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PLASTICS PROFILE

PETG Adds ‘POP’ to Displays

PETG is the generic term given to materials made from glycol modified polyester terephthalate. Widely used in POP displays, packaging applications and signage, it typically offers a greater impact strength than acrylics while providing many of the benefits of polycarbonate at a lower cost.

The material can be formed, fabricated, bonded and finished easily. Deep draws, complex cuts and molded-in details are possible without any adverse effect to the structural integrity of the material.

Forming Applications

PETG can be easily brake formed, strip heated, drape formed, free blown and thermoformed. Most vacuum formers with infrared heating elements work well on PETG.

In typical applications, the heating range for the sheet falls between 280F and 320F; when the sheet reaches forming temperature, uniform sag will occur. The amount of sag depends upon the size and thickness of the sheet. For example, a 12-inch by 12-inch by 0.060-inch sheet will sag approximately 1 inch. Likewise, a 36-inch by 36-inch by 0.177-inch sheet will sag approximately 4 to 6 inches in the center. Once the uniform temperature has been achieved, timers can be used to accurately reproduce the condition for part consistency.

PETG is also suitable for registration vacuum forming. Because the material is extruded, the sheet must be oriented so that each part is screened and formed in the same direction each time. Materials can be specially ordered for this type of application.

Fabricating Methods

One of the advantages of PETG is that it can be easily sawn, routed and laser cut.

A circular saw blade with carbide-tipped teeth, utilizing a “triple tooth” design is a preferred method straight cutting of the material. Blades should have three to five teeth per inch; in general, a thicker gauge sheet requires fewer teeth per inch. The saws should be run in the range of 8,000 to 12,000 linear feet per minute.

Bandsaws, on the other hand, should be run at 2,000 feet per minute and have three to 15 teeth per inch; larger tooth blades are generally preferred with thicker gauge materials. In all cases, the material must be supported during cutting as vibration from the saw operation can cause it to crack.

Routing can be used to cut curved or irregular shapes. For the best results, routers with a speed of 20,000 to 25,000 rpm, used in conjunction with straight fluted carbide-tipped bits or HSS bits in 3&Mac218;8 inch to 1&Mac218;2 inch diameter are preferred. Portable, over-arm or inverted routers can also be used.

When routing, it is important to feed the sheet against the rotation of the router bit. Cooling the bit with compressed air during routing will aid chip removal and also prolong the bit’s sharpness. The material can also be milled, using standard high-speed milling cutters for metal, provided the cutters have sharp edges and adequate clearance at the heel. Use of a 5&Mac218;8 inch diameter bit at 500 rpm and a travel of 5 inches per minute will produce favorable results.

Laser beams can also be used to cut up to 0.187-inch sheets of PETG. One of the advantages of laser cutting is cleaner edges, often with no polishing or finishing necessary.

Bonding Applications

Solvent bonding is the most common method for joining PETG. Smaller items with flat surfaces can be bonded by applying the solvent along the edges via a needle applicator or syringe. For larger items, the surface area should be immersed in the solvent until the material is softened, then clamped together into position until the bond is set.

Excessive moisture can cause joint whitening. Working in a climate-controlled area, adding 10 percent glacial acetic acid in the solvent, or thickening the solvent with resin or sawdust (to slow curing) will help reduce whitening.

Structural bonding of thin-gauge PETG can be accomplished with acrylic based transfer tapes. For this method, bend a small return, the width of the transfer tape, on the part to be fastened. Clean the contact areas with a 50/50 isopropyl alcohol-water mixture and apply the transfer tape to the return. Remove the masking and press the part into place.

Another alternative is ultrasonic welding. Individual manufacturers have suggested guidelines for welding of PETG.

The above information was supplied by Sheffield Plastics Inc. For more information, contact the company at (800) 628-5084, www.sheffieldplasticsinc.com.

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