Preparation method of double-layer antibacterial polyvinyl chloride composite pipe

Abstract

The invention discloses a preparation method of a double-layer antibacterial polyvinyl chloride composite pipe. The preparation method comprises the following steps: S1, mixing inner-layer antibacterial materials: (1) putting 55% of PVC resin, 27.5% of calcium carbonate, 4.4% of a stabilizer, 3% of CPE and 1.2% of a composite lubricant into a hot mixing machine for hot mixing to 80 DEG C; (2) adding 8.3% of a plasticizer and 0.6% of an antibacterial agent, and continuously carrying out hot mixing to 120 DEG C; (3) transferring the materials to a cold mixer for cold mixing to 60 DEG C to obtain an inner-layer antibacterial material mixture; s2, preparation of inner-layer antibacterial particles: feeding the inner-layer antibacterial material mixture obtained in the S1 into a granulator for granulation to obtain the inner-layer antibacterial particles; and S3, double-layer co-extrusion molding: respectively adding the inner-layer antibacterial particles prepared in the S2 and the outer-layer PVC-U base material into corresponding charging barrels of a co-extruder for extrusion molding to obtain the composite pipe. The invention provides a preparation method of a double-layer antibacterial polyvinyl chloride composite pipe.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plastic pipe manufacturing equipment, more particularly to a preparation method of a double-layer antibacterial polyvinyl chloride composite pipe. BACKGROUND

[0002] Polyvinyl chloride (PVC) pipes are widely used in building water supply and drainage, industrial fluid transportation and other fields due to their low cost, corrosion resistance and excellent processing performance. However, the inner wall of traditional PVC pipes is prone to bacterial and mold growth, forming biofilms, which not only affects the hygiene and safety of the transported medium, but also may shorten the service life of the pipes due to biological corrosion.

[0003] Existing antibacterial PVC pipes are mostly prepared by adding antibacterial agents throughout the pipe, which can achieve antibacterial effect, but the large amount of antibacterial agents used significantly increases the cost of the pipes, and the excessive addition of antibacterial agents in the outer layer that does not need to directly contact the transported medium is a waste of resources. Moreover, in the production of composite pipes (especially multi-layer co-extrusion composite pipes), the introduction of antibacterial agents often leads to a decrease in interlayer peeling strength, which is essentially due to the "incompatibility" between the properties of antibacterial agents and the interlayer bonding mechanism of composite pipes. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a preparation method of a double-layer antibacterial polyvinyl chloride composite pipe, which solves the problems of high cost, low utilization rate of antibacterial agents and poor interlayer bonding of traditional antibacterial PVC pipes.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solution: a preparation method of a double-layer antibacterial polyvinyl chloride composite pipe, comprising the following steps: S1: mixing of inner-layer antibacterial material: ① 55% of PVC resin, 27.5% of calcium carbonate, 4.4% of stabilizer, 3% of CPE, and 1.2% of composite lubricant are added into a hot mixer and mixed at 80℃; ② 8.3% of plasticizer and 0.6% of antibacterial agent are added and continue to mix at 120℃; ③ the material is transferred to a cold mixer and mixed at 60℃ to obtain an inner-layer antibacterial material mixture; S2: preparation of inner-layer antibacterial particles: the inner-layer antibacterial material mixture obtained in S1 is sent to a granulator for granulation to prepare inner-layer antibacterial particles; S3: double-layer co-extrusion molding: the inner-layer antibacterial particles prepared in S2 and the outer-layer PVC-U base material are added into corresponding barrels of a co-extrusion machine for extrusion molding to obtain a composite pipe.

[0006] The present application further provides that the composite pipe comprises an outer layer and an inner layer, the outer layer is formed by solidification of the outer-layer PVC-U base material, and the wall thickness of the outer layer accounts for 87.5% of the wall thickness of the composite pipe; the inner layer is formed by solidification of the inner-layer antibacterial particles, and the wall thickness of the inner layer accounts for 12.5% of the wall thickness of the composite pipe.

[0007] The composite lubricant is composed of silane coupling agent and polyethylene wax, and the mass ratio of the silane coupling agent to the polyethylene wax is 1:1 to 3:1.

