Preparation method of self-assembled multilayer co-extrusion high water-resistance high toughness PE film

Abstract

The application provides a preparation method of a self-assembled multilayer co-extrusion high-water-resistance high-toughness PE film, which comprises the following steps: using ultrahigh-viscosity polyethylene resin material as a surface layer, arranging a core layer in an alternating manner of low-viscosity polyethylene resin material and ultrahigh-viscosity polyethylene resin material, and co-assembling the surface layer and the core layer into a multilayer resin layer with an odd number of layers; using a multilayer co-extrusion technology to co-extrude the multilayer resin layer into a film to obtain the self-assembled multilayer co-extrusion high-water-resistance high-toughness PE film; the ultrahigh-viscosity polyethylene resin material has a melt index of less than 0.1 g / 10 min under a test condition of 21.6 KG / 190 DEG C; and the low-viscosity polyethylene resin material has a melt index of 0.5-2.0 g / 10 min under a test condition of 2.16 KG / 190 DEG C. By compounding the ultrahigh-viscosity polyethylene resin with other different types of polyethylene resin materials, designing a special hierarchical structure, utilizing the stress difference of the materials with different viscosities under the same mold to generate secondary flow, and self-assembling a petal-shaped or leaf-shaped interlayer structure, the barrier property of the film product is significantly improved, and the film has the characteristics of high toughness.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a method for preparing a self-assembled multilayer co-extruded high water-barrier and high-toughness PE film. Background Technology

[0002] The barrier properties of thin film materials against specific permeable substances are a key indicator for their applications in numerous fields such as packaging, electronics, and medicine. The barrier process follows a four-stage mechanism: adsorption-dissolution-diffusion-desorption. Based on this mechanism, performance improvements in high-barrier thin film materials typically revolve around these four stages, enhancing the barrier effect by controlling one or more of these stages. Currently, commonly used techniques in the industry include: depositing dense coatings or plating materials on the film surface to block permeation pathways using their low permeability; increasing the density of the barrier material itself to reduce internal porosity and free volume, thereby inhibiting the diffusion of permeating molecules; and filling with nanosheet materials to create tortuous diffusion paths for permeating molecules within the material, extending the permeation distance and thus reducing the permeation rate.

[0003] In the field of polyethylene (PE) film, existing technologies have also drawn on the above-mentioned ideas to improve water vapor barrier performance, resulting in a variety of conventional solutions. For example, vacuum aluminizing or alumina plating is used to form a metal or metal oxide coating on the PE film surface, utilizing the density of the coating to block water vapor penetration; or a barrier layer material is coated on the film surface, relying on the chemical properties of the barrier layer to reduce the adsorption and dissolution capacity of water vapor; or nano-inorganic materials are filled into the PE matrix, improving performance through the barrier effect and path tortuosity of nanoparticles. However, these methods all have obvious limitations: First, the additional coating, plating, or nanofilling processes significantly increase the processing cost of the film, which is not conducive to large-scale industrial applications; second, the introduced barrier materials often have a negative impact on the inherent properties of PE film, such as reducing the transparency of the material, making it unable to meet the appearance requirements of high-end packaging, or changing the toughness and high temperature and humidity resistance of the film, affecting its application range.

[0004] Furthermore, the industry has attempted to improve the water vapor barrier properties of PE films by adding a high proportion of high-density polyethylene (HDPE). However, practice has shown that this method leads to a sharp decrease in the film's flexibility: the elongation at break of ordinary polyethylene films is typically 600%-800%, while adding a high proportion of HDPE significantly reduces the elongation at break to 3%-50%. This performance degradation directly causes a series of application problems: during the manufacturing process of packaging bags, the film is prone to tearing due to insufficient toughness, making it difficult to ensure the stability of continuous processing; during the transportation and use of packaged products, it is also prone to breakage due to external forces such as drops, failing to provide effective protection for the contents and severely restricting the application of PE films in fields requiring both barrier and mechanical properties.

