High-productivity digital printing device

Abstract

 A device for digital printing is described, comprising a plurality of printing heads (10) and at least one conveying element (110) carrying the product to be printed. The digital printing heads are assembled in a plurality of printing groups (101,102,103,104) which are stationary relative to the conveying element (110) and each of the groups is provided with an independent cleaning system (50) for the digital printing heads.

Description

[0001] The present invention relates to a device for digital printing, such as a device suitable to be mounted on high-throughput converting machines in replacement of the traditional printing systems currently being used.

[0002] The operation of digital printing heads being applied to plotter devices to carry out multicolour printouts is known. The printing heads can be either of the piezoelectric or electrostatic type as a function of the inks (whether water-, solvent-, oil-based and the like, either sublimation ones or not) which one desires to use. With the known machines, the plotter comprises one or more printing heads being displaced crosswise to the machine direction of the substrate to be printed.

[0003] The operation of the so-called "converting" machines, also when provided with a printing unit, is also known. These machines carry out a conversion on the material being worked by modifying the appearance, shape and colour thereof by means of high-speed operations in a manufacturing line, such as the machines for the preparation and/or production of corrugated cardboard containers.

[0004] A converting machine for use in the paper-cardboard industry, and particularly a so-called "casemaker" is described by way of example. This type of machine produces corrugated cardboard packaging (i.e. printed parallelepipeds) starting from a sheet of corrugated cardboard. The conversion is carried out by the sheet passing through various machine stations that will sequentially carry out a modification on the material.

[0005] After the sheet has been introduced, in phase with the subsequent operations, the printing is carried out, such as by means of blocks (rubber stamps) being applied on suitable cylinders. A simultaneous cutting and creasing (marking without breakage) operation on the sheet at the parallelepiped future corners is then performed.

[0006] In the subsequent stations, the cardboard is folded from two sides thereof until they meet along a previously adhesive-coated flap, thereby obtaining a hollow element from the original flat sheet. Each of these is then flattened and packaged in packs, such as to have a minimum bulk when shipped to the end customer, who will be able to obtain the parallelepiped-shaped packaging as ordered by performing easy operations.

[0007] There is currently the need of extending the advantages of digital printing also to converting machines in general.

[0008] The digital printing heads being applied to the plotter for colour printing, particularly of sizes greater than 50 centimetres, with oscillatory operation and pitch feeding of the product being printed, are used on a large scale in the advertising field and in the personalization industry, for those outputs being characterized by small batches and reduced output speed.

[0009] In the converting machines with a printing unit, the product to be printed is carried at high speed through printing machinery elements being provided with the colour-transfer tools (cylinders, stamps, screens, etc). These machines consist of an inlet unit (a continuous feeder for long products, or an alternate one for small-sized elements) and a subsequent part destined to the finish printing (cutting, shaping, folding operations, etc.) to manufacture the finished product.

[0010] The problems found with the known technique are:

• in the converting machines, the use of printing tools dedicated to a production order (cylinders, stamps, colours) requiring to be replaced and washed upon completion of the production order.
  Besides entailing a considerable waste of time, it is also required to arrange storage areas for these tools and arrange a handling system for the wastewater produced by continuous washing;
• in the digital printing, the high printing quality with the known plotters is only ensured by repeating several alternate coatings onto the image to be printed. Indeed, only one coating cannot offer the desired quality. Furthermore, a need exist for a head cleaning system ensuring continuous production without interruptions due to the standard washing steps.

[0011] Therefore, it is necessary to create a complete printing device to be coupled to the converting machines, whether new and existing ones, and which takes the above-mentioned problems into account.

[0012] The object of the present invention is to provide a device allowing to obtain high-speed digital printouts, such that this technique may be used in the industrial field.

[0013] In accordance with the invention, this object is achieved by means of a device for digital printing, comprising a plurality of digital printing heads and at least one conveying element for drawing the product to be printed, characterized in that the digital printing heads are assembled in a plurality of printing groups which are stationary relative to the conveying element, and in that each of the groups is provided with an independent cleaning system for the digital printing heads.

[0014] At least two stationary support groups are provided per head module and relative cleaning system, even though the number of groups being required to obtain the desired quality may be greater, particularly they should be at least equal to the number of passages deemed necessary plus one, the latter being required to carry out the cleaning on the printing heads without having to interrupt the production process.

[0015] For example, according to the current quality standard, the number of groups required to obtain good quality printing can be of four groups; each group is cyclically brought in a washing phase for the printing nozzles to be kept efficient and clean, without having to interrupt the production process.

