The performance characteristics and development and application of powder coatings for steel piles

China Coatings Online News Information
Abstract: Through the selection of epoxy resins, curing agents, additives, pigment fillers, precise design formula, repeated adjustment of test formulations, combined with construction process, on-site applications, the development and production of steel piles outside the anti-corrosion melt epoxy powder coating.
ocean is not only a huge treasure trove of resources, but also an indispensable space environment for human survival and development, and it is the hope to solve the three major problems of population growth, shortage of resources and environmental degradation. With the continuous improvement of China's economic strength and the need for rapid economic development in coastal areas, the cross-sea bridge and the sea-facing bridge as the infrastructure of economic development are constantly being built. Data show that China has built and is under construction a large number of cross-sea bridges, it will bring economic benefits far more than the bridge itself. For example, as the first cross-sea bridge in China. The Shanghai Donghai Bridge extends the radius of Shanghai people's activities to the sea by more than 30 kilometers, which is a historic breakthrough. At the same time, Shanghai Nanhui, Fengxian and other regions have thus become the new highland of Shanghai's manufacturing industry. For example, the construction of the Hangzhou Bay Bridge has perfected the regional highway layout of the Yangtze River Delta and the main national highway, eased the pressure of self-flow of Shanghai, Hangzhou and two highways, and helped the cities in Hangzhou Bay area to take the initiative to connect with Shanghai. Expanding opening-up has promoted cooperation and exchanges in the Yangtze River Delta region. Due to the high strength, toughness, easy processing and easy quality of steel, these advantages promote the extensive application of steel in marine harbor facilities. As a stand for cross-sea bridges, corrosion is its fatal weakness in the marine environment. The corrosion resistance of steel materials in the ocean is poor, which affects the service life of steel structures and directly affects the safety of bridge. Because the cross-sea bridge is built in a rather harsh marine environment, the serious salt spray corrosion of the ocean atmosphere is a subject that must be paid attention to in the design and construction of cross-sea bridge. In order to ensure safety and save maintenance costs, the corrosion protection of steel structure should be designed according to the type, structure, material, size and geographical location of the bridge across the sea.
this project is based on the original double-layer epoxy powder research technology results, according to the characteristics of the steel pile application environment and the required coating characteristics, a formula technology improvement.of steel pile powder coating
bottom:
has strong boiling adhesion and good bending resistance;
coating tough wear resistance, good impact and scratch resistance, can withstand soil stress,
coating is convenient, fast curing,
can play a protective role in a larger temperature range, and has long-lasting anti-corrosion effect,
has excellent anti-cathode stripping performance, chemical and electrochemical corrosion resistance, water, acid, alkali, salt.
Middle Layer (if required): the
has a certain elastic function to absorb and slow-release energy,
has excellent chemical resistance, corrosion and insulation, solvent resistance, cathode peeling, leveling and adhesion, as well as flexibility, impact resistance and other mechanical properties.
surface layer:
and the front of the coating at the same time construction, one-time molding,
coating with excellent anti-wear, wash, shock and scratch resistance, excellent resistance to chemicals, corrosion, insulation, solvent resistance, leveling and adhesion and flexibility and other mechanical properties,
coating tough wear resistance, impact resistance, resistance to soil stress,
has a certain degree of resistance.
In accordance with the above standard requirements, through the selection of epoxy resin, curing agent, additives, pigments, precise design formula, repeated adjustment of the test formula, combined with the construction process and field applications, developed and produced in line with the requirements of the steel pile outside the anti-corrosion layer melt epoxy powder coating.1, experimental part
1.1 resin selection
epoxy resin has good regenerative properties, high bonding properties, low curing shrinkage, excellent comprehensive performance and so on, widely used in the field of corrosion protection. The type of epoxy resin and relative molecular mass have a great influence on the performance of the coating, and the bisphenol A epoxy resin molecule contains highly polar adipose family hydroxyl and ether bonds. It has a high immersion and adhesion to the substrate, and high chemical resistance, and because of its rigid structure of benzene ring and flexible hydrocarbon bonds alternate arrangement, thus giving the coating better physical and mechanical properties. In order to improve the high temperature permeability and adhesion of the coating, in the design of the underlying powder coating formulation, there is no common BPA epoxy resin, but the use of medium relative molecular mass modified epoxy resin 1 as a film-forming substance. The ether bond and C-C bond of the modified epoxy resin 1 make its large molecules flexible. The benzene ring gives the polymer heat resistance and rigidity, and isopropyl also gives the large molecule a certain rigidity. Modified epoxy resin 1 has a flexible long-chain structure, giving the coating good impact resistance, its structure is like (1).
