Low-temperature curing powder coating for inner wall of drinking water steel pipe and preparation method and application thereof

Abstract

The application discloses a low-temperature curing powder coating for the inner wall of a drinking water steel pipe and a preparation method and application thereof. The bisphenol F type epoxy resin, the polyamide curing agent, the modified aliphatic cyclic amine curing agent and the diphenyl imidazoline modifier are used in combination, can effectively coat and wet other inorganic materials in the formula, form a crosslinked body, increase the adhesion of the coating to the base material, and the catalysis of the diphenyl imidazoline modifier can provide a product coating construction temperature of 120 DEG C to 130 DEG C. The addition of the diphenyl imidazoline modifier helps to reduce the pre-reaction, and the application to the inner wall of the drinking water steel pipe can form a coating with excellent mechanical properties and high safety. In addition, the ACM grinding column and the gear ring are made of medium / low carbon alloy steel, and the surface is subjected to carbonitriding heat treatment, so that the wear resistance is high, the surface damage of the grinding column and the gear ring in high-speed operation is avoided, the metal content exceeds the standard, and the water quality meets the requirements of GB-5749 drinking water.

Description

Technical Field

[0001] The present invention relates to the field of powder coating preparation, and in particular to a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, and a preparation method and application thereof. Background Art

[0002] Adding a lining or plastic coating to the inner surface of a steel pipe can prevent rust, which can harm health when transporting drinking water, and extend the pipe's service life. Therefore, corrosion protection of the inner surface of steel pipes is crucial. This requires ensuring that the coating releases no or minimal amounts of harmful substances during long-term use, and that the water quality meets the drinking water requirements of GB-5749. Furthermore, the coating must possess good adhesion and deformation resistance.

[0003] In recent years, many powder coating products for the inner surface of steel pipes have been launched, and related technical solutions have also been disclosed in the prior art. For example, the Chinese patent number CN201811155995.3 discloses a food-grade powder coating, its preparation method and application. The prepared coating can meet food-grade hygiene and safety performance, and the curing temperature during coating is 160°C. However, bisphenol A epoxy resin is used in the raw materials, which poses a safety hazard and does not have the property of curing at a low temperature of 120-130°C; another example is the Chinese patent number CN202010025113.2 discloses an anti-corrosion powder coating for drinking water pipes and its preparation method The prepared coating is also used for drinking water pipes, but bisphenol A epoxy resin is also used in the raw materials, which poses a safety hazard and does not have the characteristic of low-temperature curing at 120-130°C; for example, the Chinese patent No. CN202011209403.9 discloses an epoxy powder coating for the inner wall of a drinking water pipe and a preparation method thereof. The prepared coating is applied to the inner wall of a drinking water pipe, but bisphenol A epoxy resin is used in the raw materials (the medium molecular weight solid epoxy resin is GESR904H, the high molecular weight solid epoxy resin is GESR907 and a modified phenol curing agent), which poses a safety hazard and does not have the characteristic of low-temperature curing.

[0004] Therefore, the powder coatings used on the inner surface of steel pipes in the prior art still have the problems of low safety and high energy consumption that need to be solved, and the need for low-temperature curing is required without adding bisphenol A epoxy resin. Summary of the Invention

[0005] Based on this, in order to solve the existing problems of low safety and high energy consumption, and to achieve the use requirements of low-temperature curing without adding bisphenol A epoxy resin, the present invention provides a low-temperature curing powder coating for the inner wall of drinking water steel pipes, and its preparation method and application. The specific technical solutions are as follows:

[0006] A low-temperature curing powder coating for the inner wall of a drinking water steel pipe, comprising the following components in percentage by mass:

[0007] Bisphenol F epoxy resin: 55.000%-65.000%;

[0008] Polyamide curing agent: 5.000%-6.250%;

[0009] Modified alicyclic amine curing agent: 1.125%-1.875%;

[0010] Diphenylimidazoline modified substance: 0.300%-0.800%;

[0011] Leveling agent: 0.500%-1.000%;

[0012] Degassing agent: 0.100%-0.300%;

[0013] Defoaming agent: 0.500%-1.000%;

[0014] Wear-resistant agent: 0.100%-0.300%;

[0015] Hydrophobic silica: 0.500%-1.000%;

[0016] Fused quartz powder: 7.000%-20.000%;

[0017] Mica powder: 5.275%-16.275%;

[0018] Pigment: 0.500%-10.000%;

[0019] Alumina: 0.100%-0.200%;

[0020] The sum of the above mass percentages is 100.000%.

[0021] Furthermore, the bisphenol F epoxy resin has an epoxy content of 600 g / eq to 700 g / eq and a softening point of 70° C. to 80° C.

[0022] Furthermore, the polyamide curing agent has an amine value of 180 mgKOH / g to 219 mgKOH / g and an active hydrogen equivalent of 130 to 140 g / eq.

