Project Description:
US industry released a staggering quantity of organic solvents (> 1 billion lb for the top
10 pollutants alone.) into the atmosphere over this country in 1995, a recent year for
which Toxic Release Inventory (TRI) figures are available. The number 3 chemical
contributing to TRI air emissions for 1995 was toluene, a major constituent of printing
ink formulations [1]. In recent years the emphasis in US industry and within the EPA has
shifted from end of pipe treatment to pollution prevention, and regulatory and community
pressure to reduce dependence on solvent-based inks as a pollution prevention measure in
the future will only intensify.
Sigma Technologies received a Phase I SBIR award (68D60034) and subsequently a
Phase II award (68D70058) to promote adhesion of water-based inks to oriented
polypropylene packaging films via surface functionalization, thereby reducing
dependence of the thin film packaging industry on the use of solvent-based inks,
particularly inks containing toluene. Sigma’s approach was to employ plasma treatment
and acrylate coating technology, either alone or in suitable combination, to functionalize
the film surface, thus enabling adhesion of more polar ink formulations. All these
processes can be inexpensive, high speed, and accomplished in-line. Oriented
Polypropylene (OPP) films and polyethylene (PE) films, in particular, have historically
proven unresponsive to application of water-based or 100% solids inks due to the
hydrophobic nature of the film surfaces. Nevertheless, OPP and PE films are often less
expensive than other, more hydrophilic films, such as polyester, and therefore enjoy
widespread usage, especially in the snack food packaging industry. The two largest
domestic OPP film producers are current Sigma Technologies clients and Sigma has been
at the leading edge of OPP R&D efforts for the past several years. Thus Sigma
Technologies has been in a unique position to transition smoothly into Phase III follow-on
programs upon successful completion of the Phase II effort Several purchase orders
for Sigma proprietary surface functionalization equipment have already been received
and the equipment is either currently undergoing fabrication, or has already been placed
in commercial operation.
Surface functionalization is achieved by an appropriate combination of plasma treatment
and thin (sub-micron) acrylate coating within a vacuum environment. The
functionalization processes are performed inline at high speeds (up to 3000 fpm) using
Sigma Technologies proprietary equipment. The treatment scenario begins with plasma
treatment of one surface of the plastic film using a moderate energy flux (typically 0.1-
0.2 Joules/cm2) with a suitable gas mixture (typically oxygen plus argon). As the plastic
film continues through the web processing machinery it may be metallized and coated or
coated directly with a very thin layer (typically 0.1-0.5 micron) of an acrylate-based
monomer which is 100% active; i.e. no solvent. The monomer deposited on the surface
of the plastic film then passes in front of an electron beam gun where the monomer is
rapidly and completely polymerized. The functionalized film is now ready for printing,
labeling, or other downstream processes.
Sigma Technologies has concurrently developed radiation curable, acrylate monomer
chemistry which ranges from hydrophilic to hydrophobic. It has proven possible in many
instances to tailor monomer blends to meet specific client surface energy requirements.
As it turns out a secondary benefit accrues to selected users of Sigma’s surface
functionalization equipment. Clients who metallize plastic packaging film following
plasma treatment with a thin aluminum barrier layer observe that the “sticking
coefficient” for the metal is a little higher versus untreated film. That is, the percentage
of the evaporated metal that condenses and sticks to the surface of the film is a little
higher for film which has been plasma treated. For example, a typical, inexpensive,
oriented polypropylene, homopolymer film from a major global manufacturer displayed
an aluminum film thickness of 210Å (versus 138Å for untreated film), with all other
metallizing conditions held constant. More efficient metal deposition means less metal is
wasted and waste disposal issues are reduced.
EPA funding was pivotal to the success of our commercialization efforts. The Phase I
support allowed us to compile credible semi-works data and make some important
observations. As a result we were able to obtain Internal R&D commitments from
important clients who are major players in the packaging film industry to run
concurrently with the Phase II SBIR effort. The combined private sector/EPA resource
package got us “over the hump” and has led to the successful commercialization of our
equipment design and technology concepts.
Proof-of-concept was achieved in the Phase I effort. Sigma Technologies was indeed
able to alter the surface functionality of OPP films to the extent that water-based ink
formulations were observed to adhere well to the functionalized surfaces without
sacrifice of ink deposit quality parameters. The hollow cathode, magnetically focused
plasma and acrylate coating processes and equipment configurations employed to achieve
this positive result are considered proprietary and the acrylate coating process in
particular enjoys substantial patent protection[5,6].
Successful pilot-scale and field testing of the concepts were achieved in Phase II. Film
industry response was positive and we moved to Phase III with several clients part way
through the Phase II effort. A commercial plasma treatment unit designed and fabricated
by Sigma, and purchased and installed by the client who is a major global packaging film
producer is shown below in Figure 1.
Figure 1. Photograph of Plasma Reactor Designed and Built by Sigma Technologies and Installed at Client's Facility
Snack food packaging was the initial and obvious application for Sigma’s surface
functionalization technology. However, during the course of the Phase I and Phase II
efforts we have uncovered several other potential areas of application including; flexible
printed circuits, fabric surfaces, additional specialty packaging applications, and paper or
cavitated plastic film stock for labels. The Sigma research effort to date has resulted in
presentations at major trade conferences [2,4], publications in trade journals, and both
firm purchase orders and additional inquiries for quotations for design and fabrication of
surface functionalization equipment from several major players in the industry. If we are
able to maintain the current high level of interest and the proprietary equipment presently
undergoing fabrication proves successful, we are confident that additional firm orders for
equipment and process development for Sigma Technologies will result, and the release
of toluene and other printing solvents to the atmosphere will continue to decrease.
Publications:
Plasma Treatment of Polymer Films, S. A. Pirzada, A.
Yializis, W. Decker, R. E. Ellwanger, Society of Vacuum
Coaters 42 nd Annual Conference Proceedings, 1999.
Use of Functional Acrylate Polymers for Different Web
Coating Applications, A. Yializis, M.G. Mikhael, T.A.
Miller, R.E. Ellwanger, Proceedings of 11 th
International Conference on Vacuum Web Coating, R.
Bakish, Ed., 138-144, 1997.
Commercialization Status:
Now in Phase III with numerous clients