[0008] The melting temperature of the inner layer antibacterial material is controlled to be 160-180 DEG C in the S3 co-extrusion process, and the melting temperature of the outer layer PVC-U base material is 170-190 DEG C.

[0009] The calcium carbonate is light calcium carbonate, the PVC type resin is PVC-5 resin, the antibacterial agent is nano-silver antibacterial agent or quaternary ammonium salt antibacterial agent, the stabilizer is calcium-zinc composite stabilizer, and the plasticizer is dioctyl phthalate.

[0010] The co-extrusion equipment includes a co-extrusion die, the co-extrusion die includes a first die sleeve, a second die sleeve and a die rod, the die rod is inserted into the second die sleeve, the second die sleeve is inserted into the first die sleeve, a gap cavity is formed between the first die sleeve and the second die sleeve, the gap cavity flows with the outer layer PVC-U base material melt, a cavity is formed between the second die sleeve and the die rod, the cavity flows with the inner layer antibacterial particle melt, the die rod includes a sizing portion, a sizing cavity is formed between the sizing portion and the first die sleeve, the melt in the cavity and the gap cavity converges in the sizing cavity, the outer wall of the second die sleeve is provided with a first protrusion, and the first protrusion is uniformly distributed with a plurality of first protrusions along the circumference of the second die sleeve.

[0011] The first protrusion includes a second inclined portion, the second inclined portion gradually inclines to the side close to the axis of the second die sleeve along the melt flow direction in the gap cavity, the second die sleeve is provided with a first groove, the first groove penetrates the second inclined portion along the radial direction of the second die sleeve, and the two ends of the first groove are communicated with the cavity and the gap cavity respectively.

[0012] The first protrusion further includes a third inclined portion, the third inclined portion is connected to the inclined end of the second inclined portion towards the axis of the second die sleeve, and the third inclined portion gradually inclines to the side away from the axis of the second die sleeve along the melt flow direction in the gap cavity.

[0013] The outer wall of the first protrusion is provided with a second protrusion, the second protrusion is located on both sides of the third inclined portion, and the length direction of the second protrusion is along the axial direction of the first protrusion.

[0014] The first protrusion further includes a fourth inclined portion, the fourth inclined portion gradually inclines to the side close to the axis of the second die sleeve along the melt flow direction in the gap cavity, the fourth inclined portion is connected to the side away from the second inclined portion of the third inclined portion, the second die sleeve is provided with a second groove, the second groove penetrates the second inclined portion along the radial direction of the second die sleeve, and the two ends of the second groove are communicated with the cavity and the gap cavity respectively.

[0015] In summary, the present application has the following beneficial effects:

[0016] 1. The inner layer is added with antibacterial agent, directly contacts with conveying medium, has high antibacterial rate, effectively inhibits the growth of common bacteria such as escherichia coli and staphylococcus aureus, and guarantees the health and safety of the conveying medium. The antibacterial agent is only added in the inner layer, the outer layer adopts conventional PVC-U base material, the amount of antibacterial agent is small, compared with the whole antibacterial pipeline, the cost is reduced, and economy and practicability are combined. The outer layer accounts for 87.5% of the total wall thickness, high-strength PVC-U base material is adopted, the pipeline has good compression resistance and impact resistance, and meets the standard requirements of GB / T 10002.1-2006; the inner layer is added with CPE impact modifier, and the comprehensive mechanical properties of the pipeline are further improved.

[0017] 2. In the co-extrusion process, the first convex body is arranged in the second die sleeve, so that the inner wall of the outer layer forms a groove in the outer layer forming process, the subsequent inner layer melt enters the gap cavity through the first groove body, and then enters the groove in the inner wall of the outer layer and forms the inner layer protruding part. The inner side protruding part and the outer layer groove form an interlocking structure, improve the bonding force, thereby solving the problem of the decrease of interlayer peeling strength caused by the introduction of the antibacterial agent, and improving the bonding strength between the antibacterial layer and the PVC layer. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a sectional view of the embodiment;

[0019] Figure 2 is Figure 1 is an enlarged view of A in the middle;

[0020] Figure 3 is Figure 1 is a sectional view of M-M in the middle;

[0021] Figure 4 is Figure 3 is an enlarged view of B in the middle;

[0022] Figure 5 is Figure 1 is a sectional view of N-N in the middle;

[0023] Figure 6 is Figure 5 is an enlarged view of C in the middle;

[0024] Figure 7 is a sectional view of the composite in the embodiment;

[0025] Figure 8 is Figure 7 is an enlarged view of D in the middle.