[0005] Therefore, developing a technical solution that can improve the water vapor barrier properties of PE films while avoiding excessive processing costs and without significantly sacrificing key properties such as film transparency, toughness, and resistance to high temperature and humidity has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address at least one of the technical problems mentioned above by proposing a method for preparing a self-assembled multilayer co-extruded high water-resistant and high-toughness PE film, which can prepare a PE film with excellent flexibility and water-resistant properties simply by multilayer co-extrusion blown film processing.

[0007] The present invention provides the following solution: a method for preparing a self-assembled multilayer co-extruded high water-resistant and high-toughness PE film, comprising the following steps: using ultra-high viscosity polyethylene resin as the surface layer, and then forming a core layer by alternating arrangement of low viscosity polyethylene resin and ultra-high viscosity polyethylene resin, wherein the surface layer and the core layer are co-assembled into a multilayer resin layer with an odd number of layers; using multilayer co-extrusion technology to co-extrude the multilayer resin layers into a film to obtain a self-assembled multilayer co-extruded high water-resistant and high-toughness PE film; wherein the ultra-high viscosity polyethylene resin has a melt index of less than 0.1 g / 10 min under the test conditions of 21.6 KG / 190℃; wherein the low viscosity polyethylene resin has a melt index of 0.5-2.0 g / 10 min under the test conditions of 2.16 KG / 190℃.

[0008] This invention utilizes ultra-high viscosity polyethylene resin blended with other types of polyethylene resin to design a unique layered structure. When the resin melt passes through the extrusion die, the different viscosities of each layer create melt flows with varying melt pressures. As the melt layers converge and exit the die, secondary flows occur in addition to the longitudinal main flow, causing the melt layers to self-assemble and form a hybrid structure, resembling petals or leaves. This enhances the barrier properties and toughness of the film material.

[0009] More preferably, the number of layers in the above-mentioned multilayer resin layer is 5-11 layers.

[0010] In this solution, the melt index difference is used to generate self-assembly secondary flow of the material in the mold. Generally speaking, multi-layer resin with a 3-layer structure cannot form self-assembly secondary flow, so at least 5 layers are required, and 7, 9 and 11-layer structures are preferred.

[0011] In a further preferred embodiment, when the multi-layer co-extrusion technology is used to co-extrude the multi-layer resin layers into a film, pressure fluctuations are generated in the core layer through pulse feeding.

[0012] By appropriately increasing or decreasing the screw speed in the extruder, the secondary flow during the multi-layer co-extrusion process in this scheme can be enhanced. Similar to using an intermittently operating booster pump to pressurize the melt, this increases the melt flow rate and also causes a stronger expansion effect when the material leaves the die, both of which enhance the subsequent secondary flow.

[0013] More preferably, the co-extrusion film formation mentioned above includes, but is not limited to, casting and blown film formation.

[0014] More preferably, the ultra-high viscosity polyethylene resin material of the surface layer comprises 70-100% ultra-high viscosity polyethylene resin and 0-30% high-density polyethylene (high-density polyethylene selected from Dow Chemical: AT6900, melt index of 1.2 g / 10 min, 190℃ / 2.16 kg) by weight percentage; the low viscosity polyethylene resin material of the core layer comprises 70-100% high-density polyethylene and 0-30% metallocene linear low-density polyethylene (metallocene linear low-density polyethylene selected from Dow Chemical: TF80, melt index of 1.7 g / 10 min, 190℃ / 2.16 kg) by weight percentage; the ultra-high viscosity polyethylene resin material of the core layer comprises 70-100% ultra-high viscosity polyethylene resin and 0-30% metallocene linear low-density polyethylene by weight percentage.

[0015] Ultra-high viscosity polyethylene resin is typically used intermittently to provide a stable interlayer structure. The two surface layers are provided with a stable surface by the ultra-high viscosity polyethylene resin, preventing surface cracking due to disturbances from secondary flows. The high-density material, as a component to improve barrier properties, also helps to regulate viscosity, avoiding excessive processing difficulty.

[0016] ① Two outer layers of ultra-high viscosity polyethylene resin + high-density polyethylene material, high viscosity material, provide a stable outer layer structure.

