Fusion UV Systems, Fall 2007, world's largest manufacturer of UV equipment, Gaithersburg, MD.
Inline Metallization Adds Value for Plastic
Plastic molded parts are lightweight and inexpensive to mold into a variety of shapes at high production rates. Because color is typically throughout the plastic material, many plastic parts don’t require any coatings. But what if the part needs a metallic look, say for a cosmetic cap, or even a highly reflective surface for a headlamp reflector? In the past, metallized coating was done via batch Physical Vapor Deposition (PVD) sputtering or electroplating. Now PVD sputtering is being done inline, along with UV-curable basecoats and topcoats to deliver significant results for plastic molders and decorators.
The PVD sputtering process
PVD sputtering has been a proven coating technology in semiconductor and CD/DVD manufacturing for many years. It produces a fine, metallic layer with excellent adhesion and film quality.
Although earlier considered a “high-tech” vacuum deposition process, sputtering has been around since the 1800’s and was used as a coating method for a number of years, albeit in a very crude manner. Today metallizing inline with injection molding is the primary method used for making CD’s, DVD’s, CD-R’s and other optical media.
PVD sputtering is a very clean vacuum deposition process using argon gas, electricity and the target material (the coating material) mounted in a cathode assembly. Metal is physically ejected from a source by a plasma and subsequently deposited on a surface. PVD sputtering is a highly controllable process with instant on/off capability well suited for use with inline processing of parts.
Types of metal coating
The target material can be any type of metal or metal alloy. Most decorative parts use aluminum coatings. PVD sputtering is capable of depositing 100% aluminum as well as aluminum alloys with equal ease. Metals such as stainless steels, copper, copper alloys, chrome and nickel may also be deposited. Alloys are often used to provide corrosion resistance or to change the color or look of the sputtered film.
PVD inline with molding
D2 In-line Solutions, LLC, headquartered in Scarborough, Maine, has applied their years of experience in the Optical Disc industry to perfect the PVD sputtering process for a variety of plastic molded parts. D2 provides production engineering, coating and automation solutions to the plastic injection-molding industry including inline PVD sputtering systems. A PVD film applied inline immediately after injection molding results in a very high quality coating because the plastic parts are never cleaner and drier than immediately after molding.
Many advantages of inline metallization
PVD sputtered coatings applied inline with molding can be quite cost effective while adding value to the parts being coated. With the plastics industry facing cheap competition from overseas, the added value of metallized parts is a good way to increase margins. Also, by sputtering inline with injection molding, there is no penalty for cycle time or throughput. And with the coating process inline and in-house, the need to ship parts to an outside coating service is eliminated, reducing lead times, Work-in-Process (WIP) and cost.
A variety of plastics
Plastics such as polycarbonate, polystyrene and ABS, can be readily coated, with excellent surface properties. Some plastics, such as PMMA, require special surface treatments prior to metallizing. Polypropylene, a plastic commonly used in packaging and similar applications, is usually difficult to metallize due to its “slippery” nature. However, D2 has a proprietary process that provides excellent adhesion of metal coatings to polypropylene.
The need for UV coatings
Any scratches or dings on the surface of a plastic part are visually enhanced by metallizing. A molded part may look perfectly acceptable after injection molding, but look terribly scratched once a metal coating is applied. Primer coats applied prior to metallization hide part surface imperfections and enhance coating adhesion by acting as an interfacing layer. Clear or tinted topcoats provide scratch and chemical resistance and/or color to the metallized coating.
UV-curable basecoat paints are ideal because they can fully cure in a short distance and quickly enough as parts move to the inline metallizer. UV curing topcoats also minimizes the time and floor space needed for a finished part.
Parts entering a vacuum metallizer must not outgas into the vacuum chamber. This is true whether the process is batch evaporation or in-line PVD sputtering. Volatile gases add contaminants to the vacuum system, degrading performance and coating quality. UV-curable, 100% solids coatings emit virtually no volatile compounds after proper UV curing and provide an ideal surface upon which to deposit a metal coating. Together, UV curing and metallizing provide the shortest time period from basecoat application to part completion.
The overall process
As parts exit the injection molder (or from feed bowls), parts are fixtured onto a chain-on-edge conveyor for spraying and UV curing the basecoat. Fusion UV’s modular UV curing systems can be easily oriented around a three dimensional part for efficient and full cure of the contoured surfaces. Following basecoat cure, parts enter the metallizer.
D2’s PPM (Plastic Part Metallizer) integrates directly with conventional chain-on-edge basecoat and topcoat finishing lines. It is an inline system with a small, rapid-cycle process chamber and is approximately the size of a typical office desk. Typical production rates are nearly one part per second. Finally, topcoats are applied and cured and the parts off-loaded.
Comparison to electroplating and batch metallizing
Electroplating is used to apply chrome coatings to plastic. Recently enacted RoHS regulations (Restriction of Hazardous Substances) place restrictions on the use of plating processes. Inline PVD sputtering and coating, utilizing UV cured basecoats and topcoat finishes, is an environmentally sound alternative to electroplating. Unlike electroplating, sputtering processes produce no volatiles and no chemical waste.
Batch-oriented basecoat/metallize/topcoat processes require significant manual handling of coated parts between processes. Large batch metallizers have cycle times of 20 to 40 minutes and can process thousands of parts in each cycle. The result is large WIP inventories and a long part vulnerability window i.e. the time from the start of coating to part complete, where contamination and other factors may compromise quality. The D2 PPM system can reduce the part vulnerability window from up to one hour or more, to only a few minutes.
Plastic molders and decorators should evaluate
Inline PVD sputtering is well suited to existing decorating and metallizing providers who have a batch metallizer but a need to improve quality or reduce labor costs. Plastic molders or others looking to add metallizing to an existing molding or coating line should also evaluate inline PVD sputtering.
In addition to decorating, D2 provides a proprietary process for sputtering thick (up to 100 micron) metal layers to plastic parts. This technology is useful for EMI/RFI shielding, erosion protection and other surface improvement for plastic parts, carbon composite parts, and other temperature sensitive substrates.
D2 has a laboratory system, including a Fusion UV conveyor and F300S curing system, for evaluating metallization and coating of parts. D2 works closely with Thomas Associates of Marblehead, Massachusetts, also a Fusion UV manufacturer’s representative, in the sale of PPM and other metallizers. For additional information contact either Thomas Associates at 781-639-0715 or D2 Sales at 207-510-6888, or email sales@d2inline.com.