Polyolefin melt extrusion method based on internal source gas auxiliary lubrication and fluoride-free processing aid for realizing method

Abstract

The invention provides a polyolefin melt extrusion method based on internal source gas-assisted lubrication and a fluoride-free processing aid for realizing the method, and belongs to the technical field of plastic molding processing. According to the invention, during polyolefin melt extrusion processing molding, gas is introduced into a polyolefin melt in situ and is dissolved in the polyolefin melt under the action of pressure provided by equipment, and melt flow is assisted through plasticization and other mechanisms; gas dissolved in the tail section of melt extrusion processing equipment and a molding die area is instantly released and diffused between a melt and the inner surface of the equipment, so that the melt flow is efficiently assisted, the melt fracture is slowed down, the die expansion and die material accumulation are reduced, the energy consumption is effectively reduced while the processing speed and efficiency are improved, and the performance of a plastic product is not changed; the auxiliary agent does not contain any fluorine-containing substance, does not generate fluorine-containing chemical residues, can play a role when the addition amount is relatively low, and can replace a traditional fluorine-containing polymer processing auxiliary agent.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic processing and molding, and particularly relates to a polyolefin melt extrusion method based on endogenous gas-assisted lubrication and a fluorine-free processing aid for realizing the method. Background Art

[0002] The plastic melt extrusion processing and molding process is the main method for preparing plastic products, such as melt spinning, plastic films, pipes, medical catheters, plastic packaging materials for various cables, etc. In such plastic processing and molding processes, the molten plastic passes through an extrusion device and is extruded from a specific die, and finally cools and forms. When passing through the narrow gap of the die of the processing device, the rheological behavior of the plastic melt is very complex. When the extrusion rate exceeds a certain value, problems such as sharkskin, die swell, and die build-up caused by melt fracture often occur when the plastic melt is extruded from the forming die. These problems lead to various appearance defects in plastic products, such as rough surfaces, low film transparency, scratches on the pipe surface, and filament breakage during spinning, thus causing various product quality problems and wasting raw materials. Increasing the processing temperature or reducing the extrusion rate can alleviate these phenomena, but these means greatly limit the production efficiency and production capacity of plastic processing. For this reason, over the past fifty years or so, various fluorine-containing polymers or elastomers have been widely used as plastic processing aids in the melt extrusion processing and molding process. After being added to the molten plastic, these fluorine-containing processing aids phase-separate from the plastic melt, migrate, and coat the inner surfaces of the melt extrusion device and the forming die. The fluorine processing aid attached to the inner surface can effectively regulate the flow behavior of the molten plastic through lubrication, thereby alleviating problems such as sharkskin, die swell, and die build-up caused by melt fracture. In addition, the application of these fluorine-containing processing aids can also enable melt extrusion molding to be carried out at a higher extrusion rate, improving the yield while reducing energy consumption.

[0003] Although widely used in the plastic melt extrusion processing and molding process, the above-mentioned fluorine-containing processing aids have problems such as slow onset (taking dozens of minutes to hours to take effect), remaining on the inner surface of the processing device, resulting in time-consuming material change and machine cleaning, and remaining on the surface of plastic products. In addition, the preparation of these fluorine-containing processing aids often uses perfluorinated or polyfluorinated compounds (PFAS), and there is also PFAS residue. PFAS has accumulated in large amounts in the environment and is difficult to degrade, so it is called a "persistent compound". With the understanding of the physiological toxicity of PFAS substances, the voices at home and abroad for restricting the use of such PFAS-containing fluorine compounds are getting louder and louder. In short, the application of fluorine-containing plastic processing aids in the plastic melt extrusion processing and molding process will face great challenges.

[0004] In the above context, the development of new processing aids to replace the currently dominant fluorine-containing plastic processing aids will be the key to achieving fluorine-free processing in the plastic processing industry. At present, polysilane polymers or elastomers are the majority of the reported fluorine-free processing aids. Its working mechanism is similar to that of the above-mentioned fluorine-containing processing aids, but it has problems such as low efficiency and large addition amount. Moreover, this type of additive has a lot of residues on the surface of plastic products, which affects the surface properties of plastic products and causes problems in later ink printing, paint spraying, etc. In addition, this type of additive has the problem of migration from plastic products, which limits its application in food, medical and baby products. Other substances such as low molecular weight polyvinyl alcohol, polyether and boron carbide have also been reported for use, but they also have problems such as unclear effects and excessive addition amounts, and have not been widely accepted by the market. Summary of the invention

