EP1144194B1

EP1144194B1 - Printing block engraving process

Info

Publication number: EP1144194B1
Application number: EP99970963A
Authority: EP
Inventors: Laurent De Volder
Original assignee: PRINTING INTERNAT; PRINTING INTERNATIONAL
Current assignee: DE VOLDER, LAURENT; Feyaerts Filip
Priority date: 1998-10-26
Filing date: 1999-10-26
Publication date: 2010-08-04
Anticipated expiration: 2019-10-26
Also published as: ATE476298T1; ES2351625T3; AU1366600A; DK1144194T3; WO2000024582A1; DE69942651D1; BE1012653A5; EP1144194A1

Abstract

Process for engraving an image in a support, wherein said image is provided for pad printing, wherein the latter forms an intermediate support which is first charged with ink, after which the ink is scrapped off, wherein a flexible pad means takes over the remaining ink which is originating from the engraved support, whereby a transposed image is formed, after which said transposed image is deposited on a surface to be printed of an object to be decorated by means of the pad means which is charged with ink, remarkable in that the engraving of said image (11, 12) is effected in that a high energy beam (9) is directed on said support (10) according to a selected image pattern (11, 12) and under parametric working conditions which are set.

Description

This invention relates to a process for pad printing with engraving an image in a support.
Pad printing is a known technique in the field of printing techniques, which is used for printing and decorating all kinds of objects, made from various materials. This goes from medical tablets to all kinds of caps for closing containers and even electronic apparatus such as fuses and so on. Pad printing is an appropriate technique essentially for printing non-plane surfaces. Pad printing is an indirect printing by means of an elastic pad, which transfers the image to be printed from a deep printing plate to the object to be printed. This technique is described more in detail in EP-A 98870256.9 .
It is of common knowledge in printing techniques that ink is applied on an engraved printing block or printing plate. Subsequently, the ink is scraped off from the surface of the printing plate, and the ink remains only in the engraved parts of the plate. This remaining ink is taken over with a pad and is deposited subsequently on the surface to be printed. Thanks to the flexibility of a silicone pad, very irregular surface can be printed.
Nowadays mainly three kinds of printing block plates designated hereinafter shortly as printing plates, are used for pad printing, i.e. printing blocks in synthetic material, printing blocks in thin steel with a thickness ranging from 0,2 to 2 mm and thick steel printing blocks with a thickness between 5 mm and 10 mm. An image is engraved in the printing block. Depending on the kind of image to be engraved, of the surface to be engraved and of the kind of ink, this image has a depth, which is mostly comprised between 10 and 80 µm.
The choice, which will be made between three afore-mentioned types of printing blocks, will be greatly determined by the desired lifetime of the printing block. Indeed, the printing block is exposed to wear because of the requested step of scraping off the ink. A good scraping off of the ink is an absolute requisite and this requires a high pressure of the scrape on the printing plate. As a consequence thereof, the use of printing blocks in synthetic material and thin steel is rather limited to small printings. In comparison, thick steel printing blocks which have inherently a better resistance to wear and tear, are rather used for larger printings.
At present, an image in the printing blocks for pad printing is almost always carried out in a photochemical way. Firstly a film is thus made from the desired image. Subsequently, the film is put on the printing block, whereby the printing block must be provided with a photosensitive layer. Afterwards, the printing block is exposed together with the film during a few minutes in an exposing apparatus specifically provided therefor. After exposing, the printing block is developed and the image is finally etched out by means of chemical etching products.
This process based upon photochemical etching of printing blocks has yet the following drawbacks. The total duration for engraving a printing block also including the manufacturing of the requested film is very long (up to approximately 40 minutes).
Positioning the film on the printing block with respect to a reference angle of the printing block must be carried out manually and requires thereby the needed precision.
In addition, dust particles appearing on or under the film during the exposure, must be retouched manually thereby to prevent the formation herein of undesired holes because of these dust particles. However, this operation is quite difficult to be executed for very fine images.
In addition yet, dangerous chemical products, such as certain acids, must be used often for etching. In addition to a potential danger for the health of the operator or workman, these chemical materials also present the drawback that they need a special waste treatment. With regard thereto, the imposed environmental standards become always more severe with the time and the related treatment becomes always more complicated and expensive in a corresponding way.
It is also possible that the needed films are damaged whereby scrateches, grease and/or dirtiness are formed therein, thereby causing the films to be unusable.
In recent years, another technique has been developped, using a laser beam, which is computer driven and programmed to engrave the selected image automatically in a printing plate. This technique allows a much better flexibility, as an image can be programmed directly from a computer, and the laser engraving is quite fast, taking significantly less time than a chemical etching.
Document GB2 303 094 discloses such a solution, showing the great flexibility and the big number of possibilities in size and depth of dots given by this technique.
