The invention relates in the first place to a process for forming a resistance pattern on a cylindrical object, comprising the application of a layer of a material which is resistant or can be made resistant to a treatment agent to be used and/or the treatment condi¬ tions, and the formation, using a laser beam treatment, of a pattern of places which are freed of said material layer, if desired followed by further treatment of the material layer in order to make it resistant to the treatment agent and the treatment conditions.

A resistance pattern in this case is generally understood to mean a material pattern which protects the underlying parts of a cylinder to which it is applied against the influence of a treatment agent and/or the conditions prevailing during a treatment.

The treatment can be, for example, the etching of a cylinder made of metal or etchable plastic. The treat¬ ment can also be the electrodeposition of metal in an electrolysis bath. It will be mainly etching resistance patterns which are discussed below, but the invention is not restricted thereto, as is clear from the above.

The formation of a resistance pattern on the outside of a cylindrical object is known. During the formation of an etching resistance pattern on a cylindri¬ cal metal object, the latter is coated with a layer of material which is resistant or can be. made resistant to etching agent, such as a photographic lacquer or in general an organic lacquer. The metal cylindrical object can be, for example, a seamless metal cylindrical object such as a copper, nickel or iron sleeve; it is also possible to start from a cylindrical object which is obtained by welding the ends of a metal sheet to each other.

For the selection of the materials to be used, the choice of the type of laser beam treatment is impor¬ tant.

If the laser beam treatment is a bu ning-away 5 process, then in principle any material which is suitable for burning-away or vaporizing using a laser beam can be selected for the material layer to be used.

If the laser beam treatment is a photochemical treatment, one can opt for a material which hardens under 10 _. the influence of radiation or is soluble in a developing fluid under the influence of radiation, in which case negative or positive photographic lacquer systems are used. Following such a laser beam treatment in the carrying out of a photochemical process, a development 15 step also has to be carried out, in order to remove the material layer from the places which are still soluble or have been made soluble in a developing fluid. If neces¬ sary, following any development step, or following the laser beam treatment itself, an additional treatment can 20 be carried out in order to give the material layer the desired etching agent resistance.

In all cases, a cylindrical metal object provided

•with an etching resistance pattern which during the subsequently carried out etching protects the places of

25 the cylindrical object which must not be attacked by etching agent is obtained at the end of the treatments.

During the application of such an etching resis¬ tance pattern on the outside of the cylindrical object alone, the problem of a very considerable degree of 30 lateral etching is encountered if perforations have to be formed through etching in the wall of the cylindrical object.

Such a strong lateral etching means that the fineness of the perforation pattern to be applied is 35 greatly limited, on account of the fact that the perfora¬ tions must not overlap, particularly on the inside of the cylindrical object. ... _c

The object of the present invention is to produce a process of the type mentioned in the preamble in which

it is possible to achieve an etching resistance pattern on both sides of a metal cylindrical object, through which much greater fineness can be achieved in etching through than was the case hitherto. According to the invention, the above-mentioned process is characterized in that the material layer is applied to both the inside and the outside of the metal cylindrical object, while a pattern of places from which the material layer is removed is formed both on the inside and on the outside, and the patterns on the inside and the outside have a fixed, predetermined relationship to each other.

It was found that it is possible both on the inside and on the outside of a cylindrical metal object to form resistance patterns such as etching resistance patterns which can bό positioned with very great accuracy relative to each other, so that etching can take place on two sides.

Etching on both sides means, on the one hand, that a reduction in the lateral etching over the entire thickness of the cylindrical object is achieved, so that greater through etching fineness can be achieved, i.e. a greater perforation density (holes per unit area) . It is also possible by etching ori two sides to achieve a greater passage (open surface per unit area) with the same perforation density. Etching on both sides also means a considerable shortening of the total etching time.

It is pointed out that etching of an object on two sides is known per se. In such known processes the starting material is a flat, sheet-type metal material which is provided on two sides with an etching resistance pattern, the two patterns being positioned very accurate¬ ly relative to each other. In such a case the image- bearing photographic lacquer patterns on either side of the sheet correspond, and come about by making use of a pattern-forming stage by means of a photographic film system in which the top and bottom film are positioned accurately relative to each other within approximately 25

micrometres.

The above-mentioned known processes give no information concerning the possibility of applying an etching resistance pattern on the inside and outside of a cylindrical metal object.

The invention also relates to a device for the treatment with a laser beam, according to a predetermined pattern, of a layer of a material situated on the surface of a metal cylindrical object, at least comprising a clamping device for the rotatable mounting of the cylind¬ rical object, laser beam forming means, laser beam deflection and guide means, and electronic measuring and control systems for the regulation and control of the laser beam treatment. Such a device is according to the invention characterized in that the device has means for accom¬ modating the end parts of a cylindrical object to be treated while leaving free the inside thereof, and in that it is provided with means for the formation of two laser beams, and guide means are present to feed the two beams to two beam focusing elements which are disposed opposite the outside and inside of the cylindrical object, and provision is made for means by which the beam focusing elements can carry out a controlled, movement along lines which are parallel to the axis of the cylind¬ rical object, for the formation of patterns of places of a material layer treated with a laser beam on the inside and outside of the cylindrical object.