[0017] ② A layer of high-density polyethylene and metallocene linear low-density polyethylene provides a layered structure with good flowability. The metallocene linear low-density polyethylene material can be used as a toughening and viscosity-modifying material, while the high-density polyethylene material mainly serves as a barrier layer.

[0018] ③ The ultra-high viscosity polyethylene resin + metallocene linear low density polyethylene material layer serves as a stabilizing layer, providing a relatively stable interlayer structure and preventing materials with good flowability from damaging the interlayer isolation structure.

[0019] More preferably, the above-mentioned ultra-high viscosity polyethylene resin is prepared by mixing linear low-density polyethylene with tackifying powder and silane coupling agent.

[0020] More preferably, the mass ratio of the above-mentioned linear low-density polyethylene to the tackifying powder and silane coupling agent is: 74~92% linear low-density polyethylene + 5~20% tackifying powder + 3~6% silane coupling agent.

[0021] More preferably, the above-mentioned thickening powder is nano-kaolin or nano-bentonite powder.

[0022] Nano-kaolin or nano-bentonite can be used as fillers or additives to improve barrier properties; and as materials that react with silane coupling agents to increase the viscosity of the system.

[0023] More preferably, the linear low-density polyethylene has a density of 0.92-0.93, a melt index of 0.05-0.2 g / 10 min, and a temperature of 190°C.

[0024] Linear low-density polyethylene (LDPE) crystallizes rapidly, which is beneficial for improving the barrier properties of the final product, making it superior to low-density materials. Linear materials also have good toughness, which is superior to high-density materials. Linear materials have a simple structure with few branches and low melt strength, which is beneficial for the rapid dispersion of powder materials.

[0025] A further preferred embodiment of the preparation method of the above-mentioned ultra-high viscosity polyethylene resin includes the following steps:

[0026] Step 1: Disperse nano-kaolin or nano-bentonite powder in linear low-density polyethylene material, melt extrude at an extrusion temperature of 190-220℃, and water-cool granulate to form a primary granulated resin.

[0027] Step 2: Remelt the primary granulated resin and add a silane coupling agent at the beginning of the melting section of the extruder. The extrusion temperature is 210-220℃. After extrusion, water-cool and granulate to form secondary granulated resin. Place the secondary granulated resin in a curing chamber at 45-55℃ for 72 hours to form ultra-high viscosity polyethylene resin.

[0028] Adding both the tackifying powder and linear low-density polyethylene simultaneously will cause the powder to react with the silane coupling agent first, resulting in a rapid increase in the system viscosity, which is detrimental to the uniform dispersion of the powder. Adding them separately allows the powder to be uniformly dispersed in the polyethylene resin first, and then adding the silane coupling agent during the secondary granulation process allows the polyethylene resin to form a uniform cross-linked network.

[0029] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention uses ultra-high viscosity polyethylene resin compounded with other different types of polyethylene resins to design a special layered structure. It utilizes the stress difference between materials of different viscosities under the same mold to generate secondary flow, self-assembling to form petal-shaped or leaf-shaped interlayer structures. After forming these petal-shaped or leaf-shaped interlayer structures, the penetration path of the blocked substance molecules can be extended, significantly improving the barrier performance of the film product. Furthermore, the formation of these petal-shaped or leaf-shaped interlayer structures allows the tough material layer and the barrier material layer to form a hybrid entanglement structure. When the brittle barrier layer breaks, the tough material layer can reinforce the film by entanglement to prevent breakage, thus giving the film high toughness. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the interlayer structure of the multilayer co-extruded melt after spontaneous secondary flow in the mold in this invention. The diagrams from left to right are the initial section, middle section and end section of the mold.

[0031] Figure 2 This is a photograph of the thin film prepared in Example 1 of the present invention;

[0032] Figure 3 This is a macroscopic image of the entanglement stripes formed under the hybrid entanglement structure of the thin film in Embodiment 1 of the present invention (photographed under backlight).

