FR2760403A1 - Laser cleaning method for engraved ceramic or metal printing cylinders - Google Patents

Abstract

The cleaning method involves using a laser beam which is fed from a YAG laser to an optical fibre (18). The optical fibre sweeps the beam across a printing cylinder (10). The wavelength, power level and pulse duration can be set according to the type of dirt on the printing cylinder and the composition of the cylinder itself. The beam energy can be varied in gradations of 0.5 Joules/cm<2> and the pulse frequency between 10 and 100 Hz.

Description

The present invention relates to a method and device for dry cleaning and by laser for all the cylinders used in printing.

The technical sector of the invention is the field of cleaning.

One of the main applications of the invention is the cleaning of cylinders in the printing press without the use of any liquid, water, solvents, etc. , without contact in any way whatsoever with the surface to be cleaned, and without integrating the cleaning operation into the operation of the printing machine.

In this field, a large number of patents are known. Most of them, with the use of liquids (water, solvents or washing agents), or with the use of scrapers or cloths, wet or not, and coming into contact or friction with the surface to be cleaned.

Not falling within these characteristics, and using a laser source, processes have been the subject of patent applications, a few of which may be mentioned.

references, without counting the uses of the laser to destroy, weld, engrave, ...

which also relate to surface treatments but with a different objective from cleaning alone.

We thus note the patent application FR 2 708 877 published on February 17, 1995.
Bulletin 95/07 of Cabinet Beau de Loménie for the Société Anonyme ONET concerning a "Process and device for self-controlled decontamination of surfaces by laser" comprising at least one laser beam chosen from the wavelength range of the ultraviolet between 190 and 360 manometers, the main application of which is the decontamination of surfaces of premises, equipment, pipes, etc. contaminated by radioelements or chemical elements.

Application EP 3,803 87 published on 01/08/90 from the Regional Technological Development Agency (ARDT) concerning "Process for cleaning a surface by a laser" specially adapted for stone or other support materials with the objective of rejuvenation of monuments, works of art, antiques ,. using a laser beam whose peak power is between a few tenths of megawatts per cm2 and a few tens of megawatts per cm2 and whose wavelength is between 500 and 1100 manometers.

The patent application D 0 607 506 A1 published on 07/27 94 Bulletin 94130 of
Mr. Franz WAIZMANN concerning "Method and device for removing dirt
articles, in particular cylinders of printing machines, without contact with such articles "comprising the cleaning of dirt in the form of leftover paints, fibers and dust on the cylinders in the process of a printing machine by means of a laser beam directed at the surface to be cleaned. This process uses an "Excimer" type laser beam with a wavelength of 100 to 400 manometers, an energy density of 0.5 J / cm2 at 150J / cm2, and integrating the cleaning process into the operation of the printing machine underpinning the cleaning of residues before drying.

All these known methods clearly show that the principle of surface cleaning by laser is known and allows various applications, some of which require additional equipment as well as a choice of type of laser, in terms of frequency, power, etc., but none of these devices or methods, even if they meet certain needs, is not really satisfactory to date when a high quality cleaning is desired, without the use of liquids, without contact with the surface, outside the production machine so as to do not immobilize it and with an automated cleaning device which allows the surface to be treated uniformly with an optimum quality level.

Also, the problem posed is to be able to clean the surface, without attacking or modifying the structure of the material which constitutes it, while avoiding the redeposition of the particles removed.

The figures below represent an exemplary embodiment of the invention but are in no way limiting, other embodiments are possible within the scope and extent of this invention, in particular in adaptations of the process. suction and automation process.

FIG. 1 shows the detail of the covering obtained from the surface by the laser impacts.

Figure 2 shows a perspective view of the cylinder being cleaned.

FIG. 3 represents a schematic view of the laser head and of the suction device.

FIG. 4 represents a general schematic view of the entire device.

