High-density polyethylene super-straight bar based on single-screw extrusion process and method thereof

Abstract

The invention relates to the technical field of high-density polyethylene super-straight bars, in particular to a high-density polyethylene super-straight bar based on a single-screw extrusion process, which comprises the following components in percentage by mass: main materials: 85-95% of bimodal distribution HDPE (High-Density Polyethylene) resin with the density of greater than or equal to 0.945 g / cm < 3 > and the melt flow index MFI of 0.1-0.3 g / 10min, and 3-8% of linear low-density polyethylene with the density of 0.920-0.930 g / cm < 3 > and the MFI of 0.5-1.0 g / 10min; functional auxiliaries: 0.1%-0.5% of an antioxidant, 0.2%-0.8% of a lubricant, 1%-2% of an anti-ultraviolet agent and 0.05%-0.2% of a nucleating agent; the antioxidant comprises tetra [beta-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester; the lubricant comprises calcium stearate or polyethylene wax, and one of the calcium stearate and the polyethylene wax is selected for use; the anti-ultraviolet agent adopts carbon black master batch with the particle size of less than or equal to 50nm; the nucleating agent is sodium benzoate. Through the synergistic effect of the LLDPE and the bimodal HDPE, the fluidity and rigidity are balanced, and shrinkage deformation is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of high-density polyethylene super-straight rods, in particular to high-density polyethylene super-straight rods based on a single-screw extrusion process and a method thereof. Background Art

[0002] Currently, the extrusion molding of high-density polyethylene (HDPE) rods mainly relies on the single-screw extrusion process, the core of which is to extrude the molten material into shape through the shearing and conveying action of the screw. In the existing technology, conventional single-screw extruders achieve processing through the following steps:

[0003] Raw material mixing: HDPE resin is mixed with additives (such as lubricants and antioxidants);

[0004] Melt plasticization: The material is plasticized in the compression section and metering section of the screw;

[0005] Extrusion: The rod is formed through a die and shaped by water or air cooling.

[0006] In the existing technology, some improvement solutions improve extrusion efficiency by optimizing the screw structure (such as adding grooves or mixing elements) or adjusting the mold design (such as increasing the compression ratio). For example, patent CN4428561 proposes to reduce melt retention and degradation by increasing the thread radius, while patent CN204278477 adopts a double compression section screw design to improve material conveying.

[0007] However, in the actual production process, due to the high viscosity of HDPE melt, conventional single-screw extruders are prone to form "material plugs" in the compression section, resulting in large fluctuations in extrusion pressure and poor rod straightness. In addition, in traditional processes, the barrel heating zoning is simple and the melt temperature uniformity is poor, which can easily cause local overheating degradation or deformation caused by uneven cooling. Ordinary water cooling systems cannot achieve gradient cooling, resulting in large residual stress inside the rod and easy shrinkage and wrinkling on the surface. The length-to-diameter ratio (L / D) and compression ratio (CR) of existing screws are not optimized for HDPE ultra-straight rods, resulting in low output and high energy consumption. Summary of the Invention

[0008] The object of the present invention is to provide a high-density polyethylene ultra-straight rod based on a single-screw extrusion process and a method thereof, so as to solve the problems raised in the above background technology.

[0009] To achieve the above object, the present invention provides the following technical solution: a high-density polyethylene ultra-straight rod based on a single-screw extrusion process, comprising the following mass percentages:

[0010] Main material: density ≥0.945g / cm 3, melt flow index MFI = 0.1-0.3g / 10min, bimodal distribution HDPE resin 85%-95%, density 0.920-0.930g / cm 3 , MFI = 0.5-1.0 g / 10 min linear low density polyethylene 3%-8%;

[0011] Functional additives: antioxidant 0.1%-0.5%, lubricant 0.2%-0.8%, anti-ultraviolet agent 1%-2%, nucleating agent 0.05%-0.2%;

[0012] The antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;

[0013] The lubricant includes calcium stearate or polyethylene wax, one of which can be used;

[0014] The anti-ultraviolet agent is a carbon black masterbatch with a particle size of ≤50nm;

[0015] The nucleating agent is sodium benzoate.

[0016] A method for preparing high-density polyethylene ultra-straight rods based on a single-screw extrusion process comprises the following steps:

[0017] S1, raw material pretreatment;

[0018] S2, single screw extrusion process optimization;

[0019] S3, forming and cooling orientation;

[0020] S4. Post-processing and detection.

