IES62903B2 - A printing process - Google Patents

Abstract

A printing process (1) includes production seps which help to maintain quality of the paper during the production stages. There are also various inspection steps at appropriate times to help ensure early detection of problems. Initially, production is controlled by a production document which is automatically generated by reference to archived quality control data relating to a particular product which provides an early warning system. There is a visual plate inspection (5) before the plate is mounted on the printing press. There is automatic web centring (9) before the printing operation and subsequent to printing and heating (11,12) there is cooling followed by moistening of the web by direct contact with rollers having a silicon/water/anti-static agent coating. Strict quality control of sections after stacking to form bundles and identification of the bundles helps to ensure correct gathering of the sections and further, there is in-line verification section-by-section during dispensing onto the gathering machine conveyor. There is in-line weighing and subsequent data processing (32) subsequent to glue application.

Description

A Printing, .Process The invention relates to a printing process, and more particularly to a printing process which uses a web offset press.

Production equipment for web printing has been developed 5 over the years and has reached the stage where there can be quite a high throughput with a low discard rate.

Accordingly, there has been a shift away from the traditional sheet presses to offset web presses and the latter are being used for increasingly smaller print runs.

In conjunction with the increasing use of web offset web presses, some work has been carried out on improving quality and wastage monitoring. For example, European Patent Specification No- EP-BX-0,225,482 (Automation Inc.) describes a paper monitoring system which is particularly applicable to web offset presses. This system includes a means for continuously registering waste. While such a system would undoubtedly be of use at the input stage to a web offset press, there is a need for improved production quality, quality control monitoring, and also wastage analysis throughout the whole printing operation. Accordingly, the invention is directed towards providing an improved printing process which includes various steps to ensure that the complete printing process from beginning to end provides a high-quality product and whereby any defects are detected at an early stage. In more detail, there is a need for an overall process which includes preventative steps to prevent quality problems arising and also early detection quality control steps in recognition of the fact that quality problems of various types will always arise at different stages. - 2 According to the invention, there is provided a printing process comprising the steps of :burning-in images from films on to blank printing plates and subsequently processing the printing plates by fixing, washing and coating the plates; carrying out a visual inspection of the processed plate by use of a display stand and sliding viewing window? cataloguing and archiving the film for later use and reference and mounting the plates for a particular printing publication on the printing drums of an offset web printing machine? running web from a reel on a reel mount unit through a centring unit comprising a plurality of rollers, web edge detection means, and a roller adjustment controller and maintaining the web in a central position on the drums by automatic adjustment in response to transverse movement? printing the web with offset drums and subsequently heating the web by running the web through an oven? cooling the web by running the web through a series of drums which are water-chilled by circulation of chilled water through the drums? moistening the web by passing each surface in contact with a roller partially mounted in a reservoir of a silicon, water and anti-static agent mixture? cutting the web in a longitudinal direction to form ribbons and subsequently collating the ribbons one on top of the other according to the number of pages in a section for the publication; forming a weakening line in the ribbons and subsequently transversely cutting and folding the ribbons to form sections; stacking the sections by pressing a pre-set quantity together and tightly wrapping the sections between stiff end-boards for protection; applying an identifier to the bundle for subsequent processing; monitoring paper wastage data and inputting said data to a process controller interface; carrying out a quality control inspection of selected sections by comparing said sections with a publication objective prior to and after the stage of stacking the sections into a bundle; mounting the section bundles in relevant hoppers of a gathering machine after storage of the pattern of the front page of each section in a electronic memory of the machine; optically sensing the pattern of the first page of each section in-line before dispensing of the section onto a conveyor of the gathering machine; gathering the relevant sections for a publication together and applying glue to the non-open edges of the sections to form a bound publication; selecting a publication from the gathering machine at regular intervals and gathering out a full quality control inspection; wrapping bundles of publications together and carrying out a full edge check of every bundle; and mounting the bundles on pallets and subsequently selecting groups of bundles for a full quality control inspection and recording the results of said inspection.

Preferably, prior to mounting of a reel on the reel mounting unit a production document is generated by automatic retrieval of parameter values associated with the production including paper quantities, paper quality, allowable wastage tolerances and also by automatic retrieval of quality control data associated with a quality control code for the publication.

In one embodiment, the production controller automatically retrieves wastage data to indicate the maximum tolerance for wastage for a particular production run.

