheating temperature, stretching temperature, setting temperature, stretch ratio, and production speed.

[0043] Example 2 In this embodiment, the material composition for preparing the BOPE film is shown in Table 2: Table 2 ; Compared to Example 1, this embodiment only increases the ratio of HDPE to LLDPE in the core layer, while the material ratios of the other layers are the same as in Example 1, and the extrusion process is also the same as in Example 1.

[0044] Example 3 In this embodiment, the material formulation for preparing the BOPE film is shown in Table 3: Table 3 ; Compared to Example 1, this embodiment only further increases the ratio of HDPE to LLDPE in the core layer based on Example 2. The material ratios of the remaining layers are the same as in Example 1, and the extrusion process is also the same as in Example 1.

[0045] Example 4 In this embodiment, the material formulation for preparing the BOPE film is shown in Table 4: Table 4 ; Compared to Example 2, this embodiment increases the ratio of HDPE to LLDPE in the surface layer, sub-surface layer, sub-inner layer, and inner layer, while the extrusion process is the same as in Example 1.

[0046] Example 5 In this embodiment, the material composition for preparing the BOPE film is shown in Table 5: Table 5 ; Compared to Example 2, this embodiment only further increases the ratio of HDPE to LLDPE in the surface layer, sub-surface layer, sub-inner layer and inner layer, based on Example 4. The extrusion process is the same as in Example 1.

[0047] The thickness, tensile strength, elongation at break, thermal shrinkage, haze, gloss, coefficient of dynamic friction, and wetting tension of the BOPE films prepared in the above embodiments were tested according to the test methods in Table 6.

[0048] Table 6 ; The results are shown in Table 7.

[0049] Table 7 ; Table 7 shows that the BOPE films prepared in each embodiment exhibit differences in various aspects of performance. Comparing Examples 1 to 3, as the proportion of HDPE to LLDPE in the core layer increases, the tensile strength continuously increases while the elongation at break continuously decreases. More importantly, the heat shrinkage rate shows an overall decreasing trend. The heat shrinkage rate at 100℃ for 2 minutes decreases in both the longitudinal (MD) and transverse (TD) directions; the heat shrinkage rate at 120℃ for 2 minutes decreases continuously in the longitudinal direction, but does not continue to decrease in the transverse direction with the increase of the HDPE proportion. However, as the proportion of HDPE to LLDPE in the core layer increases, the haze of the BOPE film also increases, failing to meet the requirement of simultaneously achieving low haze and low shrinkage rate.

[0050] Therefore, the BOPE film prepared in Example 2 exhibits a low thermal shrinkage rate: 1.1% in the MD direction and 1.6% in the TD direction at 100℃ for 2 min, and 4.2% in the MD direction and 4.5% in the TD direction at 120℃ for 2 min; furthermore, the haze is only 3.4%. This film demonstrates a better balance between haze and heat resistance, combining low haze with low thermal shrinkage, making it a superior choice. Figure 1 As shown.

[0051] Furthermore, based on Example 2, the ratio of HDPE to LLDPE in the surface layer, sub-surface layer, sub-inner layer and inner layer was increased (Examples 4 and 5). Although the thermal shrinkage rate of the resulting film decreased, the haze was significantly improved.

[0052] To further demonstrate that the BOPE film prepared in Example 2 has low haze and heat resistance properties, the inventors further provide the following comparative examples.

[0053] Comparative Example 1 Unlike Example 2, in Comparative Example 1, the HDPE used was high-melting-point unimodal polyethylene with a melting point ≥130℃, composed of medium- and low molecular weight polyethylene with a molecular weight distribution range of 2.5-5, accounting for 100%; the LLDPE used was unimodal polyethylene with a low melt index and high density, with a melt index ≤2g / 10min and a density ≥0.926g / cm³. 3 BOPE films were prepared according to the method described in Example 2.

[0054] Comparative Example 2 Unlike Example 2, in Comparative Example 2, the HDPE used was high-melting-point unimodal polyethylene with a melting point ≥130℃, composed of medium-to-high molecular weight polyethylene, with medium molecular weight ranging from 4.5 to 5, accounting for 80%; and high molecular weight ranging from 5 to 8.6, accounting for 20%. The LLDPE used was unimodal polyethylene with a high melt index and high density, with a melt index ≥2g / 10min and a density ≥0.929g / cm³. 3 BOPE films were prepared according to the method described in Example 2.

[0055] Comparative Example 3 BOPE films were prepared according to the method described in Example 2 of CN117261387A.

[0056] Comparative Example 4 BOPE films were prepared according to the method described in Example 1 of CN119795716A.

[0057] The thickness, tensile strength, elongation at break, thermal shrinkage, haze, gloss, coefficient of dynamic friction, and wetting tension of the BOPE films prepared in the above comparative examples were tested according to the test methods in Table 6. The results are shown in Table 8.

[0058] Table 8 ; As shown in Table 8, the BOPE films prepared in each comparative example exhibited significantly higher thermal shrinkage rates than the BOPE film prepared in Example 2. For instance, the BOPE film prepared in Comparative Example 1 showed a thermal shrinkage rate of 2.5% in the MD direction and 1.8% in the TD direction at 100℃ for 2 min, and 5.2% in the MD direction and 4.6% in the TD direction at 120℃ for 2 min, with a haze of 4.0%. The BOPE film prepared in Comparative Example 3 showed a thermal shrinkage rate of 3.6% in the MD direction and 2.5% in the TD direction at 100℃ for 2 min, and 6.8% in the MD direction and 5.2% in the TD direction at 120℃ for 2 min.

