Preparation and application of a powder coating for drinking water pipelines

Abstract

The present invention relates to powder coatings, and in particular to the preparation and application of a powder coating for drinking water pipelines. The powder coating, in parts by mass, comprises the following components: 450-550 parts of two-step epoxy resin, 50-150 parts of polyurethane-modified epoxy resin, 140-155 parts of modified phenolic curing agent, 1-2 parts of curing accelerator, 5-8 parts of leveling agent, 3-5 parts of brightener, 2-4 parts of polyvinyl butyral, 120-200 parts of silicon micropowder, 30-50 parts of glass fiber, and 10-40 parts of pigment; the softening point of the two-step epoxy resin is 90-120°C, and the epoxy equivalent is 700-1000g / eq; the polyurethane-modified epoxy resin is a one-step epoxy resin modified by polycaprolactone-type polyurethane or polytetrahydrofuran ether-type aromatic polyurethane. The powder coating has excellent adhesion, good impact resistance and corrosion resistance, and can be applied to the inner wall coating of drinking water pipelines.

Description

Technical Field

[0001] The invention relates to powder coating, and in particular to preparation and application of powder coating for drinking water pipelines. Background Art

[0002] Drinking water refers to water that meets the corresponding standards and is produced after purification and disinfection in a drinking water treatment plant for people's living and production use. Drinking water is the source of drinking water for residents. Common urban drinking water pipelines are steel pipes, iron pipes, or PE, PVC plastic pipes. In order to ensure the quality and delivery efficiency of drinking water, the inner walls of corrosive materials such as steel pipes and iron pipes need to be protected with protective coatings for long-term protection to ensure that these pipelines have a long service life. Steel pipes are most commonly used in drinking water pipelines because of their good ductility and convenient construction and operation, as well as their outstanding service life and rigidity.

[0003] At present, the coatings used for drinking water pipe coating in China are mainly solvent-based epoxy resins, with a small amount of solvent-free epoxy coatings and powder coatings. Among them, solvent-based epoxy resin coatings contain organic solvents, which are not environmentally friendly and safe during production, transportation and construction. Moreover, after drying and curing, there will still be residual solvent in the coating, which can easily cause drinking water pollution. Solvent-free epoxy resin coatings have high viscosity and high requirements for spraying equipment, which makes the coating surface leveling poor, and it is easy to have bubbles and pinholes, which limits the application of solvent-free epoxy resin coatings.

[0004] Epoxy powder coatings have zero volatile organic matter emissions, and the coating utilization rate is as high as 95% or more. The powder coating has a high degree of automation. At the same time, the powder coating has very excellent physical and chemical properties. Therefore, the application of powder coatings in drinking water pipelines has gradually attracted attention. On the other hand, to ensure the safety and sanitation of the drinking water quality, the requirements for the delivery pipeline are very high. No matter how good the water quality output by the water plant is, the quality of drinking water may be problematic after being transported through a bad pipeline. Therefore, the epoxy powder coating used for the inner wall of the drinking water pipeline must not only have excellent application performance, but also meet the hygiene requirements and toxicological test requirements in the "Sanitary Safety Evaluation Specification for Drinking Water Delivery and Distribution Equipment and Protective Materials" (2001).

[0005] Invention patent CN102533049B discloses an epoxy powder coating for drinking water pipelines, which includes epoxy resin E604, leveling agent PV88, 800 mesh ultrafine barium sulfate, rutile titanium dioxide, additives and pigments. However, the powder coating does not include a curing agent component, making it difficult to obtain a coating with good application performance. In addition, the coating contains phthalocyanine blue and permanent violet pigments. Strictly speaking, the coating is not suitable as a coating for drinking water pipelines.

[0006] Invention patent CN109337523A discloses a food-grade powder coating, which includes a modified phenolic epoxy resin, a phenolic curing agent and an auxiliary agent. However, the modified phenolic epoxy resin used in the powder coating has a high softening point, and is relatively difficult to prepare and apply. In addition, the invention does not disclose the specific selection of silicone-modified phenolic epoxy resin or polyurethane-modified phenolic epoxy resin, and the selection of different silicone or polyurethane segments will obviously have a significant impact on the application properties of the coating, such as corrosion resistance and hydrolysis resistance.