Preferably, ribbons are transferred to a collation station by passage over rollers having air nozzles to form an air cushion to prevent contact of the ribbons with the rollers.

In another embodiment, a centre line of a ribbon is weakened by either application of a jet of water along the line, or alternatively by perforation of the line using a toothed wheel, the selection being dependant on the nature of the paper.

In a further embodiment, an identifier which is applied to a bundle of sections includes a code indicating the section order within the publication, a code indicating the bundle number, and a code indicating the particular publication.

Ideally, there is automatic thickness detection of a section after dispensing onto the conveyor, from the hopper, said thickness verification being carried out by use of optical sensors.

In another embodiment, subsequent to glue application the bound sections are automatically weighed by an in-line weighing machine connected to a data process comprising means for processing the weigh data signal transmitted to it with reference to density data for the paper, said processor monitoring weight against time and detecting a peak value.

In a further embodiment, there is an edge check of all bundles after binding at the gathering machine.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which :Figs. 1(a) to 1(c) show the sequence of steps involved in a printing process of the invention; Fig. 2 shows the manner in which a processed plate is inspected before mounting on a printing press; Fig. 3 is a diagrammatic view showing a centring arrangement for a web reel unit; Fig. 4 is a detailed view of a printing plate having markings to help reduce ink build-up; Fig. 5 is a diagrammatic view showing a web cooling arrangement; Fig. 6(a) is a perspective view showing a web moistening arrangement and Fig. 6(b) is a diagrammatic side view; Figs. 7(a) and 7(b) are diagrammatic perspective views showing the manner in which longitudinal weakening lines are made in a ribbon and Fig. 7(c) shows a section after folding; Fig. 3 is a diagrammatic view showing the manner in which a bundle of similar sections is formed for later processing; and Fig. 9 is a plan view showing the manner in which there is automatic verification of sections before gathering.

Referring to the drawings, and initially to Fig. 1, there is shown a printing process of the invention, indicated generally by the reference numeral 1. In step 2, blank plates and film are received. For a particular publication, there will be one film for each section of the publication and there may indeed be more if there are colours to be printed. As the film is received, it is verified by visual inspection against a previouslyverified copy of the publication, referred to as an objective. In step 3, the image is burnt-in by prolonged exposure to ultra-violet light in a pattern according to the relevant film. The burnt-in plate is then processed with an alcohol-based solvent to fix, wash and coat the plate so that it cannot be easily damaged at a later stage. After processing, the plate is mounted at a visual inspection station shown in Fig. 2 and indicated generally by the numeral 40. The inspection station 40 comprises a generally vertically-mounted planar support 41 having registry pins 42 to which the processed plate 43 may be mounted. A viewing template 44 is slidably mounted on the support 41 has a window 45 having a magnification glass to allow detailed visual inspection of the burnt-in image on the printing plate. This is an important aspect of the process as it helps to ensure that defects in the printing plate are detected at an early stage. In step 6, the film is catalogued and is archived, film for inner pages of a publication being archived separately from film for the covers.

Before a printing run, a computerised controller receives production parameters for the publication into an input interface having a visual template for the production operator. This allows easy inputting of such parameters as paper type, paper density, allowable wastage figures, and paper size. The computerised controller then automatically determines the amount of paper required and the number of publications which must be published to ensure that there are sufficient to supply an order with an allowance for defects. This data is used for automatic generation of a financial quote for a particular printing job and is used again in generation of a production sheet if the order is received. In generation of the production sheet, a previously-used code associated with that publication is used. This code is used by the production controller to automatically retrieve quality control historical data relating to that product. This data is printed on the production sheet and provides an early warning system as to the type of problems peculiar to that particular type of product. As each print run is completed, there is feedback at various operator interfaces of quality problems and this is automatically stored by the controller in a record linked to the product identifier. This ensures that the data is automatically retrieved for the next print run. There is versatility in operation of the production controller in this manner as the identifier code may be associated with a range of publications of a similar type instead of a specific publication. The production controller automatically monitors the production process by processing job data entered by operators, this data being identified by the production code. This step is indicated generally by the numeral 7.

In step 8, the relevant reel is mounted in the reel unit of the web offset press and in step 9, the web is run through a centring unit 50 shown in Fig. 3. The centring unit 50 has a pair of rollers 51 and 52 between which the web 54 is run. There is a set of edge directed photocells 53 to detect transverse movement of the web. A controller, not shown, operates an hydraulic circuit for rotation about a vertical axis of a support 54 for the rollers 51 and 52 to counteract any transverse movement of the web 53 and automatically centre the web at this stage. A fixed support 55 incorporates a scale 56 for a sliding support 57 of the photocell 53.

