Any material (metal, plastics, glass, composites, etc.) can be treated with reactive-gas plasma, silane and/or UV. More and more, manufacturers are realizing the cost and performance benefits of these types of "dry" and "environmentally-friendly" surface modifications. The principal function of these types of treatments is to clean and modify the surface of their materials to enhance the adhesion properties of inks, glues, paints, and coatings.

Areas benefiting from this process include:

• Medical devices: plasma-cleaning and functionalizing devices (catheters, endoscopes, stents, intra-ocular lenses, etc.) prior to the application of a specialty and/or lubricious coating, adhesive, or marking.
• Optical devices: plasma-cleaning and/or photolysis treatments to functionalize materials (polycarbonate, glass, CR-39®, Trivex®, PMMA, urethane, etc.) for lenses, films, depositions, and MOEMs.
• Pharmaceutical: functionalizing devices for drug delivery and storage.
• Biotechnology: plasma-cleaning, functionalization and silane deposition treatments for micro-arrays, micro-fluidics, MEMs, etc.
• Aerospace, Automotive and Commercial Products: improving the adhesion of gaskets and other dissimilar materials, removing the "tack" from silicon devices, and dramatically increasing the adhesion of elastomer material to metal, polymers and other elastomers.

Why would you consider outsourcing your surface modification?

• Reduce the overall per piece manufacturing cost of your device.
• Eliminate primers, solvents and other chemicals from your manufacturing process.
• Remove the potential for chemical exposure to your employees.
• No equipment or trained personnel to accommodate.

Examples of Materials that can be Treated:

Acrylic	Glass	Metal	PET
Polypropylene	CR-39®	Composites	Rubber
Polyethylene	Ceramic	Nylon 6 and 12	SBR
Polyester	Polystyrene	Urethane	EPDM
Polycarbonate	PTFE	SAN	TPR / TPU
PEEK®	Acetal	PeBax®	Silicone rubber

What are the differences between surface treatment methods?

The need to modify the surface of materials is a growing issue for most industries. Medical device manufactures, biotechnology, diagnostic, and some industrial companies are discovering the cost, manufacturing and yield benefits of using surface modification equipment or services. Plasma, corona / ozone, and ultraviolet systems offer a novel approach to solving common problems. Yet, one must choose the appropriate technique for their application. The throughput requirements, polymer type, surface needed, capital equipment budget, research budget, and project time-line should be considered and weighed before relying on one technique.

Plasma

Plasma is the fourth state of matter; a quasi-neutral cloud of ionized gas. Positive ions, negative ions, electrons, and radicals in a concert of reactions and collisions as long as an electric potential difference exist. The plasma is very reactive and can readily prime any surface for adhesion, painting, coating or printing applications.

Corona

A corona discharge is plasma at standard atmospheric pressure. This plasma is produced by high voltage and the close proximity of two metal plates (electrodes) in atmosphere. When there is an electrical discharge in atmosphere, ions and ozone is nearly always generated. The ozone compound is relatively short lived and may dissociate to molecular oxygen (O2) and oxygen radical (O`). The oxygen radical is then free to do work on the polymer or other molecules in the air.

Ultraviolet

Photolysis systems operate on principles that lie between corona and plasma. These systems use high voltage to excite a gas in an emitter which then radiates the surface of a polymer. The radiation is intense and fine tuned to chemically modify a polymer to be receptive to most adhesives, paints, coatings, and inks.

What are the Pros and Cons between surface treatments?

Plasma

Pros - Plasma's main advantage is surface chemistry selectivity. Plasma systems control the treatment conditions by controlling the gas type, flow, pressure and concentration. Moreover, there is control over energy frequency, wattage, and electrode configuration. Reactive plasma treatments provide a continuum of moieties. For example:

• Oxygen plasma provides the possibility of carboxyl, carbonyl, ester, ether, epoxy, hydroxyl and carbonate moieties on a hydrocarbon surface.
• Nitrous plasma provides the possibility of carboxyl, carbonyl, ester, ether, epoxy, hydroxyl, urethane, amide, imine, cyano, and amine moieties on a hydrocarbon surface.
• Nitrogen plasma provides the possibility of amide, imine, amine, and urethane (oxygen incorporation upon exposure to atmosphere).

Another advantage is that plasma is a three-dimensional treatment. Any object placed inside a plasma chamber will be treated on all sides (excluding areas shielded by physical contact or masking).

Cons - The main disadvantage to plasma is the system price and throughput. The price of a system is related the size of the system. This is mainly due to the pump and power requirements. As the system size increases, the price increases. An engineer must consider the cost advantage for two smaller systems relative to one large system. This should be weighed against throughput, yield, and budget requirements. The throughput of a plasma system is restricted by the batch-to-batch logistics of a plasma process. There have been attempts to make in-line plasma systems, but the manufacture price and maintenance costs usually do not meet the justification.

Corona

Pros - Corona's main advantage is price. These systems are fairly robust and easy to maintain. Moreover, corona systems are easy to use. The primary consideration for choosing this technique is polymer type, residence time in the discharge region and footprint of the system.

Cons - The main disadvantage is the lack surface chemistry selectivity. Most corona systems are designed to operate in open-air conditions. So, the treatment is as consistent as the air around the system. Moreover, the treatment is limited to air chemistry (78% nitrogen, 20% oxygen, 2% other). It is this design that limits the polymers that can be treated by this technique. More stable polymers usually cannot be treated by this method. So, another disadvantage is limited polymer choice. Lastly, the treatment is two-dimensional. Usually this system will used for reel-to-reel thin film, webs, tape, or fibers.

Ultraviolet

Pro - UV's main advantage is the high throughput treatment of stable polymers (nylon 6 and nylon 12). These systems are very efficient and effective due to the specific wavelength emitted by the radiation source. Moreover, there is no electrical discharge across the sample needing treatment. So, electrically or charge sensitive devices are easily and safely treated. These systems can be easily designed to fit on nearly any conveyor system. The cost of these systems is relatively moderate. The cost is directly related to the size of the system (usually large systems are needed for highly stable material and high throughput).

Cons - The main disadvantage of UV systems is surface chemistry selectivity. These systems, like the corona systems, are operated in standard atmospheric conditions. Therefore, treatments are restricted to air chemistry. Another disadvantage is that UV treatments are line-of-sight (two-dimensional). Though system design can be modified to treat three-dimensional objects, the treatment is still determined by the placement of the radiation sources.

In summary, the need to modify polymer surfaces is a trend in manufacturing and research. Some of the surface modification techniques available are plasma, corona, or UV. The general guide line for choosing the appropriate technique is dictated by throughput, polymer choice, surface needed, budget, and project time-line.

How long does the treatment last?

Each polymer and each treatment has a different activation lifetime. Some polymers remain active for months while others remain active for hours. It is always best to perform subsequent processes as soon as possible. But, typically most polymers will remain active for weeks.

CR-39® and Trivex® are registered trademark of PPG Industries Inc.
PEEK® is a registered trademark of Victrex plc
Pebax® is a registered trademark of Arkema