[0016] Preferably, the ink supply is carried out by only one ink receptacle per each colour to the several groups of the printing device. Due to the peculiarity of the components, at least the receptacle is protected from the outer environment by blowing filtered air with a slight overpressure to prevent that an excess amount of dust may enter, both to preserve the heads and prevent the ink from being polluted.

[0017] The groups may be manufactured with piezoelectric heads as a function of the inks being used, for example water-, solvent-, oil-based inks, or the like, possibly also of the sublimation type.

[0018] Since printing softwares are currently based on a fixed speed, as a function of the printing head translation speed within the plotter, the development will be carried out at a certain speed and then will pass to a speed step system as a function of the manufacturing speed being set on the machine. In fact, in the converting machines currently on the market, the speed of passage is generally fixed and the machine productivity is determined by varying the feed frequency of the sheets to be printed, for example by introducing one sheet per each drawing cycle (maximum productivity) or rather by introducing one sheet every 2, 3, 4... drawing cycles.

[0019] The printing software divides the image into many strips to be sent to the several heads, and in the course of the production process each one provides for the repetition of the strip assigned thereto synchronously with the other heads incident on the same strip from different groups.

[0020] Preferably, the device according to the invention has an electronic control software for the alignment of the modules on the group, the modules being plugged when arranged on the battery. For the modules there is also provided a separate check and alignment unit, to be used by the maintenance department operators. Therefore, the head replacement and head alignment operations in the module will be carried out in the factory thereby allowing the production process to be carried out continuously.

[0021] In the course of the production process the printing heads require to be washed, which can be carried out cyclically without having to stop the production process due to the presence of an additional group. The production process may nevertheless be stopped, if necessary, for the time required to perform this operation. This operating mode will be automatically managed by the software as a function of the parameters set.

[0022] In accordance with the invention, each module is formed by a pack of offset heads for the printing to have a length equal to the total length of one head, and is considered as being the replaceable element on board of the machine.

[0023] In accordance with the invention, each group is preferably capable of printing the image at least with the base four-colour process colours and thus consists of a minimum number of batteries being sufficient to achieve this purpose. For example, with heads suitable to print two colours at least two batteries are required, with one-colour head at least four batteries are required, etc. For each head battery a respective head cleaning battery is provided.

[0024] A printing station including a device according to the invention can be also arranged at processing being carried out further upstream of the current printing position in the converting machines. Generally, in a paper and cardboard factory, the printing is performed when the cardboard is turned into packaging and pre-printed paper is only seldom used. A device according to the invention may also be inserted in the corrugator, i.e. in the machine manufacturing the corrugated cardboard from paper reels, thereby allowing the printing to be performed on this machine regardless of the batch to be produced.

[0025] This entails a number of advantages compared to the current high-throughput converting machines, e.g. the reduction in the number of colours used within a factory (from a high number to the four bases only- cyan, magenta, yellow, black), as well as the absence of printing elements such as cylinders, stamps, screens or the like, with a considerable saving in terms of space, cost and management.

[0026] Furthermore, the start of production, which currently ranges from tens of minutes to several hours depending on the machine being used, is reduced to the time required for placing mechanical parts, thereby saving the time required for washing and replacing the printing elements. This also makes the product easy to be modified and tailored, thus avoiding to resort to suppliers of stamps and cylinders, thus considerably reducing the production costs.

[0027] The ecological aspect, however, is not a negligible one, since the washing waters are dramatically reduced, due to the fact that washing at each production turnover in order to obtain the desired colour on the finished product is no longer required. Similarly, it is no longer necessary to stock a great number of varnish containers for the several colours used, since due to the great consumption of basic colours, large reusable containers can be used for storage.

[0028] Further characteristics and advantages of the present invention will be better understood from the description below given by way of nonlimiting illustration, with reference to the annexed schematic drawings in which:

• Figure 1 is a plan bottom view of a head;
• Figure 2 is a plan bottom view of a module formed by a pack of offset heads allowing to print a head's total length;
• Figure 3 illustrates a set of modules assembled within a battery, still according to a plan bottom view;
• Figure 4 illustrates a section view taken along the IV-IV plan from Figure 3;
• Figure 5 illustrates a plan view of a group, with head batteries assembled in modules, together with the relative cleaning system;
• Figures 6A and 6B are section views taken along the Vl-Vl plan from Figure 5, of the unit during the operating and cleaning steps, respectively;
• Figure 7 illustrates a four-group printing station to be installed in the converting machines to perform digital printing;
• Figure 8 illustrates an exemplary application of a device according to the invention to a converting machine to manufacture corrugated cardboard packaging; and
• Figure 9 illustrates an exemplary application of a device according to the invention to a converting machine to print materials continuously.

