The performance and research of phenolic curing agent in the formulation of heavy antiseptic powder coating

1 Overview
anti-corrosion coating is a coating that can be used effectively for a long time under harsh conditions, the main role is reflected in its function. The thermoo-solid heavy antiseptic powder coating is also more focused on the protective function of the substrate than the ordinary powder coating. Currently commonly used in the market for fusion-type epoxy powder coatings (Fusion BondedEpoxy, or FBE), the workware is preheated for powder coating, quickly cured and cooled to complete the coating

. The anti-corrosion coating has a very good bonding force with the substrate, the coating surface is smooth, has a good gloss, has a strong anti-penetration, anti-corrosion ability, the coating adapts to the temperature range is large, the surface hardness is high, the coating is dense, has good anti-plant root puncture ability, the coating film has excellent anti-high temperature cathode stripping ability and other excellent performance is widely used in various types of oil, gas, water pipe protection.
2 FBE anti-corrosion mechanism and development direction
heavy anti-corrosion powder coating base is modified epoxy resin, its structure contains high polarity and active epoxy base, can form chemical bonds with the metal surface and has a strong adhesion, curing agent phenolic substances, belong to the added curing reaction, no small molecule volatiles released, will not form a needle hole and affect the corrosion of the coating is very important.
FBE powder uses epoxy resin is phenolic modified epoxy, that is, on the basis of bisphenol A epoxy resin introduced on the basis of some bisphenol aphenol epoxy resin, this resin is multi-official thermoplastic phenolic epoxy resin, very reactive Strong, coating film has excellent heat resistance, chemical resistance and high glass temperature and hardness, but cross-link density, low flexivity, the addition of BPA epoxy resin combined products, both flexive and can be severely anti-corrosion.
Commonly used phenolic curing agents are linear bisphenol Aphenolic resins with phenolic hydroxyl, linear bisphenol aphenolic resin curing agent structure and glass temperature similar to bisphenol a epoxy resin, can be very soluble with epoxy resin, and has a good pigment wetting. This curing agent reacts strongly with epoxy resin at high temperatures, forming a flexible and dense coating with good physical and chemical properties and suitable for heavy corrosion protection of long pipelines. Linear BPA phenolic resin is a multi-function curing agent, combined with phenolic modified epoxy resin will get very good resistance to high temperature, chemical resistance.
FBE coating long-lasting anti-corrosion pipe is the coating surface physical properties, coating Tg, adhesion, crosslink density, porosity rate and other indicators, which improve the coating crosslink density as a key factor. As the coating crosslink density increases coating hardness, Tg, osmosis resistance and anti-cathode stripping, but overall flexibility decreases. How to improve the crosslink density of coating by adjusting epoxy or curing agent will play an important role in the progress of FBE function.
3 film resin anticorrosion performance analysis
powder coating resins are mainly aolate polyester, acrylic, polyurethane and epoxy resin. Polyester structure exists ester chain, prone to hydrolysing, acrylic structure also contains ester chain, has been proved to be easy to break the ring in acid rain and other environments. Although some new techniques can improve the ester chain's water resistance, they still perform poorly in long-term destructive experiments. This is the low-end anti-corrosion market using a large number of recycled powder, hybrid system brought about by the biggest hidden dangers. Polyurethane can be used in anti-corrosion coatings, but the price is high, epoxy resin reasonable anti-corrosion performance is good, in the anti-corrosion is widely used. The most common of these is bisphenol A epoxy.
Bisphenol A-type epoxy resin
from the structural side hydroxyl to give good adhesion to the metal substrate surface, the ether bond in the skeleton to give excellent chemical resistance and alkaline resistance, no ester chain in the structure, with good water resistance, high cross-link density to give a good shielding effect on the substrate. In addition to BPA epoxy, linear phenolic modified epoxy and BPA F epoxy are commonly used in antiseptic powder coatings.
linear phenolic modified epoxy resin
bisphenol F epoxy resin
from the molecular structure, linear phenolic modified epoxy and bisphenol A epoxy and bisphenol F epoxy, the unit molar substance contains more The number of epoxy-based groups and aromatic rings, cured cross-linking structure is more dense, with better anti-corrosion properties, but there is also a brittleness of this defect, generally rarely used alone in powder coatings, in order to achieve excellent anti-corrosion performance and aesthetic performance. Bisphenol F epoxy is mainly to improve the leveling of coatings, can also be mixed with BPA epoxy. At the same time, phenolic modified epoxy activity is strong, Tg low will lead to the powder coating itself Tg is too low and improve storage and transportation conditions, thereby reducing its use and promotion.