[0023] Furthermore, the modified alicyclic amine curing agent is methylcyclopentanediamine, the amine value is 450mgKOH / g to 490mgKOH / g, and the active hydrogen equivalent is 60 to 65g / eq.

[0024] Further, the hydrophobic silicon dioxide is a reactant of dimethylsiloxane and silicon dioxide or a reactant of polydimethylsiloxane and silicon dioxide.

[0025] In addition, the application further provides a preparation method of the low-temperature curing powder coating for the inner wall of a drinking water steel pipe, which comprises the following steps:

[0026] The polyamide curing agent, modified alicyclic amine curing agent, diphenylimidazoline modifier, fused quartz powder and mica powder are weighed according to the weight percentage of the formula, and are put into a high-speed mixer for first mixing treatment to obtain a pre-dispersed master batch;

[0027] The bisphenol F type epoxy resin, leveling agent, degassing agent, defoaming agent, wear-resistant agent, hydrophobic silicon dioxide and pigment are weighed according to the weight percentage of the formula, and are put into a high-speed mixer, and then the pre-dispersed master batch is added, and second mixing treatment is carried out to obtain a premixed material;

[0028] The premixed material is put into a single-screw extruder for melt mixing to obtain a high-temperature extruded material;

[0029] The high-temperature extruded material is put into a tablet press for cooling, tabletting and coarse crushing to obtain a fine flaky material with an equivalent diameter of 3-5 cm;

[0030] The fine flaky material is put into an ACM powder mill for fine crushing, and is sieved through a 120-160 mesh screen to obtain powder particles with an average particle size of 40-45 μm;

[0031] Aluminum oxide is weighed according to the weight percentage of the formula, and is then added to the powder particles, and after uniform mixing, a low-temperature curing powder coating for the inner wall of a drinking water steel pipe is obtained.

[0032] Further, the length-diameter ratio of the single-screw extruder is 16:1, and the setting parameters are as follows: the temperature of a first zone is 70-80 DEG C, cooling water is supplied for 3 seconds every 5 seconds, the temperature of a second zone is 80-90 DEG C, cooling water is supplied for 3 seconds every 2 seconds, and the frequency of the main machine is 45-50 Hz.

[0033] Further, the frequency of the main machine of the tablet press is 28-43 Hz, and the surface temperature is 10-15 DEG C.

[0034] Further, the main grinding frequency of the ACM powder mill is 25-45 Hz, the auxiliary grinding frequency is 30-40 Hz, and the feeding frequency is 40-50 Hz; wherein, the grinding column and the gear ring of the ACM powder mill are made of medium / low carbon alloy steel, and are subjected to advanced carbonitriding surface heat treatment, and the hardened layer produced by carbonitriding is more than 3 mm, and the hardness is HRC 60-62.

[0035] The present invention also provides an application of a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, wherein the application is the application of the low-temperature curing powder coating for the inner wall of a drinking water steel pipe on the inner wall of the drinking water steel pipe, and the application method is: electrostatically spraying and / or roller coating and / or suction coating the low-temperature curing powder coating for the inner wall of the drinking water steel pipe on the inner wall of the drinking water steel pipe preheated at 120°C to 130°C.

[0036] 1. The present invention uses a compound of bisphenol F epoxy resin, polyamide curing agent, modified alicyclic amine curing agent and diphenylimidazoline modifier to effectively coat and wet other inorganic materials in the formula, forming a cross-linked body while increasing the adhesion of the coating to the substrate. In addition, the bisphenol F epoxy resin, polyamide curing agent and modified alicyclic amine curing agent all have low softening points and melting points, which are much lower than the cross-linking and curing reaction temperature, thereby ensuring excellent processing performance. At the same time, the bisphenol F epoxy resin does not contain bisphenol A, which can achieve non-toxic material source, eliminating the hidden danger of only soaking the cured coating and then inspecting the soaking liquid for bisphenol A precipitation in the "Standard for Hygienic Safety Evaluation of Drinking Water Transmission and Distribution Equipment and Protective Materials" (2001).

[0037] 2. The polyamide curing agent and modified alicyclic amine curing agent added in the present invention are both highly reactive. Combined with the catalytic effect of the diphenylimidazoline modifier, they can provide a product coating application temperature of 120°C to 130°C, far lower than the application temperature of conventional steel pipe anticorrosive epoxy powders (>200°C), meeting the goals of energy conservation, consumption reduction, and carbon neutrality. Furthermore, the cross-linked product (coating) after the reaction is non-toxic. After long-term immersion in tap water, the water quality still meets the requirements of GB-5749 for drinking water hygiene, environmental protection, and non-toxicity.

[0038] 3. The catalyst of the present invention is added with a modified diphenylimidazoline, and its sealing property of being unblocked at 60°C is utilized to solve the shortcoming of poor storage stability of low-temperature curing type powder coatings, ensure that the product will not pre-react during daily transportation and room temperature storage, and improve product quality.

