Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-12-05
2004-11-23
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S409000, C524S413000, C524S425000, C524S434000, C524S513000, C524S523000, C428S518000
Reexamination Certificate
active
06822024
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a composition for billboard sheeting. More particularly, the invention relates to a composition of a compounded PVC substrate for printable billboard sheeting, wherein said composition has excellent weathering, printability, colorfastness, fungicidal durability, extruder processability, non-flammability and thermal stability, where the processability and thermal stability are sufficient to form a full width billboard sheet that is seamless. The seamless billboard sheet is produced on exceptionally wide converting lines utilizing a full width extruder die.
BACKGROUND OF THE INVENTION
In the past, roadside printable billboards have been typically plastered with imaged paper and/or canvas sheeting. Today most of the paper and canvas sheeting has been replaced with plastic sheeting that is substantially a polyester scrim coated with a substrate. The substrate is comprised of a compounded PVC. There are substantially three methods used to form the sheeting. A first method is to apply multiple coats of plastisol of PVC onto the scrim. A second method is to laminate two extruded PVC films to an interposed scrim using a plastisol of PVC. A third method is to extrude, onto the scrim, a PVC composition. The latter method is preferred over applying plastisols because, generally, it is easier to print on extruded PVC than on a film formed from a PVC plastisol. The reader is reminded that a PVC plastisol is substantially a plasticizer into which is dispersed PVC. Many additives may be incorporated into the dispersion to stabilize the plastisol. In the first method, after coating the plastisol onto the scrim, the coating is heated to a temperature where the PVC and the plasticizer become miscible, whereupon the system inverts and the PVC absorbs the plasticizer. A drawback to PVC plastisols is that the additives in plastisol formulations can interfere with the printing process. The plasticizer and the additives can affect the surface tension and form a thin layer where there is poor adhesion. Another source of compounds that can interfere with printing originate from the PVC polymer. PVC plastisol formulations are compounded with emulsion PVC resins. Residual emulsifiers (soaps) from the emulsion polymerization are by design not soluble in the PVC, and their presence on the surface of the sheet can negatively impact the wetting characteristics. Plasticizers and additives tend to migrate through filmic PVC, so that even billboard sheeting prepared using the second method has similar printing issues, as the plasticizers and additives migrate to the surface. Furthermore, if the extruded PVC of the second method is compounded with lubricants that are subject to plating out, (i.e. polyethylene waxes, metallic soaps and amide waxes), the surface of the PVC film has poor printability. A major advantage of plastisols is that they can be used to coat very wide webs. Wide webs are desired because full billboard width will be seamless. Also, wide webs are desired because they can be cut down to narrower web widths, therein reducing the number of SKUs in the manufacturing queue. Narrower webs must be spliced together to form fill billboard width sheeting, and the splices or seams are thicker than a single ply sheeting. Another problem with narrow sheets is that they are “heat seamed”, using radio frequency (RF) welding, and RF welding creates a seam having potentially poor printability. Printability is affected by localized heating, which drives the additives to the surface. Poor printability causes visual distortions of the image.
As previously stated, sheeting produced using an extruded coating of compounded PVC generally has superior printing characteristics. A complicating factor is that PVC compositions are relatively thermally unstable at temperatures required for the extrusion. Uncompounded PVC starts degrading at 120° C., forming HCl gas, and the degradation is accompanied by yellowing, and losses in mechanical and rheological characteristics. Typical extrusion die temperatures are about 180° C. Thermal degradation is exacerbated with wide dies. With wide dies, the dwell time in the die lengthens, and therefore there is more time for thermal degradation. Heretofore, there has not existed a PVC composition having adequate thermal stability for exceptionally wide dies, and only narrow web extruded PVC billboard sheeting could be formed, which would then be seamed together.
A partial explanation for the difficulty in compounding a PVC composition for billboards is that in addition to having improved thermal stability, it must also have good weathering, colorfastness, fungicidal durability and be flame resistant (e.g. meet NFPA 701 vertical burn). The inclusion of additives to affect these properties has the cumulative effect of making the extrusion process even more complex and thermally challenging. For instance, in order to make the PVC composition flame resistant requires the inclusion of flame retardants, and in general, flame retardants exacerbate thermal degradation during extrusion. The PVC composition must also be compounded to be resistant to light aging, and particularly to UV light. Both flame retardants and UV stabilizers are known to cause embrittlement and yellowing during extrusion, which is unacceptable for billboard sheeting. Antimicrobials, and particularly fungicides are added to affect fungicidal durability. Biocidal agents are sensitive to heat, and loose their efficacy when exposed to high temperatures. Opacity and whitening additives are required to achieve billboard sheeting having sufficient whiteness, opacity and ink receptivity. Typically, these additives are pigments (i.e. titanium dioxide), and they like the previously enumerated flame retardants (i.e. antimony oxide) are usually powders, and their inclusion in the composition, when added to the extruder barrel can significantly increase the friction. A rule of thumb estimate is that 80% of the heat generated in an extruder is the result of the mechanical work input into shearing and mixing the polymer. The addition of powders results in higher friction and more heat being generated. Currently, the widest billboards are approximately 18 feet (>5 meters), and so an extruder having a die length of 215 inches (5,486 mm) would be required for full width seamless sheeting.
What is needed is a composition of a compounded PVC substrate that has sufficient thermal stability and printability that a full billboard width web can be produced.
What is needed is a composition where the addition of powders, particularly inorganic powders such as antimony oxide, titanium oxide and calcium carbonate, does not result in overheating in the extruder or die.
An economic consideration is the cost of the compounded PVC substrate for printable billboard sheeting. The previously discussed additives are expensive, and a component offsetting their cost is desired. The component cannot increase friction heat, nor negatively impact other processing criteria. The component cannot cause yellowing, nor reduce flame resistance, nor resistance to weathering, nor lower fungicidal durability, nor printability, and yet still lower cost.
The reader is reminded that billboard sheeting is printed using digital printing technology and ink jet printers. Ink jet printing equipment is manufactured by a number of manufactures including Sitech, Vutech, Nur and others. Current ink jet printing equipment is capable of producing indoor as well as outdoor digitally imaged printable billboard signs over five meters (5 m) in width and having at least four (4) aesthetically pleasing colors (yellow, red, blue and black).
Pigment based inks for use in producing indoor and outdoor digitally imaged printable billboards are manufactured by a number of manufactures, including A. R. Monteith, Triangle, Inkware, Akzo, Ink Design, Nur and others. A number of solvents typically used for maintaining the various pigments in solution include: lactic acid, propionic acid, methyl ethyl ketone (MEK), cyclohexanone, 4-
Panse Dattatreya Ramesh
Spirkowyc Paul Alan
Cooley Incorporated
Dougherty Clements & Hofer
Sanders Kriellion A.
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