In particular, use is made of a beam splitting device for splitting a single laser beam coming from one laser device into two partial beams.

It was found that it is possible to use two laser beams or to split a formed laser beam into two partial beams using a laser beam splitting device which is known per se, and to use the two beams or partial beams for processing material layers lying on the inside and outside of a cylindrical object, in order to form therein a pattern of places which have the material in question removed from them, so that in that way an etching

resistance pattern is formed on both sides of the cylind¬ rical object.

It is pointed out that a device of the type described above as the point of departure is known per se from Austrian Patent Specification 382558.

The above-mentioned patent specification descri¬ bes a device in which a lacquered screen printing stencil can be clamped on a clamping roller and a programmed laser beam is used to burn open those holes which lie in the parts of the stencil corresponding to the pattern parts which have to be printed using the stencil. The present application describes a device for the treatment of material layers present on the inside and outside of a cylindrical object, such as a metal sleeve. For this purpose, the clamping of the cylindrical object is arranged in such a way in the device according to the invention that the inside thereof remains free.

In its entirety, the device according to the invention will, as indicated, comprise two laser devices with the corresponding deflection, guide, control and regulating means. If two lasers with separate control and regulation are used, a separate pattern can be formed simultaneously or otherwise on the inside and outside of a cylinder. Through coupling of the two systems a rela- tionship between the two patterns can be ensured. The device according to the invention expediently has one laser device whose beam is split into two partial beams by means of a beam splitting device.

In order to make allowance for any wobbling of the cylindrical object to be treated, means are advan¬ tageously present in at least one of the beam focusing elements for keeping constant the distance between the centre of the lens system forming part of a beam focusing element and the centre of the point where the beam strikes the cylindrical object to be treated.

Such a-system of keeping the distance constant is described in Dutch Patent Application 8801551 (not a prior publication) ; the incorporation thereof results in the distance between focusing lens assembly and the

surface of a clamped cylinder being kept largely con¬ stant.

For a precise determination of the distance between, for example, a focusing lens system and an object on which focusing has to take place, use can be made of the process and device for measuring distance described in Dutch Patent Application 8802397, which is not a prior publication.

The distance-determining means described in the latter application can be used successfully in the means for keeping a constant distance disclosed in the above- mentioned Dutch Patent Application 8801551.

The content of the above-mentioned Dutch Patent Applications 8801551 and 8802397, which are not prior publications, is considered to be incorporated in this description, on account of the above-described use in the device according to the present invention. In particular, it is possible with the device according to the invention to form patterns which have a fixed, predetermined relationship to each other on the inside and outside of the cylindrical element.

As will be indicated later, this can mean that the patterns on the inside and outside of the metal cylinder are identical, but it can also mean that the patterns are not identical and are displaced relative to each other.

Finally, -the invention relates to an etched metal cylinder, obtained by etching of a metal cylinder using an etching resistance pattern which is removed after the etching operation, characterized in that the point of departure is a cylinder having on the inside and outside thereof an etching resistance pattern which was obtained by use of the process according to the invention, as described above. The invention will now be explained with refer¬ ence to the drawing, in which i

Fig. 1 shows a schematic picture of a device according to the invention; and

Fig. 2 shows in cross-section a number of

possible pattern forms and pattern positionings.

Fig. 1 shows a device indicated by 1 for treating a cylindrical metal object which is provided on the inside and outside with material layers. The cylindrical metal object 20 is, for example, a seamless sleeve which is formed by electrodeposition of nickel and is provided on the inside and outside with a suitable organic lacquer which can be burned away locally using laser radiation. The device has a laser 11 and laser guide and splitting means 12 and 13 respectively. The beam splitter 13 divides the beam into 2 parts which can be of equal or, if desired, unequal intensity. The two partial beams are guided via the mirror means 8, 8' and 6, 6' to the laser focusing means 5 and 5' , and the focus of the two partial beams comes to lie in the centre of the material layer which is at the inside and outside of the cylin¬ drical metal object 20. The focusing point is shown schematically by 21. The cylindrical metal object is clamped by means of end rings 25 (in enlarged cross-section detail indi¬ cated by 25'), rotary means and clamping means 2 and 3.

The cylindrical metal object 20, which is provi¬ ded on the inside and outside with a suitable material layer, is rotated about its axis, and during the rotation the focusing means 5 and 5' carry out a predetermined movement which is parallel to the axis of the cylinder 20, and during which the actuation of the partial beam guide means is such that the partial beams can carry out their action on the relevant material layers as desired and according to a predetermined programme.