[0033] Figure 4 The images show a comparison of the hybrid winding structure of the thin film in Embodiment 1 of the present invention (left image) and a conventional product (right image) under the same magnification microscope. Detailed Implementation

[0034] To facilitate understanding of the present invention, it will be described more fully and in detail below, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0037] The present invention is as follows: Nano-kaolin or nano-bentonite powder (mass fraction 5-20%) is dispersed in linear low-density polyethylene material (density 0.92-0.93, melt index 0.05-0.2 g / 10 min, 190℃), and melt-extruded at an extrusion temperature of 190-220℃, followed by water-cooled granulation to form primary granulated resin; the primary granulated resin is remelted, and 3-6% of silane coupling agent is added at the beginning of the melting section of the extruder, with an extrusion temperature of 210-220℃, followed by water-cooled granulation to form secondary granulated resin; the secondary granulated resin is placed in a curing chamber and cured at 45-55℃ for 72 hours to form ultra-high viscosity polyethylene resin granules, requiring a melt index of less than 0.1 g / 10 min under the test conditions of 21.6 kg / 190℃.

[0038] Films are made from ultra-high viscosity polyethylene resin granules using multi-layer co-extrusion technology (the number of layers must be odd, at least 5 layers, and at most 11 layers). Co-extrusion methods include, but are not limited to, casting and blown film production. The structure and formulation of each layer of the film should follow the table below. The proportions of high-density polyethylene and metallocene linear low-density polyethylene added should be adjusted according to the actual barrier properties and toughness requirements.

[0039]

[0040]

[0041] Example 1

[0042] 10% by mass of nano-bentonite powder (nanoscale, Dongguan Ruiheng Mineral Products Co., Ltd.) was dispersed in linear low-density polyethylene material (FB2310, density 0.93, melt index 0.2 g / 10 min, 190℃, 2.16 kg). The mixture was melt-extruded at an extrusion temperature of 200℃ and water-cooled granulated to form primary granulated resin. The primary granulated resin was remelted, and 3.4% of silane coupling agent (FT560, Nanjing Feiteng New Material Technology Co., Ltd.) was added at the beginning of the melt section of the extruder. The extrusion temperature was 205℃, and the mixture was water-cooled and granulated to form secondary granulated resin. The secondary granulated resin was placed in a curing chamber and cured at 45℃ for 72 h to form ultra-high viscosity polyethylene resin granules. The melt index was 0.07 g / 10 min under the test conditions of 21.6 kg / 190℃.

[0043] The granules containing ultra-high viscosity polyethylene resin were blown into a 30µm film on a blown film production line (Hosokawa Alpina) with the following 5-layer structure.

[0044]

[0045] The high-density polyethylene is Dow AT6900 with a melt index of 1.2 g / 10 min (190℃ / 2.16 kg); the metallocene linear low-density polyethylene is Dow TF80 with a melt index of 1.7 g / 10 min (190℃ / 2.16 kg).

[0046] Example 2

[0047] 20% by mass of nano-bentonite powder (nanoscale, Dongguan Ruiheng Mineral Products Co., Ltd.) was dispersed in linear low-density polyethylene material (FB2310, density 0.93, melt index 0.2 g / 10 min, 190℃, 2.16 kg). The mixture was melt-extruded at an extrusion temperature of 190℃ and water-cooled granulated to form primary granulated resin. The primary granulated resin was remelted, and 5.0% of silane coupling agent (FT560, Nanjing Feiteng New Material Technology Co., Ltd.) was added at the beginning of the melt section of the extruder. The extrusion temperature was 210℃, and the mixture was water-cooled and granulated to form secondary granulated resin. The secondary granulated resin was placed in a curing chamber and cured at 50℃ for 72 h to form ultra-high viscosity polyethylene resin granules. The melt index was 0.03 g / 10 min under the test conditions of 21.6 kg / 190℃.

[0048] The granules containing ultra-high viscosity polyethylene resin were blown into 30µm films on a blown film production line (Hosokawa Alpina) with the following 11-layer structure.

[0049]

[0050] The high-density polyethylene is Dow AT6900 with a melt index of 1.2 g / 10 min (190℃ / 2.16 kg); the metallocene linear low-density polyethylene is Dow TF80 with a melt index of 1.7 g / 10 min (190℃ / 2.16 kg).

