Anti-ultraviolet high-strength polyethylene film and preparation method therefor

Abstract

In the present invention, during ethylene polymerization, carbon black is added for in-situ polymerization to generate a carbon black-modified polyethylene raw material, the carbon black-modified polyethylene raw material is then processed into a polyethylene base film by means of a solid-state molding process, and the base film undergoes ultra-high ratio stretching to prepare an anti-ultraviolet high-strength polyethylene film. In the present invention, the carbon black is added in situ during the polymerization of an ethylene monomer, enabling more uniform dispersion of the carbon black in polyethylene powder without increasing the cost of raw material preparation. The present invention does not require additional high-temperature melting and high-speed mixing processes, effectively preventing molecular chain breakage, and preserving the integrity of polyethylene molecular chains to the greatest extent, thereby facilitating the achievement of high strength of polyethylene films.

Description

A UV-resistant high-strength polyethylene film and its preparation method Technical Field

[0001] This invention belongs to the field of polymer material processing, specifically relating to a UV-resistant high-strength polyethylene film and its preparation method. Background Technology

[0002] Polyethylene is a common general-purpose plastic widely used in various fields. The application of carbon black in polyethylene can: (1) improve the mechanical properties of polyethylene materials, increase their hardness, strength and stiffness, reduce their ductility and improve their impact resistance; (2) improve the heat resistance and weather resistance of polyethylene materials, making them more suitable for outdoor use; (3) improve the electrical conductivity of polyethylene materials, making them more suitable for electronic products and conductive materials; (4) be used as a colorant in the manufacture of black polyethylene products.

[0003] Patents CN106093614A and CN114479256A respectively prepared carbon black masterbatch for polyethylene pipes with a carbon black content of 25-50% and carbon black masterbatch for polyolefins with a carbon black content of 40-50% by internal mixer melt blending granulation and single screw melt extrusion granulation.

[0004] Patent CN105086079B describes the preparation of a modified weather-resistant high-density polyethylene black sheath material for bridge cables with a carbon black content of approximately 2.6% using a twin-screw melt extrusion granulation method with carbon black masterbatch.

[0005] Patent CN109593248A and patent CN111154164A respectively prepared antistatic ultra-high molecular weight polyethylene composite materials with a carbon black content of 1-10% and ultra-high molecular weight polyethylene composite materials with a carbon black content of 0.5-1.5% by high-speed mixing-high temperature molding and single screw melt extrusion methods, respectively. In the latter, carbon black is mainly used as a nano-nucleating plasticizer to regulate the crystallization properties of ultra-high molecular weight polyethylene.

[0006] The aforementioned patents cover carbon black applications in polyethylene or polyolefin masterbatches, polyethylene sheathing materials, and polyethylene composites (sheets or pipes). The application of carbon black in polyethylene films has not yet been reported. Furthermore, in order to ensure the carbon black is dispersed as uniformly as possible in the matrix polymer, the aforementioned patents employ melt extrusion blending or high-speed mixing-high-temperature molding methods. The high shear and high temperature during processing inevitably cause a certain degree of breakage in the molecular chains of the matrix polymer, thereby reducing the strength of the product. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies and to ensure that carbon black can be uniformly dispersed in polyethylene while ensuring that the polyethylene molecular chains are not damaged during processing, this invention discloses a UV-resistant high-strength polyethylene film and its preparation method.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a UV-resistant high-strength polyethylene film, characterized in that the UV-resistant high-strength polyethylene film comprises polyethylene, wherein the polyethylene viscosity-average molecular weight is not less than 500,000, the film further comprises carbon black, the carbon black content is 0.1-2.0 wt%, the thickness of the film is less than 100 μm, the strength is greater than 15 g / d, and the original particle size of the carbon black is less than 35 nm.

[0010] Furthermore, the viscosity-average molecular weight of the polyethylene raw material is preferably not less than 1 million, and more preferably not less than 1.5 million.

[0011] Furthermore, the carbon black content in the high-strength polyethylene film is preferably 0.2-1.5%, more preferably 0.4-1.0%. If the carbon black content is too high, it will affect the stability of the film during processing; if the carbon black content is too low, the UV resistance will be significantly reduced.

[0012] Furthermore, the thickness of the high-strength polyethylene film is preferably less than 50 μm, more preferably less than 30 μm.

[0013] Furthermore, the strength of the high-strength polyethylene film is preferably greater than 20 g / d, more preferably greater than 25 g / d.