[0059] To test the effect of the extrusion process on the properties of BOPE, the inventors set up comparative examples 5 to 9. When preparing BOPE films in each comparative example, the material ratio of each layer was the same as in Example 2. The only difference from Example 2 was that some temperature parameters of the extrusion process were different, as shown in Table 9.

[0060] Table 9 ; As shown in Table 9, in Comparative Example 5, the preheating temperature, stretching temperature, and setting temperature for longitudinal stretching were all 5°C higher than those in Example 2; in Comparative Example 6, the longitudinal stretching ratio was 0.5 higher than that in Example 2; in Comparative Example 7, the preheating temperature, stretching temperature, and setting temperature for transverse stretching were all 5°C higher than those in Example 2; in Comparative Example 8, the cooling water temperature was increased to 50°C, while it was 30°C in Example 2; in Comparative Example 9, the longitudinal stretching ratio was further increased compared to Example 2 based on that in Comparative Example 6.

[0061] The thickness, tensile strength, elongation at break, thermal shrinkage, haze, gloss, coefficient of dynamic friction and wetting tension of each BOPE film prepared in Comparative Examples 5 to 9 were tested according to the test methods in Table 6, and compared with the BOPE film prepared in Example 2. The results are shown in Table 10.

[0062] Table 10 ; Table 10 shows that increasing the longitudinal stretching temperature (Comparative Example 5) or the transverse stretching temperature (Comparative Example 7) can reduce the heat shrinkage rate to some extent, but at the same time, the haze will increase. Increasing the longitudinal stretching ratio (Comparative Examples 6 and 9) reduces the haze, but significantly increases the heat shrinkage rate. Increasing the cooling water temperature (Comparative Example 8) reduces the heat shrinkage rate, but significantly increases the haze, far exceeding the standard. Therefore, changing the parameters of the BOPE extrusion process can also cause BOPE films to not simultaneously possess both low haze and low heat shrinkage rate.

[0063] In summary, only with specific material ratios and specific process parameters can BOPE films with both low haze and low heat shrinkage (i.e., heat resistance) be prepared.

[0064] Furthermore, it should be understood that after reading the foregoing contents of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a low-haze, heat-resistant BOPE film, characterized in that, The BOPE film comprises, in sequence, a surface layer, a sub-surface layer, a core layer, a sub-inner layer, and an inner layer. The preparation method includes the following steps: Prepare materials for each layer. Surface and inner layers: 80%~90% w / w high-density polyethylene, 9.5%~19.5% w / w linear low-density polyethylene, 0.5%~3.5% w / w anti-sticking agent. Secondary surface and secondary inner layers: 80%~90% w / w high-density polyethylene, 9.5%~19.5% w / w linear low-density polyethylene, 0.5%~1.5% w / w antistatic agent. Core layer: 75%~90% w / w high-density polyethylene, 9.5%~19.5% w / w linear low-density polyethylene, 0.5%~1.5% w / w antistatic agent; The materials for the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer are fed into five extruders for heating, melting, and extrusion. The five melts are co-extruded to form a cast sheet on a chilling roll, which is then biaxially stretched.

2. The preparation method according to claim 1, characterized in that, The steps of the biaxial stretching are as follows: The casting is preheated at a longitudinal stretching preheating temperature and stretched at a longitudinal stretching temperature. After being stretched to a predetermined longitudinal stretching ratio, it is shaped at a longitudinal stretching shaping temperature. The film, after being stretched longitudinally, is preheated at a transverse stretching preheating temperature and stretched at a transverse stretching temperature. After being stretched to a predetermined transverse stretching ratio, it is then set at a transverse stretching setting temperature.

3. The preparation method according to claim 2, characterized in that, The longitudinal stretching preheating temperature is 100℃~120℃, the longitudinal stretching temperature is 95℃~110℃, and the longitudinal stretching setting temperature is 105℃~115℃; the transverse stretching preheating temperature is 125℃~140℃, the transverse stretching temperature is 115℃~130℃, and the transverse stretching setting temperature is 120℃~135℃.

4. The preparation method according to claim 3, characterized in that, The longitudinal stretching preheating temperature is 115℃, the longitudinal stretching temperature is 105℃, and the longitudinal stretching setting temperature is 110℃; the transverse stretching preheating temperature is 135℃, the transverse stretching temperature is 125℃, and the transverse stretching setting temperature is 130℃.

5. The preparation method according to claim 2, characterized in that, The longitudinal stretch ratio is 4-5, and the transverse stretch ratio is 8-9.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The temperature of the cooling roller is 50℃~80℃.

7. The preparation method according to any one of claims 1 to 5, characterized in that, The anti-adhesion agent includes one or more of silicates, silica, and glass microspheres.

8. The preparation method according to any one of claims 1 to 5, characterized in that, The antistatic agent includes one or more of ethoxylated lauramide, ethoxylated stearamide, glyceryl monostearate, and alkyl sulfonates.

9. A BOPE film prepared by any one of the preparation methods according to claims 1 to 7.

10. The use of the BOPE film according to claim 9 in the preparation of product packaging.

Images