[0026] : first die sleeve 1, second die sleeve 2, feeding cavity 21, feeding hole 22, guide ring 23, tapered surface 231, first convex body 24, first inclined part 241, first straight part 242, second inclined part 243, third inclined part 244, second straight part 245, fourth inclined part 246, first groove body 247, second groove body 248, arc surface 249, end part 2491, second convex body 250, die rod 3, fixing ring 31, hole 311, guide part 32, sizing part 33, cavity 4, gap cavity 5, sizing cavity 6, composite pipe 7, outer layer 71, recess 711, inner layer 72, protruding part 721. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0028] The embodiment discloses a preparation method of a double-layer antibacterial polyvinyl chloride composite pipe, and the specific method is as follows:

[0029] Step S1: mixing of inner-layer antibacterial material.

[0030] In this step, the uniform dispersion of components is realized by a step-by-step hot mixing-cold mixing process, and the agglomeration of antibacterial agents is avoided. The specific operation is as follows:

[0031] ①According to the mass percentage, 55% of PVC type resin, 27.5% of calcium carbonate, 4.4% of stabilizer, 3% of CPE (chlorinated polyethylene), and 1.2% of composite lubricant are put into a hot mixer, the hot mixer is started, the rotating speed is controlled to be 800-1000 r / min, and the material temperature is heated to 80℃. Among them, the PVC type resin selects PVC-5 resin, which has good processing fluidity and mechanical strength; the calcium carbonate is light calcium carbonate, which can improve the rigidity and dimensional stability of the inner-layer material; the stabilizer is a calcium-zinc composite stabilizer, which is environmentally friendly and free of heavy metals, and can effectively inhibit the degradation of PVC resin during high-temperature processing; the CPE serves as an impact modifier, which can improve the toughness of the inner-layer material and avoid pipe brittle fracture at low temperature; the composite lubricant is composed of silane coupling agent and polyethylene wax in a mass ratio of 1:1 to 3:1, the silane coupling agent can enhance the interfacial bonding force between inorganic fillers and organic resins, and the polyethylene wax can reduce the friction between the material and the equipment and improve the processing fluidity.

[0032] ② Add 8.3% plasticizer and 0.6% antibacterial agent into the hot mixer, and continue to mix until the material temperature reaches 120°C. At this time, the plasticizer fully penetrates into the PVC resin particles, and the antibacterial agent is uniformly dispersed in the melt. The plasticizer selected is dioctyl phthalate (DOP), which has high plasticizing efficiency and good compatibility with PVC. The antibacterial agent selected is nano-silver antibacterial agent or quaternary ammonium salt antibacterial agent. The nano-silver antibacterial agent achieves antibacterial effect by destroying the bacterial cell membrane through metal ions, and the quaternary ammonium salt antibacterial agent inhibits bacterial reproduction through cation adsorption. Both have the characteristics of wide antibacterial range and good durability.

[0033] ③ Rapidly transfer the hot-mixed material to the cold mixer, control the rotation speed of the cold mixer to be 600-800 r / min, and cool-mix until the material temperature drops to 60°C to obtain the inner layer antibacterial material mixture. The cooling process can avoid the failure of stabilizers caused by residual heat, and at the same time, it can reduce the material temperature, preparing for the subsequent granulation process.

[0034] Step S2: Preparation of inner layer antibacterial particles.

[0035] The inner layer antibacterial material mixture obtained in S1 is fed into a double-screw granulator, and the temperature of each section of the granulator is controlled to be 140-170°C, and the screw rotation speed is controlled to be 150-200 r / min. After melting, shearing, extruding and granulating, inner layer antibacterial particles with uniform particle size are prepared. The granulation process can improve the processing stability of the material and avoid the problem of uneven feeding during direct extrusion.

