Steel pipe for water supply and preparation method thereof

Abstract

The present invention relates to the technical field of steel pipes, and proposes a steel pipe for water supply and a preparation method thereof. A steel pipe for water supply comprises a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe, the anti-corrosion layer comprising a fused epoxy layer, an adhesive layer, and a polyethylene layer, arranged in sequence from the inside to the outside; the raw materials of the polyethylene layer comprise the following components in parts by mass: 90-110 parts of high-density polyethylene, 24-30 parts of composite kaolin, 4-8 parts of lubricant, and 1-3 parts of antioxidant; the preparation method of the composite kaolin comprises the following steps: A1, adding kaolin and wollastonite to water, mixing evenly to obtain a mixed solution A; A2, adding acid to the mixed solution A to adjust the pH to 3-4, sand-milling to obtain a mixed solution B; A3, adding acid to the mixed solution B to adjust the pH to 1-2, sand-milling, filtering, washing, and drying to obtain the composite kaolin. The above technical solution solves the problem of poor UV aging resistance in the related art.

Description

Technical Field

[0001] The present invention relates to the technical field of steel pipes, and in particular to a steel pipe for water supply and a preparation method thereof. Background Art

[0002] Steel pipes for water supply are widely used in municipal water supply and industrial water transportation, combining the high strength of steel with the corrosion resistance of their polyethylene layer. However, their high-density polyethylene (HDPE) layer faces severe aging issues when exposed to long-term UV radiation. The energy from UV rays causes the HDPE molecular chains to break and oxidize, leading to gradual embrittlement, cracking, and even shedding of the polyethylene layer, ultimately losing its protective effect on the steel pipe. This problem is particularly acute when pipes are stored outdoors, laid on the ground, or located in high-UV intensity areas such as high altitudes and tropical regions. This not only shortens the pipe's service life but can also lead to safety hazards such as leaks, increasing maintenance costs and environmental risks.

[0003] Currently, conventional methods in the industry to improve the UV resistance of polyethylene layers include adding UV absorbers, hindered amine light stabilizers and other additives, but there are generally limitations: since small molecule additives are easy to migrate and volatilize during use, the protective effect is not ideal.

[0004] Therefore, it is of vital importance to develop a water supply steel pipe with improved anti-ultraviolet aging performance. Summary of the Invention

[0005] The present invention provides a steel pipe for water supply and a preparation method thereof, which solves the problem of poor UV aging resistance of the steel pipe for water supply in the related art.

[0006] The technical solutions of the present invention are as follows:

[0007] The present invention provides a steel pipe for water supply, comprising a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer provided in sequence from the inside to the outside;

[0008] The raw materials of the polyethylene layer include the following components in parts by mass:

[0009] 90-110 parts of high-density polyethylene, 24-30 parts of composite kaolin, 4-8 parts of lubricant, 1-3 parts of antioxidant;

[0010] The preparation method of the composite kaolin comprises the following steps:

[0011] A1. Add kaolin and wollastonite to water and mix well to obtain a mixed solution A;

[0012] A2, adding acid to the mixed solution A to adjust the pH to 3-4, and sand-milling to obtain a mixed solution B;

[0013] A3. Add acid to the mixed solution B to adjust the pH to 1-2, sand-mill, filter, wash, and dry to obtain the composite kaolin.

[0014] In the present invention, the use of a lubricant in the polyethylene layer of the water supply steel pipe improves the processing performance of the polyethylene layer, thereby enhancing the quality of the final product. The good fluidity enables the polyethylene layer to more evenly cover the adhesive layer during installation, forming a polyethylene layer with uniform thickness and a dense structure, thus ensuring the overall quality and protective performance of the polyethylene layer. Furthermore, the lubricant reduces the adhesion of materials to equipment, avoids polyethylene layer defects caused by local overheating or material accumulation, and further improves the stability and reliability of the polyethylene layer.

[0015] In the present invention, the addition of an antioxidant to the polyethylene layer of the steel pipe for water supply ensures the antioxidant performance of the polyethylene layer and slows down the aging rate of polyethylene during processing and use. During high-temperature processing, the antioxidant can inhibit the oxidative degradation of polyethylene and maintain the stability of its physical properties. During long-term use, the antioxidant continues to play a role and prevents the performance degradation of polyethylene due to oxidation, such as decreased tensile strength and reduced flexibility, thereby extending the service life of the steel pipe for water supply.