[0005] The object of the present invention is to provide a polyolefin melt extrusion method based on endogenous gas assisted lubrication and a fluorine-free processing aid for implementing the method. When the fluorine-free processing aid of the present invention is used in the polyolefin melt extrusion processing and molding process, it can play the role of traditional fluorine-containing processing aids, reduce melt fracture such as shark skin phenomenon, reduce die swell and die accumulation, etc. At the same time, there is no fluorine-containing chemical residue on the surface of plastic processing equipment and plastic products, and it has excellent performance when the addition amount is low.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides a method for endogenous gas-assisted lubrication for polyolefin melt extrusion processing and molding. Under polyolefin melt extrusion processing and molding conditions, gas is introduced into the polyolefin melt in situ and dissolved in the polyolefin melt under the action of pressure provided by processing equipment. The dissolved gas changes the flow behavior of the polyolefin melt through mechanisms such as plasticization, thereby assisting the flow of the polyolefin melt. Due to pressure drop in the rear section of the extrusion equipment and near the molding die area, the gas dissolved in the polyolefin melt is instantly released and migrates between the melt and the inner wall of the die, thereby efficiently assisting the polyolefin melt to flow in the die, alleviating melt fracture caused by melt fracture, reducing die expansion and die accumulation, and effectively reducing energy consumption while improving processing speed and efficiency.

[0008] Preferably, the gas includes but is not limited to one or a mixture of two or more of nitrogen, carbon dioxide and ammonia; the mass of the gas is 0.01-1% of the mass of the polyolefin melt.

[0009] Preferably, a fluorine-free processing aid capable of autonomously generating gas under melt extrusion processing conditions is added to the polyolefin resin.

[0010] Preferably, in terms of mass percentage, the fluorine-free processing aid includes but is not limited to the following components:

[0011] Polymer resin carrier 1% - 99.99%,

[0012] Active ingredient 0.01% - 99%,

[0013] Decomposition temperature regulator 0% - 1%,

[0014] Antioxidant 0% - 1%,

[0015] Dispersing aid 0% - 1%.

[0016] Preferably, the polymer resin carrier includes but is not limited to at least one of LLDPE, LDPE, HDPE, and PP.

[0017] Preferably, the active ingredient is a substance that can generate gas under processing conditions or a combination of chemical substances that can generate gas through chemical reactions; the substances that can generate gas under processing conditions include but are not limited to at least one of sodium bicarbonate, ammonium bicarbonate, citric acid, calcium carbonate, 4,4'-bis-sulfonylhydrazide diphenyl ether, azodicarbonyl, N, N-dinitrosopentamethylenetetramine, azobisisobutyronitrile, azodicarbonamide, and 4,4'-oxybisbenzenesulfonylhydrazide; the combination of chemical substances that can generate gas through chemical reactions includes but is not limited to carbonates and organic acids; the carbonates include but are not limited to at least one of sodium carbonate, potassium carbonate, and calcium carbonate; the organic acids include but are not limited to at least one of citric acid, malic acid, and benzoic acid.

[0018] Preferably, the decomposition temperature regulator includes but is not limited to at least one of ethylene bisstearate, palmitic acid, zinc stearate, calcium stearate, and erucamide.

[0019] Preferably, the antioxidant includes but is not limited to at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, and 2,6-di-tert-butyl-4-methylphenol.

[0020] Preferably, the dispersing aid includes but is not limited to at least one of liquid paraffin, white oil, polyvinyl alcohol, and silicone oil.

[0021] Preferably, the mass of the fluorine-free processing aid is 0.01 - 5‰ of the mass of the polyolefin.

