Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2000-06-13
2002-03-12
Parker, Fred J. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S459000, C427S208400, C427S180000, C427S370000
Reexamination Certificate
active
06355309
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of forming a thermoplastic layer on a layer of adhesive.
BACKGROUND OF THE INVENTION
Image graphics are omnipresent in modem life. Images and data that warn, educate, entertain, advertise, etc. are applied on a variety of interior and exterior, vertical and horizontal surfaces. Nonlimiting examples of image graphics range from posters that advertise the arrival of a new movie to warning signs near the edges of stairways.
A surface of an image graphic film requires characteristics that permit imaging using at least one of the known imaging techniques. Nonlimiting examples of imaging techniques include solvent based inks, 100% solids ultraviolet curable inks, water based inkjet printing, thermal transfer, screen printing, offset printing, flexographic printing, and electrostatic transfer imaging.
Electrostatic transfer for digital imaging employs a computer to generate an electronic digital image, an electrostatic printer to convert the electronic digital image to a multicolor toned image on a transfer medium, and a laminator to transfer the toned image to a durable substrate. Electrostatic transfer processes are disclosed in U.S. Pat. No. 5,045,391 (Brandt et al.): U.S. Pat. No. 5,262,259 (Chou et al.); U.S. Pat. No. 5,106,710 (Wang et al.); U.S. Pat. No. 5,114,520 (Wang et al.); and U.S. Pat. No. 5,071,728 (Watts et al.), the disclosures of which are incorporated by reference herein, and are used in the SCOTCHPRINT™ electronic imaging process commercially available from 3M.
Nonlimiting examples of electrostatic printing systems include the SCOTCHPRINT™ Electronic Graphics System from 3M. This system employs the use of personal computers and electronically stored and manipulated images. Nonlimiting examples of electrostatic printers are single-pass printers (Models 9510 and 9512 from Nippon Steel Corporation of Tokyo, Japan and the SCOTCHPRINT™ 2000 Electrostatic Printer from 3M) and multiple-pass printers (Model 8900 Series printers from Xerox Corporation of Rochester N.Y., USA and Model 5400 Series from Raster Graphics of San Jose, Calif., USA).
Nonlimiting examples of electrostatic toners include Model 8700 Series toners from 3M. Nonlimiting examples of transfer media include Model 8600 media (e.g., 8601, 8603, and 8605) from 3M.
Nonlimiting examples of laminators for transfer of the digital electrostatic image include Orca III laminator from GBC Protec, DeForest, Wis.
After transfer of the digital electrostatic image from the transfer medium to a film or tape, optionally but preferably, a protective layer is applied to the resulting imaged film or tape. Nonlimiting examples of protective layers include liquid-applied “clears” or overlaminate films. Nonlimiting examples of protective clears include the Model 8900 Series Scotchcal™ Protective Overlaminate materials from 3M. Nonlimiting examples of protective overlaminates include those materials disclosed in U.S. Pat. No. 5,681,660 (Bull et al.) and copending, coassigned, PCT Pat. Appln. Ser. No. US96/07079 (Bull et al.) designating the USA and those materials marketed by 3M as SCOTCHPRINT™ 8626 and 3645 Overlaminate Films.
Thermal ink jet hardware is commercially available from a number of multinational companies, including without limitation, Hewlett-Packard Corporation of Palo Alto, Calif., USA; Encad Corporation of San Diego, Calif., USA; Xerox Corporation of Rochester, N.Y., USA; LaserMaster Corporation of Eden Prairie, Minn., USA; and Mimaki Engineering Co., Ltd. of Tokyo, Japan. The number and variety of printers changes rapidly as printer makers are constantly improving their products for consumers. Printers are made both in desk-top size and wide format size depending on the size of the finished graphic desired. Nonlimiting examples of popular commercial scale thermal ink jet printers are Encad's NovaJet Pro printers and H-P's 650C and 750C printers. Nonlimiting examples of popular desk-top thermal ink jet printers include H-P's DeskJet printers.
3M markets Graphic Maker Ink Jet software useful in converting digital images from the Internet, ClipArt, or Digital Camera sources into signals to thermal ink jet printers to print such images.
Ink jet inks are also commercially available from a number of multinational companies, particularly 3M which markets its Series 8551; 8552; 8553; and 8554 pigmented ink jet inks. The use of four principal colors: cyan, magenta, yellow, and black permit the formation of as many as 256 colors or more in the digital image.
Current image graphic films contain vinyl chloride polymers, such as marketed by 3M under the SCOTCHCAL™ brand. Alternatively, multilayer films such as disclosed in U.S. Pat. No. 5,721,086 (Emslander et al.) can be used for reception of image graphics. In both instances, specialized coatings are used as the receptor surface on an underlying substrate to improve image graphics transfer and image quality. Regardless, both types of image graphic films have an adhesive layer (and protective release liner until use) on the opposing surface of the film substrate. Thus, image graphic films currently are laminates of some specialized coating, a substrate, an adhesive, and a release liner until use.
In another art, powder coating typically involves applying a specially formulated powder to a substrate by one of several known techniques and then heating the powder in an oven in order to cause the powder to melt and flow to form the coating. The process may also include a curing step to allow a chemical reaction to occur in the coating. The result is a coating with desirable visual and functional properties. A primer may be required to achieve adequate adhesion to the substrate. This method is generally used with metal or heat resistant plastic parts because of the high temperatures that are necessary to achieve complete melting and flowing of the powder. Polymers used in powder coatings typically have a relatively low viscosity when melted so that the powder will be able to form a continuous film under the applied heat. While powder coating is a solvent-free process, it generally requires significant oven cycle times and large, energy-intensive ovens.
A common method of producing polymeric powders for powder coating is to melt and mix the desired resins in a twin screw extruder, extrude and cool the polymer mass and grind the mass to a desired size. The resulting powder, when viewed microscopically, has irregularly-shaped particles with sharp, pointed edges. These particles may exhibit low packing density when deposited on a substrate, resulting in a coating that is susceptible to voids. The irregular shapes also do not achieve the maximum charge to mass ratio as noted in U.S. Pat. No. 5,399,597 that is desirable for certain types of powder coating.
SUMMARY OF THE INVENTION
The present invention has addressed a problem not recognized by the prior art, namely: that image graphic films need not have a film substrate to provide structural integrity between the thermoplastic film and the adhesive, if the thermoplastic film can be formed directly on the adhesive.
The present invention has solved the problems in the art by developing a method of forming a thermoplastic layer on an adhesive layer by powder coating without the use of solvents. The method can be successfully practiced with combinations of polymers that may be chemically incompatible or unstable in processing systems such as emulsions or latices. The method provides a shortened and simplified manufacturing process by avoiding long curing ovens and convoluted web lines, instead relying on the combined application of heat and pressure to the coated substrate. The absence of solvents in the process means that capital costs for scrubbing equipment and special ventilation systems are eliminated, along with the environmental effects associated with solvent coating.
In one aspect, the present invention provides a method of forming a thermoplastic layer on an adhesive layer having two major opposing surfaces. The method comprises the following steps: a) pr
Fleming Danny L.
Rinehart Ernest M.
Bjorkman Dale A.
Parker Fred J.
Peters Carolyn A.
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