[0016] As a further technical solution, the mass volume ratio of the kaolin to the water is 1g:10~12mL.

[0017] As a further technical solution, in the anti-corrosion layer, the raw materials of the fused epoxy layer include the following components in parts by mass: 55-60 parts of epoxy resin, 22-30 parts of ethylene-vinyl acetate copolymer, 12-20 parts of petroleum resin, 18-30 parts of titanium hydride, 2-5 parts of benzoin, and 1-4 parts of adipic acid dihydrazide.

[0018] As a further technical solution, in the anti-corrosion layer, the raw materials of the adhesive layer include the following components in parts by mass: 18 to 45 parts of ethylene acrylic resin, 7 to 14 parts of polyvinyl butyral, 8 to 20 parts of polyisobutylene, and 1 to 3 parts of dioctyl phthalate.

[0019] As a further technical solution, the mass ratio of kaolin to wollastonite is 10:4~5.

[0020] In the present invention, the mass ratio of kaolin to wollastonite can be 10:4, 10:4.1, 10:4.2, 10:4.3, 10:4.4, 10:4.5, 10:4.6, 10:4.7, 10:4.8, 10:4.9, or 10:5, and is preferably 10:4.5.

[0021] In the present invention, in the composite kaolin of the polyethylene layer of the steel pipe for water supply, wollastonite is a key raw material for providing a silicon source for kaolin to form a silicon dioxide composite kaolin. The mass ratio of wollastonite to kaolin directly affects the composite effect. When the mass ratio of kaolin to wollastonite is in the range of 10:4~5, wollastonite can provide sufficient and appropriate silicon source. In the subsequent sand milling and acidification reaction process, an appropriate amount of silicon source can ensure the formation of a uniform silicon dioxide coating layer on the surface of kaolin. If the ratio of kaolin to wollastonite is lower than 10:4, the silicon source is insufficient, which may lead to incomplete silicon dioxide coating on the surface of kaolin, affecting the coating effect of kaolin and the ultimate performance improvement in the polyethylene layer. On the contrary, if the ratio of kaolin to wollastonite is higher than 10:5, excessive silicon source may cause the generated silicon dioxide to agglomerate in the solution, which not only cannot be evenly coated on the surface of kaolin, but may also form an impurity phase in the polyethylene layer, destroying the microstructure of the polyethylene layer and having a negative impact on the performance of the steel pipe.

[0022] As a further technical solution, in step A2, the sand grinding is performed at a temperature of 20-30° C. and for a time of 4-5 hours.

[0023] As a further technical solution, in step A3, the sand grinding is performed at a temperature of 60-80° C. and for a time of 2-3 hours.

[0024] During sand milling in step A2, the temperature is controlled at 20-30° C. This temperature range is relatively mild, which can ensure that the dissolution reaction of wollastonite in an acidic environment can proceed slowly and steadily, and will not cause the reaction to be too violent and difficult to control due to excessively high temperature. The time is 4-5 hours to ensure that wollastonite can be fully dissolved and fully contacted with kaolin under this temperature and acidic conditions; during sand milling in step A3, the temperature is increased to 60-80° C. A higher temperature can accelerate and promote wollastonite to form a silica coating layer on the surface of kaolin faster. Within this temperature range, molecular thermal motion intensifies, the activity of silicate ions is enhanced, and the frequency of collisions between them increases, which is conducive to the formation of a denser silica network structure. The time is 2-3 hours, which ensures that the reaction of forming a silica coating layer on the surface of kaolin can proceed fully. During this period, as the reaction proceeds, silica gradually deposits and grows on the surface of kaolin to form a continuous, uniform and dense coating layer.

[0025] As a further technical solution, in steps A2 and A3, the acid is independently hydrochloric acid or nitric acid.

[0026] As a further technical solution, the concentration of the hydrochloric acid or nitric acid is 1-3 mol / L.

[0027] In the present invention, hydrochloric acid and nitric acid are both common and easily available chemicals in industry, with relatively low cost and wide sources, which help to reduce the preparation cost of kaolin coated with silicon dioxide. The acid concentration is controlled within a range of 1 to 3 mol / L. Within this concentration range, it can be ensured that the reaction between the acid and wollastonite has a suitable rate and the controllability of the reaction can be ensured. When the acid concentration is 1 mol / L, the hydrogen ion concentration is moderate, and the dissolution rate of the wollastonite is relatively slow, but the reaction process is easy to control, which is conducive to uniformly releasing the silicon source and creating conditions for forming a uniform silicon dioxide coating layer. As the acid concentration gradually increases to 3 mol / L, the hydrogen ion concentration increases, the reaction rate accelerates, and the wollastonite can be fully dissolved in a shorter time. When the concentration is further increased, the problem of excessive reaction will occur.

