Monthly Archives: August 2015

Knowing Your Powder

Powder For Powder CoatingNow that we have discussed the advantages of powder coating and the benefits of bringing your coating system in house, it’s time to talk powder. There are a number of different kinds of powder available, and selecting the right one is a key component to your finishing operation.

 

The Base Powder Coating Resin

When we talk about powder quality and performance, we always reference the powder’s base resin. The base resin is what the powder is made of (polyester, epoxy, etc) and will greatly impact two things: the final coating quality and your pretreatment process.

Depending on the specific performance criteria of your customer or your parts, there are multiple base resin qualities to be considered. We always recommend researching your requirements and deciding on your powder quality prior to purchasing equipment so that you don’t buy the wrong size oven or the wrong pretreatment solution.

Polyester Powder Coatings

The most widely used base resin for powder coating is polyester. Polyester has great exterior durability, good hardness, excellent chemical resistance, and is fairly easy to cure. Most start-up powder coating operations use a form of polyester due to its performance, affordability, and ease of application.

Polyester powder comes in many varieties. A couple of the most common are:

Low-Cure: Can be cured at 325F-350F. Lower cure temperature helps with some under powered ovens or quick cure applications. The downside of low cure is shelf life reduction and reduced performance.

Super-Durable: These polyesters have specific resins for longer retention of gloss and improved color fade resistance. They are used for exterior equipment applications such as high end tractors and trucks. They also use specific pigments that are designed to be UV ray resistant. This improvement comes at a higher price and may have tighter application tolerances.

TGIC-Free: Most polyesters are made from a TGIC resin. Certain architectural specifications require TGIC-Free polyester powder coating. They are usually a little higher in price and have tighter application specifications, but they may be less sensitive to cross-powder contamination.

Example product sheet: http://www.tcipowder.com/pdfs/product-literature/tru-illusion-product-flyer.pdf

Hybrid Powder Coatings

Hybrid powder coatings are a mix of polyester and epoxy resins. Most of your special effect coatings are this quality due to the pliability of the formulation. River textures, metallics, base coats, veins, and other effects are possible with this quality of powder. They are primarily for indoor applications since the epoxy part can degrade with exposure to UV radiation. Some formulations allow polyester clear coats to be applied after the hybrid coating for exterior quality. Hybrids are usually less expensive than polyesters and usually have lower cure temperatures.

Example video: https://www.youtube.com/watch?v=d1cIz1pj_yI

Epoxy Powder Coatings

Epoxy powder coatings are used for parts that need superior chemical resistance but will not be exposed to sunlight. Under hood car parts, pipelines that are buried, and interior lab components are some common applications for epoxy powder coating. Powder primers are typically made from epoxy resins due to their affordability and extreme salt-spray performance. They usually are cured at lower temperatures than polyester and can be partially cured in the case of primers.

Example data sheet: http://www.tiger-coatings.us/fileadmin/user_upload/downloads_us_new/product-data-sheets/tiger-drylac/interior-applications/TIGER_Drylac_Series_69_Interior.pdf

Urethane Powder Coatings

Urethane powder coatings are used for high end parts that need great flexibility and exterior sunlight exposure performance. Typical applications for urethane powder coatings are marine exterior components, tight tolerance automotive parts, and impact-resistant surfaces. They are usually much higher in price than typical polyesters and are for specific applications that need them. Application is fairly normal with cure times similar to polyesters.

Example data sheet: http://www2.dupont.com/Powder/en_US/assets/downloads/tds/Channel_Green_AFG507S7.pdf

Kynar™ Powder Coatings

Kynar™ powder coatings are used primarily in aluminum applications on the outside of high-rises or anywhere that requires a ten year warranty against gloss loss and color fade. They are extremely expensive and difficult to apply correctly. They require specific pretreatment and applicators must be certified by the powder supplier with extensive testing be fore the powder coater is even approved to use the powder.

Example data sheet: http://www.ppgideascapes.com/getmedia/7ea7c346-46ac-4572-a91a-1123dcbc1554/DuranarPowder.PDF.aspx

Choosing The Right Powder For Your Process

Using this guide will help you determine the powder you need for the most common powder coating applications. However, if your process is very specific, you may also use acrylic coating, high-temp powders, and/or blends of the above resins for certain specialty purposes. Again, we always recommend researching your customer’s requirements (longevity, gloss, salt-spray resistance, etc) prior to making your powder or equipment purchase as it will determine the cure time, pretreatment required, and the application amount of the specific powder.

Once you’ve determined exactly what sort of powder and pretreatment you need, it’s time to plan your powder coating system. If you need assistance in planning please give one of our systems specialists a call.