[0022] The present invention provides a method for in-situ gas-assisted lubrication in the melt extrusion processing and shaping of polyolefins. Under the conditions of melt extrusion processing and shaping of polyolefins, gas is introduced in-situ into the polyolefin melt and can be dissolved in the polyolefin melt under the pressure provided by the processing equipment. Through mechanisms such as plasticization, it assists the flow of the melt. In the last section of the melt extrusion equipment and the die region, due to the decrease in pressure, the dissolved gas is instantaneously released and diffused between the melt and the inner surface of the equipment, efficiently assisting the demolding of the melt, slowing down melt fracture, reducing die swell and die build-up, effectively reducing energy consumption while improving the processing speed and efficiency; it does not change the properties of plastic products; at the same time, it does not contain any fluorine-containing substances and does not produce any fluorine-containing chemical residues; and it can play an excellent role even at a low addition amount, and can replace traditional fluoropolymer processing aids. The results of the examples show that the method provided by the present invention does not show phenomena such as melt fracture, melt swell and die build-up during the processing. Description of the Drawings

[0023] Figure 1 It is a graph showing the relationship between the volume of gas released by the fluorine-free processing aid in Example 1 and time;

[0024] Figure 2 It is a graph showing the relationship between the torque and time of polypropylene added with the fluorine-free processing aid in Example 1 and pure polypropylene;

[0025] Figure 3 It is a macroscopic view of the polypropylene products prepared in Example 4 and Comparative Example 1;

[0026] Figure 4 It is a macroscopic view of the polypropylene filaments prepared in Example 5 and Comparative Example 2. Detailed Description of the Invention

[0027] The present invention provides a method for in-situ gas-assisted lubrication in the melt extrusion processing and shaping of polyolefins. Under the conditions of melt extrusion processing and shaping of polyolefins, gas is introduced in-situ into the polyolefin melt and dissolved in the polyolefin melt under the pressure provided by the processing equipment. The dissolved gas changes the flow behavior of the polyolefin melt through mechanisms such as plasticization to assist the flow of the polyolefin melt; in the rear section of the extrusion equipment and near the die region, due to the pressure drop, the gas dissolved in the polyolefin melt is instantaneously released and migrates between the melt and the inner wall of the die, efficiently assisting the flow of the polyolefin melt in the die, reducing melt fracture caused by melt fracture, reducing die swell and die build-up, and effectively reducing energy consumption while improving the processing speed and efficiency.

[0028] In the present invention, the gas preferably includes, but is not limited to, one or a mixture of two or more of nitrogen, carbon dioxide or ammonia.

[0029] In the present invention, the mass of the gas is preferably 0.01% to 1% of the mass of the polyolefin melt. By controlling the mass of the gas within the above range, the present invention can ensure the mitigation of melt fracture, the reduction of die swell and die build-up, while not having an adverse impact on the performance and quality of the polyolefin product.

[0030] The present invention preferably adds a fluorine-free processing aid capable of autonomously generating gas under melt extrusion processing conditions to the polyolefin resin.

[0031] In the present invention, in terms of mass percentage, the fluorine-free processing aid preferably includes, but is not limited to, the following components:

[0032] Polymer resin carrier 1% to 99.99%,

[0033] Active ingredient 0.01% to 99%,

[0034] Decomposition temperature regulator 0% to 1%,

[0035] Antioxidant 0% to 1%,

[0036] Dispersing aid 0% to 1%.

[0037] In terms of mass percentage, the fluorine-free processing aid of the present invention preferably includes 1% to 99.99% of polymer resin carrier.

[0038] In the present invention, the polymer resin carrier preferably includes, but is not limited to, at least one of LLDPE, LDPE, HDPE, and PP. The present invention has no special limitation on the source of the polymer resin carrier, and commercially available products well-known to those skilled in the art can be used.

[0039] In terms of mass percentage, the fluorine-free processing aid of the present invention preferably includes 0.01% to 99% of active ingredient.

[0040] In the present invention, the active ingredient is preferably a substance capable of generating gas under processing conditions or a combination of chemical substances capable of generating gas through chemical reactions.

[0041] In the present invention, the substance capable of generating gas under processing conditions preferably includes, but is not limited to, at least one of sodium bicarbonate, ammonium bicarbonate, citric acid, calcium carbonate, 4,4'-bis-sulfonylhydrazide diphenyl ether, azodicarbonyl, N,N-dinitrosopentamethylenetetramine, azobisisobutyronitrile, azodicarbonamide, and 4,4'-oxybis(benzenesulfonylhydrazide).

[0042] In the present invention, the combination of chemical substances capable of generating gas through chemical reactions preferably includes, but is not limited to, carbonates and organic acids.

[0043] In the present invention, the carbonate preferably includes at least one of, but is not limited to, sodium carbonate, potassium carbonate, and calcium carbonate.