Unfortunately, this technique produces an evaporation of the engraved material, and some of the evaporated material solidifies on the plate nexte to the engravement, producing protrusions, which are nefast to the use of such printing plates. The scrapping off of the ink in excess is made difficult by such protrusions, and produces high wear of the scraping blades and the printing plate.
Document DE 40 12 279 discloses a solution to avoid such protrusions. It consists in choosing aluminum printing plates, and practice a surface anodization on the surface to be engraved. As a consequence a laser engraving can be made, and no protrusion appears.
Document DE 195 18 587 discloses a similar technique, with surface anodized aluminum.
The drawback of this solution is that it limits the application to one very type of printing plate material, whereas many other materials are often cheaper or more adapted as printing plates
Document DE 195 07 827 discloses a different solution, with a specific laser beam, producing a cold removal effect, and applied to various materials. By utilising an excimer laser, the laser beam works exclusively in the UV range, and produces very little heat. Thus the material next to the engravement is not significantly heated, and the evaporated material does not fix on the printing plate. The protrusions are thus avoided. As materials used this document discloses polymers and ceramics.
But such a specific excimer laser solution leads to higher costs, as these lasers are very specific. The more so this solution is limited to only a few microns engraving depth. When more depth is needed, a complementary etching is necessary.
Therefor the need for another solution exists.
This invention aims at remedying the aforementioned drawbacks. For this purpose, there is proposed according to the present invention a process as defined in the main claim, which is remarkable in that a ceramic material is exposed to the action of said energy beam, and in that said energy beam is a pulsed laser beam, with frequencies, comprised between 10 and 70 kHz.
According to a preferred embodiment of the invention, said laser beam is brought into a relative motion with respect to the support to be engraved under automatic control by an external control unit.
According to a specific embodiment, said support is formed by a plate-like element provided for a linear pad printing.
According to an alternative embodiment, a ceramic plate is exposed to the action of said energy beam. When metal vapours condense, protrusions can be formed indeed on the edge of the engraved areas, particularly when steel plates are engraved. The elimination thereof causes the risk of a possible deletion of the engraving. This situation can not occur however with ceramic materials. The latter can not be etched.
According to a further alternative embodiment, a plate of glass material is exposed to the action of said energy beam.
According to a still further preferred embodiment, said support is made from a basis plate and a layer to be treated, which is exposed to the action of said energy beam and which is deposited on the basis plate.
More particularly said basis plate is made of metal.
Alternatively Said basis plate is made of a material, the stiffness and/or the hardness of which is greater than the one of the layer to be treated, particularly of a synthethic material.
In a further alternative way, said basis plate is made of a composite material.
Advantageously, said layer to be treated is made of a ceramic layer having a determined thickness, particularly wherein the thickness of said layer to be treated is much smaller that the one of the basis plate. In a particularly remarkable way, the combination thereof with metal as a basic layer shows an advantageous behaviour.
Said layer to be treated can also be made of an amorphous material, particularly a glass material.
According to a remarkable embodiment of the invention, said layer to be treated is made with a thickness which is selected in correspondence with the selected engraving depth in the printing plate.
Alternatively said layer to be treated can be selected with a thickness which is greater than the selected engraving depth.
It is thereby achieved thanks to the process according to the invention that the aforementioned drawbacks are prevented. In particular no more films need to be manufactured thanks to the possibility of a direct engraving of the image in the printing block from a computer unit, in particular by means of a plotter. Thanks to this as well, the requested engraving time is very short and it can be limited to merely 5 to 10 minutes.
The very high precision of the repetition of the image position is also achieved thereby because of the fact that no more manual positioning of the film is required. This elimination of a manual intervention further considerably increases the reliability of this operation.
In addition, dust particles no longer affect the quality of the laser engraving.
Special chemicals are no longer needed as well.
Additional features are defined in the remaining subclaims.
Further details and advantages of the invention will appear from the description hereinafter of an exemplary embodiment of a process according to the invention, which will be illustrated with the appended drawings. It is to be understood that this description is given exclusively by way of an example and the latter does not limit the invention by any means.
The reference numerals refer to the drawings.
Figure 1 is a diagrammatic view of an arrangement provided for carrying out the process according to the invention.
Figures 2 to 5 show a cross section of respective plate elements to be treated according to the process of the invention with variants.
Figures 6 and 7 represent a respective top view of printing blocks engraved according to said process with a variant.