[0039] 4. The grinding column and ring gear used in this ACM mill are made of medium / low carbon alloy steel and undergo an advanced carbonitriding surface heat treatment. The carbonitriding produces a hardened layer of at least 3mm thick with a hardness of HRC60-62. This significantly improves the mill's wear resistance, preventing surface damage to the grinding column and ring gear during high-speed operation, which could lead to excessive metal content in low-temperature curing anti-corrosion pipe coatings. This meets the drinking water hygiene requirements of GB-5749. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of the preparation process of a low-temperature curing powder coating for the inner wall of a drinking water steel pipe according to Example 1 of the present invention;

[0041] Figure 2 Schematic diagram of the application method of the low-temperature curing powder coating for the inner wall of the drinking water steel pipe prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with its embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] In one embodiment of the present invention, a low-temperature curing powder coating for the inner wall of a drinking water steel pipe is provided. The low-temperature curing powder coating for the inner wall of a drinking water steel pipe comprises the following components in percentage by mass:

[0045] Bisphenol F epoxy resin: 55.000%-65.000%;

[0046] Polyamide curing agent: 5.000%-6.250%;

[0047] Modified alicyclic amine curing agent: 1.125%-1.875%;

[0048] Diphenylimidazoline modified substance: 0.300%-0.800%;

[0049] Leveling agent: 0.500%-1.000%;

[0050] Degassing agent: 0.100%-0.300%;

[0051] Defoaming agent: 0.500%-1.000%;

[0052] Wear-resistant agent: 0.100%-0.300%;

[0053] Hydrophobic silica: 0.500%-1.000%;

[0054] Fused quartz powder: 7.000%-20.000%;

[0055] Mica powder: 5.275%-16.275%;

[0056] Pigment: 0.500%-10.000%;

[0057] Alumina: 0.100%-0.200%;

[0058] The sum of the above mass percentages is 100.000%.

[0059] In one embodiment, the bisphenol F epoxy resin has an epoxy content of 600 g / eq to 700 g / eq and a softening point of 70° C. to 80° C.

[0060] In one embodiment, the polyamide curing agent has an amine value of 180 mgKOH / g to 219 mgKOH / g and an active hydrogen equivalent of 130 to 140 g / eq.

[0061] In one embodiment, the modified alicyclic amine curing agent is methylcyclopentanediamine, the amine value is 450 mgKOH / g to 490 mgKOH / g, and the active hydrogen equivalent is 60 to 65 g / eq.

[0062] In one embodiment, the modified alicyclic amine curing agent has a viscosity of 1500 to 3500 cps at 25°C.

[0063] In one embodiment, the diphenylimidazoline modified substance has a melting point of 120°C to 130°C, a sealing agent deblocking temperature of 60°C, and a density of 1.12 g / cm 3 .

[0064] In one embodiment, the leveling agent is an acrylic leveling agent.

[0065] In one embodiment, the degassing agent is a modified polyethylene wax degassing agent with a melting point of 100°C and a density of 0.95 g / cm 3 , the average particle size is 5μm.

[0066] In one embodiment, the defoaming agent is a polyamide wax defoaming agent with a melting point of 75°C and a density of 1.0 g / cm 3 , the average particle size is 20μm.

[0067] In one embodiment, the wear-resistant material is a polytetrafluoroethylene material with a density of 2.28 g / cm 3 , the average particle size is 3μm.

[0068] In one embodiment, the hydrophobic silica is a reaction product of dimethylsiloxane and silica or a reaction product of polydimethylsiloxane and silica.

[0069] In one embodiment, the average particle size of the hydrophobic silica is 1 μm to 2 μm.

[0070] In one embodiment, the fused quartz powder is obtained by purifying and melting natural quartz.

[0071] In one embodiment, the average particle size of the fused silica powder is 12 μm.

[0072] In one embodiment, the mica powder is sericite.

[0073] In one embodiment, the average particle size of the mica powder is 16 μm to 18 μm, and the diameter-to-thickness ratio is (120 to 150):1.

[0074] In one embodiment, the pigment is at least one of titanium dioxide, phthalocyanine blue, and carbon black.

[0075] In one embodiment, the aluminum oxide is aluminum oxide with an average particle size of 13 nm and a BET surface area of ​​85 to 115 m 2 / g.

