A modified polyoxymethylene composite material and a method for producing the same

Abstract

The application discloses a kind of low abrasion, low warping, high dimensional stability polyoxymethylene composite material and preparation method thereof.The composite material includes: copolymer POM 100 parts, composite self-lubricating wear-resistant agent 8-20 parts, composite low warping dimensional stabilizer 15-30 parts, processing stabilizing system 0.5-1.2 parts, lubricant 0.2-0.5 parts by weight.The preparation method includes filler silane treatment, premixing, twin-screw extrusion, annealing and other steps.The abrasion amount of the material is ≤1.3 mg / 1000r, the friction coefficient is ≤0.17, the warping amount is ≤0.20 mm / 100 mm, the 5-time temperature change dimensional change rate is ≤0.07%, and the original mechanical properties of POM are maintained, which is suitable for automobile precision structural parts, electronic and electrical precision parts and other fields.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a modified polyoxymethylene composite material and its preparation method. Background Technology

[0002] Polyoxymethylene (POM) is an engineering plastic with excellent comprehensive properties, including high rigidity, high strength, good self-lubrication, fatigue resistance, and chemical corrosion resistance, making it widely used in various precision structural components and transmission parts. However, with the increasing demands for precision, lifespan, and reliability in high-end precision manufacturing, conventional POM materials and existing modification schemes have revealed the following significant technical defects, and there are also contradictions and constraints among these properties: Insufficient wear resistance: Pure POM has a high coefficient of friction (approximately 0.32) and a large wear rate (approximately 3.9 mg / 1000r), making it prone to wear, abnormal noise, and even failure under long-term dynamic friction conditions. Existing technologies modify it by adding lubricants such as PTFE and silicone oil, but single lubricants have problems such as uneven dispersion and poor compatibility with the POM matrix, resulting in limited modification effects. Moreover, excessive addition will seriously degrade mechanical properties.

[0003] Severe warpage: During POM injection molding, the molecular chains are highly oriented along the flow direction, resulting in a significant difference in shrinkage rates between the flow direction and the perpendicular direction (anisotropic ratio of approximately 0.86). This leads to large warpage in the molded parts (approximately 1.30 mm / 100 mm), severely affecting assembly accuracy. Although glass fiber filler can reduce shrinkage, it easily causes a reversal of shrinkage rates (shrinkage rate in the flow direction is greater than in the perpendicular direction), generating internal stress and causing the parts to crack.

[0004] Poor dimensional stability: Conventional filler-modified POM composite materials have poor filler dispersion and weak interfacial bonding with the matrix. During environmental temperature and humidity changes (such as cycling from -40℃ to 80℃), the dimensional change rate is large (>0.6%), which cannot meet the dimensional accuracy requirements of precision parts in a wide temperature range.

[0005] Existing modification schemes suffer from performance imbalances: adding glass fiber to improve dimensional stability significantly increases material wear (the rough surface of glass fiber exacerbates wear on abrasive parts); adding a single mineral filler to reduce warpage makes it difficult to balance the mechanical properties of the matrix and processing fluidity; adding lubricants often reduces the warpage control effect. Currently, there is no modification scheme that can simultaneously achieve low wear, low warpage, high dimensional stability, and maintain the original mechanical properties of the POM matrix. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A modified polyoxymethylene composite material, comprising the following components by weight: Copolymer polyoxymethylene resin (POM): 100 parts, melt index of 8-12 g / 10min, 190℃ / 2.16kg; Composite self-lubricating wear-resistant agent: 8-20 parts, composed of polytetrafluoroethylene (PTFE) micro powder, organosilicone masterbatch, and molybdenum disulfide (MoS2); Composite low warpage size stabilizer: 15-30 parts, composed of solid glass microspheres and talc powder; Processing stabilization system: 0.5–1.2 parts, composed of formaldehyde absorbent and composite antioxidant; Lubricant: 0.2 to 0.5 parts, selected from one or more of calcium stearate and zinc stearate.

[0007] Furthermore, the composite material further includes at least one of the following components: 0.1 to 0.5 parts of anti-hydrolysis agent, 0.2 to 0.6 parts of light stabilizer, and 0.1 to 1.0 parts of colorant.

[0008] Preferably, the composite self-lubricating wear-resistant agent contains 6-15 parts of PTFE micro powder with a particle size of 500 mesh, 1-3 parts of silicone masterbatch with a silicon content of 30%, and 1-3 parts of molybdenum disulfide with a particle size of 2000 mesh; more preferably, it contains 8-12 parts of PTFE micro powder, 1.5-2.5 parts of silicone masterbatch, and 1.5-2.5 parts of molybdenum disulfide.