[0044] In the present invention, the organic acid preferably includes at least one of, but is not limited to, citric acid, malic acid, and benzoic acid.

[0045] In the present invention, the active ingredient can generate gas (one or more of nitrogen, carbon dioxide, or ammonia) under the conditions of polyolefin melt extrusion processing and dissolve in the polyolefin melt under the pressure provided by the processing equipment. It can assist the melt flow through mechanisms such as plasticization. In the final section of the melt extrusion equipment and the die region, due to the decrease in pressure, the dissolved gas is instantaneously released and diffused between the melt and the inner surface of the equipment, efficiently assisting the melt demolding, slowing down melt fracture, reducing die swell, and reducing die build-up.

[0046] In terms of mass percentage, the fluorine-free processing aid of the present invention preferably includes 0% - 1% of a decomposition temperature regulator.

[0047] In the present invention, the decomposition temperature regulator preferably includes at least one of, but is not limited to, ethylene bisstearamide (EBS), palmitic acid (PA), zinc stearate, calcium stearate, and erucamide.

[0048] In terms of mass percentage, the fluorine-free processing aid of the present invention preferably includes 0% - 1% of an antioxidant.

[0049] In the present invention, the antioxidant preferably includes at least one of, but is not limited to, pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, and 2,6-di-tert-butyl-4-methylphenol.

[0050] In terms of mass percentage, the fluorine-free processing aid of the present invention preferably includes 0% - 1% of a dispersion aid.

[0051] In the present invention, the dispersion aid preferably includes at least one of, but is not limited to, liquid paraffin, white oil, polyvinyl alcohol, and silicone oil.

[0052] In the present invention, the fluorine-free processing aid further preferably includes other processing aids. The present invention has no special limitation on the types of the other processing aids, and common aids in the polyolefin melt extrusion molding methods well-known to those skilled in the art can be used.

[0053] The present invention has no special limitation on the form of the fluorine-free processing aid, and both powder or masterbatch forms are acceptable.

[0054] In the present invention, the preparation method of the fluorine-free processing aid masterbatch preferably includes:

[0055] Mix the active ingredient, polymer resin carrier, decomposition temperature regulator, antioxidant and dispersing aid, and then carry out melt extrusion granulation with a twin-screw extruder to obtain a granular fluorine-free processing aid masterbatch.

[0056] In the present invention, the temperature of the mixing is preferably below the decomposition temperature of the active ingredient; the mixing time is preferably 1 to 5 minutes.

[0057] In the present invention, the temperature of the melt extrusion granulation is preferably below the decomposition temperature of the active ingredient. The present invention has no special limitation on the specific operation of the melt extrusion granulation, and the technical solutions of melt extrusion granulation well-known to those skilled in the art can be adopted.

[0058] In the present invention, the fluorine-free processing aid masterbatch is preferably cylindrical; the diameter of the cylinder is preferably 1 to 2 mm; the length of the cylinder is preferably 3 to 4 mm.

[0059] In the present invention, the preparation method of the fluorine-free processing aid powder preferably includes:

[0060] Mix the active ingredient, polymer resin carrier, decomposition temperature regulator, antioxidant and dispersing aid to obtain a fluorine-free processing aid powder.

[0061] In the present invention, the temperature of the mixing is preferably below the decomposition temperature of the active ingredient; the mixing time is preferably 1 to 5 minutes.

[0062] The present invention has no special limitation on the equipment used in the preparation process of the fluorine-free processing aid, and commercially available equipment well-known to those skilled in the art can be adopted.

[0063] In the present invention, the polyolefin preferably includes, but is not limited to, one of LLDPE, LDPE, HDPE, ULDPE, XHDPE, XLLDPE and PP.

[0064] In the present invention, the mass of the fluorine-free processing aid is preferably 0.01 to 5‰ of the mass of the polyolefin, more preferably 0.01 to 3‰. The fluorine-free processing aid adopted in the present invention has excellent performance even at a low dosage.

[0065] In the present invention, the melt extrusion processing and forming preferably include, but are not limited to, any one of melt extrusion spinning, blown film, cast tube, pipe extrusion and cable sheathing.

[0066] The present invention has no special limitations on the devices and specific steps in the melt extrusion processing and molding of polyolefins. Existing devices and specific steps well-known to those skilled in the art can be used, which are fully compatible with existing processing equipment and technological processes.