[0076] In addition, the present application also provides a method for preparing a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, the preparation method comprising the following steps:

[0077] Weighing a polyamide curing agent, a modified alicyclic amine curing agent, a diphenylimidazoline modified product, fused quartz powder, and mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for a first mixing process to prepare a pre-dispersed masterbatch;

[0078] Weighing bisphenol F epoxy resin, leveling agent, degassing agent, defoaming agent, wear-resistant agent, hydrophobic silica and pigment according to the weight percentage of the formula, and putting them into a high-speed mixer, and then adding the pre-dispersed masterbatch to perform a second mixing process, thereby preparing a premixed material;

[0079] The premixed material is put into a single screw extruder for melt mixing to obtain a high-temperature extrusion material;

[0080] The high-temperature extruded material is put into a tablet press for cooling, tableting and coarse crushing to obtain fine fragments with an equivalent diameter of 3 cm to 5 cm;

[0081] The finely pulverized material was put into an ACM mill for fine grinding, and sieved through a 120-160 mesh sieve to obtain powder particles with an average particle size of 40 μm to 45 μm;

[0082] Aluminum oxide is weighed according to the weight percentage of the formula, and then added to the powder particles. After uniform mixing, a low-temperature curing powder coating for the inner wall of a drinking water steel pipe is obtained.

[0083] In one embodiment, the rotation speed of the first mixing process is 1500 r / min to 2000 r / min, and the mixing time is 1 min to 3 min.

[0084] In one embodiment, the rotation speed of the second mixing process is 800 rpm to 1000 rpm, and the mixing time is 3 min to 5 min.

[0085] In one embodiment, the length-to-diameter ratio of the single-screw extruder is 16:1.

[0086] In one embodiment, the screw structure of the single-screw extruder is 50% feeding section, 30% mixing section 1 (45° angle screw block), and 20% mixing section 2 (90° angle screw block).

[0087] In one embodiment, the aspect ratio of the single-screw extruder is 16:1, and the setting parameters are as follows: the temperature of zone 1 is 70°C to 80°C, cooling water is passed for 3S at an interval of 5S, the temperature of zone 2 is 80°C to 90°C, cooling water is passed for 3S at an interval of 2S, and the main engine frequency is 45Hz to 50Hz.

[0088] In one embodiment, the frequency of the tablet press main unit is 28 Hz to 43 Hz, and the surface temperature is 10° C. to 15° C.

[0089] In one embodiment, the main grinding frequency of the ACM mill is 25Hz~45Hz, the auxiliary grinding frequency is 30Hz~40Hz, and the feeding frequency is 40Hz~50Hz; wherein, the grinding column and the gear ring of the ACM mill are made of medium / low carbon alloy steel and undergo advanced carbonitriding surface heat treatment. The hardened layer produced by carbonitriding is more than 3mm and the hardness is HRC60-62.

[0090] The present invention also provides an application of a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, wherein the application is the application of the low-temperature curing powder coating for the inner wall of a drinking water steel pipe on the inner wall of the drinking water steel pipe, and the application method is: electrostatically spraying and / or roller coating and / or suction coating the low-temperature curing powder coating for the inner wall of the drinking water steel pipe on the inner wall of the drinking water steel pipe preheated at 120°C to 130°C.

[0091] In one embodiment, the time for preheating the inner wall of the drinking water steel pipe is 30 minutes to 60 minutes.

[0092] The above solution can obtain a powder coating with high safety performance and long-term storage stability by optimizing the composition and ratio of the powder coating. When applied to the inner wall of drinking water steel pipes, it still has the advantages of high safety and excellent coating adhesion.

[0093] The embodiments of the present invention will be described in detail below with reference to specific examples.

[0094] Example 1:

[0095] A low-temperature curing powder coating for the inner wall of a drinking water steel pipe comprises the following components in percentage by mass: 60.000% of bisphenol F epoxy resin; 5.625% of a polyamide curing agent; 1.500% of a modified alicyclic amine curing agent; 0.500% of a diphenylimidazoline modifier; 0.500% of a leveling agent; 0.300% of a degassing agent; 0.700% of a defoaming agent; 0.200% of a wear-resistant agent; 0.750% of hydrophobic silica; 11.277% of fused quartz powder; 8.498% of mica powder; 10.000% of titanium dioxide; and 0.150% of aluminum oxide.

[0096] A method for preparing a low-temperature curing powder coating for the inner wall of a drinking water steel pipe comprises the following steps:

[0097] Step 1: Weigh the polyamide curing agent, modified alicyclic amine curing agent, diphenylimidazoline modifier, fused quartz powder and mica powder according to the weight percentage of the formula, and put them into a high-speed mixer for mixing (mixer parameters: mixing motor speed is 1700 r / min, mixing time is 2 min) to prepare a pre-dispersed masterbatch;

[0098] Step 2: Weigh bisphenol F epoxy resin, leveling agent, degassing agent, defoaming agent, wear-resistant agent, hydrophobic silica and titanium dioxide according to the weight percentage of the formula and put them into a high-speed mixer, and add the pre-dispersed masterbatch and mix them (high-speed mixer parameters: mixing motor speed is 900 r / min, grinding motor speed is 1100 r / min, mixing time is 4 min), thereby preparing a premixed material;

