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

Abstract

The invention discloses a low-temperature curing powder coating for the inner wall of a drinking water steel pipe as well as a preparation method and application thereof. The bisphenol F type epoxy resin, the polyamide curing agent, the modified alicyclic amine curing agent and the diphenylimidazoline modifier are compounded for use, other inorganic materials in the formula can be effectively coated and wetted, the adhesive force of the coating to a base material is also increased while a cross-linked body is formed, and the catalytic action of the diphenylimidazoline modifier improves the adhesion of the coating to the base material. And the product coating construction temperature of 120-130 DEG C can be provided. By adding the diphenyl imidazoline modifier, the pre-reaction can be reduced, and a coating with excellent mechanical property and high safety can be formed when the coating is applied to the inner wall of the drinking water steel pipe. Besides, the grinding column and the gear ring of the ACM flour mill are made of medium / low carbon alloy steel, carbonitriding surface heat treatment is carried out, the abrasion resistance is high, the situation that the metal content exceeds the standard due to the fact that the surfaces of the grinding column and the gear ring are damaged in the high-speed running process is avoided, and it is further ensured that the anhydrous quality meets the requirement of GB-5749 drinking water.

Description

Technical Field

[0001] The 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 lining or plastic coating (coating) to the inner surface of steel pipes can prevent the metal of steel pipes from rusting, prevent rust and corrosion when steel pipes transport drinking water, endanger health and extend the service life of steel pipes. Therefore, corrosion protection of the inner surface of steel pipes is very important. The corrosion protection of the inner surface of steel pipes must ensure that no harmful substances are dissolved or slightly dissolved in the coating during long-term use and that the water quality meets the requirements of GB-5749 drinking water; secondly, it is necessary to ensure that the coating has 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 and 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, but bisphenol A epoxy resin is used in the raw materials, which poses a safety hazard and does not have the characteristic 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 coating applied to the inner surface of the steel pipe in the prior art still has the problems of low safety and high energy consumption that need to be solved, and the demand for low-temperature curing is achieved 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 a drinking water steel pipe and a preparation method and application thereof. The specific technical scheme is as follows:

[0006] A low-temperature curing powder coating for the inner wall of a drinking water steel pipe, the 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 epoxide content of 600 g / eq to 700 g / eq and a softening point of 70° C. to 80° C.

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

[0023] Furthermore, 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.

[0024] Furthermore, the hydrophobic silica is a reaction product of dimethylsiloxane and silica or a reaction product of polydimethylsiloxane and silica.

[0025] 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:

[0026] Weighing a polyamide curing agent, a modified alicyclic amine curing agent, a diphenyl imidazoline modified substance, a fused quartz powder and a mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for a first mixing treatment to obtain a pre-dispersed masterbatch;

[0027] 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;

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

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

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

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

[0032] Furthermore, the aspect ratio of the single screw extruder is 16:1, and the setting parameters are that 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.

[0033] Furthermore, the frequency of the tablet press main machine is 28 Hz to 43 Hz, and the surface temperature is 10° C. to 15° C.

[0034] Furthermore, 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 gear ring of the ACM mill are made of medium / low carbon alloy steel, and undergo advanced carbonitriding surface heat treatment, and the hardened layer produced by carbonitriding is more than 3mm and the hardness is HRC60-62.

[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 can effectively coat and wet other inorganic materials in the formula by compounding bisphenol F epoxy resin, polyamide curing agent, modified alicyclic amine curing agent and diphenyl imidazoline modifier, and form 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 temperatures, which are much lower than the cross-linking curing reaction temperature, and can ensure excellent processing performance; at the same time, the bisphenol F epoxy resin does not contain bisphenol A substances, and can achieve non-toxic materials at the source, which can eliminate the hidden danger of only soaking the cured coating and then checking whether the soaking liquid has bisphenol A substances precipitated in the "Sanitary Safety Evaluation Standard for Drinking Water 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, and can provide a product coating construction temperature of 120°C to 130°C in combination with the catalytic effect of the diphenylimidazoline modifier, which is much lower than the construction temperature of conventional steel pipe anticorrosive epoxy powder>200°C, and meets the goals of energy saving and carbon neutrality. Moreover, the cross-linked body (coating) after the reaction is a non-toxic material. After long-term immersion of the coating in tap water, the water quality still meets the requirements of GB-5749 for drinking water hygiene, green environmental protection, and non-toxicity.

[0038] 3. The catalyst of the modified diphenylimidazoline is added to solve the disadvantage of poor storage stability of low-temperature curing type powder coatings by utilizing its sealing property of being unblocked at 60°C, ensuring that no pre-reaction occurs during daily transportation and room temperature storage of the product, thereby improving product quality.