A solution to the problem posed is a process for cleaning the surface of the printing rollers or cylinders (10) which are fouled following their use in the printing process, after removal of said cylinders from the printing machine resulting in the complete drying of the residues of printing. materials to be peeled off or cleaned, and using at least one laser beam (11) transported by optical fiber (18), which makes it possible to obtain a laser impact (1) on the cylinder (10) with a uniformly distributed energy ("Top beam" Hat instead of "Gaussian" beam from a direct laser shot).

The laser beam (11), in the infrared wavelength range projected on said surface, and a device allowing the support and the rotation of the cylinder (16) (17) at a configurable speed coupled to a device allowing a lateral displacement (8) of the laser head (9) at a speed which can also be parameterized allowing precise and regular coverage of the entire surface to be cleaned (1) (2) (3) (4) (5) (6), and a suction device (14) integrated into the laser head (9) allowing both the removal of cleaning residues (13) and the protection of dirt from the laser head (9); the process according to the invention is such that:
- A pulsed YAG technology laser is used associated with a flexible or non-flexible optical fiber (18), used as a means of transporting the laser beam;
the wavelength of the beam is chosen in a range greater than 35,800 nanometers depending on the nature of the fouling;
- the energy density of the laser beam is set in a range less than
0.5 J / cm2 depending on the characteristics of the material to be cleaned and the pulse frequency between 10 and 100 Hz depending on the nature of the fouling and the speed of movement (8) of the beam (11) on said area;
- the cylinder (10) is positioned on a horizontal base (17) allowing the rotation (16) of the cylinder (10) on itself, the speed of rotation (7) of which is adjusted as a function of the speed of lateral displacement (8 ) the laser beam (11) and the adjustment parameters thereof;
- As the laser head (9) moves (8), the plume of residues ejected (13) by the laser impacts (12) is sucked up with a system (15) which integrates the suction (14) and the laser head (9) to avoid redeposition of said residues (13).

The result is a new device that can be transported and used on the customer's site (17), meeting the problem and the objectives set and making it possible to eliminate the drawbacks of the systems known to date.

The invention applies to printing cylinders or rolls (10) of various types of materials, in particular the so-called "screen" cylinders of engraved ceramics, or of chromed engraved metal.

The parameters of use of the method and of the device according to the invention will therefore be chosen with regard to the number of pulses, the frequency of use, the energy density, the size of the beam (11) (one or more fibers (18)), the scanning speed (8) and rotation (7) depending on the materials to be cleaned, the state of soiling and within the ranges indicated above.

We could cite other advantages of the present invention such as the fact that there is no creation of industrial waste, such as cleaning fluids, which is important for the protection of the environment by reducing the amount of waste. total volume of industrial waste.

Claims (4)

1. Dry process and laser cleaning process for all cylinders (10) used in printing, in particular cylinders engraved on ceramics and metals, characterized by: - the use of a pulsed YAG technology laser associated with an optical fiber (18) used for transporting the laser beam (11); - the choice of a wavelength of the beam in an infrared range chosen according to the nature of the fouling, - adjusting the energy density of the laser beam (11) in a range of less than 0.5 J / cm2 depending on the characteristics of the material to be cleaned, the choice of the pulse frequency between 10 and 100 Hz depending on the nature of the fouling and the speed of movement of the beam on said surface; 2. Laser cleaning method according to Claim 1, characterized by the use of a laser source associated with an optical fiber (18) making it possible to clean the cylinders (10) on the industrial site, in complete safety as regards the danger of laser radiation , and also allowing to distribute the energy uniformly (the "Top Hat" beam from an optical fiber compared to the "Gaussian" beam from a direct shot), 3. A method of laser cleaning according to claims 1 and 2, characterized by a system ensuring the support and rotation (16) (17) of the cylinder (10) and coupling the lateral displacement (8) of the laser head (9) , allowing the cleaning of so-called "screened" printing cylinders, in particular engraved ceramics, chromed engraved metal; 4. A method of laser cleaning according to any one of claims 1 to 3, characterized by controlling the speed of rotation (7) of the cylinder (10) and the speed of lateral movement (8) of the laser beam (11). ) thus allowing to cover in a precise and regular way (1) (2) (3) (4) (5) (6) the surface of the cylinder (10);