Large-diameter thick-wall PVC-O pipe and preparation method thereof

Abstract

The application discloses a large-diameter thick-wall PVC-O pipe and a preparation method thereof, and belongs to the field of pipe processing. The pipe mixing material contains 100 parts of PVC resin, 1.5-1.8 parts of a heat stabilizer, 1.3 parts of a lubricant, 1 part of an anti-aging agent and 10 parts of a filler in terms of weight units; the heat stabilizer is a mixture of organic tin and a sodium salt; the proportion of the organic tin in the heat stabilizer is 1.0-1.2 parts, and the proportion of the sodium salt is 0.4-0.6 parts; in the preparation method, a parallel double-screw extruder is used to extrude the pipe, the heating setting outside the extruder cylinder is not less than 12 heating zones, and a process temperature curve of first climbing and then falling is set to match the mixing material. The sodium salt is introduced into the heat stabilizer of the mixing material, which not only delays the degradation time of the material, effectively prolongs the stabilization time, but also enables the extruded pipe to no longer be decomposed and discolored due to secondary heating, thereby ensuring normal production of the pipe and improving the product performance of the pipe.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipe processing, in particular to a large-diameter thick-wall PVC-O pipe and a preparation method thereof. BACKGROUND

[0002] PVC-U pipe is formed into PVC-O pipe after molecular orientation, and the PVC-U pipe before orientation is called a blank pipe. The wall thickness of traditional PVC-U pipe is thin, for example, the wall thickness of a pipe with an outer diameter of 630 mm is generally 15-24 mm, while the wall thickness of a blank pipe with the same outer diameter is 40-60 mm, which is more than 2.5 times the wall thickness of traditional PVC-U pipe. Since PVC-U material is a poor conductor of heat, the thermal conductivity coefficient is generally in the range of 0.14-0.17 W / (m·K), and the temperature of the blank pipe when leaving the extrusion die is 180-200℃. When the blank pipe cools down, the cooling speed of the core and inner wall of the pipe is slow, and after 30-60 minutes, the inner wall and core of the blank pipe will decompose and discolor, and the pipe wall will crack during the orientation process.

[0003] The effect is not obvious by increasing the amount of existing tin stabilizer. Moreover, the tin stabilizer is in a liquid state, and excessive addition will act as a plasticizer, reducing the Vicat softening temperature and material strength of the pipe. Under this background, a new high-efficiency stabilizer can only be introduced to solve the problem of long-term thermal stability of the blank pipe. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a large-diameter thick-wall PVC-O pipe and a preparation method thereof. A sodium salt is introduced as a heat stabilizer in the mixed material, which cooperates with the organic tin in the heat stabilizer. A parallel double-screw extruder is used to extrude the pipe in the preparation method. The extruder barrel is provided with no less than 12 heating zones, and the process temperature curve of first climbing and then falling is matched with the mixed material to solve the problem of secondary thermal decomposition of the large-diameter (more than 500 mm) thick-wall (more than 40 mm) blank pipe.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0006] A large-diameter thick-wall PVC-O pipe, wherein the mixed material contains, in terms of weight units, 100 parts of PVC resin, 1.5-1.8 parts of heat stabilizer, 1.3 parts of lubricant, 1 part of anti-aging agent, and 10 parts of filler; the heat stabilizer is a mixture of organic tin and sodium salt; the fraction of organic tin in the heat stabilizer is 1.0-1.2 parts, and the fraction of sodium salt is 0.4-0.6 parts.

[0007] Further improvement of the technical scheme of the present application is that the sodium salt comprises sodium perchlorate, sodium hypochlorite, fine calcium carbonate and stearic acid; wherein, sodium perchlorate:sodium hypochlorite = 1:2; the fine calcium carbonate and the stearic acid are carriers of the sodium salt.

[0008] Further improvement of the technical scheme of the present application is that the heat stabilizer comprises 1.0 parts of organic tin and 0.5-0.6 parts of sodium salt.