In the design of surface powder coating formulation, in order to improve coating film adhesion, hardness and resistance to chemical corrosion, a certain amount of special modified epoxy resin 2 and modified epoxy resin 1 were added to the formulation, the resin molecular structure not only contains more benzene ring and hydroxyl, but also has a longer flexible chain. With the corresponding curing agent has excellent compatibility, high reaction activity, strong adhesion, fast curing, cross-link density, strong media penetration, coating film has excellent rigidity, moisture and heat resistance, chemical resistance, solvent resistance, anti-cathode peeling and impact resistance and other mechanical properties, its structure (2).
In the special modified epoxy resin 2 is too large, although it will significantly improve the hardness of the coating film, heat resistance, wear resistance and chemical corrosion resistance, but also lead to the brittleness of the coating film, affecting the coating film low temperature bending performance. A number of formulation scheme tests with different ratios were carried out on the two resins, and the reasonable matching ratio of the two resins was finally determined according to the test results.
the selection of 1.2 curing agents
the performance of the curing agent is determined by the epoxy resin, which determines the corrosion resistance of the powder coating. The underlying epoxy powder coating has been proved to be most effective from the beginning of the use of pyrchic and phenolic resins as curing agents to polymer phenolic compounds as curing agents. The structure of polymer phenol curing agents is as good as (3).
can be seen in its molecular structure. It is actually a long-chain resin with a hydroxyl seal, with a similar structure to a cyclic resin. From its synthesis method, it is essentially the use of BPA and low relative molecular mass epoxy resin in the presence of catalyst reaction, the generation of high relative molecular mass epoxy resin, and then with excessive BPA reaction, the production of hydroxyl-containing compounds. Therefore, when used as a curing agent for epoxy powder coatings, it has better mixing with resins. And part of the free biphenol A in the reaction is equivalent to the resin of the bi-official group, its activity is larger, easy to cause the open-loop reaction of epoxy- base, but also improve cross-link density. Therefore, polymer phenol curing thorns have a high reaction activity, the resulting coating film has a very high gloss, excellent corrosion resistance and mechanical properties.
polymer phenol compounds curing epoxy powder coating curing process is more complex, mainly as shown in the type (4) one (5):
(1) phenol hydroxyl and epoxy etheric reaction:
<6> (2) Hydroxyl and epoxy etherization reaction:
curing process shows that no small molecules released during the curing process, the coating surface does not exist "bubbles" and other disadvantages, will not be due to increased coating thickness resulting in performance decline. In addition, the curing agent contains a large amount of -0H, which greatly promotes the adhesion to the substation. Through a large number of tests, it has been proved that this phenolic curing agent curing pipe powder coating in the flat or pipe outside the wall of the boiling adhesion and -30 degrees C anti-3 degrees bending performance is very good.
surface powder coating curing agent is selected as a multi-functional group functional curing agent, this is a new type of synthetic resin curing agent containing a variety of functional groups, can be combined with a variety of solid epoxy resins, with excellent melting, reaction activity is very high, fast curing, has a very high cross-link density, giving the coating film excellent corrosion resistance, chemical resistance, solvent resistance, as well as good fluidity, flexibility and excellent adhesion and impact resistance.
1.3 Curing Promoter Choice
2-Methyl Methamphetamide is a commonly used curing promoter for powder coatings, type (6) for 2-methyl-mimiwa lively hydrogen to make the epoxy ring process.the addition of
2-methyl methazole seriously affects the curing temperature and curing time of the entire coating system, according to a large number of laboratory data and combined with the spray conditions at the construction site, respectively, determined the addition of the bottom layer and surface powder coating formula, to ensure inter-layer binding force.
1.4 additive selection
In order to increase the density of each coating and prevent the production of pinholes, a certain proportion of degassing agents are added to the formulation, in addition to a certain amount of leveling agents. In terms of improving powder fluidity, flexibility and curing, the appropriate amount of functional additive 1 was chosen.
in order to improve the hardness and smoothness of the surface powder and enhance the scratch resistance of the coating, a certain amount of functional additive 2 was added to the formulation.
1.5 pigment filler selection
pigment selection greatly affects the final performance of the coating, suitable pigment can not only improve the physical mechanical properties of the coating and chemical resistance performance, but also the construction performance, storage performance will be improved. This project selected silica ash, mica powder and a functional filler as the main filler.