[0009] Preferably, the composite low warpage size stabilizer contains 10-22 parts of solid glass microspheres with a particle size of 10 μm and 5-10 parts of talc powder with a mesh size of 2500; more preferably, it contains 15-20 parts of solid glass microspheres and 6-8 parts of talc powder.

[0010] Preferably, in the processing stabilization system, the formaldehyde absorbent is melamine-based, 0.2-0.5 parts; the composite antioxidant is antioxidant 1010 and antioxidant 168 mixed in a 1:1 mass ratio, 0.3-0.7 parts.

[0011] Preferably, the solid glass microspheres and talc powder are surface activated by silane coupling agent KH550, and the amount of coupling agent is 0.5% to 1.2% of the total mass of the filler.

[0012] This invention also discloses a method for preparing the above-mentioned polyoxymethylene composite material, comprising the following steps: S1. Raw material pretreatment: Solid glass microspheres and talc powder were placed in a high-speed mixer, and silane coupling agent KH550 was added, accounting for 0.8% of the total mass of the filler. The mixture was stirred at 300 rpm at room temperature for 20 minutes to ensure that the coupling agent uniformly coated the surface of the filler. The treated filler was then placed in an 80℃ oven to dry for 2 hours for later use.

[0013] S2. Premix: PTFE micro powder and silicone masterbatch are premixed in a low-speed mixer at a weight ratio of 4-6:1 for 5 minutes to form a wear-resistant premix and improve dispersibility.

[0014] S3. Main Mixing: According to the weight ratio, the dried POM resin, pretreated filler, wear-resistant premix, molybdenum disulfide, processing stabilizer, lubricant and other additives are added to the high-speed mixer in sequence. The speed is set to 800 r / min, and the mixture is mixed at room temperature for 5 to 8 minutes until the components are evenly dispersed to obtain the mixture. S4. Extrusion granulation: The extruder employs a co-rotating, meshing twin-screw extruder with a length-to-diameter ratio of 40:1 and features a two-stage vacuum exhaust system. The mixture is fed into the main feed hopper for melt extrusion. The extruder temperature settings for each zone are: Zone 1 175℃, Zone 2 190℃, Zone 3 195℃, Zone 4 195℃, Zone 5 195℃, Zone 6 185℃, Zone 7 180℃, Zone 8 180℃, Zone 9 180℃, Zone 10 185℃, and Die Head 195℃; the screw speed is 300–400 rpm.

[0015] Vacuum exhaust: The first stage of vacuum is located in zone 5, with a vacuum degree of -0.06 to -0.08 MPa; the second stage of vacuum is located in zone 8, with a vacuum degree of -0.08 to -0.10 MPa. After the molten material is extruded through the die head, it enters a 30°C water cooling tank for cooling.

[0016] S5. Post-processing: After cooling, the material strips are cut into pellets and dried in an 80℃ oven for 2.5 hours. Then, they are annealed: kept at 90℃ for 1 hour and allowed to cool naturally to room temperature to eliminate internal stress from processing.

[0017] S6. Injection molding: The finished composite material is formed by precision injection molding with the following parameters: barrel temperature 200℃, nozzle temperature 190℃, mold temperature 70℃, injection pressure 65MPa, holding pressure 45MPa, holding time 8s, and cooling time 15s.

[0018] The beneficial effects of this invention are: 1. Significant Improvement in Wear Resistance: Through a ternary compound self-lubricating system of "PTFE micro powder + silicone masterbatch + MoS2", PTFE forms a continuous self-lubricating film, silicone improves dispersibility, and the layered structure of MoS2 forms an auxiliary lubricating layer on the friction surface. The synergistic effect of these three components reduces wear to 1.0–1.3 mg / 1000r and the coefficient of friction to 0.15–0.17, which is 66.7%–74.4% lower than pure POM and 48.0%–60.0% lower than glass fiber modified POM. After 100,000 cycles of dynamic friction, the wear increase is only 1.8–2.3 mg, demonstrating excellent long-term wear resistance.

[0019] 2. Precise optimization of warpage characteristics: The spherical structure of solid glass microspheres inhibits molecular chain orientation through steric hindrance, while the sheet-like structure of ultrafine talc powder forms a spatial network to restrict chain movement. The combination of the two reduces the warpage to 0.12-0.20 mm / 100 mm, which is 84.6%-90.8% lower than that of pure POM. Moreover, it always maintains the intrinsic shrinkage law of POM (the shrinkage rate in the flow direction is slightly less than that in the vertical direction), and there is no risk of shrinkage reversal.