[0099] Step 3: The premixed material was put into a single-screw extruder for melt mixing (parameter settings: the temperature of the first zone was 75° C., cooling water was passed through for 3 seconds at an interval of 5 seconds, the temperature of the second zone was 85° C., cooling water was passed through for 3 seconds at an interval of 2 seconds, and the main engine frequency was 50 Hz) to obtain a high-temperature extruded material;

[0100] Step 4: The high-temperature extruded material is put into a tablet press for cooling, tableting and coarse crushing (parameter settings: main machine frequency is 43 Hz, surface temperature is 10° C.), to obtain fine fragments with an equivalent diameter of 3 cm to 5 cm;

[0101] Step 5: The fine fragments were put into an ACM mill for fine grinding (parameter settings: main grinding frequency 30 Hz, auxiliary grinding frequency 35 Hz, feeding frequency 47 Hz), and sieved through a 160-mesh sieve to obtain powder particles with an average particle size of 43 μm;

[0102] Step 6: Add the aluminum oxide in the formula to the powder particles and mix them evenly to obtain a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, which is recorded as sample powder 1.

[0103] The application method of this embodiment includes: using a suction coating process to apply the above-mentioned sample powder 1 to the inner wall of a DN50 drinking water steel pipe that has been preheated at 125°C for 50 minutes, and using the residual heat of the drinking water steel pipe to initiate and complete the cross-linking and curing reaction, so that a coating is formed on the inner wall of the drinking water steel pipe, which is recorded as coating 1.

[0104] Example 2:

[0105] A low-temperature curing powder coating for the inner wall of a drinking water steel pipe comprises the following components in percentage by mass: 55.000% of bisphenol F epoxy resin; 5.000% of polyamide curing agent; 1.55% of modified alicyclic amine curing agent; 0.300% of diphenylimidazoline modifier; 1.000% of leveling agent; 0.100% of degassing agent; 0.500% of defoaming agent; 0.100% of anti-wear agent; 0.500% of hydrophobic silica; 20.000% of fused quartz powder; 15.000% of mica powder; 0.7000% of phthalocyanine blue; 0.100% of carbon black; and 0.150% of aluminum oxide.

[0106] A method for preparing a low-temperature curing powder coating for the inner wall of a drinking water steel pipe comprises the following steps:

[0107] Step 1: Weigh the polyamide curing agent, modified alicyclic amine curing agent, diphenylimidazoline modifier, fused quartz powder and mica powder according to the weight percentage of the formula, and put them into a high-speed mixer for mixing (mixer parameters: mixing motor speed is 1500 r / min, mixing time is 2 min) to prepare a pre-dispersed masterbatch;

[0108] Step 2: Weigh bisphenol F epoxy resin, leveling agent, degassing agent, defoaming agent, wear-resistant agent, hydrophobic silica, phthalocyanine blue and carbon black according to the weight percentage of the formula and put them into a high-speed mixer, and add the pre-dispersed masterbatch and mix them (high-speed mixer parameters: mixing motor speed is 900 r / min, grinding motor speed is 1000 r / min, mixing time is 3 min), thereby preparing a premixed material;

[0109] Step 3: The premixed material was put into a single-screw extruder for melt mixing (parameter settings: the temperature of the first zone was 80° C., cooling water was passed through for 3 seconds at an interval of 5 seconds, the temperature of the second zone was 90° C., cooling water was passed through for 3 seconds at an interval of 2 seconds, and the main engine frequency was 45 Hz) to obtain a high-temperature extruded material;

[0110] Step 4: The high-temperature extruded material is put into a tablet press for cooling, tableting and coarse crushing (parameter settings: main machine frequency is 28 Hz, surface temperature is 15° C.), to obtain fine fragments with an equivalent diameter of 3 cm to 5 cm;

[0111] Step 5: The fine fragments were put into an ACM mill for fine grinding (parameter settings: main grinding frequency 25 Hz, auxiliary grinding frequency 30 Hz, feeding frequency 50 Hz), and sieved through a 160-mesh sieve to obtain powder particles with an average particle size of 43 μm;

[0112] Step 6: Add the aluminum oxide in the formula to the powder particles and mix them evenly to obtain a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, which is recorded as sample powder 2.

[0113] The application method of this embodiment includes: using a suction coating process to apply the above-mentioned sample powder 2 to the inner wall of a DN50 drinking water steel pipe that has been preheated at 125°C for 50 minutes, and using the residual heat of the drinking water steel pipe to initiate and complete the cross-linking and curing reaction, so that a coating is formed on the inner wall of the drinking water steel pipe, which is recorded as coating 2.

[0114] Comparative Example 1:

[0115] The powder coating of Comparative Example 1 includes the following components in percentage by mass: bisphenol A epoxy resin: 60.000%; polyamide curing agent: 5.625%; modified alicyclic amine curing agent: 1.500%; diphenylimidazoline modifier: 0.500%; leveling agent: 0.500%; degassing agent: 0.300%; defoaming agent: 0.700%; wear-resistant agent: 0.200%; hydrophobic silica: 0.750%; fused quartz powder: 11.277%; mica powder: 8.498%; titanium dioxide: 10.000%; aluminum oxide: 0.150%;

[0116] Among them, the softening point of bisphenol A epoxy resin is 90°C.

