Sealing Oxide Protective Layers on Metal Substrates
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Solution Overview
Problem
Existing methods for sealing porous oxidic protective layers on metal substrates, particularly those based on oxides and hydroxides of Si, Ti, and Zr, fail to provide long-term protection against corrosive media due to their porosity and inability to create a suitable paint bonding base, with conventional sealing methods like hydrolysis and organic resin crosslinking being complex or ineffective.
Innovation Solution
A method involving a wet chemical treatment with a copolymer or copolymer mixture of aliphatic and acyclic alkenes with α,β-unsaturated carboxylic acids in an aqueous composition, applied via conventional methods like spraying or dipping, which reduces porosity and enhances barrier properties by adjusting the acid number and using crosslinkers to form a dense, effective seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sealing methods (hydrolysis or organic resin crosslinking) are used on porous oxide protective layers, then the sealing process becomes complex, but the porosity reduction and corrosion protection remain insufficient
Solution Approach 1:
The invention changes the chemical parameters of the sealing composition by using a copolymer with specific acid number (20-200 mg KOH/g) and specific functional groups (carboxylic acid, hydroxyl, or amine groups). This parameter optimization allows the copolymer to effectively seal pores through simple adsorption and crosslinking without requiring complex hydrolysis or high-temperature treatment, thus achieving good corrosion protection with a simplified process
Solution Approach 2:
The invention uses a composite sealing composition containing a copolymer as the main component (5-50 wt%), optional inorganic compounds (silicates, phosphates, or vanadates) as additives, and water as the solvent. This composite formulation combines the advantages of organic polymers (flexibility, adhesion) and inorganic compounds (hardness, corrosion resistance) to achieve effective pore sealing and corrosion protection while simplifying the sealing process
2Reliability
If the oxide protective layer is made thicker (at least 2 μm) to ensure corrosion protection, then the protection ability improves, but the porosity increases making sealing more difficult
Solution Approach 1:
The copolymer acts as an intermediary substance that penetrates into the porous structure of the oxide protective layer and forms a sealing film within the pores. The copolymer's molecular structure with appropriate acid number and functional groups enables it to adsorb onto the oxide surface and crosslink, creating a dense barrier that blocks ion transport pathways without requiring changes to the underlying porous structure
Solution Approach 2:
The invention specifically addresses porous oxide protective layers (including plasma electrolytically produced layers) by using a sealing composition designed to penetrate and seal the porous structure. The copolymer's ability to enter pores and form a continuous sealing film transforms the porous structure into an effective barrier, maintaining the benefits of thick oxide layers while eliminating their porosity-related drawbacks
3Strength
If the copolymer acid number is increased to improve adhesion to the oxide layer, then the bonding strength improves, but the hydrophilicity increases reducing barrier properties
Solution Approach 1:
The invention optimizes the acid number parameter of the copolymer to a specific range (20-200 mg KOH/g) that balances adhesion and barrier properties. Within this range, the copolymer has sufficient carboxylic acid groups to form strong chemical bonds with the oxide surface while maintaining appropriate hydrophobicity from the polymer backbone to provide effective barrier properties against corrosive media
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively seals oxidic protective layers, reducing ion permeability and maintaining adhesion to the metal substrate, providing enhanced corrosion resistance and a suitable surface for organic coatings, even on substrates with high porosity like titanium oxide-based layers.
Implementation Method 1
The copolymer or copolymer mixture forms a dense seal on the porous oxide protective layer... providing enhanced corrosion resistance
Implementation Method 2
using crosslinkers to form a dense, effective seal
Implementation Method 3
The methods outlined here for applying oxide protective layers have in common that, due to the nature of the deposition process carried out under electrolytic conditions, porous layers are formed which therefore cannot offer effective, long-lasting protection against highly corrosive media
Data Source
AI summary
The invention relates to a method for sealing oxide protective layers on metal substrates using aqueous compositions containing a copolymer or a copolymer mixture of at least one aliphatic and acyclic alkene with at least one α,β-unsaturated carboxylic acid in a water-dispersed and/or water-dissolved form with a copolymer or copolymer mixture acid number of at least 20 mg KOH / g, but not more than 200 mg KOH / g, however. In particular, the invention also relates to the use of such copolymers or such a copolymer mixture for sealing protective layers based on oxides and/or hydroxides of the elements Si, Ti, and/or Zr on an aluminum substrate, said protective layer having a thickness of at least 2 µm.