The arrangement represented in Figure 1 comprises a laser 7, for example a so-called Yag laser, provided as an engraving means for a printing plate 10 to be used in pad printing, particularly in linear pad printing. The laser apparatus emits a pulsed laser beam, which is directed on the plate to be engraved 10. The emitted laser beam is deflected 9 by means of a mirror system 8 provided therefor. A computer unit (not represented) is further provided for controlling said mirror system 8.
A part of the surface of the plate 10 corresponding to the places where the laser beam 9 impinges the printing 10 is evaporated. Advantageously, the laser beam is passed one or several times on the image 11 thereby to form an engraving 1 with a desired depth as shown on Figure 6.
The laser beam has a thickness, which is limited, e.g. to some tens of micrometers. Consequently, engraving with said laser beam of a complete surface or of areas with dimensions, which are greater than the available laser beam thickness requires that these areas are filled up with the laser.
In pad printing, so-called rasters 12 are also used in some cases as shown in Figure 7. This can be carried out by not taking any material away on selected predetermined locations 13 in the image.
In conventional engraving methods, metallic plates are used because they have a long lifetime and because they can be etched with chemical products. The used metal is mostly a special chromium steel in this case which is submitted to a lap process after a hardening treatment. However, using metallic printing plates 2 in order to engrave by means of a laser causes the problem that an accumulation of metal 14 is created on the edges of the produced engravings 1, which protrudes over a determined height, up to some micrometers above the metal surface 15 of the plate 2 as shown in Figure 2.
This accumulation of material 14 is undesired because they render the printing plate unsuitable for use in modern pad printing. This results in the need of a subsequent treatment of the printing plate, e.g. by lapping or polishing.
An alternative method for remedying thereto consists in modulating the laser beam used to such an extent as to velocity, power and frequency, that this parasitic accumulation of material is not generated. However this method is very time consuming.
A further remarkable alternative against the generation of accumulation of material around the engraved areas 1 is proposed according to this invention. It consists in a specific choice of selected materials for the printing plate. In this respect, the choice of ceramics appeared to be very appropriate because of its high resistance to wear on the one hand and the verification of the absence of the generation of accumulations of materials when engraving with laser on the other hand.
However, ceramics has in turn a drawback with this technique, i.e. the fragility of this material in addition to the cost. This problem is of subsequent order however insofar it could be established yet that it could be solved easily by using an additional basis plate as shown in Figures 3 and 4. Said basis plate 4 consists advantageously in a more usual, unhardened or lapped material for example, which appears thereby to be cheaper, on which a ceramic layer 3, 5 is further deposited. In addition, the whole as a superposition of layers appears to be substantially cheaper, the more that it is to be considered that the respective ratios of the layers (bottom and top layer) are not shown at scale in the Figures for a sake of clarity of the representation. The top layer 3, respectively 5 in must thinner that the bottom layer 4.
The top layer forming the layer to be treated may have different thicknesses, depending on the required application. A fixed thickness 3 can thereby be allocated thereto which is substantially equal to the desired depth of the engraving 1 as shown in Figure 3. In this case, the laser is set in such a way that the beam 9 takes away only the ceramic layer 3. The engraving depth is set yet beforehand for a determined thickness of the ceramic layer 3.
A thickness which is greater than the desired depth of the engraving can also be allocated to the layer 5 as shown in Figure 3. In this case, the parameters of the laser beam, in particular the wavelength, the pulse frequency, the velocity of the beam and the power can be set in such a way that the desired depth is engraved.
The tremendous gain in time which can be achieved thanks to the use of laser engraving of printing plates for pad printing, or possibly by other high energy techniques provides particularly interesting prospectives for customers having a need in printing plates. The cycle times are reduced from approximately one hour with the classical methods to merely 5 to 10 minutes. A still greater flexibility in making the printing plates is requested. For the customer himself, it is often not an efficient investment to etch or to engrave himself metallic printing plates, resulting in that this operation is mostly sub-contracted.
Thanks to a laser engraving system as described above, a manufacturer of printing plates for pad printing can respond very quickly to the query of the customer. The customer designs himself the desired image on his computer. This image is sent out via e-mail for instance directly to the manufacturer of pad printing plates, where it arrives almost simultaneously. The manufacturer thus receives the image straight away on his computer and he may engrave directly the printing plate with minimum actions. Because lapping or polishing of the printing plate is no longer required after the engraving, said printing plate can be sent out immediately to the customer.
This invention can also be used for rotary pad printing. For this aim, the support 10 can be adapted as to its shape for use in rotary pad printing,
Particularly aluminium and silicon ceramics material can be used as composite materials.
When engraving in steel with subsequent treatment of plates with depositing titanium, particularly titanium nitrite and/ or on a chromium basis can also be used advantageously.