[0009] Further improvement of the technical scheme of the present application is that the lubricant comprises 0.4 parts of calcium stearate, 0.1 parts of oxidized polyethylene and 0.8 parts of low molecular weight polyethylene; the anti-aging agent is titanium dioxide; and the filler is calcium carbonate.

[0010] A preparation method of a large-diameter thick-wall PVC-O pipe, comprising the following steps:

[0011] Step 1, first preparing a sodium salt, and then physically mixing the organic tin and the sodium salt to obtain a heat stabilizer;

[0012] Step 2, then putting the PVC resin, the lubricant, the anti-aging agent and the filler into a heat mixer in a mixer group, and finally putting the physically mixed heat stabilizer into the heat mixer, and then performing hot mixing and cold mixing, and then transferring the mixed material to a storage bin;

[0013] Step 3, the mixed material in the storage bin is sucked into an extruder hopper through a vacuum suction device at the upper part of a parallel double screw extruder, and the parallel double screw extruder extrudes the pipe material, and the process parameters are selected as follows: the screw diameter of the parallel double screw extruder is not less than 155 mm, the length-diameter ratio L / D of the screw is 36:1, the extruder barrel is provided with not less than 12 heating zones, and the process temperature curve is set to be a curve of first climbing and then falling; the extrusion amount of the blank pipe is 1000 kg / h-1300 kg / h; and the minimum value of the extrusion line speed is not more than 0.10 m / min;

[0014] Step 4, the extruded pipe material is formed after vacuum sizing, first-stage cooling, first-stage traction, secondary heating, orientation expansion, second-stage cooling and second-stage traction;

[0015] Step 5, fixed-length cutting, detection and storage of qualified products.

[0016] Further improvement of the technical scheme of the present application is that in step 1, the preparation process of the sodium salt is as follows:

[0017] S1, using perchlorate and hypochlorite as anions and sodium ions as cations, a mixture of sodium perchlorate and sodium hypochlorite is prepared, wherein the ratio of perchlorate to hypochlorite is 1:2;

[0018] S2, fine calcium carbonate with particle size range of 5-10 mu m 100 parts is heated to 105 DEG C, stearic acid is added in proportion of 3-5 parts, high speed stirring is carried out for 10 minutes, stirring speed is 600 rpm, then it is cooled to below 35 DEG C, then the mixture of sodium perchlorate and sodium hypochlorite prepared in S1 is added in proportion of 3-5 parts, and after mechanical mixing, sodium salt is obtained.

[0019] Further improvement of the technical scheme of the present application is that in step 2, the operation process of the mixer group is as follows: starting the hot mixer at low speed and then at high speed, under the high-speed stirring of the paddle of the hot mixer, the temperature of the mixed material reaches 120 DEG C, then the valve is opened, the mixed material enters the cold mixer, and the mixed material is cooled through the cooling pipeline, and after the temperature of the mixed material reaches 40 DEG C, the mixed material is transmitted to the storage bin through the pipeline.

[0020] Further improvement of the technical scheme of the present application is that the highest rotating speed of the hot mixer is 1000-1200 rpm.

[0021] Further improvement of the technical scheme of the present application is that in step 3, the extrusion process temperature of the 12 heating zones is set as 150 DEG C, 155 DEG C, 155 DEG C, 160 DEG C, 190 DEG C, 195 DEG C, 195 DEG C, 200 DEG C, 200 DEG C, 195 DEG C, 160 DEG C and 160 DEG C.

[0022] Due to the adoption of the above technical scheme, the present application has the following technical progress:

[0023] 1. The present application introduces sodium salt into the heat stabilizer of the mixed material by synthesizing sodium salt, delays the degradation time of the material, prolongs the stable time of the pipe by one period of time (for example, 60 minutes or even longer), and cooperates with the process parameters of the extruder matched with the formula (such as the process temperature curve of climbing first and falling later), so that the pipe is no longer decomposed and discolored due to secondary heating, which not only ensures the normal production of the pipe material, but also improves the product performance of the pipe material.

[0024] 2. The present application uses sodium salt and organic tin in a certain proportion as a heat stabilizer to produce synergistic effect and ensure the long-term stability of the mixed material under high temperature.