[0067] In the present invention, a fluorine-free processing aid is uniformly mixed with polyolefins and fed into a melt extrusion processing device for full mixing, shearing, and kneading. At this stage, the fluorine-free processing aid decomposes or reacts under high temperature to generate gas, and the generated gas is fully dissolved into the polyolefin melt under sufficient pressure provided by the processing device, thereby realizing the in-situ introduction of gas into the polyolefin melt. In the region of the rear end of the melt extrusion processing device and the forming die, due to the pressure reduction, the dissolved gas is instantaneously released from the polyolefin melt and diffused between the melt and the inner surface of the device. After being extruded from the forming die, the gas escapes, while the melt is formed according to the conventional process after being extruded from the forming die.

[0068] Compared with the prior art, the method of internal gas-assisted lubrication disclosed by the present invention and the fluorine-free processing aid capable of autonomously releasing gas in the plastic melt to realize this method have the following technical advantages: 1) In terms of improving the plastic melt extrusion processing, it can be equivalent to the performance of traditional fluorine-containing processing aids, that is, it can slow down melt fracture, reduce die swell, and die build-up. While improving the processing speed and efficiency, it effectively reduces energy consumption. 2) The onset time is fast. 3) The fluorine-free processing aid capable of releasing internal gas disclosed by the present invention only needs an addition amount of less than 3‰ to play a role. 4) It is prepared based on non-toxic and harmless materials and does not contain any fluorine-containing substances. 5) Such processing aids will not change the properties of plastic products and there is no any fluorine-containing chemical residue.

[0069] The self-releasing gas fluorine-free processing aid provided by the content of the present invention for realizing the internal gas-assisted lubrication molding method is mainly used to replace traditional fluorine-containing polymer plastic processing aids and can match the polyolefin melt extrusion processing technology based on traditional fluorine-containing processing aids, that is, the devices and specific steps of polyolefin melt extrusion processing and molding can be referred to the existing devices and specific steps. Specifically speaking, the method and the use of the fluorine-free processing aid provided by the present invention can match the use method of the original fluorine-containing processing aid, and no major changes need to be made to the processing equipment, process, and parameters.

[0070] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0071] Example 1

[0072] A fluorine-free processing aid is composed of 94.986 wt% of a polymer resin carrier (polyethylene with a melt index of 10 g / 10 min), 5 wt% of an active ingredient (sodium bicarbonate), 0.003 wt% of palmitic acid, 0.005 wt% of calcium stearate, 0.005 wt% of polyvinyl alcohol (molecular weight: 120,000), and 0.001 wt% of silicone oil (viscosity: 50 CS).

[0073] The preparation method of the fluorine-free processing aid is as follows: Mix the active ingredient, palmitic acid, calcium stearate, polyvinyl alcohol, silicone oil, and the polymer resin carrier at 60 °C for 2 min, then add them into a single-screw extruder, and extrude, draw, cool, and pelletize in the temperature range of 100 - 110 °C to obtain the fluorine-free processing aid. The fluorine-free processing aid is cylindrical, with a diameter of 1.5 mm and a length of 3 mm.

[0074] Example 2

[0075] Replace the active ingredient sodium bicarbonate in Example 1 with ammonium bicarbonate, and keep other parameters the same as in Example 1.

[0076] Example 3

[0077] Replace the active ingredient sodium bicarbonate in Example 1 with azodicarbonamide, and keep other parameters the same as in Example 1.

[0078] Test Example 1

[0079] Take 20 g of the fluorine-free processing aid in Example 1 and place it in a test tube of a drainage method gas volume test device, heat it in an oil bath at 130 °C, and record the relationship between the released gas volume and time. The results are as Figure 1 shown. It can be seen from Figure 1 that after reaching the decomposition temperature, the gas is rapidly released and reaches equilibrium within 6 min.

[0080] Test Example 2

[0081] Add the fluorine-free processing aid in Example 1 to polypropylene (PP) (melt index: 3 g / 10 min, model T30S). The mass of the fluorine-free processing aid is 3‰ of the mass of polypropylene to obtain a mixed resin. Take 45 g of the mixed resin or pure polypropylene resin and use a POTOP torque rheometer. Set the temperature in the mixing chamber to 200 °C and the rotation speed to 70 rpm, and record the relationship between torque and time. The results are as Figure 2 shown. It can be seen from Figure 2It can be seen that after the resin melts, the torque applied to the rotor by adding 3‰ of PP is lower than that of pure PP. This is because the release of endogenous gas changes the force exerted by the PP melt on the rotor. As time goes by, the torque of the PP with 3‰ of the fluorine-free processing aid in Example 1 gradually approaches that of pure PP. This is because the mixing chamber of the POTOP torque rheometer is not a closed system, and the endogenous gas escapes.