[0007] Invention patent CN112480778B discloses an epoxy powder coating for the inner wall of a drinking water pipe, which includes medium molecular weight solid epoxy resin, high molecular weight solid epoxy resin, polyvinyl butyral, modified phenolic curing agent, hyperbranched polymer, dimethylimidazole and other raw materials. The obtained coating meets the safety performance requirements of domestic water, but the adhesion and flow resistance reduction performance of the coating need to be further improved.

[0008] Invention patent CN116376407A discloses a sintered epoxy powder for the inner wall of a large-diameter steel pipe, which includes components such as a multi-epoxy functional masterbatch, bisphenol A epoxy resin, a phenolic curing agent, an accelerator, a thermoplastic elastomer, a filler and an auxiliary agent. The dendritic epoxy resin and TGIC in the multi-epoxy functional masterbatch react with the curing agent to form a network macromolecule, thereby improving the wet adhesion of the epoxy powder coating. The wet adhesion of the coating is assisted by the thermoplastic elastomer. However, the thermoplastic elastomer POEEngage8407 used in the invention is non-polar and has poor compatibility with epoxy resin. The mechanical properties of the coating obtained by blending modification are often not ideal. Summary of the invention

[0009] The invention aims to provide an epoxy resin type drinking water pipeline powder coating with excellent coating mechanical properties, good compactness and good adhesion to a substrate.

[0010] The drinking water pipeline powder coating provided by the present invention comprises the following components in parts by mass:

[0011] 450-550 parts of two-step epoxy resin, 50-150 parts of polyurethane modified epoxy resin, 140-155 parts of modified phenolic curing agent, 1-2 parts of curing accelerator, 5-8 parts of leveling agent, 3-5 parts of brightener, 2-4 parts of polyvinyl butyral, 120-200 parts of silica powder, 30-50 parts of glass fiber, and 10-40 parts of pigment.

[0012] The softening point of the two-step epoxy resin is 90-120° C., and the epoxy equivalent is 700-1000 g / eq.

[0013] Furthermore, the two-step epoxy resin includes one or more of Hongchang GESR-904, GESR-904H, OlinDER-663U, Anhui Hengyuan HY905, and HY903H.

[0014] The polyurethane modified epoxy resin is a polyether or polyester type polyurethane modified epoxy resin.

[0015] Furthermore, the epoxy resin in the polyurethane-modified epoxy resin is a one-step epoxy resin.

[0016] Furthermore, the one-step epoxy resin is one or more of E12, E20, E44, and E51.

[0017] Furthermore, the raw materials for preparing the polyether or polyester polyurethane include polymer polyols with flexible segments. The polymer polyols include polyether diols and / or polyester diols.

[0018] Furthermore, the polyether diol is polytetramethylene ether glycol; and the polyester diol is polycaprolactone diol.

[0019] Furthermore, the polyurethane of the polyurethane-modified epoxy resin is aromatic polyurethane.

[0020] Furthermore, the raw materials for preparing the polyurethane include aromatic diisocyanate, and the aromatic diisocyanate is specifically selected from toluene diisocyanate and / or diphenylmethane diisocyanate.

[0021] Furthermore, the preparation method of the polyurethane modified epoxy resin comprises the following steps:

[0022] Step 1, preparing polyurethane prepolymer: putting polymer polyol into a reaction kettle, heating to 110-120°C, dehydrating under vacuum at -0.08MPa for 0.5-1h, cooling to 50-60°C, adding aromatic diisocyanate, heating to 80°C for reaction for 2-4h, and cooling to 50°C for standby use when the NCO content reaches the theoretical value;

[0023] Step 2, prepare polyurethane modified epoxy resin: put the epoxy resin into a reactor, heat it to 90-120°C, add polyurethane prepolymer and catalyst, react for 2-4 hours, take samples, stop the reaction when no NCO peak is detected by infrared, release the reactants, cool, and obtain polyurethane modified epoxy resin.

[0024] In the polyurethane modified epoxy resin, the mass ratio of the polyurethane prepolymer to the epoxy resin is 1:(5-15).

[0025] The molar ratio of aromatic diisocyanate to polymer polyol in the polyurethane prepolymer is (1.2-4):1.

[0026] The modified phenolic curing agent includes one or more of Dow DEH-84, Anhui Hengyuan HYH-381, HYH-300, and HYH600.

[0027] The curing accelerator is 2-methylimidazole.