[0025] 3. The present application partially replaces metal tin with metal sodium, reduces the content of metal tin in the pipe material within a certain range, improves the safety and health of drinking water transportation, meets the requirements of the “Hygienic and Safety Evaluation Standard for Drinking Water Transportation Equipment and Protective Materials” (2001) issued by the Ministry of Health, and the minimum mass detection concentration of metal tin of the water-immersed product (PVC-O pipe material) is 0.002 mg / L.

[0026] 4、The application uses sodium salt to partially replace part of organic tin as a heat stabilizer, under the premise of ensuring long-term stability of the extruded blank pipe, the Vicat softening temperature and material strength of the pipe are improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description:

[0028] Figure 1 is a schematic diagram of the color change of the sample of formula 1-10 after a certain time of testing in the rotor rheometer in the embodiment of the present application;

[0029] Figure 2 is a rheological curve graph and a temperature curve graph of formula 1-5 in the embodiment of the present application;

[0030] Figure 3 is a rheological curve graph and a temperature curve graph of formula 6-10 in the embodiment of the present application. DETAILED DESCRIPTION

[0031] It should be noted that the terms “include” and “have” and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0032] The present application will be further described in detail below in combination with the drawings and embodiments:

[0033] A large-diameter thick-wall PVC-O pipe, the pipe mixed material contains, in weight units, 100 parts of PVC resin, 1.5-1.8 parts of heat stabilizer, 1.3 parts of internal and external lubricant, 1 part of anti-aging agent, and 10 parts of filler; the heat stabilizer is a mixture of organic tin (such as mercaptan tin) and sodium salt; the fraction of organic tin in the heat stabilizer is 1.0-1.2 parts, and the fraction of sodium salt is 0.4-0.6 parts. Preferably, the fraction of organic tin in the heat stabilizer is 1.0 part, and the fraction of sodium salt stabilizer is 0.5-0.6 parts. The commonly used organic tin in the PVC industry can be mercaptan tin, carboxylic acid tin, and maleic acid tin. The internal and external lubricant includes 0.4 parts of calcium stearate, 0.1 parts of oxidized polyethylene, and 0.8 parts of low molecular weight polyethylene; the anti-aging agent is titanium dioxide; and the filler is calcium carbonate.

[0034] The sodium salt includes sodium perchlorate, sodium hypochlorite, micro-fine calcium carbonate, and stearic acid; wherein, sodium perchlorate:sodium hypochlorite = 1:2; the micro-fine calcium carbonate and the stearic acid are carriers of the sodium salt; the specific preparation process is as follows:

[0035] S1, using perchlorate and hypochlorite as anions, sodium ion as a cation, the two synthesize to prepare a mixture of sodium perchlorate and sodium hypochlorite, wherein the ratio of perchlorate: hypochlorite is 1:2; prepared sodium perchlorate: sodium hypochlorite = 1:2;

[0036] S2. Heat 100 parts of fine calcium carbonate with a particle size range of 5 μm-10 μm to 105°C, add 3-5 parts of stearic acid, and stir at high speed for 10 minutes at a stirring speed of 600 rpm. Cool to below 35°C, then disperse 3-5 parts of the sodium perchlorate and sodium hypochlorite mixture prepared in S1, and mechanically mix until uniform to obtain the sodium salt, which is set aside. The sodium salt comprises 100 parts of fine calcium carbonate, 3-5 parts of stearic acid, 3-5 parts of sodium perchlorate, and 6-10 parts of sodium hypochlorite, with a sodium perchlorate:sodium hypochlorite ratio of 1:2.

[0037] Sodium perchlorate in sodium salt has strong oxidizing properties, while sodium hypochlorite is highly active and has a bleaching effect. Sodium hypochlorite is used as the main oxidant, and a combination of sodium perchlorate and sodium hypochlorite is used to react with mercaptan compounds (tin mercaptides), creating a synergistic effect during the processing.