Cleaning & Pretreatment Primer, Part One

Get_better_powder_coating_results_with_clean_partsBefore the first coat of powder ever gets applied, you have a decision to make: “How are you going to prepare your metal?

To get the best powder coating results, the surface you will be coating must be clean. Depending on the quality and type of metal, there are different levels of cleaning and pretreatment for powder coating to consider. You should also account for your customer’s requirements and how long the part should last in the field.

With all of these factors you may be wondering where to start, but it is as simple as asking:

What’s the best way to clean my metal?

What kind of pretreatment should I use?

What requirements does the finished product have?

The Best Ways To Clean Your Metal Surfaces For Powder Coating

First, determine what you’ll be coating the most often. If you are coating sheet steel, for example, you will usually only need light oil cleaning. Angle iron or castings often need sand/shot blasting to remove scale and surface rust. Aluminum is prepared differently than galvanized or regular steel; the oxidation layer of aluminum must be removed, which requires certain chemicals that provide a good etched layer for paint adhesion. Identifying which type of cleaning is right for your process is the first step in long-lasting, quality results.

The most common types of metal cleaning are:

Blasting. Blasting with sand or shot is a great way to clean up metal scale, laser scale, rough welds, or heavily rusted steel. Blasting is also used to strip off previously coated metal for refinishing. While blasting smooths out a lot of surface defects in raw metal, it does not fully clean the metal of oils or other contaminants. However, blasting does create a more adhesive surface for the powder coating after the part has been cleaned of residual soils.

Washing. Pressure washing, dipping, or automatic washing (with a soap specifically formulated for the soils specific to your fabricating process) are the most effective ways of cleaning the metal prior to the next finishing stage. Steam cleaning or hot water helps break down the oils and can reach difficult spots or gaps in the surface. Detergent is the best way of cleaning metal of oils, waxes, polishing compounds, or other substances that will prevent the powder from sticking to the metal.

Wiping. Solvent wiping is another way to clean up the metal of surface oils and contaminants, but it is an inaccurate way to clean. Since the part is manually wiped with rags, the rags can become saturated with the oil you are trying to remove.

Pretreatment For Better Powder Coating Results

Clean metal by itself can be immediately powder coated but that will not give you superior performance and weathering characteristics. A good pretreatment allows the powder coating to better bond physically to the metal, withstand exterior weathering, and prevents flash rust prior to powder coating.  Because of all the benefits associated with it, you should always consider adding metal pretreatment to your coating process.

There are a few of methods of pretreatment. The first one is chemically etching the metal with an acid based product that promotes adhesion of the powder coating to slick or difficult to adhere to metals. Aluminum is typically a very slick substrate, so it needs some sort of surface treatment to remove oxidation and to etch the surface. Etching chemicals are usually more difficult to work with than the next method.

The second method of pretreatment, phosphating, is used to improve the corrosion resistance of the product.  Iron phosphate is the oldest method of pretreatment. It is a great way to improve the adhesion of the powder as well as doubling or tripling the corrosion resistance of powder by itself. In a pure steel fabrication process, it is the most common chemical pretreatment. Zinc Phosphate is a more robust process that results in the best corrosion resistance for steel products that are meant for ships or near coastal areas.

Here are a couple of links to some data pages for iron phosphate and zinc phosphate products:

Iron Phosphate: http://www.ppgtruefinish.com/getattachment/3448357e-3e53-4cf9-bf96-a70b51160dd7/CHEMFOS-146FD.pdf.aspx

Zinc Phosphate: http://www.williams-oakey.co.uk/gardobondz3480.pdf

Besides etching and phosphating, a third method of pretreatment is Zirconium Non-Phosphate pretreatment. In essence, it is a combination etching chemical such as zirconium fluoride in a low solids acrylic sealer that bonds to the metal. This newer process is used for multi-metal operations and also combines well with cleaners for a 1-3 step spray system, depending on the chemical manufacturer.

Here is a more technical description of Zirconium: http://www.duboischemicals.com/pretreatment/links/zirconization.pdf

Meeting Your Customer’s Powder Coating Specifications

Finally, your customer’s specifications will determine the cost and complexity of your pretreatment process. If a tractor-trailer wheel needs to last 5-10 years on the road under heavy use in ice and snow, then the powder coater needs a superior pretreatment process. A decorative base for an interior table would not need the corrosion resistance as the wheel, but might need a good etch or blast profile to prevent powder loss due to being bumped from time to time. An interior fluorescent light fixture would need neither improved adhesion or corrosion resistance, but would still need clean metal for the powder to be applied defect-free.

With all these questions answered, you’ll be able to implement a pretreatment process that produces quality and consistent results for you and your customers.