[0028] The leveling agent is one or more of Nanhai Chemical GLP588, GLP505, and GLP599.

[0029] The brightener is one or more of CM701, CF701B, WK701, and WK702.

[0030] The silicon micropowder is active silicon micropowder. Further, the silicon micropowder is one or more of Haike HY-GA-1, HY-GA-2, and HY-GB-1.

[0031] Furthermore, the silicon micropowder is epoxy-modified silicon micropowder, and its D 50 The particle size is 3-11 μm. Preferably, the D 50 The particle size is 8-11μm.

[0032] The glass fiber is any one of Jushi EMG13-70C or EMG13-250.

[0033] Furthermore, the glass fiber is Jushi EMG13-70C.

[0034] The pigment includes one or more of titanium dioxide, carbon black, and organic pigments.

[0035] The present invention also discloses a method for preparing the powder coating, comprising the following steps:

[0036] Step a, preparing polyurethane modified epoxy resin.

[0037] Step b, quantitatively weighing the raw materials of the powder coating according to the preparation formula, adding them into a mixer, and mixing them evenly to obtain a prefabricated mixture;

[0038] Step c: adding the prefabricated mixture into a twin-screw extruder for extrusion at a temperature of 90-120°C;

[0039] Step d: tabletting, cooling, crushing and screening the extruded material, and selecting D 50 The powder with a particle size of 30-50 μm is the finished powder coating product.

[0040] The invention also discloses the application of the powder coating, including application in coating the inner wall of a drinking water pipeline.

[0041] The beneficial effects of the present invention are as follows:

[0042] (1) The present invention selects polycaprolactone diol or polytetramethylene glycol with good flexibility and excellent hydrolysis resistance as the diol raw material of polyurethane, and selects diphenylmethane diisocyanate with high strength and similar molecular structure to bisphenol A epoxy resin as the isocyanate raw material of polyurethane, and reacts with a small amount of one-step epoxy resin to prepare a polyurethane modified epoxy resin polymer with good flexibility and strength, and then the polyurethane modified epoxy resin polymer is compounded with a high molecular weight two-step epoxy resin to prepare a powder coating. The adhesion and impact resistance of the powder coating are improved.

[0043] (2) By selecting specific silica powder and glass fiber as fillers for powder coatings, the application performance of powder coatings is further improved. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with specific embodiments.

[0045] It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments, and are merely used to explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0046] Preparation Example

[0047] Preparation of polyurethane modified epoxy resin. The raw materials for its preparation are as follows:

[0048] Epoxy resin E-20, hydroxyl content 5.44%, Baling Petrochemical; diphenylmethane diisocyanate (MDI), Japan NPU; toluene diisocyanate (TDI), Wanhua Chemical; polycaprolactone diol 2000 (PCL-2000), Japan Daicel; polytetramethylene ether diol 2000 (PTMG-2000), BASF; catalyst: organic bismuth catalyst DY-20, Deyin Chemical.

[0049] The preparation method is as follows:

[0050] Step 1, prepare polyurethane prepolymer: put polymer polyol into a reaction kettle, heat to 120°C, dehydrate under vacuum at -0.08MPa for 0.5h, cool to 55°C, add aromatic diisocyanate, heat to 80°C for reaction for 3h, wait until the NCO content reaches the theoretical value, cool to 50°C, and set aside. The molar ratio of aromatic diisocyanate to polymer polyol is 2:1.

[0051] Step 2, preparing polyurethane modified epoxy resin: putting epoxy resin E-20 into a reactor, heating to 100°C, then adding measured polyurethane prepolymer and organic bismuth catalyst, reacting for 3 hours, sampling, stopping the reaction when the infrared can no longer detect the NCO peak, releasing the reactants, cooling, and obtaining polyurethane modified epoxy resin. The mass of the catalyst is 0.03wt% of the polyurethane prepolymer.

[0052] Preparation Example 1: The raw material polymer polyol is PCL-2000, the aromatic diisocyanate is MDI, the theoretical value of the NCO content of the polyurethane prepolymer is 3.36wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:9.

[0053] Preparation Example 2: The raw material polymer polyol is PTMG-2000, the aromatic diisocyanate is MDI, the theoretical value of the NCO content of the polyurethane prepolymer is 3.36wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:9.

[0054] Preparation Example 3: The raw polymer polyol is PTMG-2000, the aromatic diisocyanate is TDI, the theoretical value of the NCO content of the polyurethane prepolymer is 3.58wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:9.