4 curing agent antiseptic performance analysis
the anti-curing agent has an important impact on powder coating performance and process. Early heavy anti-corrosion powder coating curing agent selection of double cyanide, due to its small molecular weight, large heat, large stress in the coating, brittleness and other characteristics, has been rarely used. High melting point aromatic amine curing agent performance can be adapted to the needs of anti-corrosion coating, but because of its toxicity, at the same time the molecular weight is small, the official energy is too high, the coating toughness is not enough and other defects are basically unused.
is a common epoxy curing agent. From the molecular structure of the molecular structure of the molecular structure is simple, the active group is single, it is difficult to form extended linear structure molecules, resulting in curing of the coating brittleness is too large. However, the group-NH is extremely active and reacts with epoxy at 120-130 degrees C, so it is used as a curing promoter in antiseptic products. In order to control the yellowing caused by high-activity reactions, it can also be replaced by products such as 2,4-mimithylamine or methamphetamine with lower activity, but the addition will increase slightly.
present, the industry commonly used antiseptic curing agents for end hydroxyl polymer-type curing agents, such as phenols and epoxy compounds copolymers, linear phenolic resins. This large molecule curing agent has a similar structure with epoxy resin, and the system resin has better mutual solubility, at the same time, the cured coating has better flexibility. However, it should be noted that after the reaction, the viscosity of the system increases with the reaction completion rate, and the reaction completion rate is not high due to the curling wrap of the reaction active group, which makes the reaction unsustainable. To avoid this kind of phenomenon, it is often necessary to add some phenolic hydroxyl compounds and catalysts to improve the speed of reaction.
shrinking glycerol seal end bisphenol A epoxy chloropropane copolymer
end hydroxyphenol aldehyde modified curing agent can also be regarded as a phenolic resin, in order to control the reaction activity of hydroxyl, with propylene or butyl etherization, and finally the curing agent end of the phenolic hydroxyl and epoxy resin epoxy reaction film. Side hydroxyl in the structure ensures the adhesion of the system to the ground. The structure is closer to epoxy resin to ensure the compatibleness of the system, while reducing the magnitude of stress release between molecules after filming. A large number of benzene ring structures improve the resistivity of the coating volume and fully improve the coating's anti-cathode stripping capability. The linear structure provides excellent flexibility of the coating to some extent.
the appropriate introduction of some small molecule phenol hydroxyl curing agent can effectively improve the reaction speed and reaction completion rate. The activity of these curing agents is stronger than that of hydroxyphenol-modified curing agents, and the electrical insulation on molecular structure is also stronger. Therefore, the use of such curing agents will cause the thermal properties of the coating and anti-cathode stripping to increase significantly. However, due to the small molecules, the film after the brittleness is large, can not be used alone.
the characteristics of several curing agents, mainly end hydroxyphenol aldehyde modified curing agent, can make the final coating get better mechanical properties and adhesion. And the reaction is relatively soft and controllable, the process adaptability is strong. Adding a certain proportion of phenolic hydroxyl curing agents to thermal properties and anti-cathode stripping can be effectively improved. The specific ratio should be based on the actual requirements and detection data.
5
The effect of phenol curing agent dosage on the performance of anti-corrosion coating
Take the formula in Table 4-1.
the coking time is reduced with the increase of phenolic curing agents in the comparison formula, and the amount of methamphetrylamide is reduced as appropriate for a more balanced comparison of performance data. At the same time, with the increase of branch chain structure, it is bound to greatly improve the cross-link density of the system, thereby improving the anti-penetration capability of the coating. The coating performance indicators for each formulation are shown in Table 4-2.
the use of phenolic curing agents for formulation adjustment compared to the use of epoxy adjustment advantage is that the coating itself Tg point is not very low, the degree of reaction is easier to control, convenient for product storage and use. According to the test data, it is not difficult to see that with the addition of the branch chain system coating cross-link density and Tg point have increased significantly, but the overall brittleness has improved. Depending on the requirements for the final use of the antiseptic coating, the curing agent used can be adjusted accordingly to achieve optimal performance. However, the H-value in the thermal characteristics can decay significantly depending on the increase in storage time, up to 10-15J/g. In the production of products with thermal characteristics demand, the H-value should be controlled above the standard value of more than 10.
6 Summary
heavy anti-corrosion powder coating is mainly used in pipeline oil transmission, gas transmission, water transmission of internal and external wall corrosion-proof coating. There are some differences in corrosion prevention requirements and different emphasis in different environments. In the design process of anti-corrosion coating formulation, more consideration should be given to the reasonable matching between different film-forming objects. Ensure that the required indicators are qualified under the premise of ensuring the mutual solubility of the system. The composition of epoxy and curing agent should take more account of the actual environment and process needs to complete the ratio design.