[0117] The preparation method of the powder coating of Comparative Example 1 comprises the following steps:

[0118] Step 1: Weigh the polyamide curing agent, modified alicyclic amine curing agent, diphenylimidazoline modifier, fused quartz powder and mica powder according to the weight percentage of the formula, and put them into a high-speed mixer for mixing (mixer parameters: mixing motor speed is 1500 r / min, mixing time is 2 min) to prepare a pre-dispersed masterbatch;

[0119] Step 2: Weigh bisphenol A epoxy resin, leveling agent, degassing agent, defoaming agent, wear-resistant agent, hydrophobic silica and titanium dioxide according to the weight percentage of the formula and put them into a high-speed mixer, and add the pre-dispersed masterbatch and mix them (high-speed mixer parameters: mixing motor speed is 900 r / min, crushing motor speed is 1000 r / min, mixing time is 3 min), thereby preparing a premixed material;

[0120] Step 3: The premixed material was put into a single-screw extruder for melt mixing (parameter settings: the temperature of the first zone was 80° C., cooling water was passed through for 3 seconds at an interval of 5 seconds, the temperature of the second zone was 90° C., cooling water was passed through for 3 seconds at an interval of 2 seconds, and the main engine frequency was 50 Hz) to obtain a high-temperature extruded material;

[0121] Step 4: The high-temperature extruded material is put into a tablet press for cooling, tableting and coarse crushing (parameter settings: main machine frequency is 28 Hz, surface temperature is 15° C.), to obtain fine fragments with an equivalent diameter of 3 cm to 5 cm;

[0122] Step 5: The fine fragments were put into an ACM mill for fine grinding (parameter settings: main grinding frequency 25 Hz, auxiliary grinding frequency 30 Hz, feeding frequency 50 Hz), and sieved through a 160-mesh sieve to obtain powder particles with an average particle size of 43 μm;

[0123] Step 6: Add the aluminum oxide in the formula to the powder particles and mix them evenly to obtain a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, which is recorded as comparative sample powder 1.

[0124] The application method of this comparative example includes: using a suction coating process to apply the above-mentioned comparative sample powder 1 to the inner wall of a DN50 drinking water steel pipe that has been preheated at 125°C for 50 minutes, and using the residual heat of the drinking water steel pipe to initiate and complete the cross-linking and curing reaction, so that a coating is formed on the inner wall of the drinking water steel pipe, which is recorded as comparative coating 1.

[0125] Comparative Example 2:

[0126] The powder coating of Comparative Example 2 includes the following components in percentage by mass: bisphenol F epoxy resin: 60.000%; polyamide curing agent: 5.625%; modified alicyclic amine curing agent: 1.500%; diphenylimidazoline: 0.500%; leveling agent: 0.500%; degassing agent: 0.300%; defoaming agent: 0.700%; wear resistant agent: 0.200%; hydrophobic silica: 0.750%; fused quartz powder: 11.277%; mica powder: 8.498%; titanium dioxide: 10.000%; and aluminum oxide: 0.150%.

[0127] The purity of diphenylimidazoline in the formula is above 99.5%, and the active groups are not blocked.

[0128] The preparation method and application method of the powder coating in Comparative Example 2 are the same as those in Example 1, to obtain comparative powder sample 2 and comparative coating 2.

[0129] Comparative Example 3:

[0130] The difference between Comparative Example 3 and Example 1 is that no polyamide curing agent is added in Comparative Example 3, and the rest is the same as Example 1, to obtain comparative powder 3 and comparative coating 3.

[0131] Comparative Example 4:

[0132] The difference between Comparative Example 4 and Example 1 is that no modified alicyclic amine curing agent is added in Comparative Example 4. Other steps are the same as in Example 1, and comparative powder 4 and comparative coating 4 are obtained.

[0133] Comparative Example 5:

[0134] The difference between Comparative Example 5 and Example 1 is that hydrophobic silica is not added in Comparative Example 5, and the rest is the same as Example 1, to obtain comparative sample powder 5 and comparative coating 5.

[0135] The performance tests were performed on the above coatings 1 to 2 and comparative coatings 1 to 5, respectively. The test standards and results are shown in Table 1 below.

[0136] Among them, the powder gel time (200℃) refers to GB / T6554-2003; the coating roughness refers to GB / T6062-2009, unit is μm; the coating pinhole test refers to CJ / T120-2016; the coating adhesion / grade (75℃±3℃, 48h) refers to CJ / T120-2016; the coating impact strength (hammer weight 6.3kg, drop height 1000mm) refers to CJ / T120-2016; the coating bending The test (bending angle 30°) refers to CJ / T120-2016. The physical and chemical testing of the coating refers to the sanitary safety evaluation specifications for drinking water distribution equipment and protective materials. The bisphenol A test of the coating refers to EU Commission Regulation 1935 / 2004 (October 27, 2004), French Directive 2007-766 and subsequent amendments and French Decree 2012-1442 (December 24, 2012) - Total content of bisphenol A (BPA).

