Digital thermal printing process

Details Digital thermal printing process Digital thermal printing process

1998-09-14

2003-01-07

Hilten, John (Department: 2861)

Incremental printing of symbolic information

Thermal marking apparatus or processes

Reexamination Certificate

active

06504559

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to processes for applying a digital image to a substrate and more particularly to processes for applying an image to a rigid or three-dimensional substrate or object, either directly or indirectly, using digital imaging processes.
2. Background of the Invention
Decorative and other Images are applied to rigid or three dimensional substrates, such as plates, cups, tiles, and various forms of glassware by employing screen printing processes. This is made possible by the versatility of the screen printing process which can be used to print on any material surface having almost any shape since the pigment(s) passes through a printing screen onto the substrate rather than requiring contact between a printing plate and the substrate. In addition to its use on rigid or three dimensional objects, screen printing is used for printing ceramic inks onto a substrate which is then fired to fuse the ink and the substrate. This is done most commonly either by direct printing a decorative image on ceramic or glass surfaces or indirect decorating through the use of ceramic decals which are then applied to the substrate. Such substrates include tile, flat glass, hollow-ware, ceramic sheets and objects, and porcelain, including porcelain enameled steel and aluminum. Many of these application processes require the controlled deposition of precise thicknesses and relatively large particles to meet the parameters of diverse decorating and marking applications.
Since ceramic inks include pigment and glass frit (as well as other materials), it is necessary for the pigment and frit particles to be capable of passing through the print mechanism (screen) and onto the substrate. Screen printing, however, is limited by the fact that it requires substantial set-up and corresponding clean-up time feasible only for long product runs using the same image. Economies of set-up/clean-up produce large inventories of a limited variety of printed products. The present popularity, or necessity of just-in-time inventories render screen printing methods unattractive.
As an alternative to screen printing or other similar analog printing methods, much attention has recently been directed to digital printing methods first developed mainly for printing on paper. Storing and printing a digital image allows the flexibility of changing, customizing, or altering the image being printed thereby avoiding the set-up/clean-up time associated with screen printing.
With regard to digital printing, much attention has been directed to laser and ink jet technologies due to their ability to produce high resolution images at high speed. These methods, however, are very costly and not proven to provide the most durable image. Further, many industrial applications do not require high resolution but do require reduced set-up time or the flexibility of shorter production runs which digital methods can cost effectively supply.
Electrophotographic technologies are not easily applied directly to rigid or three dimensional substrates, nor do they employ ceramic inks (frits). Additional problems have been encountered when printing with ceramic inks using ink jet technologies due to the fact that the size of the frit particles is important in producing a vivid image after firing. Large particles which are necessary for some colors cannot pass through an ink jet necessary for high resolution. A need, therefore, exists for a digital print process allowing immediate changes in image design and short product runs capable of printing on rigid or three dimensional substrates and for use with ceramic inks. A particular need exists for such a digital print process for applications where high print resolution is not required.
Presently, glassware such as automotive or appliance glass is screen printed using ceramic or metallic inks. The perimeter edges of present automotive glass are printed with ceramic ink to hide and protect the adhesive used to secure the glass in place. Ceramic inks including metallic powders are printed on tempered glass and then fired to form conduct circuits electric heater plates for rear window defroster applications and antennae for signal reception and transmission. Heater plates are printed so as to form an electrical circuit providing heat from current flow through the printed lines. Here, control of the ink lay down is an important factor for proper current flow. Appliance glass is similarly printed to form decorative border patterns. Ceramic ink is used for its durability and because it is unaffected by high temperatures. The inventory and set-up problems associated with screen printing is present in these printing applications as well. A need also exists for a digital print process capable printing on rigid substrates, such as glassware, flat glass, hollow ware, ceramic sheets and objects, tile, and porcelain, including porcelain enameled steel and aluminum.
SUMMARY OF THE INVENTION
The present invention is, generally, a process for fixing an image onto a substrate using a digital thermal transfer printing process. Specifically, the present process is useful for applying a ceramic ink to a substrate(s) which is then cured and/or fired to completion. The substrate could be a rigid sheet of material such as flat glass, ceramic sheets or tile; or a three dimensional object such as ceramic objects, hollow ware, and porcelain, including porcelain enameled steel or aluminum. The present process may include an intermediate step of applying the image to a temporary member and then transferring the image to the substrate. In this alternate method, inks, other than ceramic inks, may be applied to a rigid or the alternate substrate.
The process includes either direct image transfer from an image transmission device or storing the image digitally in a digital computer system or other suitable storage medium; transferring the transmitted or stored digital image to a digital thermal transfer printer wherein the printer includes a ribbon having ceramic ink thereon; transferring the image to the desired substrate via the digital thermal transfer printer; and firing out the substrate such that the ceramic ink fuses (thermochemically bonds) to the substrate.
Further, an image may be transferred to a rigid or three dimensional substrate using the present process through the inclusion of an intermediate step of applying the image to a transfer member, such as a silicone (or silicone impregnated rubber or polytetrafluoroethylene) pad, and then transferring the image from the temporary member to the substrate. Other transfer members include silicone group containing resin, silicone group containing rubber, fluorine containing resin, fluorine containing rubber or the like. However, usable therefore is any resin having a favorable transfer surface tension while possessing elasticity, and heat resistance to a satisfactory extent.
Other transfer methods include printing the image on a decal and then transferring the decal to the substrate. Here the decal could be stored for later transfer or the transfer step may even occur at a different location. This embodiment of the process is equally useful for inks other than ceramic inks wherein the firing step is unnecessary. In this alternate method, the ink may be dried (thermal, convection, induction, oxidation) or cured (photo or radiation activated) or bonded to the substrate.
The present invention can be an in-line process useful in manufacturing and industrial production lines or small shop environments wherever there is an application to print an image on a rigid or three dimensional substrate, and especially suitable for printing decorative images using ceramic inks. For example, a decorative image, such as a flower, may be printed on an object, such as a coffee mug or a ceramic tile, wherein the flower image is digitally stored on a digital computer system and then transferred to a digital thermal transfer printer including a ceramic ribbon therein at which point the flower image is printed onto the coffee mu

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