[0029] The element illustrated in Figure 1 is an exemplary two-colour printing head seen from the bottom side (the one facing the product to be printed) where the set of aligned nozzles 1A and 1B delivering a first colour A and a second colour B in the support 10, respectively, and an area protruding from the side opposite to the nozzles containing the operation electronics and the connection systems to the main board can be observed; the dimension D indicates the printing head's length.

[0030] In Figure 2 there is represented a set of heads 10 being grouped within a module 20 which is made such that the length F of the head nozzle set is greater than the length D of a single head.

[0031] Figure 3 illustrates a battery consisting of a slotted support 30 having seats with suitable fitted centering systems to accommodate the modules 20 containing the printing heads 10. If the width M of the machine is not required to be completely covered, one or several seats 31 or 32 may be kept empty.

[0032] Figure 4 illustrates a section of the battery from Figure 3 where a module comprising three two-colours printing heads such as that indicated in Figure 1 can be seen, together with the hydraulic systems 25 supplying the inks to the heads 10.

[0033] Figure 5 illustrates a complete group 70 consisting of two batteries 30 provided with two-colour printing heads. The batteries 30 are assembled on a moving support 40 further supporting the ink feeding ducts 35 and the lines 36 communicating the control signals to the printing heads. A respective battery 60 of the cleaning system 65 is provided for each printing battery 30. The cleaning batteries 60 are assembled on a moving support 50 further supporting the suction ducts 66 to transfer the inks removed upon carrying out each cleaning cycle. Briefly, each complete group comprises a printing battery support and a washing battery support. Cleaning may also be fractionated via software for the heads to be possibly restored in the course of the production process.

[0034] In the section view from Figure 6A there is represented the complete group 70 from Figure 5 in the work position, the movements of the moving parts within the group being evidenced (bi-directional arrows), whereas in Figure 6B there is sectionally represented the same complete group 70 in the cleaning position, i.e. with the cleaning batteries being placed underneath the printing batteries. In the same views, there is further represented a lid 75 for the cleaning caps.

[0035] In Figure 7 there is represented a device 100 for digital printing according to a possible embodiment of the invention, for example of the type suitable to be inserted in high-throughput converting machines.

[0036] The device 100 comprises for example four printing groups 101, 102, 103, 104 placed above a conveying element for the material, for example consisting of a perforated belt 110 which, due to the depression formed in a suction box 120, allows the product to be transported under the printing heads without slippage.

[0037] In Figure 8 there is illustrated a device 100 for digital printing installed in a package converting machine 200 (casemaker), where an inlet station 201, followed by a planarity checker station 202, the device for digital printing 100, and a cutting station 203 (slotter), a folding and gluing station 204, and finally a collection and counter station 205.

[0038] In Figure 9 there is illustrated the device for digital printing 100 being applied to the printing of a continuous sheet material which is taken from a reel 301 and winded at the outlet on a reel 302 collecting the product printed on the material.

Claims

1. A device for digital printing, comprising a plurality of digital printing heads and at least one conveying element to carry the product to be printed, characterized in that said digital printing heads are assembled in a plurality of printing groups which are stationary relative to said conveying element, and in that each of said groups is provided with an independent cleaning system for said digital printing heads.

2. The device according to claim 1, wherein at least two of said stationary printing groups are provided.

3. The device according to claim 1, wherein said groups comprise one or several main printing groups which are normally activated and at least one auxiliary printing group normally kept in stand-by mode.

4. The device according to claim 1, wherein each of said printing groups comprises a sufficient number of digital printing heads to make at a least four-colour printing.

5. The device according to any of the preceding claims, wherein four printing groups are provided.

6. The device according to claim 1, wherein only one ink-supplying container for said groups is provided.

7. The device according to claim 1, wherein said printing heads are of the piezoelectric type.

8. The device according to claim 1, wherein said printing heads are of the electrostatic type.

9. The device according to claim 1, wherein each of said printing groups comprises a plurality of removable modules, each module consisting of a plurality of offset printing heads.

10. The device according to claim 9, wherein each of said printing groups comprises a plurality of printing batteries, each of said batteries containing a sufficient number of said modules to ensure printing in the total number of desired colours.

11. The device according to claim 10, wherein to each of said printing batteries there is associated a corresponding cleaning battery which is separate from the others provided within the same printing group.

12. The device according to claim 9, wherein each of said modules comprises a sufficient total number of offset printing heads to cover the overall length of a printing head.

13. The device according to claim 1, wherein said conveying element consist of a suction belt moving underneath said printing groups.

14. A machine for preparing cardboard containers, characterized by comprising one or several devices for digital printing according to any of claims 1 to 13.

Drawing