[0137] Table 1: Test results

[0138]

[0139] Analysis of the data in Table 1 demonstrates that the present invention, through the compounding of bisphenol F epoxy resin, polyamide curing agent, modified alicyclic amine curing agent, and diphenylimidazoline modifier, effectively coats and wets the other inorganic materials in the formulation, forming a crosslinked structure while also increasing the coating's adhesion to the substrate. Furthermore, no bisphenol A components are leached out after immersion in drinking water, demonstrating high safety. The present invention combines the polyamide curing agent and modified alicyclic amine curing agent with the catalytic effect of the diphenylimidazoline modifier to achieve low-temperature curing.

[0140] In Comparative Example 1, the bisphenol F epoxy resin is replaced with the commonly used bisphenol A epoxy resin on the market. Compared with Coating 1, the surface roughness, adhesion, and deformation resistance of Comparative Coating 1 are consistent. Although it meets the physical, chemical, and toxicological tests of the "Specifications for the Hygiene and Safety Evaluation of Drinking Water Distribution Equipment and Protective Materials", after the coating is digested according to "European Commission Regulation 1935 / 2004 (October 27, 2004), French Directive 2007-766 and subsequent amendments and French Decree 2012-1442 (December 24, 2012) - Total Content of Bisphenol A (BPA)", the free bisphenol A content in the coating is detected to be as high as 15.1 mg / kg. If the inner coating of the drinking water steel pipe is lost, the fine powder will be suspended in the drinking water, which will damage the human endocrine system and pose a safety hazard.

[0141] In Comparative Example 2, the modified diphenylimidazoline was replaced with a raw material of diphenylimidazoline having a purity of 99.5% or more and whose active groups were not blocked. The initial performance of the powder coating was close to that of the present invention.

[0142] Comparative Example 3 did not add polyamide curing agent, and Comparative Example 4 did not add modified alicyclic amine curing agent, which affected the adhesion of the coating. This shows that the compounded curing agent of the present invention helps to improve the adhesion of the coating and has a significant effect on the impact strength and flexibility of the coating.

[0143] Comparative Example 5 does not add hydrophobic silica, which slightly affects the coating performance, but Example 1 is more excellent.

[0144] In order to test the storage performance of the powder coating of the present invention, the sample powder 1 of Example 1 and the comparative powder samples 1 to 5 of Comparative Examples 1 to 5 were subjected to a storage stability test. The test method was to place them at 40°C for 7 days, and then repeat the above-mentioned powder gelation, coating roughness, coating adhesion, coating impact strength, coating bending test, coating toxicology test and coating bisphenol A test. The results are shown in Table 2.

[0145] Table 2: Storage performance results

[0146]

[0147]

[0148] From the data analysis in Table 2, it can be seen that the powder coating of the present invention has the characteristic of excellent storage stability.

[0149] In Comparative Example 1, the bisphenol F epoxy resin was replaced with the commonly used bisphenol A epoxy resin on the market. Although the storage was stable, the adhesion of the coating was not as good as that of Coating 1. Moreover, after the coating was digested according to "European Commission Regulation 1935 / 2004 (October 27, 2004), French Directive 2007-766 and subsequent amendments and French Decree 2012-1442 (December 24, 2012) - Total content of bisphenol A (BPA)", free bisphenol A was detected in the coating, which is less safe.

[0150] In Comparative Example 2, the modified diphenylimidazoline was replaced with a raw material in which the active groups of diphenylimidazoline were not blocked and the storage stability of the obtained powder coating was significantly reduced, and the gelation time was shortened, indicating that the powder had pre-reacted during storage, and the roughness of the coating surface and the adhesion of the coating to the substrate were affected, resulting in a significant decrease in the performance of the coating.

[0151] Comparative Example 3 did not add a polyamide curing agent, Comparative Example 4 did not add a modified alicyclic amine curing agent, and Comparative Example 5 did not add hydrophobic silica. The overall storage performance was relatively stable, but the performance of the coating was still inferior to that of Coating 1. This illustrates that the present invention, through the compounding of the components, as a technical solution as a whole, interacts with each other, helping to address the shortcomings of low-temperature curing type powder coatings with poor storage stability, ensuring that the product does not pre-react during daily transportation and room temperature storage, thereby improving product quality. At the same time, the powder coating forms a coating with excellent adhesion, impact resistance, and bending properties on the inner wall of a drinking water steel pipe preheated at 120°C to 130°C, which not only reduces energy consumption but also has high safety.

