China Coatings Online News Information
Reviewer: Highland Gao Jingmin
Introduction: Universal epoxy primers usually with BPA type relative to low molecular quality epoxy resin as the main film-forming substances, add active rust-proof pigment, fillers (including multi-functional fillers), additives, etc. prepared into component A. Component B usually uses polyamide resin or cashew phenol modified phenol aldehyde as a curing agent, adding a little solvent;
use: Universal epoxy primers are used for base coating on substrates such as metals and non-metallics, and are generally iron red, gray (for ferrous or non-metallic substrates) or yellow-green (for galvanized plates or aluminum). Can be with alcoholic acid, chlorinated rubber, vinyl paint, epoxy coating, two-group polyurethane, acrylic and other surface coating matching.
main properties: 1) have good leveling and moisture, 2) have good adhesion to steel, galvanized steel and non-metallic concrete, suitable for wet blasting treatment on the substrate (moisture) construction, 3) coating film has good water and corrosion resistance; 4) The curing temperature of the coating system can be as low as 5 degrees C; 5) during the construction process, the weld and epoxy paint can be repaired with this primer, which has good cathode protection adaptability, 6) the epoxy paint and polyurethane paint, can have a long coating interval (internal).
, the basic principles of epoxy primer formulation and the principles of raw material use are introduced, taking yellow-green two-part polyamide-cured epoxy primer as an example.
Use ratio: wA:wB=4:1 or 5:1
Construction process parameters: A, B parts mixed after ripeness period: 20 to 30 min;
the selection of raw materials
universal epoxy primer follows the following principles.
1 The choice of epoxy resin
from the bisphenol A epoxy resin molecule hydroxyl content and reaction activity to consider, commonly used for E-20 and E-44, comprehensive comparison and consideration of cost factors, generally using E-20. E-44 epoxy resin volatility is less, epoxy value is also higher, so cross-link density is also higher, so that the coating made of high density. It is also possible to use the two to match the strengths and weaknesses. In the case of poor wetting substrate, can be spelled into 5% to 10% liquid phenolic resin, participate in cross-linking reaction and can improve the toughness of the coating film, at the same time can be used as an impermeable anti-rust agent to improve the wetting performance of the coating film.
2. Curing agent selection
Commonly used curing agents are Balling Petrochemical 593 curing agent, Sanmu Group T31, 650 curing agent, Jinan Yunjia YJC-1041 curing agent, the United States Kadle NX-5444 and so on.
593 curing agent is the product of the reaction of diethyl triamine and epoxy propane butyl ether addition, which can cure at room temperature and epoxy resin, and has better toughness and bending, impact strength, but higher cost. T31 curing agent is polyamine, formaldehyde, phenol by the Manich reaction added to the polyamine, is a non-toxic grade curing agent, safe application, can cure at low temperature, but also in humidity 80% and underwater application, curing shrinkage is small. 650 curing agent is a polyamide-type curing agent, the structure contains a longer fatty acid carbon chain and amino, can make the coating film with high elasticity, bonding force and water resistance, its construction performance is better, add a broad proportion, less toxicity, can be built on wet metal and concrete surface, the disadvantage is that the curing speed is slow, heat resistance is relatively low, heat deformation temperature is low. YJC-1041 curing agent is cashew phenol modified phenolic amine curing agent, in -5 to 10 degrees C can also be completely cured with epoxy resin, its characteristics can be compared with non-polyamide. This curing agent contains benzene ring, with bisphenol A epoxy resin has better compatibility to reduce the viscosity of the coating, and has a good permeability, so it can be coated on rusty surface; NX-5444 modified phenolic amine curing agent is the United States Kadle products, fast curing, coating film hardness fast, good toughness, can be ultra-low temperature curing, suitable for high-fixing system or fast curing system, excellent results, but high cost. Among these curing agents, 650 polyamide and YJC-1041 curing agents are generally selected, and the performance is more comprehensive. The former is low cost, the latter has excellent performance and good suitability.
