Melt extrusion molding method of ultra-high molecular weight polyethylene wide sheet

Abstract

The invention belongs to the technical field of high polymer material processing, and particularly relates to a melt extrusion molding method of an ultra-high molecular weight polyethylene wide sheet. Aiming at the technical bottlenecks of poor melt flowability, extrusion fracture and the like caused by molecular chain entanglement of UHMWPE, continuous and stable extrusion of UHMWPE wide sheets is realized by compounding a specific flow modifier and combining a stepped precise temperature control strategy and a forced symmetric cooling process. According to the method, the melt fracture phenomenon is eliminated, the intrinsic performance such as high wear resistance and low temperature resistance of UHMWPE is completely reserved, the efficiency and size limitation of a traditional mold pressing process is broken through, and a large-scale production solution of high-performance sheets is provided for the high-end fields such as food machinery and medical implants.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, specifically to a melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) has an extremely high molecular weight (over 1.5 million), tightly wound molecular chains, extremely high melt viscosity, and an extremely low critical shear rate, making continuous melt extrusion difficult to achieve using traditional processing methods. Existing technologies mainly rely on compression molding, which has a long process cycle (single molding > 1 hour), high energy consumption, and limited product size (width typically < 500 mm), resulting in poor surface smoothness and failing to meet the high-efficiency production requirements of wide, thin sheets.

[0003] While some technologies attempt to improve flowability by adding plasticizers or blending with low molecular weight polymers, this significantly degrades the core properties of UHMWPE, such as abrasion resistance and impact resistance. The technical challenges of processing pure materials, required in fields such as medical applications, have not yet been overcome, making it difficult for existing methods to simultaneously achieve efficient continuous production and preserve the material's intrinsic properties. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the prior art, the inventors have proposed the present invention.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material, comprising the following steps:

[0008] (1) Raw material pretreatment: Dry mix UHMWPE resin with viscosity-average molecular weight of 1.5 million to 6.5 million with flow modifier at a ratio of 100:0.5-3 parts by weight for 10-15 minutes. The flow modifier is composed of low molecular weight polyethylene (LMWPE, molecular weight 20,000-50,000) and metal stearate at a mass ratio of 2-4:1.

[0009] (2) Melt extrusion: The mixture is added to a single screw extruder and plasticized by step heating to extrude sheet melt. The temperature is controlled as follows: 130-150℃ in the feeding section, 160-180℃ in the compression section, 190-210℃ in the homogenization section, and 200-220℃ in the die. The melt residence time at the die is <60 seconds.

[0010] (3) Shaping and cooling: The melt is cooled by double-sided air knife with air pressure of 0.3-0.8MPa and air temperature of 10-25℃, and then enters the calendering roller for shaping with calendering roller temperature of 20-40℃, pressure of 0.5-2MPa, and gap accuracy of ±0.05mm.

[0011] (4) Traction and winding: The cooled sheet is wound up by traction rollers at a speed of 1-5m / min to produce a sheet with a thickness of 0.3-2mm and a width of 130-700mm.

[0012] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material according to the present invention, wherein: the metal stearate is calcium stearate, zinc stearate or a mixture of the two, and the stearate particle size is ≤10μm.

[0013] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material according to the present invention, the single screw extruder has a screw length-to-diameter ratio of 30-40:1, a compression ratio of 2.5-3.5:1, and a screw speed of 5-20 rpm.

[0014] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material described in this invention, wherein: 0.1-0.5 parts by weight of antioxidant 1010 are added during dry mixing in step (1), and the moisture content of UHMWPE resin is ≤0.01%.

[0015] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material described in this invention, the air speed uniformity deviation of the air knife double-sided air cooling is ≤5%, and the distance between the air knife and the melt surface is 5-15mm.

[0016] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material according to the present invention, the calendering roller includes a three-stage roller, the roller surface temperature difference is ≤2℃, and the roller surface roughness Ra is ≤0.1μm.

[0017] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material described in this invention, the die head is a coat hanger type wide die head, and the die lip gap is 1.5-2 times the thickness of the finished product.

[0018] As a preferred embodiment of the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet material according to the present invention, wherein the melt index of LMWPE in the flow modifier is 20-50 g / 10 min.