[0152] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0153] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A low-temperature curing powder coating for the inner wall of a drinking water steel pipe, characterized in that: The low-temperature curing powder coating for the inner wall of the drinking water steel pipe comprises the following components in percentage by mass: Bisphenol F epoxy resin: 55.000%-65.000%; Polyamide curing agent: 5.000%-6.250%; Modified alicyclic amine curing agent: 1.125%-1.875%; Diphenylimidazoline modified substance: 0.300%-0.800%; Leveling agent: 0.500%-1.000%; Degassing agent: 0.100%-0.300%; Defoaming agent: 0.500%-1.000%; Wear-resistant agent: 0.100%-0.300%; Hydrophobic silica: 0.500%-1.000%; Fused quartz powder: 7.000%-20.000%; Mica powder: 5.275%-16.275%; Pigment: 0.500%-10.000%; Alumina: 0.100%-0.200%; The sum of the above mass percentages is 100.000%; Wherein, the deblocking temperature of the modified diphenylimidazoline is 60°C.

2. The low-temperature curing powder coating for the inner wall of a drinking water steel pipe according to claim 1, characterized in that: The bisphenol F epoxy resin has an epoxy content of 600 g / eq to 700 g / eq and a softening point of 70° C. to 80° C.

3. The low-temperature curing powder coating for the inner wall of a drinking water steel pipe according to claim 1, characterized in that: The polyamide curing agent has an amine value of 180 mgKOH / g to 219 mgKOH / g and an active hydrogen equivalent of 130 g / eq to 140 g / eq.

4. The low-temperature curing powder coating for the inner wall of a drinking water steel pipe according to claim 1, characterized in that: The modified alicyclic amine curing agent is methylcyclopentanediamine, with an amine value of 450 mgKOH / g to 490 mgKOH / g and an active hydrogen equivalent of 60 g / eq to 65 g / eq.

5. The low-temperature curing powder coating for the inner wall of a drinking water steel pipe according to claim 1, characterized in that: The hydrophobic silica is a reaction product of dimethylsiloxane and silica or a reaction product of polydimethylsiloxane and silica.

6. A method for preparing a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, characterized in that: The preparation method is used to prepare the low-temperature curing powder coating for the inner wall of a drinking water steel pipe according to any one of claims 1 to 5, and the preparation method comprises the following steps: Weighing a polyamide curing agent, a modified alicyclic amine curing agent, a diphenylimidazoline modified product, fused quartz powder, and mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for a first mixing process to prepare a pre-dispersed masterbatch; Weighing bisphenol F epoxy resin, leveling agent, degassing agent, defoaming agent, wear-resistant agent, hydrophobic silica and pigment according to the weight percentage of the formula, and putting them into a high-speed mixer, and then adding the pre-dispersed masterbatch to perform a second mixing process, thereby preparing a premixed material; The premixed material is put into a single screw extruder for melt mixing to obtain a high-temperature extrusion material; The high-temperature extruded material is put into a tablet press for cooling, tableting and coarse crushing to obtain fine fragments with an equivalent diameter of 3 cm to 5 cm; The fine fragments were put into an ACM grinder for fine grinding, and sieved through a 120-160 mesh sieve to obtain powder particles with an average particle size of 40 μm to 45 μm; Aluminum oxide is weighed according to the weight percentage of the formula, and then added to the powder particles. After uniform mixing, a low-temperature curing powder coating for the inner wall of a drinking water steel pipe is obtained.

7. The preparation method according to claim 6, characterized in that The single-screw extruder has an aspect ratio of 16:1, and the setting parameters are: the temperature of zone 1 is 70°C~80°C, cooling water is passed for 3S every 5S, the temperature of zone 2 is 80°C~90°C, cooling water is passed for 3S every 2S, and the main engine frequency is 45Hz~50Hz.

8. The preparation method according to claim 6, characterized in that The frequency of the tablet press main machine is 28 Hz to 43 Hz, and the surface temperature is 10° C. to 15° C.

9. The preparation method according to claim 6, characterized in that The main grinding frequency of the ACM mill is 25Hz~45Hz, the auxiliary grinding frequency is 30Hz~40Hz, and the feeding frequency is 40Hz~50Hz; among them, the grinding column and gear ring of the ACM mill are made of medium / low carbon alloy steel and undergo advanced carbonitriding surface heat treatment. The hardened layer produced by carbonitriding is more than 3mm and the hardness is HRC60-62.

10. An application of a low-temperature curing powder coating for the inner wall of a drinking water steel pipe, characterized in that: The application is the application of the low-temperature curing powder coating for the inner wall of the drinking water steel pipe according to any one of claims 1 to 5 on the inner wall of the drinking water steel pipe, and the application method is: electrostatically spraying and / or roller coating and / or suction coating the low-temperature curing powder coating for the inner wall of the drinking water steel pipe on the inner wall of the drinking water steel pipe preheated at 120°C to 130°C.

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