Composite modification formula and preparation method of high-weatherability PE black film

Abstract

The application discloses a kind of composite modification formula and preparation method of high weatherability PE black film.The application is aimed at the problems of existing PE black film, such as carbon black surface active group accelerating PE degradation, compatibility conflict of traditional antioxidant system and additive easy migration and precipitation, and proposes the following solutions: using mercapto-imidazole compound to carry out chemical passivation grafting modification on the surface of carbon black, converting quinone group and hydroxyl group on the surface of carbon black into imidazole ring structure connected by sulfide bond or sulfur ester bond, so that carbon black is changed from free radical initiator into free radical capturer; meanwhile, space hindered imidazolium salt with large molecular weight and containing multiple imidazolium ring units is added. The application also provides a preparation method of the PE black film. The tensile strength and elongation at break retention rate of the PE black film prepared by the application after accelerated aging are significantly better than those of prior art, there is no additive precipitation on the surface after heat aging, the free radical concentration is very low and does not increase, and the outdoor service life is greatly extended.

Description

Technical Field

[0001] This invention relates to the field of polymer film materials technology, specifically to a composite modified formulation and preparation method for a high weather-resistant PE black film. Background Technology

[0002] Polyethylene (PE) black film is widely used in agricultural mulch films, waterproof membranes, and electronic product protective films due to its excellent light-blocking properties and good processability. By adding carbon black to the PE matrix, almost complete opacity can be achieved, effectively inhibiting weed growth and preventing photodegradation of the protected material. However, PE black film faces severe aging challenges during long-term outdoor use. Under the influence of ultraviolet light and heat-oxygen environments, the PE molecular chains degrade and cross-link according to the free radical chain reaction mechanism, leading to surface cracking, decreased strength, and even powdering failure.

[0003] In existing technologies, the following methods are mainly used to improve the weather resistance of PE black film: 1. Add light stabilizers and antioxidants. Commonly used systems include hindered amine light stabilizers (HALS), benzotriazole UV absorbers, phenolic primary antioxidants, and thioether or phosphite secondary antioxidants. However, this system has inherent drawbacks: the quinone and hydroxyl groups on the carbon black surface catalyze the oxidation of antioxidants, inhibiting their effectiveness; simultaneously, when HALS is used in conjunction with thioether secondary antioxidants, the acidic components produced by the thioethers also inhibit the light-stabilizing effect of HALS. 2. Antioxidants are loaded onto inorganic fillers or carbon black is surface-coated to modify it, in order to delay the migration of additives and reduce the negative effects of carbon black; 3. A multi-layer co-extrusion structure is adopted to disperse carbon black in different layers to optimize the shading effect. However, the design focus of existing multi-layer structures is on reducing the amount of carbon black or improving the uniformity of shading, without systematically optimizing the spatial distribution and long-term consumption behavior of anti-aging components. Summary of the Invention

[0004] The purpose of this invention is to provide a composite modified formulation and preparation method for a high weather-resistant PE black film, aiming to solve the three major problems in the existing technology of lacking a PE black film that can systematically solve the problems of free radical activity on the carbon black surface, compatibility conflicts of anti-aging components, and migration and consumption of additives during long-term use.

[0005] To address the aforementioned technical problems, this invention provides a composite modified formulation and preparation method for a high weather-resistant PE black film, comprising the following components: (a) Surface chemical passivation modified carbon black, wherein the modified carbon black is prepared by chemical bonding grafting reaction of carbon black and mercapto-imidazolium compounds, wherein the original quinone groups and hydroxyl groups on the surface of carbon black are converted into imidazolium ring structures connected by thioether bonds or thioester bonds, thereby transforming the free radical initiation sites on the surface of carbon black into free radical trapping sites. (b) A sterically hindered imidazolium salt with a molecular weight ≥800 and containing at least two imidazolium ring units; The imidazole rings on the surface of the modified carbon black interact with the imidazole rings in the sterically hindered imidazole onium salt through dynamic hydrogen bonding, forming a free radical capture-regeneration network that runs through the entire film. Furthermore, the raw material formulation of the PE black film does not contain phenolic antioxidants, thioester antioxidants, benzotriazole UV absorbers, or traditional hindered amine light stabilizers.

[0006] Furthermore, the thiol-imidazolium compound is selected from 1-(2-mercaptoethyl)-2-methylimidazolium, 1-(2-mercaptoethyl)imidazolium, or a combination thereof.