[0051] Comparative Example 1

[0052] 20% by mass of nano-bentonite powder (nanoscale, Dongguan Ruiheng Mineral Products Co., Ltd.) was dispersed in linear low-density polyethylene material (FB2310, density 0.93, melt index 0.2 g / 10 min, 190℃, 2.16 kg). The mixture was melt-extruded at an extrusion temperature of 190℃ and water-cooled granulated to form primary granulated resin. The primary granulated resin was remelted, and 5.0% of silane coupling agent (FT560, Nanjing Feiteng New Material Technology Co., Ltd.) was added at the beginning of the melt section of the extruder. The extrusion temperature was 210℃, and the mixture was water-cooled and granulated to form secondary granulated resin. The secondary granulated resin was placed in a curing chamber and cured at 50℃ for 72 h to form ultra-high viscosity polyethylene resin granules. The melt index was 0.03 g / 10 min under the test conditions of 21.6 kg / 190℃.

[0053] The granules containing ultra-high viscosity polyethylene resin were blown into 30µm films on a blown film production line (Hosokawa Alpina) with the following 11-layer structure.

[0054]

[0055] The high-density polyethylene is Dow AT6900 with a melt index of 1.2 g / 10 min (190℃ / 2.16 kg); the metallocene linear low-density polyethylene is Dow TF80 with a melt index of 1.7 g / 10 min (190℃ / 2.16 kg).

[0056] Comparative Example 2

[0057] 20% by mass of nano-bentonite powder (nanoscale, Dongguan Ruiheng Mineral Products Co., Ltd.) was dispersed in linear low-density polyethylene material (FB2310, Borealis, density 0.93, melt index 0.2 g / 10 min, 190℃, 2.16 kg). 5.0% of silane coupling agent (FT560, Nanjing Feiteng New Material Technology Co., Ltd.) was added at the beginning of the melting section of the extruder. The mixture was melt-extruded at an extrusion temperature of 190℃ and water-cooled to form granulated resin. The granulated resin was then placed in a curing chamber and cured at 50℃ for 72 h to form high-viscosity polyethylene resin granules. The melt index was 0.7 g / 10 min under the test conditions of 21.6 kg / 190℃.

[0058] The granules containing ultra-high viscosity polyethylene resin were blown into 30µm films on a blown film production line (Hosokawa Alpina) with the following 11-layer structure.

[0059]

[0060] The high-density polyethylene is Dow AT6900 with a melt index of 1.2 g / 10 min (190℃ / 2.16 kg); the metallocene linear low-density polyethylene is Dow TF80 with a melt index of 1.7 g / 10 min (190℃ / 2.16 kg).

[0061] Comparative Example 3

[0062] Linear low-density polyethylene material (FB2310, density 0.93, melt index 0.2 g / 10 min, 190℃, 2.16 kg) was melt-extruded at an extrusion temperature of 190℃ and water-cooled granulated to form primary granulated resin. The primary granulated resin was remelted and extruded at a temperature of 210℃, and then water-cooled granulated to form secondary granulated resin. The secondary granulated resin was placed in a curing chamber and cured at 50℃ for 72 h to form ultra-high viscosity polyethylene resin granules. Under the test conditions of 21.6 kg / 190℃, the melt index was 0.9 g / 10 min.

[0063] The granules containing ultra-high viscosity polyethylene resin were blown into 30µm films on a blown film production line (Hosokawa Alpina) with the following 11-layer structure.

[0064]

[0065] The high-density polyethylene is Dow AT6900 with a melt index of 1.2 g / 10 min (190℃ / 2.16 kg); the metallocene linear low-density polyethylene is Dow TF80 with a melt index of 1.7 g / 10 min (190℃ / 2.16 kg).

[0066] The PE films prepared in the examples and comparative examples were subjected to multi-point sampling performance testing. The test results are shown in Table 1.

