High-weather-resistant environment-friendly water-based composite finishing layer for outer wall of nodular cast iron pipe and preparation method

Abstract

The invention discloses a nodular cast iron pipe outer wall high-weather-resistance environment-friendly water-based composite finishing layer and a preparation method, and relates to the technical field of nodular cast iron pipe outer wall coatings. The method comprises the steps that the outer wall of the nodular cast iron pipe is evenly coated with a zinc-based coating material and then cooled; the preparation method comprises the following steps: mixing quick-drying hybrid emulsion resin and silane modified mineral powder according to a ratio, uniformly stirring after mixing, adding a silicon-based emulsion material into the mixture, uniformly dispersing, uniformly coating the surface of a zinc-based coating, heating and drying after coating, and migrating the silicon-based emulsion material to the surface of the coating in the drying process to form a compact weather-resistant film layer; and finally, heating is conducted, and the coated nodular cast iron pipe is subjected to final curing treatment. The physical property and weather resistance of the composite finishing layer can well meet the outer wall protection requirement of the nodular cast iron pipe, the preparation method is simple and easy to operate, the drying speed of the water-based coating is high, the VOC detection is zero, and the process is more environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of ductile iron pipe outer wall coatings, and in particular to a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe and a preparation method thereof. Background Art

[0002] The outer wall of the ductile iron pipe is coated with a zinc-based coating plus a final coating. The zinc-based coating is an active metal that can provide cathodic protection for the base cast iron. However, the active zinc-based coating is also easily corroded by external oxygen, moisture, etc. and gradually loses its protective effect on the iron. Therefore, the protection of the zinc-based coating by the final coating is also very important.

[0003] The traditional finishing layer uses solvent-based coatings, solvent-based asphalt coatings, solvent-based chlorinated polyethylene coatings, solvent-based epoxy coatings, etc. These coatings can protect the zinc-based coating very well, but these solvent-based coatings are not resistant to aging, which causes ductile iron pipes to age during storage or ground installation and affects the protective performance. At the same time, during the production of the finishing layer, the paint used in the solvent-based coating will produce a large amount of VOCs, which are emitted into the atmosphere, seriously polluting the atmospheric environment. Water-based coatings can solve the VOC emission problem very well, but the water-based coatings used in the water-based coatings are difficult to meet the requirements of low-temperature and fast drying speed in the process of the outer coating of ductile iron pipes, and the life of the water-based coatings is usually difficult to guarantee. Therefore, there is an urgent need for a highly weather-resistant and environmentally friendly water-based composite finishing layer on the outer wall of a ductile iron pipe and a preparation method to solve this problem. Summary of the invention

[0004] The object of the present invention is to provide a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe and a preparation method thereof, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer on the outer wall of a ductile iron pipe, comprising the following specific steps:

[0006] The temperature of the ductile iron pipe after annealing is controlled within the required range for coating the zinc-based coating, and the zinc-based coating material is evenly coated on the outer wall of the ductile iron pipe by arc thermal spraying. After coating, the pipe is cooled at room temperature.

[0007] The quick-drying hybrid emulsion resin and the silane-modified mineral powder are mixed in proportion, wherein the quick-drying hybrid emulsion resin is TiO 2 -SiO 2 - acrylic acid-vinylidene chloride polymerization hybrid emulsion, silane-modified mineral powder is prepared by directly spraying a silane coupling agent on the mineral powder, mixing and stirring to obtain a water-based coating, into which a silicon-based emulsion material for forming a weather-resistant film layer is added and dispersed evenly;

[0008] The coating mixed with the silicon-based emulsion material is evenly coated on the surface of the zinc-based coating by spraying, brushing or dipping. After the coating is completed, it is heated and dried. During the drying process, the silicon-based emulsion material migrates to the coating surface to form a dense weather-resistant film layer;

[0009] Finally, heating is carried out for the final curing treatment of the coated ductile iron pipe.

