Preparation method and application of polypropylene for preparing corrugated pipe

Abstract

The invention belongs to the technical field of corrugated pipes for wire harness protection, and particularly relates to a preparation method and application of polypropylene for preparing a corrugated pipe. The preparation method comprises the following steps: mixing ultra-low melt index polypropylene, a PP halogen-free flame retardant, an antioxidant and a lubricant, and putting the mixture into a twin-screw extruder, wherein the MFR of the ultra-low melt index polypropylene is less than or equal to 0.5 g / 10min; the extrusion temperature of the double-screw extruder is 210 DEG C or below, and the screw rotation speed is 220-260 rpm. The corrugated pipe prepared by the technical scheme provided by the invention is environment-friendly and halogen-free, and accords with RoHS (Room of Hazardous Substances) instructions; by optimizing the combined distribution of the screws of the double-screw extruder, the problem that the additive is easy to agglomerate in the processing process of the low-melt-index polypropylene is solved, the stability of melt extrusion is ensured, and the double-screw extruder is particularly suitable for molding of complex corrugated pipes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of corrugated pipes for harness protection, and particularly relates to a preparation method and application of polypropylene for preparing corrugated pipes. BACKGROUND

[0002] Currently, the corrugated pipe materials for harness protection mainly adopt polyvinyl chloride (PVC), polyethylene (PE) or polyamide (PA), and the above materials have some defects or shortcomings: PVC: poor environmental protection, easy to decompose at high temperature; PE: not flame-retardant, insufficient mechanical strength; PA: high cost, and some models do not meet the flame-retardant performance standard.

[0003] In order to solve the problems of flame-retardant, environmental protection and high temperature resistance of the corrugated pipe, the industry selects flame-retardant polypropylene (PP), but the flame retardant in the current flame-retardant PP is generally halogen-based flame retardant (such as bromine-based), which has good flame-retardant effect but does not meet the environmental protection requirements; if a halogen-free flame retardant is used, a high addition amount is required, thereby causing the mechanical performance to decrease and causing the problem of being unable to be practically applied.

[0004] The processing of the corrugated pipe, especially the corrugated pipe with a complex structure, requires that the processing of the material has good stability and uniformity, otherwise the problems of cracking and decreased comprehensive performance will be caused. In order to meet the mechanical performance requirements of the corrugated pipe and meet the V2 flame-retardant condition under the condition of halogen-free environmental protection, an ultra-low melt index PP material is used as a base material.

[0005] The ultra-low melt index material generally refers to a material with a melt flow rate (MFR) of 0.5 g / min or less, which is mainly used for manufacturing materials that need high strength, high toughness, weight bearing and pressure resistance. Compared with ordinary polypropylene, the ultra-low melt index material has higher melt strength and impact strength, which can partially improve the above-mentioned problem of decreased mechanical performance and meet the processing requirements of the corrugated pipe material. SUMMARY

[0006] The application provides a preparation method and application of polypropylene for preparing a corrugated pipe, to solve the technical problem that the flame retardant is easy to agglomerate when the polypropylene is melt extruded under the condition that the mechanical and flame-retardant performances are met at the same time with a low addition amount of flame retardant.

[0007] To solve the above technical problem, the application provides a preparation method of polypropylene for preparing a corrugated pipe, which comprises the following steps: mixing an ultra-low melt index polypropylene, a PP halogen-free flame retardant, an antioxidant and a lubricant, and then putting them into a double-screw extruder, wherein the MFR of the ultra-low melt index polypropylene is less than or equal to 0.5 g / 10 min; the extrusion temperature of the double-screw extruder is 180-210 DEG C, and the screw rotation speed is 220-260 rpm.

[0008] The process selects an ultra-low flow PP base material, and avoids degradation of PP molecular chain and flame retardant through low-temperature extrusion (≤210℃). Low rotation speed reduces shear heat and improves process stability, ensuring low melt index of the material. At the same time, the higher residence time brought by low rotation speed also enables the material to be more fully melted and mixed.

[0009] Optionally, the twin-screw extruder shear zone comprises, from front to back, a first shear section, a first vacuum port, a second shear section, a second vacuum port, and a third shear section.

[0010] First, through two strong shearing and two negative pressure vacuum exhaust, the volatile components are fully removed, and then a round of strong shearing is performed to improve the dispersion of each component, especially the flame retardant, so as to reduce the use amount of the flame retardant.

[0011] Optionally, the melt is compressed before the first vacuum port.