[0007] Furthermore, the space-hindered imidazolium salt has the following general structural formula: (In the formula, R1 and R2 are each independently C1-C) 12 Alkyl; X - (These are halide ions or organic acid radicals; n is an integer from 2 to 6) Further, by weight, its raw material formulation consists of the following components: 70-90 parts of resin matrix, 6-15 parts of the modified carbon black, 0.5-2.5 parts of the sterically hindered imidazole onion salt, and 0.8-2.5 parts of processing aids; the resin matrix is ​​a mixture of high-density polyethylene and low-density polyethylene or linear low-density polyethylene.

[0008] The present invention also provides a method for preparing the above-mentioned high weather-resistant PE black film, comprising the following steps: (1) Disperse carbon black powder and mercapto-imidazolium compounds in an organic solvent at a mass ratio of 100:5-15, stir and react at 80-110°C for 6-12 hours under nitrogen protection, filter the reaction solution, wash with organic solvent and vacuum dry to obtain the modified carbon black; (2) The modified carbon black obtained in step (1), the space-hindered imidazole onion salt, the resin matrix and processing aids are premixed in a high-speed mixer, and then melt-blended and granulated in a twin-screw extruder at 180-210°C to obtain modified PE granules; (3) The modified PE granules obtained in step (2) are blown into a film, and the blown temperature is controlled at 170-200℃ and the blown ratio is 2.0-3.0 to obtain a PE black film with a thickness of 50-150μm.

[0009] Further, the organic solvent in step (1) is toluene, xylene or dimethylformamide; the washing is washing with ethanol and deionized water in sequence; the vacuum drying temperature is 60-80°C and the drying time is 8-12 hours.

[0010] Further, the grafting reaction in step (1) is carried out in the presence of a catalyst selected from triethylamine, pyridine or 4-dimethylaminopyridine, and the amount of catalyst used is 0.5% to 2% of the mass of carbon black.

[0011] Furthermore, the blow molding process described in step (3) adopts a two-layer co-extrusion blow molding process to form an outer layer and an inner layer structure: the concentration of modified carbon black and space-hindered imidazolium salt in the outer layer is higher than that in the inner layer, and the content of space-hindered imidazolium salt in the inner layer does not exceed 50% of the content in the outer layer.

[0012] In summary, due to the adoption of the above-mentioned technologies, the beneficial effects of this invention are: 1. This invention utilizes a chemical grafting reaction between thiol-imidazolium compounds and quinone / hydroxyl groups on the surface of carbon black to transform the original free radical-initiating active sites into imidazolium ring-modified free radical-trapping sites, thereby fundamentally eliminating the aging-promoting effect of carbon black.

[0013] 2. The modified carbon black surface of the present invention forms a dynamic hydrogen bond network between the imidazole ring and the sterically hindered imidazole onium salt. This network can continuously capture free radicals and can be regenerated through adjacent sites after capture, thus achieving a long-term free radical scavenging capability similar to enzyme catalysis.

[0014] 3. This invention does not add any phenolic antioxidants, thioester antioxidants, benzotriazole UV absorbers, or traditional HALS, thus avoiding compatibility conflicts between multiple components, simplifying the formulation, reducing costs, and eliminating the problem of small molecule additive migration and precipitation. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention, making other features, objects, and advantages of the invention more apparent. The illustrative embodiments of the invention illustrated in the drawings and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of the preparation process of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] In the description of this invention, it should be understood that the terms indicating orientation or positional relationship are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0018] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific context of the specification.

[0019] This invention provides a composite modified formulation and preparation method for a high weather-resistant PE black film. Example 1

[0020] I. Raw material formula (parts by weight) High-density polyethylene (HDPE, Daqing Petrochemical 5000S): 80 parts Linear low-density polyethylene (LLDPE, Maoming Petrochemical 7042): 20 parts Surface chemical passivation modified carbon black: 12 parts Space-hindered imidazolium salt (homemade): 1.2 parts Processing aids: 1.0 part polyethylene wax (dispersant), 0.5 parts zinc stearate (lubricant) This embodiment does not contain any phenolic antioxidants, thioester antioxidants, benzotriazole UV absorbers, or traditional hindered amine light stabilizers.

[0021] II. Synthesis of sterically hindered imidazolium salts 0.1 mol of 2,2,6,6-tetramethylpiperidinol and 0.12 mol of 1,6-dibromohexane were refluxed in anhydrous acetonitrile in the presence of potassium carbonate for 24 hours to give a bis(2,2,6,6-tetramethylpiperidoxy)hexane intermediate. This intermediate was then reacted with excess 1-methylimidazole at 100 °C for 12 hours to give an imidazole-terminated product. Finally, quaternization with chloromethane yielded the target product with a molecular weight of approximately 980, containing two imidazole onium rings. The structure was verified to be correct by mass spectrometry and NMR.