[0028] As a further technical solution, the composite kaolin is functionalized composite kaolin;

[0029] The raw materials of the functionalized composite kaolin include composite kaolin and ethylene-methacrylic acid copolymer in a mass ratio of 10:0.5-1.

[0030] In the present invention, the molecular structure of the ethylene-methacrylic acid copolymer lays the foundation for its role in improving impact strength. In the ethylene-methacrylic acid copolymer molecule, the ethylene segment has a similar chemical structure and good compatibility with polyethylene, and can form a tight bond with the polyethylene matrix, thereby improving the compatibility between the composite kaolin and polyethylene; and the polar groups on the methacrylic acid segment can be connected with the polar groups on the surface of the composite kaolin through interaction. This unique structure enables the ethylene-methacrylic acid copolymer to build an efficient interface connection between the composite kaolin and polyethylene. When the water supply steel pipe is subjected to an impact load, the impact force first acts on the polyethylene layer. Due to the enhanced interfacial bonding force of the ethylene-methacrylic acid copolymer, the stress can be more effectively transferred from the polyethylene matrix to the composite kaolin particles. The composite kaolin particles have high strength and rigidity, can disperse stress, and avoid stress concentration in the polyethylene matrix, thereby improving the ability of the polyethylene layer to resist impact damage, and ultimately improving the impact strength of the water supply steel pipe.

[0031] As a further technical solution, the preparation method of the functionalized composite kaolin comprises the following steps:

[0032] The composite kaolin is added to xylene and mixed evenly, and ethylene-methacrylic acid copolymer is added, stirred, concentrated, and dried to obtain the functionalized composite kaolin.

[0033] As a further technical solution, the mass volume ratio of the composite kaolin to the xylene is 1 g:7~8 mL.

[0034] As a further technical solution, the stirring time is 3 to 4 hours and the rotation speed is 200 to 300 rpm.

[0035] In the present invention, the temperature during the stirring process can be any temperature that ensures that the ethylene-methacrylic acid copolymer can be completely dissolved.

[0036] As a further technical solution, the lubricant includes one or more of zinc stearate, calcium stearate, and polyethylene wax.

[0037] As a further technical solution, the antioxidant includes one or more of antioxidant 126, antioxidant 1076, and antioxidant 168.

[0038] The present invention also provides a method for preparing a steel pipe for water supply, which is used to prepare the steel pipe for water supply, comprising the following steps:

[0039] S1, blending, extruding, and crushing the raw materials of the fusion-bonded epoxy layer to obtain epoxy layer powder;

[0040] S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer;

[0041] S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fusion-bonded epoxy layer to obtain an adhesive layer;

[0042] S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and press and laminate to obtain the steel pipe for water supply.

[0043] The working principle and beneficial effects of the present invention are:

[0044] The present invention uses silicon dioxide composite kaolin as the raw material of the polyethylene layer, which improves the anti-ultraviolet aging property of the polyethylene layer. In the prior art, kaolin is often added to improve the strength of the polyethylene layer of the water supply steel pipe. However, since kaolin contains metal impurities such as iron, manganese, and copper, these metal ions will become catalysts for photooxidation reaction under ultraviolet light irradiation, accelerating the aging of the polyethylene layer. In order to improve the anti-ultraviolet aging property of the polyethylene layer of the water supply steel pipe, the present invention uses composite kaolin and composites silicon dioxide on the surface of the kaolin. When ultraviolet rays irradiate the anti-corrosion polyethylene layer of the water supply steel pipe, the silicon dioxide is first used to absorb and scatter the ultraviolet rays, reducing The probability of metal impurities in kaolin coming into contact with ultraviolet rays. At the same time, after silica is compounded on the surface of kaolin, the lamellar structure of kaolin and the different refractive indices of kaolin and silica to ultraviolet rays are utilized, so that ultraviolet rays will be blocked by the lamellar structure and the difference in refractive index during propagation, resulting in reflection and scattering, making the propagation path of ultraviolet rays in the polyethylene layer tortuous, further weakening the ability of ultraviolet rays to penetrate the polyethylene layer. Therefore, the present invention uses silica-compounded kaolin as the raw material for the polyethylene layer of the steel pipe for water supply, and works together from the optical and physical levels to comprehensively improve the anti-ultraviolet aging performance of the polyethylene layer. In practical applications, the steel pipe for water supply prepared by the present invention is particularly suitable for steel pipes for water supply laid outdoors. It is exposed to sunlight for a long time and can effectively resist ultraviolet erosion, greatly prolonging the service life of the polyethylene anti-corrosion layer, reducing problems such as pipeline corrosion and breakage caused by ultraviolet aging, reducing maintenance costs, and ensuring the long-term stable operation of the water supply system. DETAILED DESCRIPTION

