In virtually every application the quality of the bond between the resin system and the surface to which it is applied is improved if the surface is clean and dry.
This is particularly true of adhesive applications where stress will be applied to the cured bond line.
It is also true where protective coatings are used. The following surface preparation procedures are recommended.

METALS 1. Degrease – Wipe faying surfaces with Methyl Ethyl Ketone (MEK) to remove all oil, dirt, and grease.   2. Etch – For optimum results, metal parts should be immersed in a chromic acid bath solution consisting of: Sodium dichromate – 4 parts by weight Sulfuric acid – 10 parts by weight Water – 30 parts by weight The solution should be held at a temperature of 160°F (71°C), and the parts left immersed for 5 to 7 minutes.   3. Rinse – remove metal parts from etching bath and rinse in clean cold water (de-ionized water is recommended). If thoroughly clean, metal surfaces so treated will hold a thin film of water.   4. Dry – To accelerate drying, items to be bonded can be placed in an air-circulating oven.   ALTERNATE PROCEDURE 1. Degrease, scour and dry – Often etching as outlined above is not practical. The metal surfaces may be cleaned by degreasing as noted above, scouring with an alkaline cleanser followed by rinsing and drying.   2. Degrease and dry – Degrease the surface as noted above, sand or sandblast the surface lightly but thoroughly. Rinse with acetone or Methyl Ethyl Ketone (MEK), and dry

GLASS 1. Degrease – With MEK as above, or with a strong boiling solution of a good grade household detergent.   2. Etch – For optimum results, degreasing can be followed by the chromic acid bath outlined above.   WOOD 1. Sand – Bonding surfaces should be sanded lightly, but thoroughly to remove all external contamination.   2. Clean – Carefully remove all dust, or particles of wood from sanded areas. A stiff and clean brush or compressed air can be used.   PLASTIC 1. Clean – Remove all dirt, oil, or other surface contaminants with soap and water, followed by thorough rinsing and allow to dry. A solvent that does not have a detrimental effect may also be used.   2. Sand – Surfaces to be bonded should be sanded lightly, but thoroughly to remove surface sheen.   3. Clean – Carefully remove all dust or particles of plastic from the sanded area. A clean brush, lint-free cloth, or compressed air may be used.

Flame Treatment of Plastic Substrates for Adhesive Bonding

Obtaining an adequate bond strength when bonding plastic-to-plastic substrates or plastic to dissimilar substrates is often a challenge for resin system.
In general, plastic surfaces demonstrate poor ‘wettability’ or the ability of a liquid to form a continuous film. These types of substrates or are called LSE or Low Surface Energy substrates and typically thermoplastic surfaces fall within this category. Teflon or its generic name PTFE and other polyethylene derivatives such as HDPE, LDPE, UHMW and olefinic-based plastics demonstrate poor liquid wettability due to its low surface energy.
To create a viable bondable surface condition with these types of plastics, it must be surface treated by creating a superficial oxidized surface to increase its dynamic surface tension.
Various types of physical treatment can be used to increase the surface energy of plastics,  mostly through oxidation of the superficial layer. Flame treatment is the most widely used and cost-effective pre-treatment for polyethylene (HDPE, LDPE, UHMW) and polyolefin-based plastics prior to polymer bonding or printing.
It consists of exposing the surface to be coated to a suitable oxidizing flame during a short period of time (0.2 to 3 sec.).The resulting change of the surface by creating an oxidized surface greatly improves the liquids ability to wet-out the surface thus creating a strong adhesive bond between the surface and the coating. A Flame Treating process consists of exposing the surface to a suitable oxidizing flame for a period in the range of 0.2 to 3.0 seconds.
This treatment brings about a change to the polymer surface that increases its surface energy allowing fluids to effectively wet-out the surface.

Commercially Available Propane Torch

 

  

Adjust the propane torch so that a low oxygen burning flame is achieved and pass over the area to be treated several times until a slight haze is noticed on the surface of the substrate.

Note the fluid behavior on the flame treated area demonstrating improved substrate wetting thus making adhesion possible for polymers such as adhesives and inks.
Note the improved wettability of the flame treated side allowing the tension modified liquid to effectively wet-out the surface.
By modifying the surface condition of the plastic, polymer bonding is now possible. 

1 CC Of Distilled Water Low Surface Energy Substrate. The Extreme Angle Of Droplet Is Due To Low Surface Energy Of The Substrate Yielding Poor Surface Wettability. In Order To Achieve An Adequate Bond To This Substrate, The Substrate Most Be Treated By Either Mechanical Sanding Or Chemical Etching To Increase The Surface Energy Which Will Allow A Lower 'truncated Sphere' Or Meniscus Height Profile.

1 CC Of Distilled Applied On This Glass Surface That Is Measured With A High Surface Energy Characteristic And Note Low Angle Of The Meniscus Or Truncated Sphere Of The Droplet Un Comparison To The Brass Plate. An Application Of A Reactive Polymer Will Yield Structural Adhesion Which Means The Bond Strength Will Be As Strong Or Stronger Than The Glass Substrate

POLISHED BRASS PLATE

GLASS PLATE

 

EFFECTIVE BONDING DESIGN AND DYNAMICS