[0021] Preferably, the raw material pretreatment in S1 includes drying, wherein the HDPE resin and LLDPE are dried at 60-80° C. for 2-4 hours, and the moisture content is ≤0.02%;

[0022] Premixing: Add the main ingredients and additives into a high-speed mixer at a speed of 800-1200 rpm and mix for 5-10 minutes to ensure uniform dispersion.

[0023] Preferably, the screw structure in the S2, single-screw extrusion process optimization adopts a segmented dual-compression ratio screw with a total length-to-diameter ratio L / D = 30:1, including a feeding section, a screw groove depth of 8 mm, a first compression section, a compression ratio CR = 1.5, a second compression section, CR = 2.5, a pin mixing section and a metering section to reduce melt fluctuations.

[0024] Preferably, the temperature of the single screw is controlled as follows: feeding section: 160-180°C, compression section: 190-210°C, metering section: 210-230°C, die head: 200-220°C, using PID closed-loop control, with fluctuation ≤±2°C;

[0025] The screw speed is 20rpm-40rpm, and the extrusion pressure is 25MPa-35MPa. The extrusion pressure is compensated in real time by the mold dynamic pressure sensor, and the fluctuation range is ≤±0.5MPa.

[0026] Preferably, the first compression section and the second compression section adopt a gradual groove depth, with the depth decreasing from 3 mm to 1.5 mm.

[0027] Preferably, the S3, molding and cooling orientation includes mold design, the mold adopts a tapered runner mold with an inlet diameter of 60 mm, an outlet diameter of 50 mm, a compression ratio of 2.0, and a pressure compensation device is set at the outlet to eliminate elastic expansion of the melt.

[0028] Preferably, the S3, forming and cooling orientation includes gradient cooling, using three-level gradient water cooling plus core rod oil cooling; first-level water cooling tank: 80℃-85℃, second-level water cooling tank: 50℃-55℃, third-level water cooling tank: 20℃-25℃, core rod oil cooling: 40℃-45℃.

[0029] Preferably, the S4, post-processing and detection, includes:

[0030] Traction cutting: The traction speed is synchronized with the extrusion speed, and the cutting accuracy error is ≤0.5mm;

[0031] Annealing treatment: annealing at a constant temperature of 80-90℃ for 2-4 hours to further release residual stress;

[0032] Performance testing:

[0033] Straightness: Laser measuring instrument detection deviation ≤ 0.1mm / m;

[0034] Mechanical properties: tensile strength ≥28MPa, impact strength ≥50kJ / m 2 ;

[0035] Surface quality: roughness Ra≤0.8μm.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] Through the synergistic effect of LLDPE and bimodal HDPE, the fluidity and rigidity are balanced and shrinkage deformation is reduced.

[0038] Process optimization: Segmented screw and dynamic pressure compensation technology improve melt uniformity by 30% and reduce extrusion fluctuation to ±0.5%.

[0039] Cooling system: Gradient cooling combined with mandrel oil cooling reduces residual stress by 50% and achieves straightness up to international standards (ISO11925).

[0040] Energy consumption and efficiency: Energy consumption is reduced by 25% compared with traditional processes, and production capacity is increased by 40% (φ50mm bar production capacity is 50kg / h). BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 This is a table of components of the high-density polyethylene super-straight rod of the present invention;

[0043] Figure 2 This is a flow chart for preparing the high-density polyethylene ultra-straight rod of the present invention;

[0044] Figure 3 This is a table of existing technology benchmark parameters;

[0045] Figure 4 It is a performance comparison table of the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] See also Figures 1 to 4 , the present invention provides a technical solution:

[0048] High-density polyethylene ultra-straight rods based on single-screw extrusion process, including the following mass percentage composition:

[0049] Main material: density ≥0.945g / cm 3 , melt flow index MFI = 0.1-0.3g / 10min, bimodal distribution HDPE resin 85%-95%, density 0.920-0.930g / cm 3 , MFI = 0.5-1.0 g / 10 min linear low density polyethylene 3%-8%;

[0050] Functional additives: antioxidant 0.1%-0.5%, lubricant 0.2%-0.8%, anti-ultraviolet agent 1%-2%, nucleating agent 0.05%-0.2%;

[0051] The antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;

[0052] The lubricant includes calcium stearate or polyethylene wax, one of which can be used;

[0053] The anti-ultraviolet agent is a carbon black masterbatch with a particle size of ≤50nm;

[0054] The nucleating agent is sodium benzoate.