In step 11, the web is run through the offset printing press in conventional manner. However, an important aspect of the printing plate which is mounted in the press is that where there is relatively little print on a page, there is a series of colour bars 61 shown on a plate 60 in plate 4» These colour bars are generally elliptical in shape being spaced by approximately half of the longitudinal dimension of the bar. It has been found that this pattern is particularly effective at ensuring that enough ink is drawn from the various offset printing drums to prevent ink build-up. Of course, this pattern is incorporated at the stage of development of the film which is used for burning-in. the plate in the first instance.

In step 12, the web is run through a gas-driven oven for immediate heating after the printing to ensure satisfactory adherence of the print to the paper. This is an important step as it ensures good adherence which is particularly important for offset printing in which print is simply adhered to the surface of paper rather than being impacted into the body of the paper. The oven temperature is in the range 200°C to 220°C and heating is by convection. It has been found that this heating temperature and method provides especially good print adherence while at the same time minimising paper moisture reduction.

In step 13, the web is immediately cooled as shown in Fig. 5 by a cooling arrangement 70. This comprises a series of four water-chilled drums 71, 72, 73 and 74 between which the webs 74 passes. There is a continuous supply of chilled water temperature in the range 9°C or 11°C into the ends of the drums. It has been found that this arrangement cools the web at a correct pace. By having four drums in this arrangement there is a sufficiently large contact surface area.

A side-effect of heating the web is that the moisture content is reduced, usually from something of the order of 7% to 3.5%. This of course affects the density of the paper and its texture and appearance and indeed may damage the paper in the long term. Accordingly, the web is moistened at the next stage and this is achieved by use of a pair of moisture applicators 80 in sequence for opposite sides of the web. Only one applicator 80 is shown. The applicator 80 comprises a sump 81 to which a supply of water at approximately 80% and silicon at approximately 20% is pumped. A very small quantity, in the order of 1% by volume, of anti-static agent is added. The applicator 80 has a drum 82 around which there is a movable cover 83 which may be moved into place to prevent application of moisture to the web on that particular side for some printing runs.

The web is cut in the longitudinal direction to form ribbons which then pass through a series of rollers some of which are diagonally-directed to change the direction of travel as indicated by steps 15 and IS . These rollers have air applied at a pressure of 7 bar which is expelled through apertures in the drums to form an air cushion to prevent contact of the ribbon with the transfer roller, and thus helping to keep the ribbon clean. In step 17, a series of rollers is used for collation of the ribbons, one above the other. The set of collated ribbons then has a centre line weakening formed therein to allow easy folding of a number of superimposed ribbons to form a section when they have been cut in the transverse direction. As shown in Fig. 7(a), this line may be formed in a ribbon 90 as a series of perforations 91 cut by a cutting wheel 92. Alternatively, as shown in Fig. 7(b), there may be a water line 96 formed in a ribbon 95 by a syringe 97 to which there is a continuous supply of water. A folded section 96 having perforations 91 is shown in Fig. 7(c).

After transverse cutting, the sections are automatically folded and stacked in step 20 in a three-sided format. A pneumatic ram drives a pre-set quantity of sections 9S into a tight bundle and applies a pair of end boards 97 of stiff material such as plywood, having a similar surface area and configuration to the sections. In step 21, the sections and the end-boards are automatically wrapped by a tape 98 to form a tight bundle. Identification of each bundle is important and this is carried out in step 22, the identifier including a section code to indicate the section of the book, a bundle identifier which is simply a sequential code, and a publication identifier to indicate the publication. It has been found that by stamping such an identifier on each bundle, it is very easy to handle the sections, there is quick identification and further by use of the end-boards in this manner sections are highly unlikely to be damaged. As this identifier is being applied, there is a cross-check with the relevant objective. This helps to ensure that the identifier is not incorrectly applied. At this stage there is monitoring of the wastage from each of the different stations in the printing process and wastage data is inputted to an interface of the production controller for monitoring. The production job code is used by the production controller to automatically generate quality control data and if there is wastage above a pre-set level, this may be flagged to the quality record which is automatically retrieved the next time a production document is to be generated for that publication.