[0012] The compressed melt is more conducive to the precipitation of low molecular substances, and at the same time, under the condition of vacuum negative pressure, the residual monomers, moisture and other reaction byproducts are effectively extracted. The first shear section and the first vacuum port are the main volatile component removal stage. The second shear section and the second vacuum port are the auxiliary volatile component removal stage.

[0013] Optionally, the melt index fluctuation of the twin-screw extruder shear process is controlled to be <±0.5 g / 10 min.

[0014] Optionally, the screw combination of the first shear section is 40 / 40 / 5R, 40 / 40 / 5R and 40 / 40 / 5N in turn.

[0015] The specific meaning of the screw combination represents the lead (mm) / pitch (mm) / helix angle (°), R represents right-handed meshing block, N represents neutral meshing block, and L represents left-handed meshing block.

[0016] The 5° meshing block performs strong shearing, and the meshing block with a small angle provides high shear force and good dispersion and mixing effect, can completely break the solid bed, make the polymer completely melt, and preliminarily melt the filler added at the beginning. The 5° neutral meshing block at the end plays a role in buffering and redistributing the material.

[0017] Optionally, the screw combination of the second shear section is 40 / 40 / 5R and 40 / 40 / 5L in turn.

[0018] The second strong shearing section uses left-handed 5° meshing block to resist material forward conveying and form melt seal to prevent the vacuum degree of the vacuum port from being affected. At the same time, strong backflow and distribution mixing make the material dispersion more uniform.

[0019] Optionally, the screw combination of the third shearing section is 40 / 40 / 5R, 40 / 40 / 5N, 20 / 40 / 20, 40 / 40 / 5R, 40 / 40 / 5N and 40 / 40 / 5L in sequence.

[0020] By reasonable design of screw combination distribution, good dispersion state of components is ensured.

[0021] Optionally, the PP halogen-free flame retardant is a phosphorus-nitrogen synergistic intumescent flame retardant.

[0022] The phosphorus-nitrogen synergistic flame retardant has a small particle size, and the phosphoric acid group is easy to absorb water and has strong polarity, so the compatibility with PP is poor, and therefore the phosphorus-nitrogen synergistic flame retardant is very easy to agglomerate in the PP material, resulting in a decrease in mechanical properties and flame retardant properties of the material.

[0023] Optionally, the ultra-low melt index polypropylene is dried at 75-90 DEG C for 1.5-3 hours before being mixed with the PP halogen-free flame retardant.

[0024] Optionally, the feeding ratio of each component is as follows in terms of weight parts:

[0025] Ultra-low melt index polypropylene 96-97 parts

[0026] PP halogen-free flame retardant 3-4 parts

[0027] Antioxidant 0.5-1 part

[0028] Lubricant 0.5-1 part.

[0029] Optionally, the antioxidant is antioxidant 1010 and / or antioxidant 168.

[0030] Optionally, the lubricant is oleic acid amide and / or EBS (ethylene bis stearamide).

[0031] Optionally, the twin-screw extruder comprises a feeding section, a first compression section, an exhaust hole, a first shearing section, a first conveying section, a second compression section, a first vacuum port, a second shearing section, a second conveying section, a second vacuum port, a third shearing section, a third conveying section, a third compression section and extrusion in sequence.

[0032] The application further provides a corrugated pipe obtained by the preparation method of the polypropylene corrugated pipe.

[0033] The corrugated pipe prepared by the technical scheme provided by the application is environmentally friendly and halogen-free, and meets the RoHS directive; by optimizing the screw combination distribution of the twin-screw extruder, the problem of easy agglomeration of additives in the processing of low melt index polypropylene is solved, and the stability of melt extrusion is ensured, and the corrugated pipe is particularly suitable for complex corrugated pipe forming. DETAILED DESCRIPTION

[0034] For the convenience of understanding, the preparation method of the polypropylene for preparing the corrugated pipe is described below in combination with the examples, and it should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application.

[0035] Example 1

[0036] The polypropylene for preparing the corrugated pipe comprises the following components by weight parts:

[0037] ultra-low melt index polypropylene 96-97 parts

[0038] PP halogen-free flame retardant 3-4 parts

[0039] antioxidant 0.5-1 part

[0040] lubricant 0.5-1 part.

[0041] The ultra-low melt index polypropylene is M710 (GS Caltex), MFR≤0.5g / 10min, the PP halogen-free flame retardant is a phosphorus-nitrogen synergistic intumescent flame retardant, specifically Sutao Sutao EP704A, the antioxidant is antioxidant 1010, and the lubricant is EBS.