[0014] Furthermore, by measuring using ASTM D3849-07 (2011), the primary particle size of carbon black in the high-strength polyethylene film is preferably less than 30 nm, more preferably less than 25 nm. It was observed that the smaller the primary particle size of carbon black, the better the UV resistance of the high-strength polyethylene film.

[0015] Furthermore, the side lamellar size of the high-strength polyethylene film is 90.133 nm-152.319 nm. During polymerization, the introduction of carbon black increases the side lamellar size of the polyethylene film. Carbon black acts as a heterogeneous nucleator in the polymer crystallization process, giving the polymer a higher nucleation density, shorter crystallization time, and finer spherulite size, thus improving the polymer's crystallinity. Simultaneously, higher crystallinity allows the polymer to induce more crystals during stretching, resulting in a more complete crystal structure and improved film performance. However, heterogeneous nucleation of carbon black requires a certain amount of space on the polymer surface. Due to the limited surface space of the polymer, excessive carbon black content (e.g., carbon black content exceeding 1.5% in the polyethylene film) does not lead to more crystal formation and does not increase the side lamellar size.

[0016] Furthermore, measured using ASTM D6556-10, the nitrogen adsorption specific surface area (BET) of carbon black in the high-strength polyethylene film is greater than 75 m². 2 / g, preferably greater than 150m 2 / g, more preferably greater than 200m 2 / g. The larger the specific surface area of ​​carbon black, the easier it is to disperse in the polyethylene matrix, and the better the UV resistance of the polyethylene film produced.

[0017] Furthermore, the DBP (dibutyl phthalate) absorbance of the carbon black in the high-strength polyethylene film is greater than 100 cm⁻¹. 3 / 100g, preferably greater than 150cm 3 / 100g, more preferably greater than 200cm 3 / 100g. The higher the DBP absorption value of carbon black, the richer the pore structure between its aggregates, and the better its dispersibility in organic solvents.

[0018] Furthermore, an accelerated ultraviolet aging test was conducted according to GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Method for Plastics" and the strength test standard GB T1040.3-2006. After 500 hours of exposure, the strength of the polyethylene film decreased by no more than 10%, preferably no more than 8%, and more preferably no more than 5%.

[0019] On the other hand, the present invention provides a method for preparing a UV-resistant high-strength polyethylene film, comprising the following steps:

[0020] 1) A certain amount of carbon black is added to an organic solvent and dispersed evenly. A co-catalyst and a catalyst are added, and ethylene is introduced to carry out a polymerization reaction under certain conditions to generate carbon black modified polyethylene raw material in situ.

[0021] Optionally, the organic solvent is an alkane organic solvent, such as gasoline, heptane, hexane, cyclohexane, or methylpentane.

[0022] Optionally, the catalyst is a Zieglar-Natta catalyst or a metallocene catalyst and its corresponding co-catalyst.

[0023] Furthermore, by controlling the pressure and temperature during the polymerization reaction, the polymerization rate is made lower than the polyethylene crystallization rate, so that the generated polyethylene chain segments crystallize before forming entanglement. This results in the raw material having a high degree of crystallinity (above 70%) and a low degree of molecular chain entanglement, thus possessing the characteristic of easy solid-state processing.

[0024] 2) The polyethylene raw material obtained in step 1) is processed into a polyethylene base film by solid molding process, and the base film is prepared into the UV-resistant polyethylene high-strength film of the present invention by super stretching.

[0025] Optionally, the solid forming process is hot pressing, molding, rolling, or pressing with a steel strip press.

[0026] Furthermore, the temperature during the solid-state molding process is controlled below the melting point of polyethylene.

[0027] Unless otherwise stated in this invention, the polymerization method for polyethylene and the preparation method for high-strength polyethylene films are also applicable to this invention. For example, the polyethylene raw material of this invention can be prepared using the polymerization method for ultra-high molecular weight polyethylene as described in CN116462786A; furthermore, the polyethylene solid-state molding process for processing polyethylene into a polyethylene-based film can be prepared using the preparation method for high-strength polyethylene sheets as described in patent US2009243138A. The above preparation methods are incorporated herein by reference.

[0028] The UV-resistant high-strength polyethylene film of the present invention is prepared by low-temperature solid-state processing of polyethylene powder with more uniform carbon black dispersion. It can achieve excellent UV resistance with a significant reduction in carbon black content. Moreover, since the amount of carbon black is small, it has no impact on the film processing, allowing the film to undergo super-stretching process to further improve its strength. The strength of the UV-resistant high-strength polyethylene film is preferably greater than 20 g / d, more preferably greater than 25 g / d.