[0055] A method for preparing high-density polyethylene ultra-straight rods based on a single-screw extrusion process comprises the following steps:

[0056] S1, raw material pretreatment;

[0057] S2, single screw extrusion process optimization;

[0058] S3, forming and cooling orientation;

[0059] S4. Post-processing and detection.

[0060] Specifically, the raw material pretreatment in S1 includes drying, the HDPE resin and LLDPE are dried at 60-80°C for 2-4 hours, and the moisture content is ≤0.02%;

[0061] Premixing: Add the main ingredients and additives into a high-speed mixer at a speed of 800-1200 rpm and mix for 5-10 minutes to ensure uniform dispersion.

[0062] Specifically, in the S2 single-screw extrusion process optimization, the screw structure adopts a segmented dual-compression ratio screw with a total length-to-diameter ratio of L / D = 30:1, including a feeding section, a screw groove depth of 8 mm, a first compression section, a compression ratio CR = 1.5, a second compression section, CR = 2.5, a pin mixing section and a metering section to reduce melt fluctuations.

[0063] Specifically, the temperature control of the single screw is as follows: feeding section: 160-180°C, compression section: 190-210°C, metering section: 210-230°C, die head: 200-220°C, using PID closed-loop control, fluctuation ≤±2°C;

[0064] The screw speed is 20rpm-40rpm, and the extrusion pressure is 25MPa-35MPa. The extrusion pressure is compensated in real time by the mold dynamic pressure sensor, and the fluctuation range is ≤±0.5MPa.

[0065] Specifically, the first compression section and the second compression section adopt a gradual groove depth, with the depth decreasing from 3 mm to 1.5 mm.

[0066] Specifically, the S3, molding and cooling orientation includes mold design. The mold adopts a tapered runner mold with an inlet diameter of 60 mm, an outlet diameter of 50 mm, a compression ratio of 2.0, and a pressure compensation device is set at the outlet to eliminate elastic expansion of the melt.

[0067] Specifically, the S3, forming and cooling orientation includes gradient cooling, using three-level gradient water cooling plus core rod oil cooling; first-level water cooling tank: 80℃-85℃, second-level water cooling tank: 50℃-55℃, third-level water cooling tank: 20℃-25℃, core rod oil cooling: 40℃-45℃.

[0068] Specifically, the S4, post-processing and detection, includes:

[0069] Traction cutting: The traction speed is synchronized with the extrusion speed, and the cutting accuracy error is ≤0.5mm;

[0070] Annealing treatment: annealing at a constant temperature of 80-90℃ for 2-4 hours to further release residual stress;

[0071] Performance testing:

[0072] Straightness: Laser measuring instrument detection deviation ≤ 0.1mm / m;

[0073] Mechanical properties: tensile strength ≥28MPa, impact strength ≥50kJ / m 2 ;

[0074] Surface quality: roughness Ra≤0.8μm.

[0075] Example 1: Bimodal HDPE + Dual Compression Screw Optimization

[0076] Formulation: 95% bimodal HDPE (MFI=0.3 g / 10 min, PDI=38), 3% LLDPE (MFI=0.8), 0.5% polyethylene wax, 0.05% sodium benzoate nucleating agent.

[0077] Process:

[0078] The screw speed is 30r / min and the total compression ratio is 3.0 (double compression section design).

[0079] Barrel temperature gradient: feeding section 170℃ → compression section 200℃ → metering section 220℃.

[0080] Gradient cooling (80℃→50℃→25℃) + mandrel oil cooling (40℃).

[0081] Example 2: Nano-enhanced HDPE

[0082] Formula: 90% HDPE (MFI=0.25), 5% nano-silica (treated with coupling agent), 3% nitrile rubber (AN=18%), and 0.3% antioxidant 1010.

[0083] Process:

[0084] Twin-screw pre-mixing (70℃→85℃), single-screw extrusion (L / D=30:1).

[0085] Dynamic pressure compensation mold (pressure fluctuation ≤ ±0.5MPa).

[0086] Example 3: Modified stress-resistant HDPE

[0087] Formula: 93% HDPE (5000S), 5% EVA (VA=14%), 0.3% antioxidant 1010.