[0082] Cool the melt after the above torque rheology to obtain a hybrid material, and perform elemental analysis using X-ray photoelectron spectroscopy (XPS). The results are shown in Table 1.

[0083] Table 1 Elemental analysis table of the composite material obtained by cooling the melt after torque rheology of polypropylene and pure polypropylene with the fluorine-free processing aid of Example 1 added

[0084] C N O F Other heavy metal elements Polypropylene with fluorine-free processing aid added in Example 1 89.80％ 1.13％ 9.07％ - - Pure polypropylene 87.14％ 1.28％ 9.24％ - -

[0085] It can be seen from Table 1 that the PP melt with 3‰ of the fluorine-free processing aid of Example 1 of the present invention also does not contain fluorine elements.

[0086] Example 4

[0087] Add the fluorine-free processing aid in Example 1 to polypropylene (PP) (model T30S) with a melt index of 3 g / 10 min at a ratio of 3‰, and perform melt extrusion on a POTOP single-screw extruder equipped with a capillary die. The diameter of the capillary die is 1.5 mm, the length-diameter ratio is 30, and the three-zone temperatures of the single-screw extruder are set at 215 °C, 230 °C, and 230 °C; the temperature of the area at the capillary die is set at 200 °C, and the fixed screw speed is 20 rpm. Use a precision analytical balance to record the extrusion mass.

[0088] Comparative Example 1

[0089] According to the method of Example 4, perform melt extrusion on pure polypropylene.

[0090] Observe the morphology of the melt when it exits from the capillary die in Example 4 and Comparative Example 1. The results are as Figure 3 shown. Figure 3 In (A) is the macroscopic view of the pure PP product prepared in Comparative Example 1; (B) is the macroscopic view of the PP product prepared after adding the fluorine-free processing aid of Example 1 in Example 4; (C) is the die picture after continuous extrusion for 2 h in Example 4. From Figure 3 (A), it can be seen that the pure PP rod-shaped product without adding a processing aid at a speed of 20 rpm shows a twisted state, which is caused by typical melt fracture, proving that typical melt fracture occurs in pure PP without adding a processing aid. From Figure 3(B) It can be seen that the appearance of the PP product with 3‰ processing aid added is smooth, and no melt fracture occurs. From Figure 3 (C) It can be seen that within the extrusion time range of up to 2 h, no die build-up occurs. The diameter of the extruded PP filament after cooling is comparable to the diameter of the capillary die, indicating that the melt swelling phenomenon is also not obvious.

[0091] Example 5

[0092] This example is for the melt spinning of polypropylene, which is carried out on a laboratory-level composite melt spinning machine. This composite melt spinning machine consists of a twin-screw extruder, a melt metering pump, a spinneret assembly, a water bath cooling tank, and a stretching and winding component. The spinneret assembly is composed of a double-layer filter screen and a single-hole spinneret hole (with a pore diameter of 0.5 mm). The fluorine-free processing aid in Example 1 is added to polypropylene PP (with a melt index of 20 - 50 g / 10 min, provided by Sinopec) at a ratio of 2‰, and the mixture is fully mixed to obtain a mixed material, which is then dried at 80 °C for 5 h. The dried mixed material is added to the feed bin of the spinning machine. The melt extruded by the twin-screw extruder enters the spinneret assembly through the metering pump at a metering rate of 1.5 g / min and is ejected from the spinneret hole. The pressure of the spinneret assembly is controlled at 1 MPa, the spinning temperature is 250 °C, and the spinning speed is 40 m / min. The ejected filaments are cooled by side blowing and then enter the water bath cooling tank under the spinneret hole for cooling and solidification.

[0093] Comparative Example 2

[0094] According to the method of Example 5, pure polypropylene is melt spun.