[0029] The carbon black in this invention is uniformly dispersed in polyethylene powder through the following three steps:

[0030] 1) Initial dispersion is carried out in an organic solvent;

[0031] 2) Through chemical reactions with the co-catalyst, it is further dispersed into the catalytic system;

[0032] 3) As polyethylene molecular chains gradually polymerize on the catalyst, carbon black is uniformly distributed in the polyethylene powder along with the catalyst.

[0033] Compared with existing melt extrusion blending or high-speed mixing-high-temperature molding methods, it has the following advantages:

[0034] ① Added in situ during the polymerization process, carbon black is more evenly dispersed in polyethylene powder without increasing the raw material preparation cost;

[0035] ② No additional high-temperature melting and high-speed mixing process is required, which effectively avoids the breakage of molecular chains and preserves the integrity of polyethylene molecular chains to the greatest extent, which is more conducive to achieving high strength of polyethylene film.

[0036] ③ During the polymerization process, carbon black can also act as a nucleating agent, further increasing the crystallization rate of polyethylene molecular weight, reducing its entanglement degree, and improving the processing performance of the obtained polyethylene powder.

[0037] The UV-resistant polyethylene high-strength film of the present invention, containing carbon black, can be used in any application where the film is typically used. In particular, it can be used in architectural textiles, ropes, fishing lines and nets, cargo nets, straps, and restraints, gloves, and other protective clothing used in transportation and aviation. Therefore, in one aspect, the present invention relates to ropes, crane ropes, mooring ropes, cords, or reinforcing elements comprising the film or film of the present invention.

[0038] In another aspect, the present invention relates to multilayer composite articles for ballistic applications, the articles comprising the film of the present invention, preferably the multilayer composite articles selected from bulletproof vests, helmets, hard and soft protective plates and vehicle armor plates. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. The side lamellar size (L) of the thin film in this embodiment... SAXS The results were obtained by using the Small Angle X-ray Scattering (SAXS) instrument at the BL16B1 beamline of the Shanghai Synchrotron Radiation Source (SSRF) in China.

[0040] The X-ray wavelength used in the test was 0.124 nm. Two-dimensional SAXS images were recorded using a Pilatus 2M solid-state detector with a pixel count of 1475×1679 and a pixel resolution of 172μm×172μm. The sample-to-detector distance was 1900mm-2200mm, and the image exposure time was 50s-120s. After subtracting background scattering, air scattering, and light fluctuations, the collected SAXS two-dimensional images were processed using Fit2d software. A rectangular integral was performed along the direction perpendicular to the stretching to convert the scattering intensity of the image. The resulting curve was fitted, and the half-width at half-maximum (WHM) Δq2 of the integral curve was calculated. The result was then expressed using the formula L... SAXS The side lamellar size L can be obtained by calculating 2π / Δq2. SAXS .

[0041] Example 1: Preparation of UV-resistant high-strength polyethylene film with 0.5% carbon black content

[0042] (1) Preparation of polyethylene raw materials:

[0043] Mix 3L of heptane and 5g of carbon black with a particle size of 30nm (specific surface area of ​​254m²). 2 / g, DBP absorbance 192cm 3100g of carbon black was added to a 5L high-pressure polymerization reactor and stirred for 5 minutes to ensure uniform dispersion. Then, 0.05g of bis(ethylcyclopentadienyl)titanium dichloride and 20g of methylaluminoxane were added sequentially to the reactor. Ethylene was then introduced, and polymerization was carried out at a polymerization pressure of 0.5MPa and a polymerization temperature of 50℃. When the amount of ethylene reacted reached 1kg, the ethylene supply was stopped, and the reaction was terminated. After filtration and drying, a polyethylene raw material with a carbon black content of 0.5% was obtained. The viscosity-average molecular weight of this polyethylene raw material was tested to be 1.2 million.

[0044] (2) Preparation of UV-resistant high-strength polyethylene film:

[0045] Using a flat vulcanizing machine (BP-8170-C, Dongguan Baopin Precision Instruments Co., Ltd.), the above-mentioned carbon black modified polyethylene raw material was pressed at 135℃ and 20MPa for 5 minutes to obtain a carbon black modified polyethylene base film with a thickness of 0.5mm. This base film was then sequentially stretched by 5 times, 3 times, 2 times, and 1.5 times respectively in a tensile testing machine with a hot box (CMT-4103, Meters Industrial Systems Co., Ltd., Shenzhen Branch) at 140℃, 145℃, 150℃, and 152℃ to obtain a polyethylene film with a thickness of 55μm. The film's strength was tested to be 22g / d. Ultraviolet accelerated aging tests were conducted using GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Method for Plastics" and the strength test standard GB T1040.3-2006. After 500 hours of exposure, its strength decreased by 4.8%, indicating relatively good UV resistance. Testing revealed that the side lamellar size of the film was 90.133 nm, while the side lamellar size of the film without carbon black was 72.125 nm. The introduction of carbon black significantly increased the side lamellar size.