[0010] Preferably, before spraying the zinc-based coating, the hard oxide scale after annealing the ductile iron pipe is used as a pretreatment layer, and using the waste heat after annealing, the temperature of the cast iron pipe is maintained at 60-300 degrees.

[0011] Preferably, the zinc-based coating material is zinc, zinc-aluminum alloy or zinc-aluminum-copper alloy.

[0012] Preferably, in the silane-modified mineral powder, the mineral powder includes magnesium silicate, aluminum silicate, and barium sulfate, and the ratio of the three is 30:10:60. The silane modification is carried out with γ-glycidoxypropyltrimethoxysilane, and the silane dosage is 1-3% of the powder weight. Through mechanical force mixing reaction, after the reaction is completed, fine wet grinding is carried out to make the fineness of the powder reach 3-5 microns, and the proportion of the weather-resistant modified mineral powder in the water-based coating is 20-40%.

[0013] Preferably, the silicon-based emulsion adopts an acrylic-siloxane composite emulsion, whose glass transition temperature (Tg) is -10 to 20 °C, and its mass ratio in the coating mixed with the silicon-based emulsion material is 1-10%.

[0014] Preferably, for the coating mixed with the silicon-based emulsion material, the high-pressure spraying method is adopted. After the coating is evenly coated, low-temperature drying is carried out, the drying temperature is 40-60 °C, and the heat preservation time is 10-15 minutes.

[0015] Preferably, the curing temperature for the final curing treatment is 60-80 °C, and the time is 20-30 minutes.

[0016] An outer wall high-weather-resistant and environmentally friendly water-based composite finish layer for ductile iron pipes is prepared by the above preparation method, and includes a zinc-based coating closely attached to the outer wall of the ductile iron pipe, a water-based coating coated on the outside of the zinc-based coating, and a weather-resistant film layer formed on the surface of the water-based coating. The material of the zinc-based coating is zinc, zinc-aluminum alloy or zinc-aluminum-copper alloy, and the weather-resistant film layer is formed by the migration of the silicon-based emulsion.

[0017] Preferably, the amount of the zinc-based coating on the outer wall of the ductile iron pipe is 200-600 g / m 2 , the coating thickness of the water-based coating is 50-200 microns, and the thickness of the weather-resistant film layer is 5-10 microns.

[0018] Preferably, the QUV aging test of the finish layer is greater than 1000h, and the VOC detection is zero.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. The high weather-resistant and environmentally friendly waterborne composite finish layer on the outer wall of the ductile iron pipe can well meet the needs of protecting the outer wall of the ductile iron pipe. It not only meets the physical property requirements but also has excellent weather resistance, which is beneficial to ensuring its service life. At the same time, it expands the application range of the ductile iron pipe. In addition, the VOC detection of its finish layer is 0, and the process is more environmentally friendly.

[0021] 2. The preparation method of the high weather-resistant and environmentally friendly waterborne composite finish layer on the outer wall of the ductile iron pipe only requires two-step spraying and heat curing. The steps are simple and easy to operate. The vinylidene chloride component in the fast-drying hybrid emulsion resin used in the waterborne coating has a relatively low glass transition temperature, which can also endow the emulsion with a lower film-forming temperature, thereby achieving the fast-drying effect of the emulsion. At the same time, it has a wider construction temperature range. The weather-resistant film layer uses a migration film, which is mixed into the coating together before spraying the waterborne coating. One-time spraying can produce two functional coating layers, which simplifies the production process, shortens the production time, and is beneficial to saving spraying energy consumption and manpower, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the order of the high weather-resistant and environmentally friendly waterborne composite finish layer on the outer wall of the ductile iron pipe of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The preparation method of the finish layer of the present invention includes:

[0024] Preparation of zinc-based coating: Control the temperature of the ductile iron pipe after annealing within the range required for coating the zinc-based coating. Uniformly coat the zinc-based coating material on the outer wall of the ductile iron pipe by means of arc thermal spraying. After coating, cool it at room temperature to ensure the tight combination of the zinc-based coating and the substrate;