[0020] 3. Significantly Enhanced Dimensional Stability: Surface treatment with silane coupling agent strengthens the interfacial bonding between the filler and the POM matrix, forming a stable spatial network structure. The dimensional change rate after 5 temperature changes (-40℃→80℃) is only 0.04%~0.07%, a reduction of 89.7%~94.1% compared to pure POM; after 10 temperature changes, it remains only 0.06%~0.09%, meeting the dimensional accuracy requirements of high-end applications such as automotive electronics and precision instruments.

[0021] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0023] Examples and Comparative Examples To verify the necessity and synergistic effect of the various functional systems of the present invention, Examples 1-3 and Comparative Examples 1-7 were set up. All examples and comparative examples were carried out according to the above preparation method and injection molding process, with only the formulation composition adjusted. The formulation ratios are shown in Tables 1 and 2.

[0024] Table 1. Formulation ratios (parts by weight) for Examples 1-3

[0025] Table 2. Formulation ratios (parts by weight) for Comparative Examples 1-7

[0026] Comparison of proportions: Comparative Example 1: Pure POM.

[0027] Comparative Example 2: Abrasion-resistant modification of single PTFE (silicone-free, MoS2-free).

[0028] Comparative Example 3: Single low warpage modification (glass microspheres + talc, no wear-resistant agent).

[0029] Comparative Example 4: Existing technology glass fiber composite modification (PTFE + glass fiber).

[0030] Comparative Example 5: Silane-deficient surface treatment (the rest is the same as Example 1).

[0031] Comparative Example 6: Wear-resistant agent lacking MoS2 (other aspects are the same as in Example 1).

[0032] Comparative Example 7: The wear-resistant agent lacks silicone (the rest is the same as in Example 1).

[0033] Performance testing methods Test according to the following standards: Friction coefficient / wear amount: GB / T3960-2016, for grinding parts of 45# steel, load of 50N, rotation speed of 200r / min; wear increment after 100,000 cycles of dynamic friction was tested simultaneously.

[0034] Shrinkage / Anti-axis ratio: GB / T15585-1995, 100mm×100mm×2mm spline.

[0035] Warpage: GB / T14483-2021, 100mm×100mm×2mm spline.

[0036] Dimensional change rate: GB / T1036-2008, -40℃ (2h) → 80℃ (2h) cycle 5 times, 10 times.

[0037] Tensile strength: GB / T1040.2-2006.

[0038] Bending strength: GB / T9341-2008.

[0039] Notched impact strength: GB / T1843-2008.

[0040] Performance test results Table 3 Performance Test Results

[0041] Results Analysis 1. Examples 1-3 exhibit excellent overall performance: friction coefficient ≤0.17, wear amount ≤1.3 mg / 1000r, warpage ≤0.20 mm / 100mm, dimensional change rate after 5 temperature changes ≤0.07%, and tensile strength retention rate ≥95%, fully meeting the requirements of precision components.

[0042] 2. Comparative Example 2 (Single PTFE): Coefficient of friction 0.20, wear loss 1.8, wear resistance better than pure POM but worse than the example; no low warpage component, warpage as high as 1.00 mm / 100 mm. This proves that a single wear-resistant agent cannot solve the warpage problem.

[0043] 3. Comparative Example 3 (Single Low Warpage): Warpage amount was 0.45, showing some improvement, but the coefficient of friction was as high as 0.38, and the wear amount was 4.1, indicating poor wear resistance. This proves that single low warpage modification cannot simultaneously achieve good wear resistance.

[0044] 4. Comparative Example 4 (glass fiber modified): Warpage was 0.38, shrinkage anisotropy ratio was 0.86 (risk of reversal), friction coefficient was 0.28, and wear was 2.5, all of which were inferior to the Example. Although glass fiber reduced warpage, it increased wear, and the reversal of shrinkage easily led to internal stress cracking.

[0045] 5. Comparative Example 5 (Silane-deficient treatment): Its performance falls between the comparative example and the example, with a warpage of 0.22 and a dimensional change rate of 0.10% after 5 temperature changes, both inferior to the example. This demonstrates that silane treatment is crucial for filler dispersion and interfacial bonding.