[0055] Preparation Example 4: The raw material polymer polyol is PTMG-2000, the aromatic diisocyanate is MDI, the theoretical value of the NCO content of the polyurethane prepolymer is 3.36wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:5.

[0056] Preparation Example 5: The raw material polymer polyol is PTMG-2000, the aromatic diisocyanate is MDI, the theoretical value of the NCO content of the polyurethane prepolymer is 3.36wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:15.

[0057] Preparation Example 6: The raw material polymer polyol is PTMG-2000, the aromatic diisocyanate is MDI, the theoretical value of the NCO content of the polyurethane prepolymer is 3.36wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:3.

[0058] Preparation Example 7: The raw polymer polyol is PTMG-2000, and the aromatic diisocyanate is MDI. The theoretical value of the NCO content of the polyurethane prepolymer is 3.36wt%, and the weight ratio of the polyurethane prepolymer to the epoxy resin is 1:18.

[0059] Example

[0060] The polyurethane modified epoxy resin prepared in Preparation Example 1-7 was used to prepare powder coatings. The specific sources of the raw materials of the coatings are as follows:

[0061] Two-step epoxy resin: GESR-904, epoxy equivalent 780-850g / eq, softening point 92-102℃, Hongchang Electronic Materials.

[0062] Polyurethane modified epoxy resin: Preparation example: homemade.

[0063] Modified phenol curing agent: HYH-300, phenolic hydroxyl equivalent 280-320g / eq, softening point 85-93℃, Anhui Hengyuan.

[0064] 2-Methylimidazole: Shanghai Langrui.

[0065] Leveling agent: GLP588, Nanhai Chemical.

[0066] Brightening agent: CM701, Changming New Materials.

[0067] Polyvinyl butyral: PVA17-88, Wanwei.

[0068] Silica powder: Haike HY-GA-1, epoxy modified silica powder, D 50 The particle size is 9.5±1.5μm.

[0069] Glass fiber: Jushi EMG13-70C, fiber diameter 13 μm, length 180 μm, silane impregnation.

[0070] Pigment: Titanium dioxide, commercially available.

[0071] The coating formulation is shown in Table 1.

[0072]

[0073]

[0074] Example 8, based on Example 1, the polyurethane modified epoxy resin is replaced by an equal mass of GESR-904.

[0075] Comparative Example

[0076] Comparative Example 1: Based on Example 1, the silicon powder HY-GA-1 was replaced with the same mass of Haike GE0100 spherical unmodified silicon powder. 50 The particle size is 12±2.0μm.

[0077] Comparative Example 2, based on Example 1, the glass fiber boulder EMG13-70C is replaced with EMG13-250, with a fiber diameter of 13 μm and a length of 50 μm, which is not impregnated with an impregnant.

[0078] Preparation of powder coatings

[0079] The preparation method of the powder coating for drinking water pipeline comprises the following steps:

[0080] Step a, preparing various raw materials according to the formulas of Examples 1-8 and Comparative Examples 1-2.

[0081] Step b, according to the formula of Examples 1-8 and Comparative Examples 1-2, quantitatively weigh the raw materials of the powder coating, add them into a mixer, mix them evenly, and obtain a prefabricated mixture;

[0082] Step c: adding the prefabricated mixture into a twin-screw extruder for extrusion at a temperature of 95° C.;

[0083] Step d: tableting, cooling, crushing and sieving the extruded material, and selecting powder with a D50 particle size of 30-50 μm, thereby obtaining finished powder coatings corresponding to Examples 1-8 and Comparative Examples 1-2.

[0084] The coatings obtained in Examples 1-8 and Comparative Examples 1-2 were applied to a steel substrate by an electrostatic spraying process and then cured at 220° C. for 15 min.

[0085] Performance test: the application performance of the powder coatings obtained in the examples and comparative examples was tested according to the corresponding test methods in Table 2. The water quality test after the coating was immersed was carried out according to the "Sanitary Safety Evaluation Standard for Drinking Water Transmission and Distribution Equipment and Protective Materials" (2001).

[0086] Table 2. Powder coating application performance test results.

[0087]

[0088]

[0089] From the test results of the above embodiments and comparative examples, it can be seen that the powder coatings obtained in embodiments 1-5 have grade 0 adhesion, and have good resistance to high temperature and humidity, and resistance to neutral salt spray, and can well meet the application of powder coatings for drinking water pipelines.