[0025] For the above method, no special pretreatment is required before spraying the zinc-based coating. The hard oxide scale after annealing of the ductile iron pipe can be used as the pretreatment layer. There is very good adhesion between the oxide scale and the substrate, reaching 2-5 MPa; in addition, the waste heat after annealing can be directly utilized, and the temperature of the cast iron pipe is maintained at 60-300 degrees;

[0026] The zinc-based coating material can be zinc, zinc-aluminum alloy or zinc-aluminum-copper alloy, etc. For example, in terms of mass ratio, zinc 85 aluminum 15, zinc 85 aluminum 15 copper 0.5, etc. Any zinc-based coating formula that can be used for conventional ductile iron pipes is acceptable.

[0027] Preparation of aqueous coating and weather-resistant film layer: Mix quick-drying hybrid emulsion resin and silane-modified mineral powder in proportion. The quick-drying hybrid emulsion resin is TiO 2 -SiO 2 -acrylic-vinylidene chloride polymerization hybrid emulsion. The silane-modified mineral powder is prepared by directly spraying a silane coupling agent on the mineral powder. After mixing, stir evenly to obtain an aqueous coating, and add a silicon-based emulsion material for forming a weather-resistant film layer and disperse evenly;

[0028] In a preferred embodiment, vinylidene chloride is the main monomer in the quick-drying hybrid emulsion resin, and special nano-SiO 2 and nano-TiO 2 particles are grafted. While providing good water and oxygen barrier properties, the relatively low glass transition temperature of vinylidene chloride itself can also endow the emulsion with a lower film-forming temperature, thereby achieving the quick-drying effect of the emulsion and having a wider construction temperature range. At the same time, special modified monomers are introduced into the formulation system, and gradient emulsion polymerization is used during the reaction by adding monomers and auxiliaries in different proportions in stages. By using an alkoxysilane as a surface modifier, the polymerization reaction on the surface of nano-titanium dioxide is promoted, and methacryloxypropyltrimethoxysilane is reacted with titanium dioxide nanoparticles. This step aims to introduce polymerizable groups by functionalizing the surface of the nanoparticles. The modified titanium dioxide nanoparticles are subjected to emulsion copolymerization reaction with monomers such as styrene and methyl acrylate, or vinylidene chloride and methyl acrylate to form TiO 2 -SiO 2 -acrylic-vinylidene chloride polymerization hybrid emulsion, and the polymer grows from the surface of the nanoparticles.

[0029] In an alternative embodiment, in the silane-modified mineral powder, the mineral powder includes magnesium silicate, aluminum silicate, and barium sulfate, and the ratio of the three is 30:10:60. The silane modification uses γ-glycidoxypropyltrimethoxysilane, and the silane dosage is 1-3% of the powder weight. Through mechanical force mixing reaction, after the reaction is completed, fine wet grinding is carried out to make the fineness of the powder reach 3-5 microns, and the proportion of weather-resistant modified mineral powder in the aqueous coating is 20-40%.

[0030] In an alternative embodiment, the silicon-based emulsion uses an acrylic-siloxane composite emulsion, and its glass transition temperature (Tg) is -10 to 20 °C. Generally, commercially available products can be used. For reference, for example, Shin-Etsu CNE-79 of Japan can be used; the mass ratio of the silicon-based emulsion in the coating mixed with the silicon-based emulsion material can be 1-10%.

[0031] The coating mixed with the silicone-based emulsion material is evenly coated on the surface of the zinc-based coating by spraying, brushing or dipping. After the coating is completed, it is heated and dried. During the drying process, the silicone-based emulsion material migrates to the coating surface to form a dense weather-resistant film layer. In a preferred embodiment, high-pressure spraying is used. After the coating is evenly applied, low-temperature drying is carried out. The drying temperature is 40-60°C, and the heat preservation time is 10-15 minutes. During the drying process, the silicone-based emulsion will quickly migrate to the coating surface to form a dense weather-resistant film layer.

[0032] After the above two coatings, finally, heat treatment is carried out on the coated ductile iron pipe for final curing to ensure the tight bonding between the coatings. For reference, the curing temperature can be 60-80°C, and the time can be 20-30 minutes.

