uv.eb West 2013 Formulating UV Products that Resist Corrosion 2/26/2013

Transcription

1 uv.eb West 2013 Formulating UV Products that Resist Corrosion 2/26/2013

2 So, what is corrosion? Why do we care about it? -Corrosion is the natural process where metals are oxidized from their unstable man-made state to a more natural lower energy state. -Loss of physical properties -Reduced appearance -Cost US ~$ 1/4 trillion annually

3 Step #0: Plan the Project by Understanding your Customers Needs -The most overlooked step in product development is not gathering enough initial information about the end customers requirements. A checklist of requirements eliminates half the formulators work and reduces turn around time; -Type of Substrate? -Application viscosity? -Coater type? Lamp Type and number? -Interior or Exterior use? -Flexibility? -Selling price/rmc? -Salt Spray or other performance requirements? -Cure energy? -etc, etc, etc You must understand these details before you can successfully formulate a proper coating.

4 Step #0: Plan the Project by Understanding your Customers Needs -The quality and condition of your customers substrate will affect your final products performance. If your customer has substrate that looks like this, you need to deal with it somehow; be it reduced customer expectations, use of additional wetting agents, the addition of a cleaning protocol, etc. Point is, you need to understand you customers process and substrate no matter how ugly that might be.

5 Formulating UV products that Resist Corrosion Step 1: Select the appropriate oligomer(s). -As a general rule, most of the physical properties of a UV curable system will be based on the oligomer choice. -When formulating Direct to Metal (DTM) coatings, shrinkage is a very important consideration. Free radical systems can see 20%+ shrinkage in some cases, which can dramatically reduce adhesion. Cationic systems have very little shrinkage, but have their own challenges as well. -Good Corrosion resistance requires good substrate adhesion. Thus, substrate wetting, flow, and shrinkage are all critical. The devil is in the details! -Oligomer selection will directly affect; -Cost -Adhesion -Exterior Durability -Flexibility

6 Formulating UV products that Resist Corrosion Step 2: Select the appropriate monomer(s). -As a reactive diluent, the monomer selection will not only reduce the viscosity but will also directly affect physical properties as well. -Because shrinkage affects adhesion, mono-functional monomers are often preferred. By decreasing crosslinking, additional flexibility is often gained as well. -Small details like odor can often limit certain monomers use. ie IBOA or 2-PEA

7 Formulating UV products that Resist Corrosion Step 3: Select the appropriate additives -Adhesion: Generally acidic in nature. -Carboxylic acids: bcea -Phosphate Esters: Acrylate and Methacrylate -Silanes -Acrylic acrylates -Wetting and Flow -Typically silicone or acrylics -Photo Initiators -Often high concentrations are used to offset high line speeds and slower oligomers and monomers. -Anti Corrosion Pigments -Mostly sacrificial ions such as Calcium, or Phosphates

8 Formulating UV products that Resist Corrosion: Example formulation BPA-DA TRPGDA CPK BP Adhesion Additives Application and Cure:.5 mil DFT cured with 300mW/cm2-50+ MEK DR -80 In-LB RI-Fail -F+ Pencil -X-hatch-1B/50%

9 So, how are we benchmarking corrosion? -Salt Spray performance is the most common benchmark (ASTM B117). -Salt Spray performance is well known and widely accepted, but its correlation to real world results is dubious at best. -As the industry standard test method, its lack of correlation to real world results may not matter.

10 Example of Salt Spray Corrosion -Salt Spray (ASTM B117) testing is often done in the lab using standard test panels which are taped on the edges using duct tape. Samples are often tested with duplicates, some with and some without scribe marks to show scribe creep. -As the bottom picture indicates, sometimes small details like scribe creep can kill an experimental formulation, even though corrosion performance on the face is very good. -Galvanized substrates show white rust, steel shows red rust. Eventually Galvanized substrate will also show red rust.

11 Example of Salt Spray Corrosion -Once the product is run online, it is critical to confirm salt spray performance on the customers actual production. The only way to confirm production quality is to test product off the line. -In this example from a trial run, a product which typically has 200+hrs Salt Spray performance at other coaters was beginning to show white rust at 96hrs. It turned out the coater was using D-bulbs instead of the expected Hbulbs. In UV coating, the equipment must match the formulation!

12 Benchmarking Corrosion performance: -Cyclic corrosion is considered flawed but still a much better indicator of real world performance then B117. -Nothing beats real world testing. Even then location can greatly skew results.

13 Benchmarking Corrosion Performance: -The final benchmark is generally exterior exposure. There are several commercial test facilities which will exposure your panels/ pipes for several months/years. -The aliphatic urethane system above coated over G70 HDG shows far better results then the BPA system below coated over CRS. Since many coaters apply UV as a temporary coating, the performance of the system below may be perfectly acceptable.

14 Conclusion: -Properly understanding the customers needs are half the battle. -Low shrinkage oligomers and monomers along with a proper adhesion promoter are all required. -Salt Spray may not be the best test method but often is mandatory. -Real world test results are the most valuable.