[0019] A melt extrusion molding method for ultra-high molecular weight polyethylene (UHMWPE) wide sheet materials, wherein the tensile strength is ≥30MPa and the abrasion amount is ≤15mg.

[0020] Application of UHMWPE sheets produced by melt extrusion molding of wide sheets of ultra-high molecular weight polyethylene in food machinery guides, chemical valve seals or artificial joint gaskets.

[0021] The beneficial effects of this invention are as follows: Through the synergistic effect of compound flow modifier and step temperature control, the melt flowability of UHMWPE is significantly improved, with the melt flow rate increasing from 0 to 0.15-0.3 g / 10 min (230℃ / 5 kg), and the critical shear rate increasing to 25 s. -1 The above completely eliminates melt fracture, enabling continuous and stable extrusion of wide thin sheets with a thickness uniformity deviation of ≤±0.03mm and a width of up to 700mm.

[0022] The resulting sheet fully retains the intrinsic properties of UHMWPE: abrasion loss ≤15mg (17% lower than molded products), impact strength ≥120kJ / m². 2 It has a water absorption rate of <0.01%. Production efficiency is increased by more than 10 times, and raw material utilization rate is >98%, solving the urgent need for high-performance pure UHMWPE sheets in the medical, food and other fields. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0026] Example 1

[0027] This embodiment provides a melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet.

[0028] Specifically, the raw materials and formula:

[0029] UHMWPE resin: Made from food-grade raw materials with a viscosity-average molecular weight of 1.5 million and a moisture content of 0.008%.

[0030] Flow modifier: The addition amount is 0.5 parts, which is a compound of low molecular weight polyethylene (LMWPE, molecular weight 20,000, melt index 20g / 10min) and calcium stearate in a mass ratio of 2:1.

[0031] Preferably, the calcium stearate particle size is ≤10μm.

[0032] Antioxidant: Add 0.1 parts of antioxidant 1010. Dry mix for 10 minutes and let stand for 2 hours to promote component diffusion.

[0033] Equipment and process parameters:

[0034] Extruder: Single screw diameter Φ45mm, length-to-diameter ratio 30:1, compression ratio 2.5:1, speed 5rpm.

[0035] Temperature gradient control:

[0036] Feeding section 130℃;

[0037] Compression section 160℃;

[0038] Homogenization section 190℃;

[0039] The mold head is set at 200°C.

[0040] The residence time of the melt at the die head is strictly controlled to be 50 seconds.

[0041] Die head design: wide-width coat hanger die head, with die lip clearance set at 0.45mm.

[0042] Cooling and shaping:

[0043] Double-sided air-cooled air knife: air pressure 0.3MPa, air temperature 10℃, air knife and melt distance 5mm, air velocity uniformity deviation ≤3%.

[0044] Calendering roller: The three roller temperatures are 20℃ / 22℃ / 20℃ respectively, the roller surface temperature difference is ≤1℃, the surface roughness Ra=0.08μm, the pressure is 0.5MPa, and the gap accuracy is ±0.03mm.

[0045] Traction speed: 1m / min.

[0046] Product performance and testing: The sheet material produced has a thickness of 0.30±0.02mm and a width of 130mm.

[0047] Mechanical properties: tensile strength ≥30MPa, wear amount 12mg (GB / T3960); coefficient of friction 0.07.

[0048] Hygiene: Meets FDA 21CFR177.1520 migration test standards, with total migration <0.5 mg / dm³. 2 .

[0049] Microstructure: SEM showed no melt fracture lines and surface smoothness Ra≤0.5μm.

[0050] Example 2

[0051] This embodiment provides a melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet.

[0052] Specifically, the preparation of 1.2mm sheet for chemical valve seals.

[0053] Raw materials and formulation: UHMWPE resin: molecular weight 4 million (intermediate value), moisture content 0.005%.

[0054] Flow modifier: 2.0 parts, composed of LMWPE (molecular weight 35,000, melt index 35 g / 10 min) and zinc stearate in a 3:1 ratio.

[0055] Antioxidant: Add 0.3 parts of antioxidant 1010.