During the operation the laser focusing means 5 and 5' and the appropriate deflection means 6 and 6' are moved along spindles 4 and 4' according to a predeter- mined plan, in which the movement is regulated by means of motors 18 and 19 which are coupled to a central logical unit. The rotation of the cylindrical object is also regulated by means of motor 17, which is likewise connected to the central logical unit such as a computer.

As can be seen schematically, the position of the partial beam focusing unit 5' is determined by making a part of the partial beam 22 radiate through the mirror 6' by making the latter slightly transparent. The position of the focusing device 5' is in this way fixed relative to the optical ruler 23 whose signal is fed back via connection 24 to the central logical unit 10. The laser regulation unit 14 is also coupled to the central com¬ puter, so that the computer can carry out a regulation which according to a predetermined programme regulates the displacement of the focusing units 5 and 5'; the rotation of the cylinder 20; and the functioning of the partial beams transmitted by focusing means 5 and 5' .

The position of 5' relative to the ruler can be determined as indicated above. Instead of using a part of the beam 22, a small laser which is made to shine on the ruler 23 can also be connected to 5'; in this way an accurate position fixing is also possible. Even without the use of a ruler, a position determination and regula- tion can take place by feeding the motor position of the motor 18 and/or 19 back to the logical unit 10. Of course, such an approach is possible only if the mechan¬ ical accuracy of the motor, coupling and spindle is great enough and the settings thereof are reproducible. The signal coming from a scanner can also be fed via an interface 15 to the computer, so that a direct translation can be produced between an original scanned on a scanner and the pattern applied by the laser irradiation to the inside and outside of a cylinder 20. Fig. 2 shows schematically how the etching resistance patterns on either side of the wall of a cylindrical object can be positioned relative to each other, and how the shapes of both etching resistance patterns can relate to each other. Fig. 2a shows a part of the wall of a cylindrical object 30 on which there are patterns 31 and 32 on two sides. The patterns show apertures 35 and 36, and it can be seen that an etching which formed hollows 33 and 34 has already taken place. In the situation shown, the

etching can be continued until a full perforation of the material 30 is achieved. The etching can also be ended at this moment or continued for a short time further to ensure that a pattern of hollows is formed on the inside and outside of the material, but with the material not being fully etched through.

In the latter case a pattern of pits is obtained on both sides of the cylindrical metal object, the total pits being capable of containing information which can be scanned with optical or mechanical means.

It goes without saying that such a cylinder, which is provided on two sides with a quantity of information can also be cut open to form a flat metal sheet which contains information on two sides. Fig. 2b shows the situation in which the etching resistance patterns _* 31 and 32 are in the same position relative to each other on both sides of the cylindrical object, but where the patterns on the two sides differ from each other as regards open surface. During etching, the hollow 34 will have a smaller surface than the hollow 33, due to the fact that the aperture 35 is smaller in area than the aperture 36 (for an indication see Fig. 2a) .

Such an arrangement and formation can be important if the lateral etching has ^• to be avoided to a large extent at one side of the cylindrical object. In the case illustrated here in Fig. 2b, complete etching through of the cylinder can also be produced depending on the envisaged purpose, while an etching over only part of the total thickness can also be carried out through doublesidedetching.

It can be seen from Fig. 2c that the patterns formed on both sides of the cylinder differ both in shape and in positioning. In this case an example could be a situation in which the etching resistance pattern 31 is of a grid nature at the top side, while the etching resistance pattern 32 on the inside has slit-type aper¬ tures which are arranged in a spiral form, and on through etching at predetermined places a slit-type aperture

lying in the spiral and a hole-shaped aperture touch each other. Fig. 2d shows the situation in which the etching resistance patterns are the same shape, but the position¬ ing of the patterns differs. Finally, it is also conceivable to have a situa¬ tion in which the etching resistance patterns are of different shapes on the inside and outside of the cylin¬ der, and in which the positions of the two patterns bear no relation to each other. The etching resistance patterns shown in Figs. 2a to 2d can be formed simultaneously by laser irradiation in both material layers (where necessary, in conjunction with necessary developing and/or subsequent treatment steps) , but they can also be formed one after the other. If the patterns are formed after one another, the formation can still be carried out in the same movement of the two focusing devices 5 and 5', while each of the patterns can also be formed in a separate passage and the focusing means 5 and 5' are actuated and controlled independently of each other.

With regard to the etching process as such, you are referred to Dutch Patent Application 8802927 of applicants, which was filed at the same time as the present application, and which discloses an etching process by means of which-it is possible to control the lateral etching as desired during the etching operation by building means which influence etching factors into the metal.