[0036] Step S3: Double-layer co-extrusion molding

[0037] The inner layer antibacterial particles prepared in S2 are added to the inner layer barrel of the co-extrusion machine, and the outer layer PVC-U substrate is added to the outer layer barrel of the co-extrusion machine. The melting temperature of the inner layer antibacterial material is controlled to be 160-180°C, and the melting temperature of the outer layer PVC-U substrate is controlled to be 170-190°C. The two layers of molten material enter the co-extrusion die through the corresponding flow channels, and after converging and compounding in the die cavity, cooling, sizing, pulling and cutting, a double-layer antibacterial polyvinyl chloride composite pipe (i.e. composite pipe 7 in Figure 1 ) that meets the specifications is obtained. As shown in Figure 7 , the composite pipe 7 includes an outer layer 71 and an inner layer 72 radially inside the outer layer 71. The outer layer 71 is formed by solidifying the outer layer PVC-U substrate, and its wall thickness accounts for 87.5% of the wall thickness of the composite pipe 7. The inner layer 72 is formed by solidifying the inner layer antibacterial particles, and its wall thickness accounts for 12.5% of the wall thickness of the composite pipe 7.

[0038] The introduction of antibacterial agents often leads to problems such as decreased interlayer peel strength and interface cracking. This is mainly because if the particle size of the antibacterial agent is much larger than the molecular chain spacing (nanoscale) of the composite pipe substrate, a "rigid particle barrier layer" will form at the interlayer interface. The molecular chains of adjacent layers cannot penetrate the antibacterial agent particles to achieve entanglement, resulting in tiny gaps at the interface. The interlayer bonding force decreases from "molecular-level adhesion" to "mechanical interlocking," making peeling more likely. Therefore, if... Figures 1-8 As shown, the co-extrusion molding equipment used in the above process includes a co-extrusion die to solve the problem of interlayer bonding force.

[0039] like Figure 1 As shown, the co-extrusion die includes a first die sleeve 1, a second die sleeve 2, and a die rod 3. Both the first die sleeve 1 and the second die sleeve 2 are cylindrical structures. The die rod 3 is inserted into the second die sleeve 2, and the second die sleeve 2 is inserted into the first die sleeve 1. The outer wall of the left end of the second die sleeve 2 is fixedly connected to the inner wall of the first die sleeve 1. A gap cavity 5 is formed between the first die sleeve 1 and the second die sleeve 2, through which the outer PVC-U substrate melt flows. The left end of the second die sleeve 2 is provided with a feed hole 22, which communicates with the gap cavity 5. Figure 1 The medium-sized molten material flows from left to right.

[0040] like Figure 1 As shown, a cavity 4 is formed between the second mold sleeve 2 and the mold rod 3. The cavity 4 is through which the inner layer of antibacterial granules melt flows. The left end of the mold rod 3 is provided with a fixing ring 31. The outer wall of the fixing ring 31 is fixedly connected to the inner wall of the second mold sleeve 2. The second mold sleeve 2 is provided with a feeding cavity 21. The fixing ring 31 is provided with a channel 311. The feeding cavity 21 is used to pass the inner layer of antibacterial granules melt through the channel 311 into the cavity 4.

[0041] like Figure 1 As shown, the die rod 3 has a rod-shaped structure, including a guide portion 32 and a sizing portion 33. The right end of the second die sleeve 2 has a guide opening, through which the guide portion 32 passes. The sizing portion 33 is located on the side of the die rod 3 away from the second die sleeve 2. A shaping cavity 6 is formed between the sizing portion 33 and the first die sleeve 1. The molten material in the cavity 4 and the gap cavity 5 converges in the shaping cavity 6 to form Figure 7 The composite tube 7 shown.

[0042] Combination Figures 1-4 The outer wall of the second mold sleeve 2 is provided with a first protrusion 24. The first protrusion 24 protrudes outward radially along the outer wall of the second mold sleeve 2 to form a strip-shaped structure. The length direction of the first protrusion 24 is parallel to the axial direction of the second mold sleeve 2. Four first protrusions 24 are evenly distributed along the circumference of the second mold sleeve 2.