[0033] See Figure 1 , the composite environmentally friendly water-based final finish layer prepared on the outer wall of the ductile iron pipe by the above preparation method includes a zinc-based coating closely attached to the outer wall of the ductile iron pipe, a water-based coating coated on the outer side of the zinc-based coating, and a weather-resistant film layer formed on the surface of the water-based coating.

[0034] In a preferred embodiment, the amount of the zinc-based coating on the outer wall of the ductile iron pipe is 200-600 g / m 2 , ensuring that the zinc-based coating can provide good cathodic protection; the coating thickness of the water-based coating is 50-200 microns, and the thickness of the weather-resistant film layer is 5-10 microns, having good weather resistance and anti-aging performance.

[0035] Example:

[0036] After the annealing treatment of the ductile iron pipe, keeping the pipe temperature at 200 degrees, a zinc-aluminum alloy coating material with a zinc-aluminum content ratio of 85:15 is evenly coated on the outer wall of the ductile iron pipe by arc thermal spraying. After the coating is completed, it is cooled at room temperature;

[0037] The following gradient emulsion polymerization method is used to prepare a fast-drying hybrid emulsion resin:

[0038] Monomer ratio (mass ratio): Styrene (St) 1-3%; Methyl acrylate (MA) 5-10%; Vinylidene chloride (VDC) 75-90%; Silane (such as vinyltrimethoxysilane) 1-3%; Titanium dioxide (TiO 2 ) 2-5%;

[0039] Reaction conditions: 70-80°C, 4-6 hours;

[0040] Initiator: Ammonium persulfate (APS) or azobisisobutyronitrile (AIBN), and the dosage is 0.5-1% of the total mass of the monomers;

[0041] Emulsifier (such as sodium dodecyl sulfate, SDS) 2 - 3%;

[0042] Solvent: deionized water (emulsion polymerization).

[0043] Preparation steps:

[0044] Disperse titanium dioxide (TiO 2 ) in deionized water, add a small amount of dispersant (sodium polyacrylate), and ultrasonically treat for 30 minutes to form a uniform suspension;

[0045] Weigh styrene, methyl acrylate, vinylidene chloride, and silane in proportion and mix them evenly;

[0046] Dissolve the emulsifier (such as SDS) in deionized water, add the pre-dispersed titanium dioxide suspension, and stir evenly;

[0047] Slowly add the monomer mixture to the emulsifier solution and stir at high speed to form a pre-emulsion;

[0048] Heat the reaction system to 70 - 80 °C, add an initiator (such as APS or AIBN), and start the polymerization reaction; keep the stirring speed constant and react for 4 - 6 hours.

[0049] Spray γ-glycidoxypropyltrimethoxysilane on the surface of mineral powder materials with a ratio of magnesium silicate, aluminum silicate, and barium sulfate of 30:10:60, with a dosage of 3% of the total weight of the powder. After the stirring reaction is completed, grind it to a D50 of 3 - 5 microns to obtain weather-resistant modified mineral powder;

[0050] Mix the prepared fast-drying hybrid emulsion resin and weather-resistant modified mineral powder evenly according to the ratio of 60:40, add Shin-Etsu CNE-79 from Japan as a silicone-based emulsion, with an addition amount of 5.5% by mass in the mixed coating. When adding, use fine segmented addition and assist with a fine-speed regulation cage-type stirring blade to ensure that the stirring does not damage the silicone-based emulsion and at the same time allow the silicone-based emulsion to be completely evenly dispersed in the water-based coating.

[0051] Spray the above-mentioned mixed coating evenly on the surface of the zinc-based coating through high-pressure spraying. After the coating is completed, dry it at 50 °C for 10 minutes, then raise the temperature to 80 °C and keep it warm for 20 minutes.

