Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-06-18
2002-11-26
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Transfer
C399S308000, C399S311000
Reexamination Certificate
active
06487386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for applying decorations and/or characters on glass, glass ceramic or ceramic products using electrophotography, having:
an image roller, which has an electrostatically chargeable photoconductive layer,
a photo-exposure assembly for generating an electrostatic charge image corresponding to the decorations and/or characters to be applied,
a supply container for a preferably ceramic toner and devices for developing the electrostatic charge image with this toner,
an intermediate substrate, which is in direct contact on one side with the glass, glass ceramic or ceramic product and is embodied such that it receives the toner image, and on the other side is in direct contact with the glass, glass ceramic or ceramic product,
at least two coronas, of which the first corona is disposed on the intermediate substrate and the second corona is disposed in the region of the contact zone of the product with the intermediate substrate, and
having heating means for burning in the toner image, electrostatically transferred by means of the coronas, onto the product.
2. Related Art
To glass, glass ceramic or ceramic products, decorations are applied within a wide scope to achieve desired aesthetic impressions. In certain products, captions, identification codes or the like must also be applied, for instance in order to give the user the requisite information directly. A typical example that can be named is the glass ceramic plate for a stove burner area, which along with the trademark, such as Ceran®, also has other operating and status indications, and in accordance with customer wishes, decorations, especially decorations in color, as well.
For applying such decorations and/or characters, which are designated herein by the term “images”, various methods and devices are known, of which two have thus far gained significance in the industry.
In the first typical method, ceramic dyes are imprinted using current printing techniques directly to the glass and ceramic products; the dye is first dried to the point of being wipe-proof and then burned in; in the case of the aforementioned glass ceramic plates for burner areas, the burning in of the dye typically takes place during the ceramization. In that case, the imprinting is therefore not done onto the finished glass ceramic plate but already on the green product to be ceramized.
In screen printing, which is generally used for the aforementioned printing process, a screen printing template must first be produced. To that end, the screen of fine-mesh textile or wire cloth, which is fastened over a printing frame, is covered at the image-free places with a template cut out of paper, drawn using greasy ink, or produced photographically. By means of this screen printing template, the ceramic dyes are then applied directly to the glass or ceramic product. The production of the screen printing template in the known method is very complicated and uneconomical for individual production of single items. Furthermore, with the aid of a scraper, the printing ink must be applied through the open places in the screen printing template either manually or in screen printing machines. Screen printing is also a wet process, in which ceramic dye pigments pasted up with printing oil are used as printing ink, so that relatively large, expensive machines with driers are required, and furthermore, there are major problems of worker protection and environmental pollution, especially because of the solvents required in the production process. The solvents in the printing oil evaporate relatively easily, so that complicated, expensive worker protection provisions must be made, and besides, separate filtering systems are required. Moreover, in screen printing as in offset printing, a plurality of printing operations in succession for the various colors (such as cyan, magenta, yellow and black) are needed, which again leads to very large systems. In the known printing processes there is also the problem that reproducibility of colors can not be assured in large-scale mass production, and furthermore, after even a small number of items have been produced, that is, after about one hundred printing operations, the screen printing template must be cleaned.
In addition, in screen printing the resolution of the colored imprint made is limited by the screen mesh of the screen printing template. As a result, the printed ceramic or glass products are often unsatisfactory with regard to smoothness, homogeneity, and the resolution of the color imprint. Furthermore, if a desired quality is to be achieved, various special inks must often be used.
In the second typical method, ceramic dyes are not applied directly to the glass and ceramic products but rather to a transfer means, such as a paper coated with gum arabic. This transfer means, thus prepared, is then placed on the ceramic or glass product at the desired position and moistened; as a result, the paper can be removed, leaving the inks behind on the product. Finally, the product is then fired in a manner known per se, which causes the ceramic inks to fuse to the product. Once again, this achieves a permanent imprint on the ceramic or glass product.
This second typical method works on the principle of the decal. It is known for the ceramic inks to be applied to the transfer means using current printing techniques, especially screen printing, but this has the aforementioned disadvantages of screen printing.
It has therefore also been disclosed by German Patent DE 44 13 168 C2 that instead of conventional ceramic printing inks, a novel ceramic toner be used, that is, ceramic dye compositions that comprise fine particles of ceramic pigments, fluxing agent (glass), binder resin(s) in typical additives, and which are applied to the transfer means using an electrophotography reproduction process (electrocopying process). With the aid of these provisions, a method for producing decorated successfully be created aforementioned problems. A decorated ceramic and that is superior to known products in terms of the fineness and resolution of the decoration (imprint).
The known method also enables a simplified application of the images to the transfer means. By acquisition of the data of the desired image to be applied to the ceramic or glass product, for instance using a digital color scanner or by using original graphic data and transferring these data using a personal computer to the image memory of the electrophotographic reproduction device, such as a laser printer, the user is advantageously for the first time given the capability of making changes, for instance in color graduation, or rastering, without additional effort even if the numbers being produced are quite low. In addition, all the graphics and/or modifications that are possible with modern computer technology can be transferred directly to the transfer means.
The decisive disadvantage of this known method is that a transfer means is required in conjunction with further method steps, in order to apply the image from this transfer means onto the glass or ceramic product. Aside from the additional expense for producing the images on the product, there is also the risk that the images on the moistened transfer means will slip when the substrate is applied and peeled off, a problem that is quite familiar from decals, so that the images are applied distorted, which then does not meet the required tolerances for the colored product.
A comparable electrophotographic reproduction process for applying images to tiles using a transfer means has been disclosed by international patent disclosure WO96/34319, for which the described disadvantages apply to the same extent.
From the patent literature, methods for applying decorations and/or characters to glass, glass ceramic or ceramic products (substrates) have also become known in which no transfer means as in the decal method is employed; in other words, methods in which the decorations and/or characters are applied directly to the substrate.
German Patent DE
Auchter-Krummel Petra
Jung Dieter
Weinberg Waldemar
Zimmer Michael
Pendegrass Joan
Schott Glas
Striker Michael J.
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