[0022] III. Preparation of Surface Chemical Passivation Modified Carbon Black 100 g of carbon black (Cabot Vulcan XC72) was dispersed in 800 mL of toluene, and 8 g of 1-(2-mercaptoethyl)-2-methylimidazole and 1 g of triethylamine were added. The mixture was stirred at 90 °C for 8 hours under nitrogen protection. After the reaction, the mixture was filtered, washed three times successively with ethanol and deionized water, and dried under vacuum at 60 °C for 10 hours to obtain surface-grafted modified carbon black. Fourier transform infrared spectroscopy was performed at 2560 cm⁻¹. -1 The characteristic peak of thiol disappears at 1620 cm⁻¹. -1 and 1580cm -1 The presence of a characteristic absorption peak of the imidazole ring at the graft site confirms successful grafting.

[0023] IV. Preparation of Modified PE Granules 80 parts HDPE, 20 parts LLDPE, 12 parts of the above-mentioned modified carbon black, 1.2 parts of space-hindered imidazolium salt, 1.0 part polyethylene wax, and 0.5 parts zinc stearate were premixed in a high-speed mixer for 5 minutes, and then added to a twin-screw extruder (length-to-diameter ratio 40:1) for melt blending. The extrusion temperature was set as follows: Zone 1 180℃, Zone 2 190℃, Zone 3 200℃, Zone 4 210℃, and Die head 205℃. The screw speed was 300 rpm. After granulation, modified PE granules were obtained.

[0024] V. Blow molding film formation The modified PE granules were blown into a film on a single-layer blown film unit. The temperature settings were: barrel 175°C, die head 190°C, blow-up ratio 2.5, and traction speed controlled film thickness 80μm to obtain the PE black film sample of the present invention.

[0025] Example 2

[0026] The difference from Example 1 is that after the modified PE granules were prepared, a two-layer co-extrusion blow molding process was used to form the film. The outer layer material ratio was: 15 parts modified carbon black and 1.8 parts sterically hindered imidazolium salt, with the rest being the same as in Example 1; the inner layer material ratio was: 10 parts modified carbon black and 0.6 parts sterically hindered imidazolium salt, with the rest being the same as in Example 1. The outer layer to inner layer thickness ratio was 1:1. After blow molding, a two-layer co-extruded PE black film with a thickness of 80 μm was obtained.

[0027] Comparative Example 1 (Traditional formulation, unmodified carbon black + conventional antioxidant system) Raw materials: 80 parts HDPE, 20 parts LLDPE, 12 parts unmodified carbon black, 1.0 part Tinuvin 770 (hindered amine light stabilizer), 0.5 parts Tinuvin 326 (benzotriazole UV absorber), 0.3 parts Irganox 1010 (phenolic primary antioxidant), 0.2 parts Irgafos 168 (phosphite secondary antioxidant), 0.2 parts DLTDP (thioester secondary antioxidant), and processing aids as in Example 1. Single-layer extrusion blow molding was used to form the film, with the same process parameters as in Example 1.

[0028] Comparative Example 2 (Surface Coupling Agent Modified Carbon Black + Traditional Antioxidant) Carbon black was conventionally modified by coupling with silane coupling agent KH550 (non-mercapto-imidazolium grafting). Specifically, carbon black and KH550 were reacted in an ethanol / water solution at a mass ratio of 100:8 at 80°C for 4 hours, and then dried to obtain KH550-modified carbon black. The remaining formulation and process were the same as in Comparative Example 1.

[0029] Test results show that: The PE black films prepared in Examples 1 and 2 had initial tensile strengths of 24.5 MPa and 25.1 MPa, respectively, and initial elongation at break of 520% ​​and 535%, respectively, which were similar to the initial properties of Comparative Examples 1 and 2.

[0030] After 1000 hours of accelerated aging, Example 1 retained 93.5% of its tensile strength and 89.8% of its elongation at break; Example 2 retained 94.2% of its tensile strength and 91.5% of its elongation at break. In contrast, Comparative Example 1 retained only 51.2% of its tensile strength and 43.6% of its elongation at break; Comparative Example 2 retained 63.5% of its tensile strength and 58.3% of its elongation at break. This demonstrates that the weather resistance of the embodiments of the present invention is significantly superior to that of the comparative examples.

[0031] In the 80℃×7-day thermal aging test, no additives were precipitated on the surface of Examples 1 and 2, while obvious white frost appeared on the surface of Comparative Examples 1 and 2.