Silica ash is an inorge needle-like mineral, non-toxic, chemical corrosion resistance, thermal stability and dimensional stability, glass and pearl gloss, low water absorption and oil absorption value, mechanical and electrical performance is excellent, with a certain strength, so that coatings can get better mechanical strength, increase durability, enhance adhesion and corrosion resistance, as well as good coverage and adhesion. Mica powder has a unique two-dimensional flaky structure, can effectively improve the film's impermeability, weather resistance, wear resistance and corrosion resistance, in addition to the non-containing of any radioactive elements, is a new type of functional green environmental protection filler. Functional fillers enable curings to have excellent insulation and arc resistance, increase thermal conductivity, improve hardness and wear resistance, change attachment and flame retardant properties, reduce the curing material's line expansion coefficient and curing shrinkage, thereby eliminating internal stress and preventing cracking. According to the characteristics of different fillers to do different proportion matching, from a large number of test results, respectively, selected two suitable scale matching, applied to the bottom layer and surface formula. Pigments are determined according to color requirements. 2, formula composition and performance
2.1 formula composition
steel pile outside the corrosion layer fused epoxy powder coating formula see Table 1.
2.2 Performance Detection
The performance indicators detected by the state authorities in accordance with china National Petroleum Corporation's enterprise standard Q/SY1038-2007 or Q/CNPC38-2002 (buried steel pipe double-layer fused epoxy powder outer coating technical specifications) can be seen in Table 2 and Table 3. 3, production process and construction process
3.1 production process
the main production process for
raw materials→ weighing→ premixed→ molten extrusion→ pressure sheet→ "Rough crushing→ grinding (grading, screening) → and functional additives 1 mixed→ detection→ packaging→ storage
specific operation, the required raw materials are prepared, according to the formula accurately named a variety of raw materials. According to the resin →fill, pigment →fill→ resin input order into the mixer mixture, melt extrusion (one area 65-70 degrees C, two areas 90-100 degrees C, three regions 70-80 degrees C), and then by pressure sheet, crushing, grinding, screening, while adding functional additives 1, and finally excessive sample screening, weighing, packaging after recognition.
3.2 construction process
before applying the outer surface of the steel pipe, the oil, grease and other dirt and impurities attached to the surface must be removed by appropriate methods. Surface treatment equipment and components entering the steel pipe must not contain material that contaminates the surface of the steel pipe.
the outer surface of a steel pipe transported by sea shall be checked for salt content. If the content exceeds 50 mg/m2, it needs to be treated with phosphoric acid or deionized water. The residual salt content of the outer surface should be measured at least twice per shift after treatment of phosphoric acid or deionized water, and the salt content should not exceed 50 mg/m2.
spray (throw) to remove rust, the steel pipe should be warmed up to remove moisture, the warm-up temperature is 40-60 degrees C.
spray (throw) rust from the outside surface of the steel pipe should reach the Sa2.5 level specified in GB/T8923. The anchor depth of the surface of the steel pipe should be 40-100 microns and meet the recommended requirements of the epoxy powder production plant.
spray (throw) the ball to remove rust, the rust dust remaining on the outside surface of the steel pipe should be removed, and dust and other pollutants should not be allowed. Spraying should be carried out within 4h after pre-treatment of the surface of the steel pipe. Surface pre-treatment must be re-treated when the surface of the steel pipe is rusted or contaminated.
spray to remove rust, apply clean, dry compressed air to sweep the inner surface of the steel pipe to remove the remaining steel balls/sand particles and dust. Surface dust level should reach the current national standard GB/T18570.3 (before coating paint steel surface treatment surface cleanliness assessment test Part 3: coating paint before the steel surface dust assessment (pressure-sensitive adhesion method)) provided for the level 2.
surface defects that may affect the quality of the corrosion layer should be repaired and the management of steel pipes that are seriously defective or unable to remove defects should be treated in consultation with the owner.
compressed air used for application must be clean, dry and oil-free.
the steel pipe should be heated evenly with a non-polluting heat source.
the anti-corrosion coating layer shall be carried out in accordance with the coating process determined by the test.
coating should cure 3min at 220 degrees C.
length reserved at both ends of the steel pipe should be (85 soil 5) mm, the reserved section surface must not be coated. If the owner has the requirements, should meet the relevant requirements of the owners.
the anti-corrosion layer should be cooled by water cooling method in time. 4, conclusion
through the selection of raw materials, especially epoxy resin and curing agent selection. Combined with a large number of experimental results, a reasonable ratio of resin and curing agent is achieved, which makes the powder coating have excellent adhesion and anti-cathode stripping properties. Combined with on-site construction process. By adjusting the formulation of multi-layer powder coating. Constantly changing the curing temperature and adhesive time to ensure that there is no problem with the binding force between coatings; Standardize the production process, develop and produce excellent performance outside the steel pile anti-corrosion powder coating and pass