Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2002-04-30
2004-11-30
La Ville, Michael (Department: 1775)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S428000, C428S441000, C428S436000, C428S542200, C428S480000, C428S474400, C428S426000, C428S013000, C428S029000, C428S213000, C428S220000, C428S335000, C428S437000, C428S346000, C428S354000, C428S3550AK, C428S335000
Reexamination Certificate
active
06824868
ABSTRACT:
BACKGROUND
There is significant commercial interest in the fabrication of customized glass laminates with encapsulated digitally printed images having vibrant colors for use in architectural and automotive applications. Because project delivery times for current methods of producing limited quantities of glass laminates with customized graphics can be very long with accompanying high costs, there is a strong market need for methods that will allow rapid turnaround time at reasonable cost.
Up to now options to create such laminates have been virtually limited to traditional screen printing methods involving the deposition of solvent based colored inks onto plastic substrates and subsequent encapsulation of the printed film in glass using multiple layers of adhesive. This screen printing process involves time consuming and costly preparation of multiple screens—one for each color separation. Issues related to the use of solvents must be managed in order to prevent environmental problems. In addition, the required setup and cleanup times result in a process that is not cost effective for limited quantities of printed film.
Introduction of digital methods such as inkjet printing seems like a natural fit for production of glass laminates with customized graphics. However, inkjet printing onto clear substrates suffers from the lack of visual quality due to the less than vibrant colors that are obtained. Most commercial uses of inkjet printing utilize opaque substrates such as white paper or white polyvinyl chloride film (white vinyl) for optimum appearance and when such printing is performed on clear print media such as polyester film, there is a significant loss in color vibrancy. Because of the high ink pigment loading and large pigment particle size that would be required to print more opaque, and hence more vibrant colors onto a clear film, it is not likely that this color issue will be easily resolved for ink jet printing. Inkjet printing onto high opacity media such as white polyester or vinyl might result in acceptable appearance with vibrant colors but the resulting glass laminate would have poor see-through characteristics and lose much of the desired aesthetic value.
Encapsulation of thermal transfer printed color images in glass laminates for customized applications provides the opportunity to deliver the desired laminate appearance. Thermal transfer color printing was developed in early 1980's and first used in commercial color printers for corporate office printing. In the mid-1990's inkjet printing technology became dominant because of its much lower cost. Thermal transfer printing is still broadly used today for numerous applications such as printing bar codes onto labels and tags.
Thermal transfer printing is a dry-imaging process that involves the use of a printhead containing many resistive heating elements that selectively transfer solid ink from a coated ribbon to a substrate. As the coated ribbon is transported through the print head, targeted areas of the ink layer are heated, softened and transferred to the substrate. The consumed ribbon is usually rewound and disposed.
The resolution of a typical thermal transfer printer is usually around 200-400 dpi with software capability to utilize variable dot shapes and screen angles so that output quality can be very high quality depending upon media used. Because the ink is not required to pass through a small nozzle in the printhead, larger pigment particles and greater pigment loadings can be used with thermal transfer printing to achieve the desired vibrancy of color. However, achieving acceptable quality on clear media is more challenging than opaque media and because there is little commercial activity in this area, the print media choices are limited which can also affect the quality.
One of the major advantages of thermal transfer printing is the minimal setup times required to produce an image which reduces the cost and turnaround time of a short run as compared to traditional screen printing operations.
There are numerous types of ink formulations used for thermal transfer print ribbons including those that are primarily wax, wax/resin or resin based. Resin based ribbons are usually more expensive and are primarily used for production of more durable images with the ability to withstand outdoor exposure for up to 3-5 years without lamination. Wax based ribbons are usually less expensive and used for less demanding applications.
Thermal transfer printing has been used for many years in the printing of bar codes on labels, tags, and tickets and the technology for production of these ribbons has become very specialized.
A typical color ribbon is a relatively complex composite structure that has been developed to provide for optimum performance in the thermal transfer printing process. A typical high performance thermal transfer color ribbon consists of a very thin biaxially oriented polyethylene terephthalate (PET) film substrate usually with a thickness of ~3-6 micrometers that acts as a carrier or support layer for the ink layer(s). PET film is selected as the preferred substrate because of its physical properties and ability to withstand print head temperatures of up to 120° C. This PET substrate is coated on one side with at least one thin layer of pigmented resin. With many resin based color ribbons there is also a release layer between the PET substrate and the pigmented ink layer to facilitate transfer of the ink layer to the print media. Such a release layer will end up on top of the image that in many applications will provide additional protection for the printed image. On the other side of the thin substrate is usually a “backcoating” that provides the correct frictional properties between the printhead and the ribbon.
U.S. Pat. No. 5,939,207, the contents of which are incorporated herein by reference, describes the composition of a four layer thermal transfer ribbon structure for use in the printing of black bar codes. With minor changes, this structure is thought to be representative of a typical color ribbon formulation utilized with the present invention. This structure described in the '207 Patent comprises a heat-resistant backcoat bonded to one side of a thermally and dimensionally stable substrate, such as PET film. An ultra thin release layer is provided on the other side of the substrate, with a pigmented layer then being provided on the release layer.
The pigmented layer contains carbon black and resin binder including polystryrene and polyacrylate resin with various functional groups such as methacrylic acid to promote adhesion to a variety of printing substrates. During printing, the pigmented layer is transferred to the print medium. Formulations for color ribbons used in applications requiring exterior durability will likely utilize a resin binder containing only polyacrylate resins and colored pigments with superior UV light stability. The formulation of the pigmented layer may also contain various waxes and other additives in order to achieve targeted viscosity and physical properties for optimum printing and coating performance.
In its final printed form, it is the release layer which if present functions as the top surface of the printed image. As described in the '207 Patent, the formulation of this layer contains components that provide for easy release of the pigmented layer from the substrate and may include such components as ethylene vinyl acetate copolymer, an—olefin maleic anhydride copolymer and various waxes such as Carnauba wax.
Thermal transfer printing offers various color options including the standard cyan, magenta, yellow and black (C-M-Y-K) process colors as well as a wide range of spot colors including white, metallics, fluorescents and specialized colors. The ability to print process colors onto either a clear substrate or on a white printed background provides the opportunity to generate a unique combination of vibrant colors and see-through laminate appearance that is not possible with inkjet printing.
Thermal transfer printing can be used t
Bell William Paul
Moran James R.
Yacovone Vincent J.
Howrey Simon Arnold & White , LLP
La Ville Michael
Solutia Inc.
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