[0032] Electron spin resonance spectroscopy tests showed that after 2 hours of ultraviolet irradiation, the free radical concentrations of Example 1 and Example 2 were 9% and 7% of those of Comparative Example 1, respectively, and remained stable without increasing for 240 hours of continuous irradiation, while the free radical concentration of the Comparative Example continued to increase.

[0033] The above results indicate that the PE black film prepared by this invention has an ultra-long weather resistance life.

Claims

1. A composite modified formulation for a high weather-resistant PE black film, characterized in that: It contains the following components: (1) Surface chemical passivation modified carbon black, wherein the modified carbon black is prepared by chemical bonding grafting reaction of carbon black and mercapto-imidazolium compounds, and the original quinone groups and hydroxyl groups on the surface of carbon black are converted into imidazolium ring structures connected by thioether bonds or thioester bonds, thereby transforming the free radical initiation sites on the surface of carbon black into free radical capture sites. (2) A sterically hindered imidazolium salt with a molecular weight ≥800 and containing at least two imidazolium ring units; The imidazole rings on the surface of the modified carbon black interact with the imidazole rings in the sterically hindered imidazole onium salt through dynamic hydrogen bonding, forming a free radical capture-regeneration network that runs through the entire film. Furthermore, the raw material formulation of the PE black film does not contain phenolic antioxidants, thioester antioxidants, benzotriazole UV absorbers, or traditional hindered amine light stabilizers.

2. The composite modified formulation of a high weather-resistant PE black film according to claim 1, characterized in that, The thiol-imidazolium compounds are selected from 1-(2-mercaptoethyl)-2-methylimidazolium, 1-(2-mercaptoethyl)imidazolium, or combinations thereof.

3. The composite modified formulation of a high weather-resistant PE black film according to claim 1, characterized in that, The space-hindered imidazolium salt has the following general structural formula: In the formula, R1 and R2 are each independently C1-C12 alkyl groups; X(-) is a halide ion or an organic acid anion; n is an integer from 2 to 6.

4. The composite modified formulation of a high weather-resistant PE black film according to claim 1, characterized in that, The raw material formulation, by weight, consists of the following components: 70-90 parts of resin matrix, 6-15 parts of modified carbon black, 0.5-2.5 parts of sterically hindered imidazole onion salt, and 0.8-2.5 parts of processing aids; the resin matrix is ​​a mixture of high-density polyethylene and low-density polyethylene or linear low-density polyethylene.

5. The method for preparing a high weather-resistant PE black film according to claim 1, characterized in that, Includes the following steps: (1) Disperse carbon black powder and mercapto-imidazolium compounds in an organic solvent at a mass ratio of 100:5-15, stir and react at 80-110°C for 6-12 hours under nitrogen protection, filter the reaction solution, wash with organic solvent and vacuum dry to obtain the modified carbon black; (2) The modified carbon black obtained in step (1), the space-hindered imidazole onion salt, the resin matrix and processing aids are premixed in a high-speed mixer, and then melt-blended and granulated in a twin-screw extruder at 180-210°C to obtain modified PE granules; (3) The modified PE granules obtained in step (2) are blown into a film, and the blown temperature is controlled at 170-200 degrees Celsius and the blown ratio is 2.0-3.0 to obtain a PE black film with a thickness of 50-150 micrometers.

6. The method for preparing a high weather-resistant PE black film according to claim 5, characterized in that, The organic solvent in step (1) is toluene, xylene or dimethylformamide; the washing is washing with ethanol and deionized water in sequence; the vacuum drying temperature is 60-80℃ and the drying time is 8-12 hours.

7. The method for preparing a high weather-resistant PE black film according to claim 5, characterized in that, The grafting reaction in step (1) is carried out in the presence of a catalyst selected from triethylamine, pyridine or 4-dimethylaminopyridine, and the amount of catalyst used is 0.5%-2% of the mass of carbon black.

8. The method for preparing a high weather-resistant PE black film according to claim 5, characterized in that, The blow molding process in step (3) adopts a two-layer co-extrusion blow molding process to form an outer layer and an inner layer structure: the concentration of modified carbon black and space-hindered imidazolium salt in the outer layer is higher than that in the inner layer, and the content of space-hindered imidazolium salt in the inner layer does not exceed 50% of the content in the outer layer.

9. A composite modified formulation for a high weather-resistant PE black film according to any one of claims 1 to 4, characterized in that, The modified carbon black exhibits the disappearance of the thiol characteristic peak at 2560 cm⁻¹, and the appearance of the characteristic absorption peaks of the imidazole ring at 1620 cm⁻¹ and 1580 cm⁻¹.

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