Frequently Asked Questions
Click on the questions below to view the answer.
Why bother to coat?
• Performance and decoration
• Bulk modification may be too expensive or additives may diminish integrity
• Materials are only required at the surface for attributes such as slip, therapy delivery, color.
What are the advantages of water-based coatings?
Ambient cure
• No high temperatures, which could affect proteins or other heat sensitive bioactive additives or substrates, are required.
Flammability
• Usually not an issue with water-based coatings.
Odor
• Workers love the low odor compared to conventional solvents.
Worker Safety
• Coatings are generally less hazardous to employee's health and easier to handle.
Energy Requirements
• While the specific heat of water is higher than most solvents customarily used, it will not require the venting in cleanrooms that is _required with conventional solvents, thereby reducing the need for clean, heated (humidified) make-up air.
What are the specific advantages over solvent-based coatings?
• Water wash-up of equipment.
• Easy Disposal - Dry out and toss in the trash in most instances.
• Surface acceptability - No stress crazing on solvent sensitive plastics such as polycarbonate, acrylic, polyester, urethane, etc.
• Insurance- No extra insurance needed.
How do I decide which coating to order?
Your interdisciplinary product development team should produce a project plan describing what features are needed for surface modifications on the device. For many applications that are searching for a second source of coating, there is an existing specification for coating performance which describes the test methods and other requirements for the product. In general these specifications can be described by the categories similar to those that have been shown under product lines. Ifthere is no catagory under "Products" to accomodate your requirements, please contact us. We are able to make these coatings harder or softer, more resilient or less flexible with variations in the resins we select.
Do I need to order the patented systems? They cost more, and may have shorter shelf lives.
In most instances we would suggest that you begin your evaluations with the non-patented coatings as they are usually less expensive, more forgiving, and simpler to work with when beginning a program.
The patented systems are usually selected by more seasoned coatings engineers as these cured surfaces are tougher and more durable, generally adhering better, but they can be trickier to use. Pot life on the Crosslinker A mixes can be several days, but mixes with Crosslinker B can be only 6-8 hours depending on the solids of the coating solution. Crosslinker A mixes into the coating more easily than Crosslinker B but can sometimes cause kickout of the polymer in the coating (white striations of "goo") if just dumped into the coating without mixing.
If you decide after evaluating the non-patented systems that you need more durability it is easy to order the patented system and you will have more coating experience to handle it too.
How do I decide how much coating to order?
If you are doing a rough evaluation of coating utility and can flow coat from an eye dropper or dip the device into (or pull it through) the coating then the smaller amounts should suffice. You can always order more or larger quantities. If you have a current reservoir that needs filling we can discuss larger quantities than what is listed on the forms at good economies of scale. Once utility is proven, and experience gleaned with the coating and its handling, quantities can be varied to accommodate your packaging requirements.
What if the coating will not wet, beads up, or does not stick?
Surface tension is a funny thing. If you do not have the surface tension of the coating below that of the surface, the coating will not wet- never mind stick. Water has a surface tension of 73 dyne/cm and many low energy surfaces have surface tensions less than 30. So what can you do? The solution is to either increase the surface tension of the surface with plasma, corona, acid etch, priming, etc, or bring down the surface tension of the coating with the addition of solvents and/or surfactants. (We suggest the solvent route, if possible, since solvent comes out during the drying/curing phase, but the addition of materials that remain in the final coating may alter the biocompatibility test results.)
OK - I have the coating on the device. Now how do I dry/cure it?
Each coating will dry or cure a bit differently.
• Coatings without crosslinker will simply dry by evaporation of water. This can take 5 minutes for a very thin, solvent diluted coating, or 30-50 minutes for a thicker one.
• Coatings with Crosslinker A are usually cured by the evaporation of the neutralizing base in the coating with immediate reaction of the crosslinker to the free acid functionality. Heat can improve molecular mobility with improved ability of the polymer chains to access crosslinker groups. We would recommend temperatures of 160-200F to help in the degree of cure. Excess crosslinker hydrolyzes or reacts with functional groups on the surface.
• Coatings using Crosslinker B are cured with time and temperature. Active hydroxyl groups participate in the curing and can be contributed by the surface or the polymer. Like the Crosslinker A systems, heat and time will help in the cure and subsequent
hydrolysis of the residual functional groups. This may take a week or more.
In all cases, you can accelerate drying by placing in a forced hot air oven at temperatures that are suited to your substrate materials. Most of the coatings will take temperatures up to 300 F for short periods.
It is recommended that you test the process you plan to use to mix,coat and dry/cure on your device at several different ambient conditions for temperature and humidity conditions once suitable performance is obtained.
Note: If you are experiencing problems with the application of these products, please contact us for coaching, or consider utilizing our engineering services to prepare initial samples for your evaluation.
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