[0042] The ultra-low melt index polypropylene is first dried at 85°C for 2 hours, and then the ultra-low melt index polypropylene, the PP halogen-free flame retardant, the antioxidant, and the lubricant are mixed and fed into a twin-screw extruder; the extrusion temperature of the twin-screw extruder is 180-210°C, and the screw rotation speed is 250 rpm. The melt index fluctuation of the twin-screw extruder during the shearing process is controlled to be <±0.5g / 10min.

[0043] The screw combination distribution of the twin-screw extruder is shown in Table 1.

[0044] Table 1

[0045]

[0046]

[0047] Comparative Example 1

[0048] The difference from the example is that the 19-31 section is removed from the screw combination distribution, that is, there is no second vacuum port, third shear section, and third conveying section.

[0049] Comparative Example 2

[0050] The difference from the example is that the rotation speed of the twin-screw extruder is set to 300 rpm.

[0051] Comparative Experiment

[0052] The experimental method and results are shown in Table 2.

[0053] Table 2

[0054]

[0055] Analysis of experimental results

[0056] 1. Compared with the examples, although lower shear can protect the PP molecular chain from being cut, can effectively maintain lower melt index, and higher impact strength, the lack of the third shear section, the uneven dispersion of the flame retardant, affects the flame retardant performance and other physical properties. Therefore, segmented shear must be set to balance the two.

[0057] 2. High speed can increase production, but also increase shear to enhance the dispersion of the flame retardant, but by comparing example 2 with the examples, the speed is only increased to 300 rpm, because the time of melting and dispersion is reduced, the dispersion of the flame retardant is inhibited, in addition, because there must be a high shear at one end to achieve effective dispersion of the flame retardant, therefore, the increase of the speed will bring too high shear heat, so that the flame retardant decomposes and the PP molecular chain breaks, which will lead to the decline of the flame retardant performance and physical properties. Therefore, multiple factors need to be considered and coordinated to obtain the desired technical effect.

[0058] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part or all of the technical features, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing polypropylene for corrugated pipes, characterized in that, The process includes the following steps: mixing ultra-low melt flow index polypropylene, halogen-free flame retardant and antioxidant and lubricant and feeding them into a twin-screw extruder, wherein the MFR of the ultra-low melt flow index polypropylene is ≤0.5g / 10min; the extrusion temperature of the twin-screw extruder is below 210℃ and the screw speed is 220-260rpm.

2. The method for preparing polypropylene for corrugated pipes according to claim 1, characterized in that, The shearing zone of the twin-screw extruder, from front to back, includes a first shearing section, a first vacuum port, a second shearing section, a second vacuum port, and a third shearing section.

3. The method for preparing polypropylene for corrugated pipes according to claim 2, characterized in that, The melt is compressed before the first vacuum port.

4. The method for preparing polypropylene for corrugated pipes according to claim 2, characterized in that, The screw combinations of the first shearing section are 40 / 40 / 5R, 40 / 40 / 5R and 40 / 40 / 5N, respectively.

5. The method for preparing polypropylene for corrugated pipes according to claim 2, characterized in that, The screw assembly of the second shearing section is 40 / 40 / 5R and 40 / 40 / 5L respectively.

6. The method for preparing polypropylene for corrugated pipes according to claim 2, characterized in that, The screw combinations of the third shearing section are 40 / 40 / 5R, 40 / 40 / 5N, 20 / 40 / 20, 40 / 40 / 5R, 40 / 40 / 5N and 40 / 40 / 5L in sequence.

7. The method for preparing polypropylene for corrugated pipes according to claim 2, characterized in that, The PP halogen-free flame retardant is a phosphorus-nitrogen synergistic intumescent flame retardant.

8. The method for preparing polypropylene for corrugated pipes according to claim 2, characterized in that, The ultra-low melt index polypropylene is first dried at 75-90℃ for 1.5-3 hours and then mixed with PP halogen-free flame retardant.

9. The method for preparing polypropylene for corrugated pipes according to claim 1, characterized in that, The proportions of each component by weight are as follows: Ultra-low melt index polypropylene 96-97 parts 3-4 parts of the PP halogen-free flame retardant Antioxidant 0.5-1 part 0.5-1 part lubricant.

10. A corrugated pipe, characterized in that, The polypropylene granules obtained by the polypropylene preparation method for preparing corrugated pipes according to any one of claims 1-9 are used as raw materials and injection molded to obtain the product.

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