[0056] Key process optimization:

[0057] Temperature gradient: 140℃ for feeding section; 170℃ for compression section; 200℃ for homogenization section; 215℃ for die head.

[0058] The die head temperature is 215℃, and the dwell time is ≤45 seconds.

[0059] Cooling enhancement: The air knife air pressure is increased to 0.6MPa and the air temperature is 20℃.

[0060] Precision control of calendering rollers: three-stage roller temperature 28℃ / 30℃ / 28℃, pressure 1.2MPa, and gap calibration to ±0.04mm.

[0061] Traction speed: 3m / min.

[0062] Chemical resistance test: The sheet was immersed in 40% sulfuric acid solution and 30% NaOH solution for 168 hours each:

[0063]

[0064] Example 3

[0065] This embodiment provides a melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet.

[0066] Specifically, the preparation of 2.0mm thick sheets for artificial joint pads.

[0067] Ingredients and Formula:

[0068] UHMWPE resin: medical grade, molecular weight 6.5 million, moisture content 0.003%.

[0069] Flow modifier: 3.0 parts, made by compounding LMWPE (molecular weight 50,000, melt index 50 g / 10 min) and calcium stearate / zinc mixture (1:1) in a 4:1 ratio.

[0070] Antioxidant: Add 0.5 parts of antioxidant 1010.

[0071] Medical-grade pure material processing control:

[0072] Temperature control: homogenization section 210℃, die head 220℃, melt residence time ≤40 seconds.

[0073] Calendering roller: Three-stage roller temperature 38℃ / 40℃ / 38℃, pressure 2.0MPa.

[0074] Traction speed: 5m / min, winding tension ≤10N.

[0075] Biomedical performance testing:

[0076] Wear performance: Hip joint simulation test, volumetric wear rate 8.5mm 3 / Mcycle, compared to molded products (15mm) 3 / Mcycle) decreased by 43%.

[0077] Biocompatibility: Cytotoxicity (ISO10993-5): Grade 0 (non-toxic);

[0078] Molecular weight retention (GPC): ≥99.3% (proving no degradation).

[0079] Mechanical properties: Impact strength 125 kJ / m 2 (ISO179), higher than 110 kJ / m of molded sheet. 2

[0080] This invention constructs a three-in-one technical system of "flow modification - precision plasticization - stable molding". The extreme entanglement of UHMWPE molecular chains (molecular weight above 1.5 million) is the fundamental reason for the lack of melt flowability. This invention uses a compound system of low molecular weight polyethylene (LMWPE) and stearate to achieve dual deentanglement at the molecular scale:

[0081] LMWPE acts as a "chain segment lubricant": its short molecular chains (20,000-50,000) can be embedded in the gaps between the long chains of UHMWPE, weakening the entanglement strength through intermolecular van der Waals forces and reducing the apparent viscosity of the melt.

[0082] Stearates form a “boundary slip layer”: metal ions (Ca2+) + / Zn2 + The weak interaction between stearic acid and polyethylene chains promotes the directional alignment of stearic acid molecules at the melt-equipment interface, significantly reducing melt flow resistance (friction coefficient reduced to 0.05-0.11). This compound design avoids the performance degradation caused by traditional plasticizers: LMWPE has excellent compatibility with the matrix and will not form phase separation; the thermal stability of stearates (decomposition temperature > 250℃) ensures safety during high-temperature processing.

[0083] The essence of melt fracture is elastic turbulence triggered by shear rates exceeding a critical value. This invention reconstructs the melt rheological behavior through synergistic optimization of temperature gradient and screw structure: a stepped heating strategy (temperature difference > 60℃ between feeding, compression, and homogenization sections): a high-viscosity melt layer is formed in the low-temperature zone (130-150℃) of the feeding section, enhancing screw conveying efficiency; molecular chain entanglement is fully released in the high-temperature zone (190-210℃) of the homogenization section, resulting in uniform plasticization of the melt; the die temperature (200-220℃) is slightly lower than the degradation threshold (230℃), shortening the high-temperature residence time (< 60 seconds) and avoiding oxidation and chain breakage.