[0038] Strong oxidants react with sulfur-containing organic compounds such as mercaptans or thioethers, generating sulfur dioxide that, under acidic conditions (hydrogen chloride is produced during PVC processing), produces sulfurous acid, which has a bleaching effect. Furthermore, the strong oxidizing properties of perchlorates and hypochlorites can decolorize chromogenic groups in organic compounds, thereby improving the whiteness of PVC products during processing and reducing decomposition and discoloration during PVC processing.

[0039] In order to test the amount of heat stabilizer added to large-diameter, thick-walled PVC-O pipes, a total of 10 formulations were designed and compared to demonstrate the optimal effect of the technical solution of the present invention. As shown in Table 1, the principle of formulation design is to keep the amounts of internal and external lubricants, anti-aging agents, fillers and other additives unchanged, and the amount of PVC resin unchanged, while only the amount of heat stabilizer (organic tin and sodium salt) is changed. Formulation No. 1 is the original formulation.

[0040] Table 1 Detailed list of the amount of raw materials added in each formula

[0041]

[0042] The test results of the color change of the samples extruded from each formula after testing in the rotor rheometer for a certain period of time are as follows: Figure 1 As shown. Figure 1 It can be seen that the stability of the sample extruded from formula No. 1 was obvious discoloration after 13 minutes, and severe discoloration after 17 minutes, which was considered to be decomposed and unusable.

[0043] The comparative test analysis of each formula is as follows:

[0044] (1) No. 1 and No. 3 formulations keep the total amount of heat stabilizer unchanged, wherein No. 1 formulation adds 1.5 parts of organotin (mercaptan tin) as heat stabilizer, and No. 3 formulation adds 1.0 part of organotin (mercaptan tin) and 0.5 part of sodium salt as heat stabilizer. The test results of the samples extruded from No. 1 and No. 3 formulations on the rotor rheometer show that, when the total amount of heat stabilizer is unchanged, the addition of sodium salt makes the long-term stability of the extruded parison better than that of the parison only with organotin, and prolongs the heat stabilization effect.

[0045] (2) No. 5 and No. 6 formulations reduce the total amount of heat stabilizer to 1.2 parts, wherein No. 5 formulation adds 0.8 part of organotin (mercaptan tin) and 0.4 part of sodium salt as heat stabilizer, and No. 6 formulation adds 1.2 part of organotin (mercaptan tin) as heat stabilizer. The test results of the samples extruded from No. 5 and No. 6 formulations on the rotor rheometer show that, when the total amount of heat stabilizer is unchanged, the addition of sodium salt makes the long-term stability of the extruded parison better, and prolongs the heat stabilization effect.

[0046] (3) No. 7 and No. 10 formulations increase the total amount of heat stabilizer to 1.8 parts, wherein No. 7 formulation adds 1.2 part of organotin (mercaptan tin) and 0.6 part of sodium salt as heat stabilizer, and No. 10 formulation adds 1.8 part of organotin (mercaptan tin) as heat stabilizer. The test results of the samples extruded from No. 7 and No. 10 formulations on the rotor rheometer show that, when the total amount is unchanged, the addition of sodium salt makes the long-term stability of the extruded parison better than that of the parison only with organotin, and prolongs the heat stabilization effect.

[0047] Summary: From the comparison test of the formulations (1), (2) and (3), it can be concluded that, whether the addition amount of organotin (mercaptan tin) is high or low, after the additional addition of sodium salt, the long-term stability of the parison extruded from the formulation becomes better, and the heat stabilization is prolonged.

[0048] (4) No. 6 and No. 7 formulations keep the addition amount of organotin (mercaptan tin) heat stabilizer unchanged at 1.2 parts, wherein No. 6 formulation does not add sodium salt, and No. 7 formulation additionally adds 0.6 part of sodium salt. The test results of the samples extruded from No. 6 and No. 7 formulations on the rotor rheometer show that, the parison with the additional addition of sodium salt has better stability than the parison only with organotin (mercaptan tin) as heat stabilizer.