Example 1

A plate with a very high hardness, 2.000 to 3.000 Wickles, with a thickness of an order of magnitude of 2 µ with a layer of titanium on the substrate.
The substrate is made of metal / steel or synthetic material / carbonite. The latter is very resistant to wear and tear and is completely corrosion-resistant with a resistance to wear which is 3 to 4 times more than the one of hard metal or steel. So the basis plate can also be made of synthetic material.
As materials we can also have TiN (titaniumtin), HC₂O₃/TiO₂, Cr₂O₃, Ag.TiN (silvertin).
Temperatures are comprised between 100 and 200 degrees C.
It works perfectly as basis material; it has greater sensitivity to temperatures than titanium on ceramics.
Pure carbon plates: very well and cleanly engravable with a laser; also very light, not costly, may be very thin.

Example 2

Bottom plate in metal. In this case it is covered with a coating.
A magnesium coating can be used as a coating. The hardness is relatively low in this case and the costs as well.

Example 3

Pure ceramic plates Si.C (silicon carbide), Yttria, SiC (Silicon carbide), SiSiC, SSiC, Cr₂O₃, SSN also silicon nitride.
And also: metallic support as bottom plate with a substantially thinner layer of ceramic thereon (thickness of approximately 100 µ): offers a good solution to the problem of fragility of ceramic materials;
Or further synthetic materials, particularly hard synthetic materials, instead of metals as well.
In case of pure ceramic plates, the plates present one same material and a relatively greater thickness or possibly also a smaller thickness can be used depending on the application. In the latter case, the final product is cheaper.
Further examples of combinations of the treatment layer on the basis layer are respectively: ceramic on steel or glass on steel, respectively metal.
The engraving apparatus comprises a Yag laser having a power ranging between 50 and 120 Watt, and the laser light has a wavelength ranging between 532 and 1064 nm. The laser beam is pulsed with a frequency ranging between 10 and 70 kHz.

Claims

Process for pad printing with engraving an image in a support wherein the latter is first charged with ink, thereby forming an intermediate support which is engraved, after which the ink is scrapped off, wherein a flexible pad means takes over the remaining ink which is originating from the engraved support, thereby forming a transposed image, after which said transposed image is deposited on a surface to be printed of an object to be decorated by means of the pad means which is charged with ink wherein the engraving of said image (11, 12) is effected by a high energy beam (9) directed on said support (10) according to a selected image pattern (11, 12) and under parametric working conditions which are set, wherein said support (10) comprises at least one layer of evaporable material (3), wherein the surface to be engraved (1) of the support (10) is evaporated selectively under the action of said energy beam (9) thereon (claim 5 as originally filed), characterised in that a ceramic material is exposed to the action of said energy beam, and in that said energy beam is a pulsed laser beam with frequencies comprised between 10 and 70 kHz.
Process according to claim 1, characterised in that said pulsed laser beam (9) is is brought into a relative motion with respect to the support to be engraved (10) under automatic control by an external control unit.
Process according to one of the preceding claims, characterised in that said support (10) is formed by a plate-like element provided for linear pad printing.
Process according to the preceding claim, characterised in that a plate of glass material is exposed to the action of said energy beam.
Process according to one of the claims 1 to 2, characterised in that said support is made from a basis plate (4) and a layer to be treated (3; 5) which is exposed to the action of said energy beam and which is deposited on the basis plate.
Process according to the preceding claim, characterised in that said basis plate (4) is made of metal.
Process according to the preceding claim, characterised in that said basis plate (4) is made of steel.
Process according to claim 5, characterised in that said basis plate is made of a material, the stiffness and/or the hardness of which is greater than the one of the layer to be treated.
Process according to claim 5 or 8, characterised in that said basis plate is made of a synthetic material.
Process according to claim 5, 8 or 9, characterised in that said basis plate is made of a composite material.
Process according to one of the preceding claims, characterised in that the thickness of said layer to be treated is much smaller than the one of the basis plate.
Process according to one of the preceding claims, characterised in that said layer to be treated is made of an amorphous material.
Process according to one of the preceding claims, characterised in that the layer to be treated (3, 5) is composed of a glass material.
Process according to one of the preceding claims, characterised in that said layer to be treated (3) is made with a thickness which is selected in correspondence with the selected engraving depth (1) in the printing plate.
Process according to one of the preceding claims, characterised in that said layer to be treated (5) is selected with a thickness which is greater than the selected engraving depth (1).
Process according to one of the preceding claims, wherein the support (10) is adapted as to its form to the use in rotary pad printing.
Process according to one of the claims 2 to 16, characterised in that the printing plate is designed remotely from the processing unit as to its image (11, 12) by a customer, that is subsequently sent directly to the producer of the printing plate by means of telecommunications means, particularly e-mail or Internet, wherein said image (11 or 12) is applied by means of said control unit in the printing plate to be treated in which the desired image is engraved by the high energy ray.
Process according to one of the claims 2 to 17, characterised in that the laser beam is prevented from removing material of the printing plate on predetermined locations in order to enable working with rasters (12).