Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2000-11-24
2002-11-26
Pianalto, Bernard (Department: 1762)
Coating processes
Measuring, testing, or indicating
C118S244000, C118S500000, C427S256000, C427S385500, C427S430100
Reexamination Certificate
active
06485777
ABSTRACT:
TECHNICAL SCOPE
The invention relates to a method and its use for coating sheets or sections by means of screen cylinders whose rotation is coordinated, where the sheets or sections are removed from a stack and sent by forced feed to the coating station. This invention also relates to a device for continuous precision coating of sheets or sections by means of screen cylinders and counter-pressure cylinders with a feed station and a horizontal feed device.
STATE OF THE ART
An enormous variety of coating sheets and sections are known today. On the one hand, there is the traditional offset and gravure printing, where photographic-quality results can be achieved. On the other hand, there is simple lacquering, with a large number of coating methods in between, for effect printings and special printings, e.g., with body inks, textured inks or fluorescent inks. Each consumer can select from packaging printers, gift paper manufacturers or the manufacturers of project folders and ring binders. Within the various coating and printing methods, screen printing or serigraphy, which has been known since early times, is still being used widely. Rotary web printing is often used today. The printing output with rotary web printing is much higher than that with web screen printing. The main disadvantage of rotary web printing is that only continuous paper can be processed from roll to roll at high throughput speeds. In addition, the processing width with respect to the paper is limited, usually being 20 to 60 cm. In gravure printing, both continuous webs and sheets or sections can be printed. The same thing is true of lacquering. The enormous variety of different processing techniques has the advantage that an optimum technique is available for each coating job. However, there is a great price increase with the individual techniques according to whether a small printing or a large printing is produced. This can lead to the situation where it costs only a fraction as much to produce a large printing of an advertising brochure as it does to print various reprints of portions of the large printing. For example, with a sales network of 30 sales personnel, it is often not economically feasible to generate a corresponding number of special address printings. Despite the very high level of technical advance throughout this industry, one encounters in many cases the paradoxical situation where mass printings are amazingly inexpensive, but each individually adapted small series is prohibitively expensive and even different processing companies must often be involved. The present inventors have recognized the fact that not only are screen printing, lacquering and coating with special materials such as adhesives similar techniques, but also there is a demand for a single processing department or company to be able to use these different techniques. Screen printing has the great advantage that relatively low forces are needed between the screen cylinder and the sheets. The main problem in rotary screen printing is that the movement between the screen cylinder and a printing cylinder opposite it must be synchronized with high precision during printing, so that the application to the sheets or sections can be made accurately. However, the beginning and end of the sheets to be printed must also exactly match the print original as obtained from the motion of the screen cylinder. The screen printing intended here is a finishing operation, often performed on a preprinted sheet. This may involve, for example, relief lacquering, where only narrowly defined areas within a sheet must be coated with a lacquer layer with a high precision. In the known state of the art, the sheets are held by grippers arranged with a space between them and secured to chains. The grippers are guided accurately during the printing operation. The counter-pressure rolls have recesses on the circumference for this purpose to allow the grippers to pass through. One of the main problems is satisfactory positioning of the objects relative to the printing roll and securing it during printing. Inaccurate placement or even deformation of the printed image must be avoided.
German Patent No. 693,644 is based on the object of developing a device that permits accurate positioning with regard to time and place along at least part of the path on which the objects are printed. It is proposed here that a short guide device be arranged with the highest precision within a continuous mechanical conveyor so that individual sheets can be moved in absolute synchronization with the printing cylinder. Unexamined German Patent No. 197 03 312 also concerns screen printing cylinder machines with a printing cylinder that is driven by a drive motor and receives the print material. The machine has a rotary screen cylinder which is axially arranged in parallel at a distance and is driven independently by a drive motor; it also concerns a device for synchronizing the motion of the printing cylinder and the screen cylinder during the printing operation. It has been found that the older printing method has some disadvantages with regard to acceleration of the printing cylinder, because this acceleration can cause the entire machine to vibrate. To solve this problem, it has been proposed that the printing cylinder, which has a circumference greater than or equal to the circumference of the screen cylinder, rotates at an essentially constant speed. The aforementioned patent cites as a great advantage the fact that the control expense for synchronization of the screen movement and the printing cylinder can be minimized due to the essentially constant rotational speed.
Both options have in common the fact that there are certain disadvantages, in particular with regard to mechanical controllability. Studies so far have shown that the state of the art has reached a very high quality standard with regard to flatbed printing. For example, distortion of sheets due to the effects of heat or moisture is often compensated in practice by corresponding distortion of the flatbed original or by replacing it with another flatbed original. This technique is difficult to apply to screen cylinders and would lead to complicated solutions. The present inventor has recognized that a concept must be developed to allow individual utilization of machines or a design for screen cylinders in particular, so that even smaller series can be coated inexpensively and economically in a high quality, and that one or more different operations of this type may optionally be carried out with one machine. The object of this invention was to improve upon the coating of sheets and sections so that they can be produced more rapidly and at a lower price. Another object was to increase the output from 7000 sheets or sections per minute as in the past to 10,000 per minute. According to the teaching of Dutch patent 9,201,676, the substrate such as paper or a textile which is to be printed is conveyed at a predetermined speed through the printing machine. The predetermined conveyance speed necessitates an adjustment of the rotational speed of the screen cylinder. This Dutch is based on material in the form of sheeting, such as paper or fabric which is normally wound onto rolls. However, the problems encountered with paper or fabric sheeting are completely different from those encountered with individual sheets and sections. The important task from the standpoint of the control technology is to make the rotational speed of the screen cylinder essentially the same as the conveyance speed.
EXPLANATION OF THE INVENTION
The object of the present invention was to improve on the coating of sheets and sections such that the standard quality of flatbed printing can also be achieved with rotary screen printing with the highest possible output, so that sheets and sections can be coated inexpensively and economically in small printing runs in particular, and several and/or different techniques can be employed in one installation.
The method according to this invention is characterized in that the rotation of the screen cylinder
Riedener Philipp
Sturzenegger Ernst
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Pianalto Bernard
Steinemann Technology AG
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