[0067]

[0068] As can be seen from the data in Table 1, the PE films prepared in the embodiments of the present invention are superior to the comparative examples in terms of barrier performance and toughness. Comparative Example 1 uses the same process as the present invention to produce high-viscosity polyethylene resin granules, but does not employ different interlayer structures. Table 1 shows that the water vapor transmission rate of the film prepared in Comparative Example 1 is close to that of Examples 1 and 2, but the elongation at break is significantly worse, indicating that the toughness and barrier performance of the comparative example without different interlayer structures are inferior to the product of the present invention. Comparative Example 2 does not undergo secondary granulation, directly producing high-viscosity resin through primary granulation, and produces a film using 11 layers with different interlayer structures. Since high-viscosity resin cannot be produced without secondary granulation, the final product's barrier performance and toughness are inferior to the product of the present invention. Comparative Example 3, due to the absence of nano-bentonite and silane coupling agents, undergoes secondary granulation and uses different interlayer structures to produce a film. Because it cannot form ultra-high-viscosity resin and cannot self-assemble into a winding structure, its barrier performance is inferior to Examples 1 and 2 of the present invention. However, in terms of toughness, due to the lack of filler, the elongation at break is significantly better, and its own toughness is improved to a certain extent. In addition, the data in Table 1 shows that Example 2, which uses ultra-high viscosity polyethylene resin with a low melt index (relatively high viscosity) to produce the product of the present invention with an 11-layer structure, has different product test results from Example 1. This indicates that although products with too low melt index can obtain good barrier properties and toughness, they cannot form a better self-assembled winding structure due to their low fluidity.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a self-assembled multilayer co-extruded high water barrier high toughness PE film, characterized in that, It comprises the following steps: The surface layer is made of super-high viscosity polyethylene resin, and the core layer is made of low viscosity polyethylene resin and super-high viscosity polyethylene resin arranged alternately; the multi-layer resin layer is co-extruded into a film by using multi-layer co-extrusion technology to obtain a self-assembled multi-layer co-extrusion high-water-resistance high-toughness PE film; The super-high viscosity polyethylene resin has a melt index of less than 0.1 g / 10 min under the test conditions of 21.6 kg / 190 ℃. The low viscosity polyethylene resin has a melt index of 0.5-2.0 g / 10 min under the test conditions of 2.16 kg / 190 ℃. The super-high viscosity polyethylene resin of the surface layer comprises 70-100% super-high viscosity polyethylene resin and 0-30% high-density polyethylene by mass percentage; the low viscosity polyethylene resin of the core layer comprises 70-100% high-density polyethylene and 0-30% metallocene linear low-density polyethylene by mass percentage; and the super-high viscosity polyethylene resin of the core layer comprises 70-100% super-high viscosity polyethylene resin and 0-30% metallocene linear low-density polyethylene by mass percentage. The super-high viscosity polyethylene resin is prepared by mixing linear low-density polyethylene with tackifying powder and silane coupling agent, and the tackifying powder is nano-kaolin or nano-bentonite powder. The preparation method of the super-high viscosity polyethylene resin comprises the following steps: Step one: disperse nano-kaolin or nano-bentonite powder in linear low-density polyethylene material, melt extrude at an extrusion temperature of 190-220 ℃, and water-cool to form primary granulation resin; Step two: melt the primary granulation resin again, add silane coupling agent at the starting end of the melt section of the extruder, and extrude at an extrusion temperature of 210-220 ℃, then water-cool to form secondary granulation resin; the secondary granulation resin is placed in a curing chamber for curing at 45-55 ℃ for 72 h to form super-high viscosity polyethylene resin.

2. The production method according to claim 1, characterized by, The number of layers of the multi-layer resin layer is 5-11.

3. The preparation method according to claim 2, characterized in that, When the multi-layer resin layer is co-extruded into a film by using multi-layer co-extrusion technology, pressure fluctuation is formed in the core layer by pulse feeding.

4. The preparation method according to claim 2, characterized in that, The co-extrusion into a film includes casting and blowing.

5. The preparation method according to claim 1, characterized in that, The mass ratio of linear low-density polyethylene, tackifying powder and silane coupling agent is: linear low-density polyethylene 74-92%, tackifying powder 5-20%, and silane coupling agent 3-6%.

6. The production method according to claim 1, characterized by, The linear low density polyethylene has a density of 0.92 to 0.93 g / cm 3 The melt index is 0.05 to 0.2 g / 10 min at a test condition of 2.16 kg / 190°C.

Images