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0046] In the following examples and comparative examples, the model of high-density polyethylene is HE2550, the particle size of kaolin is 3000 mesh, the particle size of wollastonite is 1250 mesh, the model of ethylene-methacrylic acid copolymer is Nucrel® 0903, the model of epoxy resin is SM601, the model of ethylene-vinyl acetate copolymer is EVA910, the model of petroleum resin is C9 petroleum resin, the model of ethylene acrylic acid resin is EAA3440, the model of polyvinyl butyral is B60H, and the model of polyisobutylene is HRD850.

[0047] Example 1

[0048] A steel pipe for water supply, comprising a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer provided in sequence from the inside to the outside;

[0049] The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 60 parts of epoxy resin, 30 parts of ethylene-vinyl acetate copolymer, 20 parts of petroleum resin, 30 parts of titanium hydride, 5 parts of benzoin, and 4 parts of adipic acid dihydrazide;

[0050] The raw materials of the adhesive layer include the following components in parts by mass: 45 parts of ethylene acrylic resin, 14 parts of polyvinyl butyral, 20 parts of polyisobutylene, and 3 parts of dioctyl phthalate;

[0051] The raw materials of the polyethylene layer include the following components in parts by mass:

[0052] 110 parts of high-density polyethylene, 30 parts of composite kaolin, 4 parts of zinc stearate, 4 parts of calcium stearate, 1 part of antioxidant 126, 1 part of antioxidant 1076, 1 part of antioxidant 168;

[0053] The preparation method of composite kaolin comprises the following steps:

[0054] A1. Add kaolin and wollastonite to water (mass ratio of kaolin to wollastonite is 10:7, mass volume ratio of kaolin to water is 1 g:12 mL), mix well to obtain a mixed solution;

[0055] A2. Add 3 mol / L hydrochloric acid to the mixture to adjust the pH to 4, then sand-mill at 30°C for 4 h, then add 3 mol / L hydrochloric acid to adjust the pH to 2, sand-mill at 80°C for 2 h, filter, wash, and dry to obtain composite kaolin;

[0056] The method for preparing a steel pipe for water supply comprises the following steps:

[0057] S1, blending, extruding, and crushing the raw materials of the fusion-bonded epoxy layer to obtain epoxy layer powder;

[0058] S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer;

[0059] S3, blending, extruding, and crushing the raw materials for the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer;

[0060] S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and pressurize and laminate to obtain a steel pipe for water supply.

[0061] Example 2

[0062] A steel pipe for water supply, comprising a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer provided in sequence from the inside to the outside;

[0063] The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 55 parts of epoxy resin, 22 parts of ethylene-vinyl acetate copolymer, 12 parts of petroleum resin, 18 parts of titanium hydride, 2 parts of benzoin, and 1 part of adipic acid dihydrazide;

[0064] The raw materials of the adhesive layer include the following components in parts by mass: 18 parts of ethylene acrylic resin, 7 parts of polyvinyl butyral, 8 parts of polyisobutylene, and 1 part of dioctyl phthalate;

[0065] The raw materials of the polyethylene layer include the following components in parts by mass:

[0066] 90 parts of high-density polyethylene, 24 parts of composite kaolin, 4 parts of calcium stearate, 1 part of antioxidant 1076;

[0067] The preparation method of composite kaolin comprises the following steps:

[0068] A1. Add kaolin and wollastonite to water (the mass ratio of kaolin to wollastonite is 5:1, and the mass volume ratio of kaolin to water is 1 g:10 mL), mix well, and obtain a mixed solution;