[0090] In Example 6, the polyurethane segment content in the polyurethane-modified epoxy resin is relatively high, and the neutral salt spray resistance and high temperature and humidity resistance of the obtained coating are relatively poor.

[0091] In Example 7, the polyurethane segment content in the polyurethane-modified epoxy resin is relatively low, and the adhesion and impact resistance of the resulting coating are relatively poor.

[0092] In Example 8, the powder coating does not contain polyurethane-modified epoxy resin, and the obtained powder coating has slightly poor adhesion and impact resistance, which cannot meet the application requirements for high adhesion, and further, it is difficult to meet the requirement of a service life of up to 50 years.

[0093] In Comparative Examples 1 and 2, the silicon micropowder is unmodified silicon micropowder, and the glass fiber is not treated by impregnation with a wetting agent. The compatibility of the two with the powder coating is poor, and the application performance of the obtained coating is poor.

[0094] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A powder coating for drinking water pipes, comprising the following components in parts by mass: Two-step epoxy resin 450-550 parts, polyurethane modified epoxy resin 50-150 parts, modified phenol curing agent 140-155 parts, curing accelerator 1-2 parts, leveling agent 5-8 parts, brightener 3-5 parts, polyvinyl butyral 2-4 parts, silicon powder 120-200 parts, glass fiber 30-50 parts, pigment 10-40 parts; The softening point of the two-step epoxy resin is 90-120°C, and the epoxy equivalent is 700-1000 g / eq; The polyurethane modified epoxy resin is a one-step epoxy resin modified by polycaprolactone type polyurethane or polytetramethylene ether type aromatic polyurethane; In the polyurethane modified epoxy resin, the mass ratio of polyurethane prepolymer to epoxy resin is 1:(5-15); The molar ratio of aromatic diisocyanate to polymer polyol in the polyurethane prepolymer is (1.2-4):1; The aromatic diisocyanate is specifically selected from toluene diisocyanate and / or diphenylmethane diisocyanate; Silica powder is epoxy modified silica powder. 50 Particle size is 8-11 μm; The glass fiber is Jushi EMG13-70C.

2. The powder coating according to claim 1, characterized in that: The modified phenolic curing agent includes one or more of Dow DEH-84, Anhui Hengyuan HYH-381 and HYH-300.

3. The powder coating according to claim 1, characterized in that: The curing accelerator is 2-methylimidazole.

4. The powder coating according to claim 1, characterized in that: The preparation method of the polyurethane modified epoxy resin comprises the following steps: Step 1, preparing polyurethane prepolymer: putting polymer polyol into a reaction kettle, heating to 110-120°C, dehydrating under vacuum at -0.08MPa for 0.5-1h, cooling to 50-60°C, adding aromatic diisocyanate, heating to 80°C for reaction for 2-4h, and cooling to 50°C for standby use when the NCO content reaches the theoretical value; Step 2, prepare polyurethane modified epoxy resin: put the epoxy resin into a reactor, heat it to 90-120°C, add polyurethane prepolymer and catalyst, react for 2-4 hours, take samples, stop the reaction when no NCO peak is detected by infrared, release the reactants, cool, and obtain polyurethane modified epoxy resin.

5. The powder coating according to claim 1, characterized in that: The leveling agent is one or more of Nanhai Chemical GLP588, GLP505, and GLP599; the brightening agent is one or more of CM701, WK701, and WK702.

6. The powder coating according to claim 1, characterized in that: The pigment includes one or more of titanium dioxide, carbon black, and organic pigments.

7. A method for preparing a powder coating according to any one of claims 1 to 6, characterized in that The steps include: Step a, preparing polyurethane modified epoxy resin; Step b, quantitatively weighing the raw materials of the powder coating according to the preparation formula, adding them into a mixer, and mixing them evenly to obtain a prefabricated mixture; Step c: adding the prefabricated mixture into a twin-screw extruder for extrusion at a temperature of 90-120°C; Step d: tabletting, cooling, crushing and screening the extruded material, and selecting D 50 The powder with a particle size of 30-50 μm is the finished powder coating product.

8. An application of the powder coating according to any one of claims 1 to 6, characterized in that: Used for inner wall coating of drinking water pipes.

Images