Process for making protected printed images

Details Process for making protected printed images Process for making protected printed images

2001-10-25

2003-09-30

Hess, Bruce H. (Department: 1774)

Incremental printing of symbolic information

Ink jet

Medium and processing means

C428S032100

Reexamination Certificate

active

06626530

ABSTRACT:

FIELD OF INVENTION
This invention relates to a process for making an article with a printed image protected by a clear fluoropolymer film.
BACKGROUND OF THE INVENTION
Fluoropolymer films have long been used as a protective and decorative overlay for a variety of substrates such as metal, wood, and thermoplastic and thermoset polymers. With its excellent chemical resistance and weathering properties, a thin layer of fluoropolymer film can protect less durable substrates from damage in both exterior and interior use. Clear fluoropolymer overlay films have also been used to protect images on printed substrates.
The very properties that make fluoropolymer films desirable for outdoor use hinder the ability of fluoropolymer substrates to directly receive images. Fluoropolymer resins are known for their low surface energy and non-stick properties as well as thermal and chemical resistance. For these reasons fluoropolymer films withstand the effects of dirt, stains, graffiti and sun. However, these fluoropolymer compositions do not stick easily to other materials, especially dissimilar materials. Many commercial inks tend to puddle on fluoropolymer surfaces.
Direct printing on fluoropolymer film is described in EP 1,024,020 to Kume et al. wherein fluoropolymer-containing ink is applied to fluoropolymer films by using thermal transfer techniques. And although there is compatibility between the ink and the film, the images are described as directly exposed to the elements of weather.
U.S. Pat. No. 5,225,260 to McNaul et al. discloses that fluoropolymer films, such as polyvinyl fluoride, have been used as substrates for outdoor signage. Images are printed on a fluoropolymer film and adhered to vehicles such as trucks and truck trailers for purposes of identification, advertising, instructional information and the like. In order for the polyvinyl fluoride film to receive such images the film is surface treated. For these vehicle applications as well as for custom interior surface decoration, it has been common to rely on screen printing techniques to produce images on the fluoropolymer film. However, screen printing techniques require that individual masks be produced for each new image. Minor changes in graphics or design require a new mask. Mask production is inflexible and expensive, especially if only a few signs are produced. In addition, in order to achieve adherability and durability on fluoropolymer surfaces, most screen printing inks require oven baking or exposure to an ultraviolet curing step.
More recently, the advantages of ink jet printing have been recognized. High quality color images can be produced for a wide range of applications at a low cost. The technology is extremely versatile permitting production of signs and displays of all sizes, including fliers, posters, banners and billboards. Images can be stored digitally and be modified easily and frequently.
In general, inkjet processes form images by depositing ink droplets emanating from nozzles onto substrates. Thermal bubblejet processes (commonly referred to as thermal ink jet printers) promote a phase change in the ink by resistive heating. Most commonly, aqueous-based inks are heated and the resulting steam expels an ink droplet from the nozzle onto the substrate. The substrate must be able to quickly absorb the deposited ink droplets to avoid blurring the printed image. Therefore, much attention has been directed to formulating a water absorptive ink receptive layer to be applied to the substrate prior to printing. This is especially true if the substrate is a plastic film or sheet rather than paper.
So although thermal ink jet printers provide the advantage of digital manipulation, the need for water absorbing layers are expensive and prone to damage by water in the environment. Perhaps better suited to plastic substrates are ink jet processes that have solvent-based inks, where the solvent is more quickly vaporized or absorbed. Solvent based ink jet printing makes printing on some synthetic polymer films possible. One particularly useful inkjet process that uses solvent-based ink is piezoelectric printing. Piezoelectric printing involves applying a voltage to a piezoelectric crystal to cause a pressure pulse in the printhead to emit droplets of ink. However it has been found that even treated fluoropolymer has not been receptive to commercial piezoelectric printers. Owing to their chemical resistance, fluoropolymer films are difficult or impossible to print on directly by this technique. The advantages of digital printing in combination with fluoropolymer protection without the drawbacks of water absorbing layers could be achieved if a means to print on fluoropolymers with piezo ink jet printing techniques could be found.
There is a need for an ink receptive composition for solvent-based inks that can be used with a clear, weatherable fluoropolymer film. Such a composition would permit formation of protected images by a digital inkjet printer. There is also a need for a compatible adhesive to adhere printed fluoropolymer films to substrates.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a process for making an article with an image protected by a clear fluoropolymer film. The process includes coating the inner surface of the fluoropolymer film with a layer of hydrophobic, ink receptive polymer composition compatible with the fluoropolymer film. An image is printed on the layer of hydrophobic, ink receptive polymer composition using an inkjet printhead supplied with a non-aqueous solvent based ink. The clear, printed fluoropolymer film is then adhered to a substrate with the inner surface facing the substrate whereby the image is viewable through and protected by the fluoropolymer film.
Preferred polymers for the hydrophobic, ink receptive coating are amine functional polymers and aliphatic polyesters and their crosslinked polyester-urethane products. In one embodiment, the hydrophobic, ink receptive polymer composition is a heat activatable adhesive and the process of adhering includes applying heat to activate the heat activatable adhesive. Preferably, the hydrophobic, ink receptive polymer composition employs an amine functional acrylic copolymer. In another embodiment, the process of adhering is achieved by applying a pressure sensitive adhesive to the inner surface of the protective film after printing and applying pressure to activate the pressure sensitive adhesive.
The present invention provides a process for making an article with an image protected by a clear fluoropolymer film. The fluoropolymer film with a layer of hydrophobic, ink receptive polymer composition enables the reverse printing of good quality printed images directly on the fluoropolymer film using an inkjet printhead supplied with a non-aqueous solvent based ink.
DETAILED DESCRIPTION OF THE INVENTION
Fluoropolymer Film
The present invention is applicable to a wide range of fluoropolymer films such as those prepared from polymers and copolymers of trifluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, dichlorodifluoroethylene, tetrafluoroethylene, perfluorobutyl ethylene, perfluoro(alkyl vinyl ether), vinylidene fluoride, vinyl fluoride, among others and including blends thereof and blends of fluoropolymers with nonfluoropolymers. For example, the fluoropolymer may be a fluorinated ethylene/propylene copolymer, i.e., FEP resins, a copolymer of ethylene/tetrafluoroethylene, a copolymer of tetrafluoroethylene/perfluoro(propyl vinyl ether), a copolymer of ethylene/chlorotrifluoroethylene, vinylidene fluoride/hexafluoropropylene, and vinylidene fluoride/perfluoro (alkyl vinyl ether) dipolymers and terpolymers with tetrafluoroethylene, polyvinylidene fluoride homopolymer (PVDF), polyvinyl fluoride homopolymer (PVF), among others.
The fluoropolymer may contain one or more light stabilizers as additives and, when assembled into the article of this invention, a light stabilizer protects the printed image by reducing the damage caused by exposure to sun. Light stabilizer additives include compounds that absorb ultr

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