In this blog, I'd like to talk about different frame materials that are used and some advantages and disadvantages of each. This will focus mostly around the different types of plastics and metals used in the industry today. There are some unusual materials such as wood, bone, and rubber, but these are very specialty types of materials and usually very expensive.
Plastics
The most widely used plastic material in zyl (or zylonite), this material is made of cellulose acetate. Zyl has good "toughness", a deep gloss and high transparency. It can be mixed with colors to produce about any color of the rainbow. All of this makes it a good material for frames. The material is also pliable when heated and can "shrink" when quickly cooled. Frames made of zyl are typically injection molded, however, when you have a color blending such as a tortoise shell color, these are usually cut from sheets of plastic.
Another type of plastic resin is propianate. It is a nylon based material which is very lightweight and hypoallergenic. Propianate is usually clear and the surface is treated to create the different colors of the frame. It also doesn't accept heat like zyl does. Usually when inserting lenses, the frame is not heated, the lenses are put into a frame at room temperature. Adjustments to this material should be done with very little heat or the use of a frame warmer.
Back in the late 1940's, nylon was introduced as a frame material. Nylon was very lightweight and comfortable. The problem with pure nylon was its brittleness. Also, it was very difficult to adjust. Nylon blends were invented to adress the problem of strength. Now, most of our sport frames (such as Rec Specs) and alot of sunglasses are made from these nylon blends. They are typically made of gliamides, which are very resistant to hot and cold and are more flexible, yet also stiff. The "wrap" sunglasses are usually made of these nylon blends because it's the best material to hold the shape. Nylon blends are still difficult to adjust.
With all plastic frames, it is best to heat the frame slowly and evenly to avoid pitting or melting the plastic. Stir the glass beads and heat only the part of the frame that needs adjusting by placing it about an inch below the surface, constantly moving it around. This will apply the heat to the frame more evenly.
Metals
Stainless steel is a lighter weight metal. Stainless steel frames tend to be slightly thinner than monel and stronger. Stainless steel frame can be a good option for the patient that has a reaction to monel or more corrosive metals. Most stainless steel frames are nickel free and thus hypoallergenic. This make a more cost effective alternative to titanium (which will be mentioned next). Stainless steel contains certain amounts of chromium which gives it its corrosion resistance. The more chromium in the frame, the best its resistance to corrosion.
Titanium, again, is a lightweight metal that is extremely durable and hypoallergenic. We all know of titanium's medical uses because of its non corrosiveness and strength. Titanium is also used in aircrafts and the Apollo and Gemini space capsules because of it being so lightweight. Originally, titanium was only available in a silver gray color. With the developement and popularity, titanium can produced in a variety of colors for a clean, more contemporary look. One thing to remember is that all titanium frames are not all 100% titanium. Some are made from an alloy that is a combination of titanium and other metals, such as nickel or copper. This is done to reduce the cost of a titanium frame. A frame only needs to be 50% titanium in order to be labelled that way. Titanium cannot be soldered should it break.
Flexon is a titanium-based alloy. This unique and popular material, which is proprietary to the eyeglass manufacturer Marchon, is called a "memory metal" because it can go back to its original shape if damaged. Frames made of Flexon come back into shape even after twisting, bending and crushing. Flexon frames are lightweight, hypoallergenic and corrosion-resistant. There are other versions of this available from other manufacturers.
Aluminum is also used as a lightweight alternative metal. Aluminum is also highly corrosion resistant. Its the most abundant metal in the world, however, it seems to only be used in very high end frames due to the unique look it creates. Pure aluminum is actually soft and weak, but commercial aluminum with small amounts of silicon and iron is hard and strong. Aluminum frames usually are very stiff and retains shape very well.
Allergic Reactions to Frames
Some frames can cause an allergic reaction. This is most often seen as either a reddish colored rash on the sides of the head (wear the temples touch the head), the cheeks and/or nose (wear the frame might rest on the face). Also, the pad arms and screws of the frame may oxidize or turn green. If metal frames cause a reaction, nickel is usually the culprit: most metal frames are made of a nickel alloy. Other metals used include: aluminum, stainless steel, titanium, zinc, copper, beryllium, gold and silver. Stainless, titanium, gold and silver are usually hypoallergenic.
Some people are allergic to the nose pads on metal frames. Most are made of silicone or acetate, but they can also be made out of polyvinyl chloride (PVC), nickel, titanium or rubber. Silicone is tricky: certain silicones are hypoallergenic (such as medical silicone), but others can trigger allergic reactions. Both PVC and titanium are usually hypoallergenic.
Most plastic glasses are made of zyl (also called zylonite, acetate and cellulose acetate) or propionate. Other materials used in plastic frames include: polyamide, nylon, polycarbonate, carbon and Optyl (a brand of epoxy resin). Propionate, polyamide, nylon and Optyl frames are all considered hypoallergenic.
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