[0095] The spun fibers prepared in Example 5 and Comparative Example 2 are as Figure 4 shown. Among them, A1 - A3 are the macroscopic diagrams of the spun fibers in Comparative Example 2 at different magnifications, and B1 - B3 are the macroscopic diagrams of the spun fibers in Example 5 at different magnifications. From Figure 4 it can be seen that under these spinning conditions, the spinning of pure PP shows a typical distortion phenomenon caused by melt fracture, and its surface is also relatively rough. However, the filaments spun from PP with 2‰ of the fluorine-free processing aid in Example 1 added have no distorted morphology and a relatively smooth surface. From the results of this example, it can be seen that when the fluorine-free processing aid adopted in the present invention is used for the chip melt spinning of polypropylene, it can effectively improve the melt fracture phenomenon.

[0096] In summary, the fluorine-free processing aid adopted in the present invention can effectively slow down melt fracture, reduce die swell and die build-up, effectively reduce energy consumption while improving the processing speed and rate; at the same time, this processing aid does not contain any fluorine-containing substances, will not change the performance of plastic products, does not produce any fluorine-containing chemical residues, and can play an excellent role even at a low addition amount, and can replace traditional fluorine-containing polymer processing aids.

[0097] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for melt extrusion molding of polyolefins using endogenous gas-assisted lubrication, characterized in that: Under the conditions of polyolefin melt extrusion processing, gas is introduced into the polyolefin melt in situ and dissolved in the polyolefin melt under the pressure provided by the processing equipment. The dissolved gas changes the flow behavior of the polyolefin melt through mechanisms such as plasticization, thereby assisting the flow of the polyolefin melt. Due to the pressure drop in the rear section of the extrusion equipment and near the molding die area, the gas dissolved in the polyolefin melt is instantly released and migrates between the melt and the inner wall of the die, effectively assisting the polyolefin melt to flow in the die, alleviating melt fracture caused by melt fracture, reducing die expansion and die accumulation, and effectively reducing energy consumption while improving processing speed and efficiency.

2. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 1, characterized in that: The gas includes but is not limited to one or a mixture of two or more of nitrogen, carbon dioxide and ammonia; the mass of the gas is 0.01-1% of the mass of the polyolefin melt.

3. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 1, characterized in that: A fluorine-free processing aid capable of autonomously generating gas under melt extrusion processing conditions is added to the polyolefin resin.

4. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 3, characterized in that: In terms of mass percentage, the fluorine-free processing aid includes but is not limited to the following components: Polymer resin carrier 1%~99.99%, Active ingredient 0.01%~99%, Decomposition temperature regulator 0%~1%, Antioxidants 0% to 1%, Dispersing aid 0%~1%.

5. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 4, characterized in that: The polymer resin carrier includes, but is not limited to, at least one of LLDPE, LDPE, HDPE and PP.

6. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 4, characterized in that: The active ingredient is a substance that can generate gas under processing conditions or a combination of chemical substances that can generate gas through chemical reactions; the substance that can generate gas under processing conditions includes but is not limited to at least one of sodium bicarbonate, ammonium bicarbonate, citric acid, calcium carbonate, 4,4'-di-sulfonylhydrazide diphenyl ether, azodicarbonyl, N,N-dinitrosopentamethylenetetramine, azobisisobutyronitrile, azodicarbonamide and 4,4'-oxybisbenzenesulfonylhydrazide; the combination of chemical substances that can generate gas through chemical reactions includes but is not limited to carbonates and organic acids; the carbonates include but are not limited to at least one of sodium carbonate, potassium carbonate and calcium carbonate; the organic acids include but are not limited to at least one of citric acid, malic acid and benzoic acid.

7. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 4, characterized in that: The decomposition temperature regulator includes, but is not limited to, at least one of ethylene distearate, palmitic acid, zinc stearate, calcium stearate and erucamide.

8. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 4, characterized in that: The antioxidant includes, but is not limited to, at least one of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl B-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(2,4-di-tert-butylphenyl)phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite and 2,6-di-tert-butyl-4-methylbenzene.

9. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 4, characterized in that: The dispersing aid includes, but is not limited to, at least one of liquid paraffin, white oil, polyvinyl alcohol and silicone oil.

10. The method for polyolefin melt extrusion molding using endogenous gas-assisted lubrication according to claim 4, characterized in that: The mass of the fluorine-free processing aid is 0.01 to 5‰ of the mass of the polyolefin.

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