I'm facing a problem when I'm placing one drop of 1% NaOH on my silane coated metal panels and are heating them at higher temperature for example 80 C for 30 minutes or 55 C for 4 hours. The silane coating is degrading after 5-10 minutes and the underneath metal surface is getting exposed. Which kind of silane or additive can solve this problem? The coating thickness is approximately 5-6 micron.
Unfortunately the resistance of thin silane coatings to alkali conditions is not good. Dipodal silanes are better than conventional silanes. A good comparison is in figure 2 found in "Enhanced Hydrolytic Stability of Siliceous Surfaces Modified with
Pendant Dipodal Silanes" a link is: https://www.gelest.com/themencode-pdf-viewer/?file=https://www.gelest.com/wp-content/uploads/Enhanced_Hydrolytic_Stability.pdf
What is the purpose of the coating?
Many organic lacquers would resist under the conditions you mentioned.
I'm developing Silane based hard coating mainly for Automotive exterior parts Andreas Holländer
Dear Saheli Bera,
The most widely used coupling agents, the aminoalkylsilanes are the most economical, but are not necessarily the best. Epoxysilanes, for example, are successfully used with acrylic acid and maleic acid copolymers. At elevated temperatures, the amines add across many double bonds although mercaptoalkylsilanes are the preferred coupling agents. Isocyanate is a mask silane which is heat triggered and functionality is frequently delivered to resin systems during elevated temperature bonding or melt processing steps. Demasking temperatures are typically 160-200°C.
We can increase the resistance by Selecting Protective Treatments on the surface and those are listed below.
(1) Applying Magnesium fluosilicate or zinc fluosilicate, Alkali silicates, sodium silicate (water glass), potassium silicate, lithium silicate, Drying oils, Coumarone-indene resin, Styrene-butadiene (SBR) copolymer resin, Chlorinated rubber, Chlorosulfonated polyethylene (hypalon), Vinyls and latex-based materials, Bituminous paints, mastics, and enamels, Polyester and vinyl ester materials, Polyurethane/urethane, Epoxy, Neoprene, Polysulfide, Coal tar and coal-tar epoxy, Chemical-resistant masonry units, mortars, grouts, and concretes, Sheet rubber, Resin sheets, Lead sheet, Glass etc.
(2) Using appropriate Organosilane-Modified Silica Nanoparticles, Trihydrosilanes, Multi-Functional and Polymeric Silanes, Vinyl and Olefin Functional Silanes, Sulfur Functional Silanes etc. are popular silanes adding with coupling agents(specially amino group- vinayl groups,epoxy groups, methacryloxy groups) can increase the resistance against the elevated temperature. Coupling agent for elevated temperature-cure epoxies Utilized in HPLC of metal chelates.
(3) For the concerete, Low water-cement ratio (w/c), cement content, — Suitable cement type,suitable water, Suitable aggregate, Supplementary cementitious materials and Chemical admixtures, Adequate curing can increase the chemical resistance. chemical resistance of concrete to certain chemicals such as formic acid and slag service record to improve sulfate resistance
If you are looking for automotive parts,
Electrodepositing of the anti- corrosion is necessary against the rust formation.
A sealer like Poly Vinyl Chloride (PVC) is applied for anti-corrosion, elimination of water leaks, and minimization of chipping and vibrational noise is useful in automotive. it is advisable to impart UV durability, HALS (hindered amine light stabilizer) chemicals are mixed with UVA (ultraviolet light absorbers) into automotive clearcoats during their manufacturing. The primary functions of these chemicals are to prevent UV-induced degradation of the polymeric backbone (by HALS) and to absorb UV radiation within the 290–400 nm wavelength range.
1K acrylic melamine clearcoat is the most common paint used in the automotive industry because of its good cost and performance balance. It is typically based on a combination of acrylic polyols (Ac) and amino cross-linking agents (MF, melamine resins). Versions of clearcoat with improved etch and scratch resistance include acrylic melamine silane and carbamate melamine. Both 1K and 2K polyurethane clearcoats also offer an excellent balance of etch and scratch resistance and 1K and 2K epoxy acid clearcoats are among the most commercially successful clearcoats regarding acid etch resistance.
Hope this is helpful for you.
Ashish
Van Ooij, W.J. and Sabata, A., Armco Steel Co LP, 1992. Steel sheet with enhanced corrosion resistance having a silane treated silicate coating. U.S. Patent 5,108,793.
We would need to know more about your project to answer specifically, but what you are describing is a requirement for mild acid resistance at moderately elevated temperature. Assuming the silane is a prime coat which will be topcoated, I would consider diluted epoxy ester or a 2K epoxy used in conjunction with perhaps an epoxy functional silane to produce a low volume solids primer. You can calculate the required thickness as a function of spread rate.
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