[0052] After natural cooling to room temperature, conduct performance tests on the outer wall of the ductile iron pipe with a highly weather-resistant and environmentally friendly water-based composite finish coating. Through pull-out test ISO 4624, cross-cut test ISO 2409, and impact test ISO 6272, its physical properties far exceed the standard requirements. The VOC detection result of GB23986-2009 is zero, and the result of method A specified in the QUV aging test GB / T 23987-2009 is greater than 1000h.

[0053] The above are only the preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope defined by the claims.

[0054] Matters not described in detail in the present invention are all well-known technologies to those skilled in the art.

Claims

1. A method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe, characterized in that: The specific steps include: The temperature of the ductile iron pipe after annealing is controlled within the required range for coating the zinc-based coating, and the zinc-based coating material is evenly coated on the outer wall of the ductile iron pipe by arc thermal spraying. After coating, the pipe is cooled at room temperature. Mix a quick-drying hybrid emulsion resin and a silane-modified mineral powder in proportion, wherein the quick-drying hybrid emulsion resin is a TiO2-SiO2-acrylic acid-vinylidene chloride polymerization hybrid emulsion, and the silane-modified mineral powder is prepared by directly spraying a silane coupling agent on a mineral powder, and stir the mixture to obtain a water-based coating, and add a silicon-based emulsion material for forming a weather-resistant film layer thereto and disperse the mixture evenly; The coating mixed with the silicon-based emulsion material is evenly applied on the surface of the zinc-based coating by spraying, brushing or dipping. After the coating is completed, it is heated and dried. During the drying process, the silicon-based emulsion material migrates to the surface of the coating to form a dense weather-resistant film layer; Finally, heating is performed to finally cure the coated ductile iron pipe.

2. The method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 1, characterized in that: Before spraying the zinc-based coating, the hard oxide scale of the ductile iron pipe after annealing is used as a pretreatment layer, and the residual heat after annealing is used to maintain the temperature of the cast iron pipe at 60 to 300 degrees.

3. The method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 1, characterized in that: The zinc-based coating material is zinc, zinc-aluminum alloy or zinc-aluminum-copper alloy.

4. The method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 1, characterized in that: The silane-modified mineral powder comprises magnesium silicate, aluminum silicate and barium sulfate in a ratio of 30:10:

60. γ-glycidyloxypropyltrimethoxysilane is used for silane modification. The amount of silane is 1-3% of the weight of the powder. The powder is mixed by mechanical force and then finely wet-ground after the reaction to make the powder fineness reach 3-5 microns. The proportion of weather-resistant modified mineral powder in water-based coatings is 20-40%.

5. The method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 1, characterized in that: The silicon-based emulsion adopts acrylic acid-siloxane composite emulsion, the glass transition temperature of which is -10 to 20° C., and the mass ratio of the emulsion in the coating mixed with the silicon-based emulsion material is 1 to 10%.

6. The method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 1, characterized in that: The coating mixed with the silicon-based emulsion material is sprayed in a high-pressure spraying manner. After the coating is evenly coated, it is dried at a low temperature at a temperature of 40 to 60° C. and a heat preservation time of 10 to 15 minutes.

7. The method for preparing a highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 1, characterized in that: The final curing treatment has a curing temperature of 60 to 80° C. and a curing time of 20 to 30 minutes.

8. A highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6, comprising a zinc-based coating close to the outer wall of the ductile iron pipe, a water-based coating coated on the outside of the zinc-based coating, and a weather-resistant film layer formed on the surface of the water-based coating, wherein the material of the zinc-based coating is zinc, zinc-aluminum alloy or zinc-aluminum-copper alloy, and the weather-resistant film layer is formed by the migration of a silicon-based emulsion.

9. The highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 8, characterized in that: The amount of zinc-based coating on the outer wall of the ductile iron pipe is 200-600 g / m2, the coating thickness of the water-based coating is 50-200 microns, and the thickness of the weather-resistant film layer is 5-10 microns.

10. The highly weather-resistant and environmentally friendly water-based composite finishing layer for the outer wall of a ductile iron pipe according to claim 9, characterized in that: The QUV aging test of the final finishing layer is greater than 1000 hours, and the VOC detection is zero.

Images