3. Choice of pigments
anti-corrosion coatings are generally used to protect metal substrates from corrosion by shielding, corrosion and cathodic protection. For universal anti-rust primer, considering the formulation cost and actual use requirements, the shielding effect is sufficient to achieve the general purpose of rust prevention. However, considering the use of aluminum alloy substrate, we use zinc-chromium yellow plus chromium-yellow to solve the adhesion to aluminum and aluminum alloy substrate, the effect is good. If it is only used on the surface of steel, it can be replaced with iron oxide red or filler. For environmental reasons, phosphate rust-proof pigments can also be used instead of heavy metal pigments to reduce environmental harm, although the cost will increase, but the anti-corrosion performance fully meets the technical requirements.
universal epoxy primer paint chooses titanium dioxide, iron oxide red and mica powder as the general rust-proof pigments (titanium white powder, iron oxide red, carbon black also play the role of paint film cover). They have high heat resistance, good weather resistance, the effect on light, water and atmosphere is very stable, and can strongly absorb ultraviolet rays, so that the protected objects from UV damage, used in anti-corrosion coating is based on its film dense, covering the material to play a physical shielding role, while it has rust resistance to the substrate, corrosion-resistant gas, alkali resistance, good color, strong covering, low price.
using wet process of the mother-in-law powder, with extremely thin two-dimensional flaky structure, tablet overlay, bendable, anti-cracking, acid-base resistance, strong electrical insulation, good suspension in the medium, has a better shielding effect on ultraviolet light. It is arranged in parallel with flaky orientation up and down in the coating film, and its aspect ratio is quite high, so it is easy to form a denser protective layer, so that the coating film strength, impermeability and elasticity have been improved.
hollow microbeads (hollow ceramic microbeads) are a standard ball-shaped powder in hollow. A closed microsphere filled with CO2 gas. The chemical components are silicon oxide, alumina, zirconium oxide, magnesium oxide and sodium silicate. Wall thickness is 1/8 of the diameter, light weight, large volume, low thermal conductivity, high pressure strength, dispersion, mobility and stability, in addition, also has insulation, self-lubrication, sound insulation, non-absorbent, fire resistance, corrosion resistance, radiation and non-toxic and other excellent performance.
The role of sedimentative sulphate and talcum powder in the primer, mainly to provide the denseness of the dry film, at the same time, talcum powder can also provide film smoothness, to ensure good polishing (talcum powder in the system is not less than 8%, there is a good polishing). As far as the composition of the filler geometry in the coating film is concerned, the non-qualitative precipitation of radon sulfate and talcum powder, and the round ceramic hollow microbeads and fine scale-like mica powder form a three-dimensional mesh structure, greatly increasing the denseness of the coating film, played an excellent shielding role, this combination is better than the use of a small amount of rust-proof pigment coating performance.
4. The choice of additives
1) adhesion promoter selection
the choice of adhesion promoter, not only consider the substrate between the adhesion, but also consider the primer and the upper coating or paint layer adhesion, many adhesion promoter only one-way action, dosage slightly larger, inter-layer adhesion will be worse. Adding the appropriate amount of silane coupled agent can not only improve the bonding ability of pigment particles and epoxy resin, but also form chemical or hydrogen bonds between film-forming material particles, thus preventing the migration of corrosion factors, so that the adhesion of coating and substrate is greatly enhanced, and the corrosion resistance of the coating is improved. Adhesion-promoting resin LTW is a better silicone-free non-ionized additive type resin, with a wide range of compatible, used to improve the adhesion of different substates such as aluminum, aluminum alloy, zinc, stainless steel, electroplating surface has excellent results. It also increases the internal adhesion of inorders and certain plastic coatings. For some substrates, adhesion promotes resin LTW and improves flexibility at room temperatures and low temperatures.
2) The choice of other additives
because the raw material contains denser fillers, so it is necessary to use a sinking agent. The pre-gel treatment is carried out with moderately priced organic bentoylation, which has a very good effect. However, the amount of organic bento is too large, can lead to a serious decrease in water resistance of the coating film, if the precipitation of silicon dioxide alone, high ratio of the surface area of silicon dioxide double-edged sword action (the amount is large, there must be strict fineness requirements, the amount is small, the effect is not obvious), resulting in the coating film pinhole, affecting the performance of the coating film. Therefore, at the same time, the precipitation of silicon dioxide and benky soil to complement each other anti-sinking effect and performance deficiencies.
General epoxy primer fineness requirements are not high, there is no need to increase costs for fineness, no special circumstances and film disease appears, while epoxy primer film surface tensor pressure is not large, solvent gradient volatility is uniform, in order to avoid the adhesion between the coating layer difference, it is not recommended that the primer using dispersants and de-foaming agents.