Integument Technology's scientists have developed a surface activation process using a cold gas plasma treatment for modifying fluoropolymer surfaces in a novel manner that promotes adhesion to a variety of materials including other polymers, adhesives, ceramics, coatings and metals. In the late 1980's, Integument researchers at the State University of New York at Buffalo discovered that a radio frequency (rf) glow discharge (cold gas plasma) of hydrogen, in combination with vaporized liquids, created a distinctive surface modification at fluoropolymer surfaces. By utilizing hydrogen plasma as a fluorine scavenger in concert with vaporized liquids, the oxygen incorporation into the surface matrix of a fluoropolymer material was found to be highly controllable. The research discovered that the plasma surface modification enabled the subject material to retain its morphology, chemical resistance, and hydrophobic properties comparable to that of the original, unmodified fluoropolymer while effectively creating highly reactive sites for bonding other materials.

Molecular View of Activated Fluoropolymer Surfaces

The research demonstrated that the oxygen functionalities created on these fluoropolymer surfaces were chemically reactive and permanent. It is this chemical functionality that allows various adhesives and polymers to form a covalent bond to the modified fluoropolymer surface. What's more, the treatment does not significantly affect the film's surface tension properties. In other words it remains the "non-stick," easy-to-clean material that fluoropolymers are famous for.

Adding an external energy source to a gaseous mixture creates plasmas that are often described as "the fourth state of matter." Plasmas consist of a low-temperature glow discharge or a low pressure, partially ionized gas comprised of a concentration of highly excited atomic, molecular, ionic and free radical species. An enclosed vacuum chamber is used to excite the gas molecules by subjecting the gas mixture to an electrified field of radio frequency (rf) energy.

Activation of Flouropolymer Surfaces

Free electrons are created by the imposed rf field which excites the molecules. The free electrons collide with neutral gas molecules as their energy increases from the imposed field and transfer energy. The collisions and transfer of energy form numerous reactive species. These particles then interact with solid surfaces placed in the plasma. This often results in dramatic modifications of the molecular structure of the solid surface. The desired effect can be controlled by judiciously selecting the process gas in order to create the desired surface properties required for the intended use of the material.

In the application specific to halogenated polymers, a mixture of hydrogen and H₂O or MeOH vapor co-reactant is used to generate the plasma. This combination partially fluorinates the fluoropolymer surface and concurrently adds permanently stable -OH functionalities at the defluorinated sites. The -OH functionality adjacent to fluorinated carbon groups is extremely stable, yet chemically reactive to various chemistries. The resultant reactivity is ideal for forming tenacious bonds with selective adhesives and polymers.

The plasma treatment process does not rely upon etching or other technically inferior forms of physical degradation to promote adhesion to fluoropolymers. The chemical covalent bond formed between the fluoropolymer materials and the adhesive is permanent, enabling them to be used in applications where no other conventional adhesive, fluoropolymer sheet, or film products can. The covalent bond withstands a wide range of mechanical and thermal stresses including extreme temperature cycling, UV, humidity and aggressive chemicals, without delaminating.

Traditional Treatments to Promote Adhesion