[0084] Matching the screw length-to-diameter ratio (30-40:1) with the compression ratio (2.5-3.5:1): extending the plasticizing path while avoiding excessive shearing, increasing the critical shear rate to 25s. -1 The above eliminates the sharkskin effect. The coat hanger-style die head's flow channel design further balances the melt pressure distribution, ensuring that the edge thickness uniformity deviation of wide sheets (700mm) is <5%.

[0085] This invention, starting from the thermodynamic essence of UHMWPE molecular chain entanglement, achieves continuous and stable extrusion of wide-width thin sheets through molecular interface design of flow modifiers, rheological control of the plasticizing process, and precise intervention in crystallization kinetics. Its technical versatility lies in its applicability to UHMWPE raw materials with molecular weights ranging from 1.5 million to 6.5 million (covering the entire commercial range), and the modifier addition amount is only 0.5-3 parts, fully preserving the "wear-resistant king" characteristics of UHMWPE. Compared to the intermittent production of compression molding processes, this method increases efficiency by more than 10 times (traction speed 1-5 m / min), while achieving a raw material utilization rate of >98%, providing a low-cost, high-performance basic material solution for high-end equipment manufacturing (such as artificial joints and nuclear power plant seals). This technological paradigm is expected to be extended to the continuous processing of other ultra-high molecular weight polymers (such as polytetrafluoroethylene).

[0086] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for melt extrusion molding of wide-width thin sheets of ultra-high molecular weight polyethylene, characterized in that: Includes the following steps: (1) Raw material pretreatment: Dry mix UHMWPE resin with viscosity-average molecular weight of 1.5 million to 6.5 million with flow modifier at a ratio of 100:0.5-3 parts by weight for 10-15 minutes. The flow modifier is composed of low molecular weight polyethylene (LMWPE, molecular weight 20,000-50,000) and metal stearate at a mass ratio of 2-4:

1. (2) Melt extrusion: The mixture is added to a single screw extruder and plasticized by step heating to extrude sheet melt. The temperature is controlled as follows: 130-150℃ in the feeding section, 160-180℃ in the compression section, 190-210℃ in the homogenization section, and 200-220℃ in the die. The melt residence time at the die is <60 seconds. (3) Shaping and cooling: The melt is cooled by double-sided air knife with air pressure of 0.3-0.8MPa and air temperature of 10-25℃, and then enters the calendering roller for shaping with calendering roller temperature of 20-40℃, pressure of 0.5-2MPa, and gap accuracy of ±0.05mm. (4) Traction and winding: The cooled sheet is wound up by traction rollers at a speed of 1-5m / min to produce a sheet with a thickness of 0.3-2mm and a width of 130-700mm.

2. The melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in claim 1, characterized in that: The metal stearate is calcium stearate, zinc stearate, or a mixture of both, and the stearate particle size is ≤10μm.

3. The melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in claim 1, characterized in that: The single-screw extruder has a screw length-to-diameter ratio of 30-40:1, a compression ratio of 2.5-3.5:1, and a screw speed of 5-20 rpm.

4. The melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in claim 1, characterized in that: In step (1), 0.1-0.5 parts by weight of antioxidant 1010 are added during dry mixing, and the moisture content of UHMWPE resin is ≤0.01%.

5. The melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in claim 1, characterized in that: The air knife with double-sided air cooling has a wind speed uniformity deviation of ≤5%, and the distance between the air knife and the melt surface is 5-15mm.

6. The melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in claim 1, characterized in that: The calendering roller comprises three rollers, with a roller surface temperature difference ≤2℃ and a roller surface roughness Ra≤0.1μm.

7. The melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in claim 1, characterized in that: The die head is a coat hanger-style wide die head, and the die lip gap is 1.5-2 times the thickness of the finished product.

8. A melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in any one of claims 1-7, characterized in that: The melt flow index of LMWPE in the flow modifier is 20-50 g / 10 min.

9. The UHMWPE sheet obtained by the melt extrusion molding method for ultra-high molecular weight polyethylene wide sheet as described in any one of claims 1-7, characterized in that: Tensile strength ≥30MPa, abrasion ≤15mg.

10. The application of UHMWPE sheets prepared by the melt extrusion molding method of ultra-high molecular weight polyethylene wide sheet as described in claim 9 in food machinery guide rails, chemical valve seals or artificial joint gaskets.

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