[0069] A2. 1 mol / L nitric acid was added to the mixture to adjust the pH to 3, followed by sand milling at 20° C. for 5 h, followed by further addition of 1 mol / L nitric acid to adjust the pH to 1, followed by sand milling at 60° C. for 3 h, filtering, washing, and drying to obtain composite kaolin;

[0070] The method for preparing a steel pipe for water supply comprises the following steps:

[0071] S1, blending, extruding, and crushing the raw materials of the fusion-bonded epoxy layer to obtain epoxy layer powder;

[0072] S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer;

[0073] S3, blending, extruding, and crushing the raw materials for the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer;

[0074] S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and pressurize and laminate to obtain a steel pipe for water supply.

[0075] Example 3

[0076] A steel pipe for water supply, comprising a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer provided in sequence from the inside to the outside;

[0077] The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 58 parts of epoxy resin, 26 parts of ethylene-vinyl acetate copolymer, 16 parts of petroleum resin, 22 parts of titanium hydride, 4 parts of benzoin, and 2 parts of adipic acid dihydrazide;

[0078] The raw materials of the adhesive layer include the following components in parts by mass: 30 parts of ethylene acrylic resin, 12 parts of polyvinyl butyral, 14 parts of polyisobutylene, and 2 parts of dioctyl phthalate;

[0079] The raw materials of the polyethylene layer include the following components in parts by mass:

[0080] 100 parts of high-density polyethylene, 26 parts of composite kaolin, 6 parts of polyethylene wax, 2 parts of antioxidant 168;

[0081] The preparation method of composite kaolin comprises the following steps:

[0082] A1. Add kaolin and wollastonite to water (the mass ratio of kaolin to wollastonite is 10:3, and the mass volume ratio of kaolin to water is 1 g:11 mL), and mix well to obtain a mixed solution;

[0083] A2. Add 2 mol / L nitric acid to the mixed solution to adjust the pH to 3.5, then sand-mill at 25° C. for 4.5 h, then add 2 mol / L nitric acid to adjust the pH to 1.5, sand-mill at 70° C. for 2.5 h, filter, wash, and dry to obtain composite kaolin;

[0084] The method for preparing a steel pipe for water supply comprises the following steps:

[0085] S1, blending, extruding, and crushing the raw materials of the fusion-bonded epoxy layer to obtain epoxy layer powder;

[0086] S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer;

[0087] S3, blending, extruding, and crushing the raw materials for the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer;

[0088] S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and pressurize and laminate to obtain a steel pipe for water supply.

[0089] Example 4

[0090] The only difference between this embodiment and embodiment 3 is that the mass ratio of kaolin to wollastonite in this embodiment is 10:6.

[0091] Example 5

[0092] The only difference between this embodiment and embodiment 3 is that the mass ratio of kaolin to wollastonite in this embodiment is 10:4.

[0093] Example 6

[0094] The only difference between this embodiment and embodiment 3 is that the mass ratio of kaolin to wollastonite in this embodiment is 10:4.5.

[0095] Example 7

[0096] The only difference between this embodiment and embodiment 3 is that the mass ratio of kaolin to wollastonite in this embodiment is 10:5.

[0097] Example 8

[0098] The only difference between this embodiment and embodiment 6 is that the composite kaolin in this embodiment is replaced with functionalized composite kaolin of equal mass;

[0099] The preparation method of functionalized composite kaolin comprises the following steps:

[0100] The composite kaolin was added to xylene (the mass volume ratio of the composite kaolin to xylene was 1 g:8 mL), mixed evenly, and ethylene-methacrylic acid copolymer was added. The mixture was stirred at 300 rpm for 3 hours until the ethylene-methacrylic acid copolymer was completely dissolved, concentrated, and dried to obtain functionalized composite kaolin; wherein the mass ratio of the composite kaolin to the ethylene-methacrylic acid copolymer was 10:1.

[0101] Example 9

[0102] The only difference between this embodiment and embodiment 6 is that the composite kaolin in this embodiment is replaced with functionalized composite kaolin of equal mass;

[0103] The preparation method of functionalized composite kaolin comprises the following steps:

[0104] The composite kaolin was added to xylene (the mass volume ratio of the composite kaolin to xylene was 1 g:7 mL), mixed evenly, and ethylene-methacrylic acid copolymer was added. The mixture was stirred at a speed of 200 rpm for 4 hours until the ethylene-methacrylic acid copolymer was completely dissolved, concentrated, and dried to obtain functionalized composite kaolin; wherein the mass ratio of the composite kaolin to the ethylene-methacrylic acid copolymer was 10:0.5.