[0049] (5) No. 2 formula, No. 3 formula, No. 4 formula, No. 7 formula, No. 8 formula, No. 9 formula, are to keep the amount of organic tin (thiol tin) in the heat stabilizer unchanged, add different parts of sodium salt, through the rotor rheometer test results to investigate the stability of the formula. Among them, the addition amount of organic tin (thiol tin) in No. 2 formula, No. 3 formula, No. 4 formula is 1.0 parts, and the addition amount of sodium salt is 0.4, 0.5 and 0.6 parts respectively, the result is that the more the amount of sodium salt added, the better the stability of the pipe. Among them, the addition amount of organic tin (thiol tin) in No. 7 formula, No. 8 formula, No. 9 formula is 1.2 parts, and the addition amount of sodium salt is 0.6, 0.4 and 0.8 parts respectively, the result is that the more the amount of sodium salt added, the better the stability of the pipe.

[0050] Summary: In the formula of organic tin (thiol tin) as heat stabilizer, the stability of the pipe extruded by adding sodium salt is better than that of the formula without adding sodium salt, and the heat stability effect is prolonged. The more the amount of sodium salt added, the better the effect.

[0051] As shown in Figure 2 , Figure 3 , through the rheological curve and temperature curve, it can be known that the pipe extruded by No. 3 formula, No. 4 formula and No. 7 formula, No. 8 formula meets the requirements of plasticizing time and stable time, and their stable time and plasticizing time are neither advanced nor delayed, and the time is moderate; the stable time keeps stable torque and melt temperature within the test time.

[0052] Conclusion: Under the premise of meeting the processing conditions, the cost of No. 3 formula and No. 4 formula is lower than that of No. 7 formula and No. 8 formula. Therefore, No. 3 formula and No. 4 formula are preferred, that is, the heat stabilizer in the original formula is replaced by: organic tin (thiol tin) 1 part, sodium salt (sodium perchlorate and sodium hypochlorite) 0.5-0.6 parts (the parts between 0.5-0.6 parts can achieve the heat stability effect of pipe extrusion), which effectively solves the problem of long-term stability in the extrusion process of large-diameter (more than 500 mm) oriented PVC-O pipe (more than 40 mm) pipe.

[0053] A preparation method of large-diameter thick-wall PVC-O pipe, comprising the following steps:

[0054] Step 1, first prepare sodium salt, then physically mix organic tin and sodium salt into heat stabilizer;

[0055] Step 2, then put PVC resin, lubricant, anti-aging agent and filler into the hot mixer in the mixer group, and finally put the physically mixed heat stabilizer, first hot mixing and then cold mixing, and the mixed material is transmitted to the storage bin;

[0056] The operation process of the mixer group is:

[0057] The hot mixer is started at low speed and then at high speed, and the highest rotating speed is 1000-1200 rpm. Under the high-speed stirring of the paddle of the hot mixer, the temperature of the mixed material reaches 120 DEG C. Then the valve is opened, the mixed material enters the cold mixer, and the mixed material is cooled through the cooling pipeline. When the temperature of the mixed material reaches 40 DEG C, the mixed material is transmitted to the storage bin through the pipeline.

[0058] In step 3, the mixed material in the storage bin is sucked into the hopper of the extruder through the vacuum suction device on the upper part of the parallel double screw extruder. The parallel double screw extruder extrudes the pipe material, and the process parameters are selected as follows: the screw diameter of the parallel double screw extruder is not less than 155 mm, the length-diameter ratio (the ratio of the length of the screw to the diameter) L / D of the screw is 36:1; the extruder barrel is provided with not less than 12 heating zones, and the process temperature curve is set to be first climbing and then falling; the extrusion amount of the blank pipe is 1000-1300 kg / h; and the minimum value of the extrusion line speed is not more than 0.10 m / min.

[0059] The extrusion process temperature setting of the extruder barrel provided with 12 heating zones is shown in Table 2.

[0060] Table 2: Extrusion process temperature setting

[0061]

[0062] In step 4, the extruded pipe material is formed after vacuum sizing, primary cooling, primary traction, secondary heating, orientation expansion, secondary cooling and secondary traction.

[0063] In step 5, the pipe material is cut to a fixed length, detected, and stored in the warehouse if qualified.