[0039] 4. The grinding column and gear ring of the ACM mill used in the production of this invention are made of medium / low carbon alloy steel, and are subjected to advanced carbonitriding surface heat treatment. The hardened layer produced by carbonitriding is more than 3mm and the hardness is HRC60-62. This greatly improves the wear resistance of the mill, avoids the excessive metal content in the low-temperature curing anti-corrosion pipeline coating caused by the surface damage of the grinding column and gear ring during the high-speed operation of the ACM mill, and meets the requirements of GB-5749 drinking water hygiene. 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 solution 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 implementation methods described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

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

[0044] A low-temperature curing powder coating for the inner wall of a drinking water steel pipe in one embodiment of the present invention 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 1500-3500 cps@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 defoamer is a polyamide wax defoamer 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 diphenyl imidazoline modified substance, a fused quartz powder and a mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for a first mixing treatment to obtain 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 a fine fragment material with an equivalent diameter of 3 cm to 5 cm;

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

[0082] Alumina is weighed according to the weight percentage of the formula, and then added to the powder particles. After mixing evenly, 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 1500r / min to 2000r / min, and the mixing time is 1min to 3min.

[0084] In one embodiment, the rotation speed of the second mixing process is 800 r / min to 1000 r / min, 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% of the feeding section, 30% of the mixing section 1 (screw block with a 45° angle), and 20% of the mixing section 2 (screw block with a 90° angle).

[0087] In one embodiment, the aspect ratio of the single screw extruder is 16:1, and the setting parameters are that 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 machine 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 gear ring of the ACM mill are made of medium / low carbon alloy steel, and advanced carbonitriding surface heat treatment is performed, and 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 of the embodiments, the inner wall of the drinking water steel pipe is preheated for 30 minutes to 60 minutes.

[0092] The above scheme 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] Embodiment 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: bisphenol F type epoxy resin: 60.000%; polyamide curing agent: 5.625%; modified alicyclic amine curing agent: 1.500%; diphenyl imidazoline 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%;

[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, weighing a polyamide curing agent, a modified alicyclic amine curing agent, a diphenyl imidazoline modifier, a fused quartz powder and a mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for mixing (mixer parameters: mixing motor speed is 1700r / min, mixing time is 2min), to obtain a pre-dispersed masterbatch;

[0098] Step 2, weighing 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 putting them into a high-speed mixer, and adding the pre-dispersed masterbatch, mixing (high-speed mixer parameters: mixing motor speed is 900r / min, crushing motor speed is 1100r / min, mixing time is 4min), thereby preparing a premixed material;

[0099] Step 3, putting the premixed material into a single screw extruder for melt mixing (parameter settings: temperature of zone 1 is 75° C., cooling water is passed for 3S at intervals of 5S, temperature of zone 2 is 85° C., cooling water is passed for 3S at intervals of 2S, and main engine frequency is 50 Hz) to obtain a high-temperature extrusion material;

[0100] Step 4: putting the high-temperature extruded material into a tablet press for cooling, tableting and coarse crushing (parameter setting: 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 are put into an ACM mill for fine grinding (parameter settings: main mill frequency 30 Hz, auxiliary mill 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 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] Embodiment 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: bisphenol F epoxy resin: 55.000%; polyamide curing agent: 5.000%; modified alicyclic amine curing agent: 1.55%; diphenyl imidazoline modifier: 0.300%; leveling agent: 1.000%; degassing agent: 0.100%; defoaming agent: 0.500%; wear-resistant agent: 0.100%; hydrophobic silica: 0.500%; fused quartz powder: 20.000%; mica powder: 15.000%; phthalocyanine blue: 0.7000%; carbon black: 0.100%; aluminum oxide: 0.150%;

[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, weighing a polyamide curing agent, a modified alicyclic amine curing agent, a diphenyl imidazoline modifier, a fused quartz powder and a mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for mixing (mixer parameters: mixing motor speed is 1500r / min, mixing time is 2min) to obtain a pre-dispersed masterbatch;

[0108] Step 2, weighing 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 putting them into a high-speed mixer, and adding the pre-dispersed masterbatch, mixing (high-speed mixer parameters: mixing motor speed is 900r / min, crushing motor speed is 1000r / min, mixing time is 3min), thereby preparing a premixed material;

[0109] Step 3, putting the premixed material into a single screw extruder for melt mixing (parameter settings: temperature of zone 1 is 80° C., cooling water is passed for 3S at intervals of 5S, temperature of zone 2 is 90° C., cooling water is passed for 3S at intervals of 2S, and main engine frequency is 45 Hz) to obtain a high-temperature extrusion material;

[0110] Step 4: putting the high-temperature extruded material into a tablet press for cooling, tableting and coarse crushing (parameter setting: 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 are put into an ACM mill for fine grinding (parameter settings: main mill frequency 25 Hz, auxiliary mill 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 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 type epoxy resin: 60.000%; polyamide curing agent: 5.625%; modified alicyclic amine curing agent: 1.500%; diphenyl imidazoline 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, weighing a polyamide curing agent, a modified alicyclic amine curing agent, a diphenyl imidazoline modifier, a fused quartz powder and a mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for mixing (mixer parameters: mixing motor speed is 1500r / min, mixing time is 2min) to obtain a pre-dispersed masterbatch;

[0119] Step 2, weighing 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 putting them into a high-speed mixer, and adding the pre-dispersed masterbatch, and mixing (high-speed mixer parameters: mixing motor speed is 900r / min, crushing motor speed is 1000r / min, mixing time is 3min), thereby preparing a premixed material;