[0105] Comparative Example 1

[0106] The only difference between this comparative example and Example 3 is that the composite kaolin in this comparative example is replaced by kaolin of equal mass.

[0107] Experimental Example 1

[0108] The polyethylene layer of the steel pipe for water supply prepared in Examples 1 to 7 and Comparative Example 1 was tested for impact strength according to the method specified in GB / T 1843-2008 "Determination of Izod Impact Strength of Plastics", with the notch being A-type. The sample was then UV-treated according to the method specified in GB / T 16585-1996 "Test Method for Artificial Weathering of Vulcanized Rubber (Fluorescent UV Lamp)", and the impact strength was tested again. The UV condition was: 0.89 W / m 2 The test results are shown in Table 1.

[0109] Table 1 Impact strength test results

[0110]

[0111] As can be seen from Table 1, the polyethylene layer of the steel pipe for water supply prepared in Examples 1 to 7 of the present invention has a smaller decrease in impact strength after UV treatment than that of Comparative Example 1. Therefore, in the present invention, the use of silica-coated kaolin improves the UV aging resistance of the steel pipe for water supply.

[0112] Experimental Example 2

[0113] The polyethylene layers of the water supply steel pipes prepared in Examples 6 and 8-9 were tested for impact strength according to the method specified in GB / T 1843-2008, "Plastics - Determination of Izod Impact Strength." The notch was A-type, the specimen dimensions were 80 mm × 10 mm, and the thickness was 4 mm. The test results are shown in Table 2.

[0114] Table 2 Impact strength test results

[0115]

[0116] As shown in Table 2, the impact strength of the water supply steel pipes prepared in Examples 8 and 9 of the present invention reached 70.9 kJ / m 2 Therefore, in the present invention, the composite kaolin is treated with an ethylene-methacrylic acid copolymer to improve the impact strength of the water supply steel pipe.

[0117] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A steel pipe for water supply, characterized in that: It comprises a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged in sequence from the inside to the outside; The raw materials of the polyethylene layer include the following components in parts by mass: 90-110 parts of high-density polyethylene, 24-30 parts of functionalized composite kaolin, 4-8 parts of lubricant, 1-3 parts of antioxidant; The preparation method of composite kaolin comprises the following steps: A1. Add kaolin and wollastonite to water and mix well to obtain a mixed solution A; A2, adding acid to the mixed solution A to adjust the pH to 3-4, and sand-milling to obtain a mixed solution B; A3, adding acid to the mixed solution B to adjust the pH to 1-2, sand milling, filtering, washing, and drying to obtain the composite kaolin; The mass ratio of kaolin to wollastonite is 10:4-5; The raw materials of the functionalized composite kaolin include composite kaolin and ethylene-methacrylic acid copolymer in a mass ratio of 10:0.5-1.

2. A steel pipe for water supply according to claim 1, characterized in that: In step A2, the sand grinding is performed at a temperature of 20-30° C. for 4-5 hours.

3. A steel pipe for water supply according to claim 1, characterized in that: In step A3, the sand grinding is performed at a temperature of 60-80° C. for 2-3 hours.

4. A steel pipe for water supply according to claim 1, characterized in that: In steps A2 and A3, the acid is independently hydrochloric acid or nitric acid.

5. The steel pipe for water supply according to claim 1, characterized in that: The preparation method of the functionalized composite kaolin comprises the following steps: The composite kaolin is added to xylene and mixed evenly, and ethylene-methacrylic acid copolymer is added, stirred, concentrated, and dried to obtain the functionalized composite kaolin.

6. A steel pipe for water supply according to claim 5, characterized in that: The stirring time is 3-4 hours and the rotation speed is 200-300 rpm.

7. The steel pipe for water supply according to claim 1, characterized in that: The lubricant includes one or more of zinc stearate, calcium stearate, and polyethylene wax; The antioxidant includes one or more of antioxidant 126 , antioxidant 1076 , and antioxidant 168 .

8. A method for preparing a steel pipe for water supply, for preparing a steel pipe for water supply according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, blending, extruding, and crushing the raw materials of the fusion-bonded epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fusion-bonded epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and press and laminate to obtain the steel pipe for water supply.

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