[0064] The processing technology in steps 4 and 5 above is a conventional technology in the prior art, and will not be described in detail in the present application.

[0065] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for 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 large-diameter, thick-walled PVC-O pipe, characterized by: The pipe material mixture contains, by weight, 100 parts of PVC resin, 1.5-1.8 parts of heat stabilizer, 1.3 parts of lubricant, 1 part of anti-aging agent, and 10 parts of filler; the heat stabilizer is a mixture of tin mercaptide and sodium salt; The sodium salt includes sodium perchlorate, sodium hypochlorite, fine calcium carbonate and stearic acid; wherein the ratio of sodium perchlorate to sodium hypochlorite is 1:2; the fine calcium carbonate and stearic acid serve as carriers of the sodium salt; The heat stabilizer contains 1.0 part of tin mercaptide and 0.5-0.6 part of sodium salt.

2. The large-diameter, thick-walled PVC-O pipe according to claim 1, characterized in that: The lubricant comprises: 0.4 parts of calcium stearate, 0.1 parts of oxidized polyethylene and 0.8 parts of low molecular weight polyethylene; the anti-aging agent is titanium dioxide; and the filler is calcium carbonate.

3. A method for preparing the large-diameter, thick-walled PVC-O pipe according to claim 1 or 2, characterized in that: The following steps are involved: Step 1: first prepare sodium salt, and then physically mix tin mercaptide and sodium salt to form a heat stabilizer; Step 2: Add PVC resin, lubricant, anti-aging agent and filler into the hot mixer in the mixing unit, and finally add the physically mixed heat stabilizer, first hot mix and then cold mix, and transfer the mixed ingredients to the storage bin; Step 3, the mixed materials in the storage bin are sucked from the storage bin into the extruder hopper through the vacuum suction device on the upper part of the parallel twin-screw extruder, and the parallel twin-screw extruder extrudes the pipe. The process parameters are selected as follows: the screw diameter of the parallel twin-screw extruder is not less than 155 mm, and the length-to-diameter ratio L / D of the screw is 36:1; the extruder barrel is externally heated with not less than 12 heating zones, and a process temperature curve is set to first climb and then fall; the billet extrusion rate is 1000 kg / h to 1300 kg / h; the minimum extrusion line speed does not exceed 0.10 m / min; The extrusion process temperatures of the 12 heating zones were set as follows: 150°C, 155°C, 155°C, 160°C, 190°C, 195°C, 195°C, 200°C, 200°C, 195°C, 160°C, and 160°C; Step 4: The extruded tube is formed after vacuum sizing, primary cooling, primary drawing, secondary heating, orientation expansion, secondary cooling, and secondary drawing; Step 5: Cut to length, inspect, and store qualified products.

4. The preparation method according to claim 3, wherein: In step 1, the sodium salt is prepared as follows: S1, using perchlorate and hypochlorite as anions, sodium ion as a cation, the two synthesize and prepare a mixture of sodium perchlorate and sodium hypochlorite, wherein the ratio of perchlorate: hypochlorite is 1:2; S2. Heat 100 parts of fine calcium carbonate with a particle size range of 5 μm-10 μm to 105° C., add stearic acid in a ratio of 3-5 parts, stir at high speed for 10 minutes at a stirring speed of 600 rpm, cool to below 35° C., and then disperse and add the sodium perchlorate and sodium hypochlorite mixture prepared in S1 in a ratio of 3-5 parts, and mix mechanically to obtain the sodium salt.

5. The preparation method according to claim 3, wherein: In step 2, the operation process of the mixing unit is as follows: start the hot mixer at low speed first and then at high speed. Under the high-speed stirring of the hot mixer blades, the temperature of the mixed materials reaches 120°C, and then open the valve, and the mixed materials enter the cold mixer. The mixed materials are cooled through the cooling pipeline. After the material temperature reaches 40°C, the mixed materials are transmitted to the storage bin through the pipeline.

6. The preparation method according to claim 5, characterized in that: The maximum speed of the hot mixer is 1000-1200rpm.

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