[0120] Step 3, putting the premixed material into a single screw extruder for melt mixing (parameter settings: temperature of zone 1 is 80° C., cooling water is passed for 3S at intervals of 5S, temperature of zone 2 is 90° C., cooling water is passed for 3S at intervals of 2S, and main engine frequency is 50 Hz) to obtain a high-temperature extrusion material;

[0121] Step 4: putting the high-temperature extruded material into a tablet press for cooling, tableting and coarse crushing (parameter setting: 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 are put into an ACM mill for fine grinding (parameter settings: main mill frequency 25 Hz, auxiliary mill 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 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 type epoxy resin: 60.000%; polyamide curing agent: 5.625%; modified alicyclic amine curing agent: 1.500%; diphenyl imidazoline: 0.500%; leveling agent: 0.500%; degassing agent: 0.300%; defoaming agent: 0.700%; wear agent: 0.200%; hydrophobic silica: 0.750%; fused quartz powder: 11.277%; mica powder: 8.498%; titanium dioxide: 10.000%; 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, and a comparative powder sample 2 and a comparative coating 2 are obtained.

[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 sample 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, and the rest is the same as Example 1, to obtain comparative sample powder 4 and comparative coating 4.

[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 Test (bending angle 30°), refer to CJ / T120-2016; physical and chemical inspection of coating, refer to the sanitary safety evaluation specifications for drinking water distribution equipment and protective materials; coating bisphenol A test 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] From the data analysis of Table 1, it can be seen that the present invention can effectively coat and wet other inorganic materials in the formula by compounding bisphenol F epoxy resin, polyamide curing agent, modified alicyclic amine curing agent and diphenyl imidazoline modifier, while forming a cross-linked body, increasing the adhesion of the coating to the substrate, and no bisphenol A component is precipitated after drinking water immersion, and the safety is high. The present invention compounds the polyamide curing agent and the modified alicyclic amine curing agent, and cooperates with the catalytic effect of the diphenyl imidazoline modifier to achieve low-temperature curing.

[0140] In Comparative Example 1, bisphenol F epoxy resin is replaced by bisphenol A epoxy resin commonly used 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 "Sanitary Safety Evaluation Specification for Drinking Water Distribution Equipment and Protective Materials", after the coating is digested by "EU Commission Regulation 1935 / 2004 (October 27, 2004), French Directive 2007-766 and Subsequent Amendment Directives and French Decree 2012-1442 (December 24, 2012) - Total Content of Bisphenol A (BPA)", it is detected that the free bisphenol A content in the coating is as high as 15.1 mg / kg. If the inner coating of the drinking water steel pipe is lost, the micropowder is 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 by a raw material of diphenylimidazoline with a purity of more than 99.5% and whose active groups were not blocked. The initial performance was close to that of the powder coating 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 did not add hydrophobic silica, which slightly affected the coating performance, but Example 1 was 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 sample powders 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 of 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, bisphenol F epoxy resin is replaced with bisphenol A epoxy resin commonly used on the market. Although storage is stable, the adhesion of the coating is not as good as that of coating 1. After the coating is digested according 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)", free bisphenol A is 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 sealed and the storage stability of the obtained powder coating was significantly reduced, and the gelation time was shortened, indicating that the powder had a pre-reaction during the storage process, and the roughness of the coating surface and the adhesion of the coating to the substrate were affected, resulting in a significant reduction in the performance of the coating.

[0151] Comparative Example 3 does not add polyamide curing agent, Comparative Example 4 does not add modified alicyclic amine curing agent, and Comparative Example 5 does not add hydrophobic silica. The overall storage performance is relatively stable, but the performance of the coating is still not as good as that of Coating 1. It is explained that after the components are compounded and used in the present invention, as a whole technical solution, there is interaction between the components, which helps to solve the disadvantage 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, improve product quality, and at the same time, the powder coating forms a coating with excellent adhesion, impact and bending properties on the inner wall of the drinking water steel pipe preheated at 120°C to 130°C, which not only has low energy consumption but also has the characteristics of high safety.

[0152] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached 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%.

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 type 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, the amine value is 450 mgKOH / g to 490 mgKOH / g, and the active hydrogen equivalent is 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 diphenyl imidazoline modified substance, a fused quartz powder and a mica powder according to the weight percentage of the formula, and putting them into a high-speed mixer for a first mixing treatment to obtain 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 a fine fragment material with an equivalent diameter of 3 cm to 5 cm; The fine fragments are put into an ACM mill for fine grinding, and sieved through a 120-160 mesh screen to obtain powder particles with an average particle size of 40 μm to 45 μm; Alumina is weighed according to the weight percentage of the formula, and then added to the powder particles. After mixing evenly, 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 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.

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; wherein, the grinding column and gear ring of the ACM mill are made of medium / low carbon alloy steel, and advanced carbonitriding surface heat treatment is carried out, and the hardened layer produced by carbonitriding is more than 3mm and the hardness is HRC60-62.

10. An application of low temperature curing powder coating for the inner wall of 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 as described in 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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