In Part I of this series on environmental responsibility (January 2008 issue), we covered PVC vinyl, various approaches to disposing of it in a cleaner way and the desirability of recycling PVC rather than land-filling or incinerating. This month I’d like to look at materials being developed that can be used as substitutes for PVC in digital printing applications. It’s not easy since PVC is a very low cost and durable substrate that bonds well to solvent and UV-curable inks. One answer may be in substituting PVC with products based on polyethylene (PE) and polypropylene (PP) which can easily be recycled along with your used milk bottles. The question then becomes, can they duplicate the printability and durability of PVC?
ALTERNATIVES TO PVC
A number of companies are beginning to offer PE and PP materials as alternatives to PVC. How can this be possible? The physical strength and durability of polyester reinforced PVC (scrim vinyl) far exceeds that of either PE or PP. These products do not incorporate the polyester scrim reinforcing fibers which give the PVC much of its strength.
When PP or PE films are oriented during the extrusion process these materials can achieve greater strength in one direction. But they are films and tear easily in the cross direction. In BOPP (biaxially oriented PP) two or more films are laminated together, one strong in one direction and the other in the cross direction. This gives rise to the tear resistance in the PP films you purchase for inkjet printing using water-based inks. Still, their strength is a long way from the strength of scrim vinyl.
Manufacturers have developed another way to add strength to these materials. By weaving strips of oriented PP or PE film into a basket weave they gain some of the characteristics of the scrim and eliminate the film’s propensity to tear. After the weaving, a very thin layer of PP or PE is extruded onto the front and back surface of the woven structure giving it a smooth continuous film finish. Like vinyl, these products can be heat-welded and can be assembled into large sheets after printing.The extrusion on the back side can be pigmented black, gray or green to achieve high opacity for billboard applications. These products are much thinner and lighter than scrim vinyl so they are easier to install, cost less to ship and provide less waste. Some incorporate UV light inhibitors to extend their outdoor durability.
A recyclable line of PE billboard called ECOS (environmentally conscious outdoor substrate), is a poster and banner media offered by Triangle Digital which incorporates this woven structure. In its current form these products are suitable only for UV-curable inks. ECOS and similar products are PE-based materials using the woven structure with a thin layer of PE film on the front and back. These products are very light weight but not very opaque. Triangle Digital offers both 3.9 oz and 2.7 oz versions (PosterFlex and FlexLite) up to 12 feet wide. The heavier weight can be used for posters and banners as well as billboards and the lighter weight can be used for billboards and provides a lower cost solution.
Circle Graphics is a Longmont, Colo.-based print provider is offering a product to its clients that it calls Eco-Flexx for billboard applications. The one-piece woven printable PE material is made exclusively for Circle Graphics and can be stretched over a billboard or other outdoor sign and affixed without the use of adhesives. They report successful installation of about 100 test site applications.
One thing to note about the PE alternatives is their weight. Typical, digitally imaged scrim vinyl ranges from 12 oz to 15 oz while these products are in the 3-4 oz weight range — a big advantage for handling and shipping of the material.
One issue which makes the use of PP or PE difficult for inkjet printing is the adhesion of solvent inks. Without a treatment or coating, solvent inks do not stick well to these substances (although UV-curable inks work fine). Without dot gain control and good adhesion these substrates will have only limited appeal since the color and durability will not be as good as their scrim vinyl counterparts. The first priority, of course, in choosing a substrate is that it provides a good, durable graphic.
Scientists are currently working to modify the surface layer of PP and/or PE materials to help them bond better with solvents so they can provide the surface characteristics and image quality as vinyl. Another important contribution to image quality is the whiteness and opacity of the substrate. The PE samples I have examined lack both the opacity and whiteness of comparable scrim vinyl products. A coating containing ingredients that add whiteness and opacity, and provide a better imaging surface properties with superior adhesion would make PE and PP materials viable (and recyclable) alternatives for solvent applications. Of course there is no free lunch since an added coating of this type could increase the cost of the product.
A GREEN RIGID ALTERNATIVE
Another new product has recently hit the market that is green in many ways. Sonoma Graphic Products is offering a re-pulpable, paper composite board called Eco X-board, which they say can be used in place of resin-based medium-density fiber board (MDF), particle board, ridged PVC and foamed core boards.
Eco X-Board is a composite fiber board with a high strength-to-weight ratio. Its closed-cell honeycomb core is manufactured from recycled Kraft papers which generate up to 90 ton/sqm core crush-resistance. In addition, it provides good sound absorption and high flexural strength. Sandwiched between two layers of an ink-receptive, acid-free recycled white paper, X-Board can be simply disposed of after its useful life in paper recycling bins or cardboard compactors. It appears to be a great alternative in applications where it can meet the end users needs.
Clearly, manufacturers are making the effort to find new ways to deliver truly greener solutions to the digital printing community. On the other hand, some are claiming green when the green component is hard to find, or was already there before “green” became important. If you are considering including green consumables in your product offerings, be sure to read all the details and learn about the products. If they meet your customers’ needs, they can help meet our global need to be more responsible consumers as well.