[0046] Example 2: Preparation of UV-resistant high-strength polyethylene film with 1.0% carbon black content

[0047] (1) Preparation of polyethylene raw materials:

[0048] Mix 3L of heptane with 10g of carbon black with a particle size of 30nm (specific surface area of ​​254m²). 2 / g, DBP absorbance 192cm 3 100g of carbon black was added to a 5L high-pressure polymerization reactor and stirred for 5 minutes to ensure uniform dispersion. Then, 30ml of 1.0M triethylaluminum heptane solution and 0.2g of CMU catalyst (a Sinopec brand) were added sequentially to the reactor. Ethylene was then introduced, and polymerization was carried out at a pressure of 0.5MPa and a temperature of 50℃. When the amount of ethylene reacted reached 1kg, the ethylene supply was stopped, and the reaction was terminated. After filtration and drying, a polyethylene raw material with a carbon black content of 1.0% was obtained. The viscosity-average molecular weight of this polyethylene raw material was tested to be 1.65 million.

[0049] (2) Preparation of UV-resistant high-strength polyethylene film:

[0050] Using a flat vulcanizing machine (BP-8170-C, Dongguan Baopin Precision Instruments Co., Ltd.), the above-mentioned carbon black modified polyethylene raw material was pressed at 135℃ and 20MPa for 5 minutes to obtain a carbon black modified polyethylene base film with a thickness of 0.3mm. This base film was then sequentially stretched by 4 times, 2.5 times, 1.8 times, and 1.3 times respectively in a tensile testing machine with a hot box at 140℃, 145℃, 150℃, and 152℃ (CMT-4103, Metersbonwe Industrial Systems Co., Ltd., Shenzhen Branch), resulting in a polyethylene film with a thickness of 38μm. The film's strength was tested to be 18g / d. Ultraviolet accelerated aging tests were conducted using GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Method for Plastics" and the strength testing standard GB T1040.3-2006. After 500 hours of exposure, its strength decreased by 2.3%, indicating relatively good UV resistance. Testing revealed that the side lamellar size of the film was 120.276 nm, while the side lamellar size of the film without carbon black was 72.125 nm. The introduction of carbon black significantly increased the side lamellar size.

Claims

1. A UV-resistant high-strength polyethylene film, characterized in that, The UV-resistant high-strength polyethylene film contains polyethylene, wherein the polyethylene viscosity-average molecular weight is not less than 500,000, the film also contains carbon black, the carbon black content is 0.1-2.0 wt%, the film thickness is less than 100 μm, the strength is greater than 15 g / d, and the primary particle size of the carbon black is less than 35 nm.

2. The UV-resistant high-strength polyethylene film according to claim 1, characterized in that, The side lamellar size of the thin film is 90.133nm-152.319nm.

3. The UV-resistant high-strength polyethylene film according to claim 1, characterized in that, The film was subjected to accelerated ultraviolet aging test according to GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Method for Plastics". After 500 hours of exposure, the strength of the polyethylene high-strength film decreased by no more than 10%.

4. A method for preparing a UV-resistant high-strength polyethylene film, characterized in that, Includes the following steps: 1) A certain amount of carbon black is added to an organic solvent and dispersed evenly. A co-catalyst and a catalyst are added, and ethylene is introduced to carry out a polymerization reaction under certain conditions to generate carbon black-modified polyethylene raw material in situ. 2) The polyethylene raw material obtained in step 1) is processed into a polyethylene-based film using a solid-state molding process; 3) The base film obtained in step 2) is subjected to super-stretching to obtain a UV-resistant polyethylene high-strength film.

5. The method for preparing the UV-resistant high-strength polyethylene film according to claim 4, characterized in that, The solid forming process is hot pressing, molding, rolling, or pressing with a steel strip press.

6. A multilayer composite article for bulletproof applications, said article comprising the UV-resistant polyethylene high-strength film as described in any one of claims 1-3.

7. A product comprising the UV-resistant high-strength polyethylene film according to claims 1-3 and / or the UV-resistant high-strength polyethylene film prepared according to the preparation method of claim 4, wherein, The products are selected from architectural textiles, ropes, fishing lines and nets, cargo nets, straps, as well as restraints, gloves and other protective clothing used in transportation and aviation.