[0088] Process:

[0089] Parallel twin-screw extrusion (drying at 85°C) and annealing treatment (90°C×3h).

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. High-density polyethylene ultra-straight rods based on single-screw extrusion process, characterized by: The composition includes the following mass percentages: Main material: density ≥0.945g / cm 3 , melt flow index MFI = 0.1-0.3g / 10min, bimodal distribution HDPE resin 85%-95%, density 0.920-0.930g / cm 3 , MFI = 0.5-1.0 g / 10 min linear low density polyethylene 3%-8%; Functional additives: antioxidant 0.1%-0.5%, lubricant 0.2%-0.8%, anti-ultraviolet agent 1%-2%, nucleating agent 0.05%-0.2%; The antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; The lubricant includes calcium stearate or polyethylene wax, one of which can be used; The anti-ultraviolet agent is a carbon black masterbatch with a particle size of ≤50nm; The nucleating agent is sodium benzoate.

2. The method for preparing a high-density polyethylene ultra-straight rod based on a single-screw extrusion process according to claim 1, characterized in that: The steps include: S1, raw material pretreatment; S2, single screw extrusion process optimization; S3, forming and cooling orientation; S4. Post-processing and detection.

3. The method for preparing a high-density polyethylene ultra-straight rod based on a single-screw extrusion process according to claim 2, characterized in that: Said S1, raw material pretreatment includes drying, HDPE resin and LLDPE are dried at 60-80°C for 2-4 hours, and the moisture content is ≤0.02%; Premixing: Add the main ingredients and additives into a high-speed mixer at a speed of 800-1200 rpm and mix for 5-10 minutes to ensure uniform dispersion.

4. The method for preparing a high-density polyethylene ultra-straight rod based on a single-screw extrusion process according to claim 2, wherein: In the S2 single-screw extrusion process optimization, the screw structure adopts a segmented dual-compression ratio screw with an overall length-to-diameter ratio L / D of 30:1, including a feeding section, a screw groove depth of 8 mm, a first compression section with a compression ratio CR=1.5, a second compression section with a compression ratio CR=2.5, a pin mixing section, and a metering section to reduce melt fluctuations.

5. The method for preparing high-density polyethylene ultra-straight rods based on single-screw extrusion technology according to claim 2, characterized in that: The temperature of the single screw extruder is controlled by PID closed loop control, with a fluctuation of ≤±2°C, with the feeding section at 160-180°C, the compression section at 190-210°C, the metering section at 210-230°C, and the die head at 200-220°C. The screw speed is 20rpm-40rpm, and the extrusion pressure is 25MPa-35MPa. The extrusion pressure is compensated in real time by the mold dynamic pressure sensor, and the fluctuation range is ≤±0.5MPa.

6. The method for preparing high-density polyethylene ultra-straight rods based on single-screw extrusion technology according to claim 5, characterized in that: The first compression section and the second compression section adopt a gradual groove depth, and the depth decreases from 3mm to 1.5mm.

7. The method for preparing high-density polyethylene ultra-straight rods based on a single-screw extrusion process according to claim 2, characterized in that: The S3, molding and cooling orientation, includes mold design. The mold adopts a tapered runner mold with an inlet diameter of 60 mm, an outlet diameter of 50 mm, a compression ratio of 2.0, and a pressure compensation device is set at the outlet to eliminate elastic expansion of the melt.

8. The method for preparing high-density polyethylene ultra-straight rods based on single-screw extrusion technology according to claim 7, characterized in that: The S3, forming and cooling orientation includes gradient cooling, using three-level gradient water cooling plus core rod oil cooling; the first-level water cooling tank: 80℃-85℃, the second-level water cooling tank: 50℃-55℃, the third-level water cooling tank: 20℃-25℃, and the core rod oil cooling: 40℃-45℃.

9. The method for preparing high-density polyethylene ultra-straight rods based on a single-screw extrusion process according to claim 2, characterized in that: The S4, post-processing and detection includes: Traction cutting: The traction speed is synchronized with the extrusion speed, and the cutting accuracy error is ≤0.5mm; Annealing treatment: annealing at a constant temperature of 80-90℃ for 2-4 hours to further release residual stress; Performance testing: Straightness: Laser measuring instrument detection deviation ≤ 0.1mm / m; Mechanical properties: tensile strength ≥28MPa, impact strength ≥50kJ / m 2 ; Surface quality: roughness Ra≤0.8μm.

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