[0046] 6. Comparative Example 6 (wear-resistant agent lacking MoS2): coefficient of friction 0.21, wear loss 2.0, wear increase per 100,000 cycles 4.2, all inferior to Example 1 (0.16 / 1.2 / 2.1). This proves that MoS2 is indispensable in wear-resistant systems.

[0047] 7. Comparative Example 7 (wear-resistant agent lacking silicone): coefficient of friction 0.19, wear loss 1.6, increase per 100,000 cycles 3.0, still inferior to Example 1. This proves that silicone has a significant effect on improving the dispersion of PTFE.

[0048] Summary of synergistic effects: Examples 1-3 simultaneously contain ternary wear-resistant compound, binary low warpage compound, silane treatment and stabilization system, and their performance is comprehensively superior to any comparative example lacking a certain component. Moreover, the overall effect far exceeds simple superposition, and it has unexpected synergistic properties.

[0049] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A modified polyoxymethylene composite material, characterized in that, The product comprises, by weight, the following components: 100 parts POM resin, 8-20 parts composite self-lubricating wear-resistant agent, 15-30 parts composite low-warpage dimensional stabilizer, 0.5-1.2 parts processing stabilizing system, and 0.2-0.5 parts lubricant; The composite self-lubricating wear-resistant agent is composed of 6-15 parts of polytetrafluoroethylene micro powder, 1-3 parts of organosilicon masterbatch and 1-3 parts of molybdenum disulfide. The composite low-warpage size stabilizer is composed of 10-22 parts of solid glass microspheres and 5-10 parts of talc powder; The processing stabilization system consists of 0.2 to 0.5 parts of formaldehyde absorbent and 0.3 to 0.7 parts of composite antioxidant.

2. The modified polyoxymethylene composite material according to claim 1, characterized in that: It also includes at least one of the following components: 0.1 to 0.5 parts of anti-hydrolysis agent, 0.2 to 0.6 parts of light stabilizer, and 0.1 to 1.0 parts of colorant.

3. The modified polyoxymethylene composite material according to claim 1, characterized in that: The composite antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:

1.

4. The modified polyoxymethylene composite material according to claim 1, characterized in that: The polytetrafluoroethylene micro powder has a particle size of 500 mesh, the silicone masterbatch has a silicon content of 30%, the molybdenum disulfide has a particle size of 2000 mesh, the solid glass microspheres have a particle size of 10 μm, and the talc powder has a particle size of 2500 mesh.

5. The modified polyoxymethylene composite material according to claim 1, characterized in that: The solid glass microspheres and talc powder are surface activated by silane coupling agent KH550, and the amount of coupling agent is 0.5% to 1.2% of the total mass of the filler.

6. The modified polyoxymethylene composite material according to claim 1, characterized in that: The lubricant is calcium stearate or zinc stearate.

7. A method for preparing the modified polyoxymethylene composite material as described in claims 1-6, characterized in that: Includes the following steps: S1. Raw material pretreatment: Solid glass microspheres, talc powder and silane coupling agent KH550 are mixed in a high-speed mixer and then dried for later use; S2. Premixing: Polytetrafluoroethylene micro powder is premixed with silicone masterbatch to form a wear-resistant agent premix; S3. Main mixing: Add the copolymerized polyoxymethylene resin, pretreated filler, wear-resistant premix, molybdenum disulfide, processing stabilizer, lubricant and other additives to a high-speed mixer and mix evenly; S4. Extrusion granulation: The mixture is added to a twin-screw extruder for melt extrusion, followed by water cooling, pelletizing, drying, and annealing to obtain the finished product; S5. Injection molding: Injecting finished granules into the required parts.

8. The method for preparing a modified polyoxymethylene composite material according to claim 7, characterized in that: In step S4, the temperatures of each zone of the extruder are as follows: Zone 1 175℃, Zone 2 190℃, Zone 3 195℃, Zone 4 195℃, Zone 5 195℃, Zone 6 185℃, Zone 7 180℃, Zone 8 180℃, Zone 9 180℃, Zone 10 185℃, and the die head 195℃. The screw speed is 300~400rpm, and the vacuum degree is -0.08~-0.10MPa.

9. The method for preparing a modified polyoxymethylene composite material according to claim 7, characterized in that: The annealing conditions in step S4 are: holding at 90℃ for 1 hour, and then naturally cooling to room temperature.

10. The method for preparing a modified polyoxymethylene composite material according to claim 7, characterized in that: The mixing conditions in step S1 are: 300 rpm, stirring at room temperature for 20 min; and drying conditions are drying in an 80℃ oven for 2 h.

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