[0043] like Figure 2As shown, the first protrusion 24 includes a second inclined portion 243. The second inclined portion 243 gradually inclines towards the axis of the second mold sleeve 2 along the direction of molten material flow within the gap cavity 5. The second mold sleeve 2 is provided with a first groove 247, which corresponds to the second inclined portion 243. The first groove 247 passes radially through the second inclined portion 243 of the second mold sleeve 2, and its two ends connect to the cavity 4 and the gap cavity 5, respectively. Figure 2 , Figure 8 By setting the first protrusion 24, a groove 711 is formed on the inner wall of the outer layer 71, allowing the molten material of the subsequent inner layer 72 to enter the gap cavity 5 through the first groove 247, thereby entering the groove 711 and forming a protrusion 721. The protrusion 721 and the groove 711 form an interlocking structure, improving the bonding force. Specifically, as... Figure 4 As shown, the wall surfaces at both ends of the second inclined portion 243 along the circumferential direction of the second mold sleeve 2 are arc surfaces 249. The arc surface 249 includes two ends 2491, one end 2491 is located on the side close to the axis of the second mold sleeve 2, and the other end 2491 is located on the side away from the axis of the second mold sleeve 2, so that the groove 711 formed by the outer layer 71 can interlock with the protrusion 721, thereby improving the bonding force.

[0044] like Figure 2 As shown, the second mold sleeve 2 includes a guide ring 23 located on the left side. The guide ring 23 has a conical surface 231 to guide the molten material into the gap cavity 5. The left end of the first protrusion 24 has a first inclined portion 241. The first protrusion 24 includes a first straight portion 242. The first inclined portion 241 connects the conical surface 231 and the first straight portion 242 to form a smooth transition. The arrangement of the first straight portion 242 causes the outer layer 71 molten material to form a groove 711 when it passes through. As the second inclined portion 243 gradually contracts, the inner layer 72 molten material enters the groove 711 through the first groove 247.

[0045] like Figure 2 As shown, as a further configuration, the first protrusion 24 also includes a third inclined portion 244, which is connected to the second inclined portion 243 at its inclined end in the axial direction of the second mold sleeve 2. The third inclined portion 244 gradually inclines away from the axial direction of the second mold sleeve 2 along the flow direction of the molten material in the gap cavity 5. The first protrusion 24 also includes a second straight portion 245 located to the right of the third inclined portion 244. As the molten material passes through the third inclined portion 244 and the second straight portion 245, it is subjected to radial outward compression along the second mold sleeve 2, causing the molten material of the inner layer 72 to be compacted in the groove 711, reducing the gap, so as to better form an interlocking structure. At the same time, as Figure 8 , Figure 6As shown, the outer wall of the first protrusion 24 is provided with a second protrusion 250, which protrudes radially outward along the outer wall of the first protrusion 24. The second protrusion 250 is located on both sides of the third inclined portion 244, and its length direction is along the axial direction of the first protrusion 24. During the compaction process of the molten material in the inner layer 72 within the groove 711, the second protrusion 250 simultaneously compresses the molten material, and the auxiliary protrusion 721 and the groove 711 form an interlocking structure.

[0046] like Figure 2 As shown, the first protrusion 24 also includes a fourth inclined portion 246. The fourth inclined portion 246 gradually tilts towards the side closer to the axis of the second mold sleeve 2 along the direction of molten material flow in the gap cavity 5. The fourth inclined portion 246 is connected to the side of the third inclined portion 244 away from the second inclined portion 243. The second mold sleeve 2 is provided with a second groove 248. The second groove 248 passes through the second inclined portion 243 radially along the second mold sleeve 2. The two ends of the second groove 248 are respectively connected to the cavity 4 and the gap cavity 5. The function of the fourth inclined portion 246 is the same as that of the second inclined portion 243, and will not be described again.

[0047] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer antibacterial polyvinyl chloride composite pipe, characterized in that, Includes the following steps: S1: Inner layer antibacterial material mixture: ① By weight percentage, add 55% PVC type resin, 27.5% calcium carbonate, 4.4% stabilizer, 3% CPE, and 1.2% composite lubricant into a hot mixer and heat mix to 80℃. ② Add 8.3% plasticizer and 0.6% antibacterial agent, and continue hot mixing to 120℃; ③ Transfer the materials to a cold mixer and cold mix at 60°C to obtain an inner layer antibacterial material mixture; S2: Preparation of inner layer antibacterial particles: The mixture of inner antibacterial materials obtained in S1 is fed into a granulator for granulation to obtain inner antibacterial granules. S3: Double-layer co-extrusion molding: The inner antibacterial granules obtained from S2 and the outer PVC-U substrate are respectively added to the corresponding barrels of a co-extruder for extrusion molding to obtain a composite pipe (7).

2. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 1, characterized in that, The composite pipe (7) includes an outer layer (71) and an inner layer (72). The outer layer (71) is formed by curing the outer PVC-U substrate and its wall thickness accounts for 87.5% of the wall thickness of the composite pipe (7). The inner layer (72) is formed by curing the inner antibacterial particles and its wall thickness accounts for 12.5% ​​of the wall thickness of the composite pipe (7).

3. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 1, characterized in that, The composite lubricant is composed of a silane coupling agent and a polyethylene wax, wherein the mass ratio of the silane coupling agent to the polyethylene wax is 1:1 to 3:

1.

4. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 1, characterized in that, During the S3 co-extrusion molding process, the melting temperature of the inner antibacterial material is controlled at 160-180℃, and the melting temperature of the outer PVC-U substrate is controlled at 170-190℃.

5. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 1, characterized in that, The calcium carbonate is light calcium carbonate, the PVC-type resin is PVC-5 resin, the antibacterial agent is nano-silver antibacterial agent or quaternary ammonium salt antibacterial agent, the stabilizer is calcium-zinc composite stabilizer, and the plasticizer is dioctyl phthalate.

6. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 1, using a co-extrusion molding equipment, wherein the co-extrusion molding equipment includes a co-extrusion die, characterized in that, The co-extrusion die includes a first die sleeve (1), a second die sleeve (2), and a die rod (3). The die rod (3) is inserted into the second die sleeve (2), and the second die sleeve (2) is inserted into the first die sleeve (1). A gap cavity (5) is formed between the first die sleeve (1) and the second die sleeve (2). The gap cavity (5) is through which the outer layer PVC-U substrate melt flows. A cavity (4) is formed between the second die sleeve (2) and the die rod (3). The cavity (4) is through which the inner layer antibacterial particle melt flows. The die rod (3) includes a sizing part (33). A shaping cavity (6) is formed between the sizing part (33) and the first die sleeve (1). The melt in the cavity (4) and the gap cavity (5) converge in the shaping cavity (6). The outer wall of the second die sleeve (2) is provided with a first protrusion (24). Multiple first protrusions (24) are evenly distributed along the circumference of the second die sleeve (2).

7. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 6, characterized in that, The first protrusion (24) includes a second inclined portion (243), which gradually tilts towards the side closer to the axis of the second mold sleeve (2) along the flow direction of the molten material in the gap cavity (5). The second mold sleeve (2) is provided with a first groove (247), which penetrates the second inclined portion (243) radially along the second mold sleeve (2). The two ends of the first groove (247) are respectively connected to the cavity (4) and the gap cavity (5).

8. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 7, characterized in that, The first protrusion (24) further includes a third inclined portion (244), which is connected to the second inclined portion (243) at its inclined end in the axial direction of the second mold (2). The third inclined portion (244) gradually inclines away from the axial direction of the second mold (2) along the flow direction of the molten material in the gap cavity (5).

9. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 8, characterized in that, The outer wall of the first protrusion (24) is provided with a second protrusion (250), the second protrusion (250) is located on both sides of the third inclined portion (244), and the length direction of the second protrusion (250) is along the axial direction of the first protrusion (24).

10. The method for preparing a double-layer antibacterial polyvinyl chloride composite pipe according to claim 8, characterized in that, The first protrusion (24) further includes a fourth inclined portion (246), which is inclined towards the side closer to the axis of the second mold sleeve (2) along the flow direction of the molten material in the gap cavity (5). The fourth inclined portion (246) is connected to the side of the third inclined portion (244) away from the second inclined portion (243). The second mold sleeve (2) is provided with a second groove (248), which passes through the second inclined portion (243) radially along the second mold sleeve (2). The two ends of the second groove (248) are respectively connected to the cavity (4) and the gap cavity (5).

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