Before gathering of the sections, there is electronic storage of the front page pattern of each section by an interface connected to a gathering machine to be used. The gathering machine includes a series of hoppers 110 mounted alongside a conveyor 1X3. The hopper 110 includes a pair of sideguide members 111 and at the base of the hopper 110 there is a pair of photographic sensors 112 in which there is a large number of sub-sensors for pattern recognition. The sensors 112 are operated in-line to repeatedly monitor the pattern of a large portion of the first page of each section in turn before it is delivered on to the conveyor 113. This helps to show that not only is the correct section being loaded at that particular stage, but it also ensures that the quality of the print on at least that portion which is viewed is correct. Thus, two major quality checks are carried out at the same time. To help ensure that the remainder of each section is correct, there is an automatic thickness check in step 28 using optical sensors. As indicated by the decision step 29, each section may have the folded, side cut by a guillotine as indicated by the step 30 and following this is glue application in step 31 to produce a bound publication.

Another important quality verification step is step 32 where there is in-line weighing, the weight signals being automatically transmitted to a controller which has been pre-programmed with the density of the particular paper, taking into account the moisture content and other parameters. In-line weighing is achieved by use of load cells mounted on a glue station output conveyor. A controller automatically monitors the conveyor speed and plots weight with time. The peak indicates the book weight and there is automatic ejection if this is outside a tolerance range. This ensures that all pages and all sections are included in the publication after gluing. A. quality operator in step 33 takes at least one publication in every thirty and carries out a complete visual check at this stage before wrapping in step 34. Each wrapped bundle is then checked at the edges to ensure conformity and in step 3S, bundles are mounted on pallets from which a set quantity of bundles is retrieved for a 100% check in a laboratory.

It will be appreciated that the various steps which are taken from the very beginning of the process to the end to ensure that very few quality problems do not arise. It will also be appreciated that the various checks and the nature of these checks help to ensure an early warning system where problems do arise. These features are thus very important commercially.

The invention is not limited to the embodiments hereinbefore described, but may foe varied in construction and detail.

Claims (5)

1. CLAIMS 1, A printing process comprising the steps of :burning-in images from films on to blank printing plates and subsequently processing the printing plates by fixing, washing and coating the plates; carrying out a visual inspection of the processed plate by use of a display stand and sliding viewing window; cataloguing and archiving the film for later use and reference and mounting the plates for a particular printing publication on the printing drums of an offset web printing machine; running web from a reel on a reel mount unit through a centring unit comprising a plurality of rollers, web edge detection means, and a roller adjustment controller and maintaining the web in a central position on the drums by automatic adjustment in response to transverse movement; printing the web with offset drums and subsequently heating the web by running the web through an oven; cooling the web by running the web through a series of drums which are water-chilled by circulation of chilled water through the drums; moistening the web by passing each surface in contact with a roller partially mounted in a reservoir of a silicon, water and anti-static agent mixture; cutting the web in a longitudinal direction to form ribbons and subsequently collating the ribbons one on top of the other according to the number of pages in a section for the publication; 5 forming a weakening line in the ribbons and subsequently transversely cutting and folding the ribbons to form sections; stacking the sections by pressing a pre-set quantity together and tightly wrapping the 10 sections between stiff end-boards for protection; applying an identifier to the bundle for subsequent processing; monitoring paper wastage data and inputting said data to a process controller interface; 15 carrying out a quality control inspection of selected sections by comparing said sections with a publication objective prior to and after the stage of stacking the sections into a bundle; mounting the section bundles in relevant hoppers 20 of a gathering machine after storage of the pattern of the front page of each section in an electronic memory of the machine; optically sensing the pattern of the first page of each section in-line before dispensing of the 25 section onto a conveyor of the gathering machine; - 16 gathering the relevant sections for a publication together and applying glue to the non-open edges of the sections to form a bound puhlicator; selecting a publication from the gathering machine at regular intervals and gathering out a full quality control inspection; wrapping bundles of publications together and carryring out a full edge check of every bundle; and mounting the bundles on pallets and subsequently selecting groups of bundles for a full quality control inspection and recording the results of said inspection.
2. A process as claimed in claim 1, wherein prior to mounting of a reel on the reel mounting unit a production document is generated by automatic retrieval of parameter values associated with the production including paper quantities, paper quality, allowable wastage tolerances and also by automatic retrieval of quality control data associated with a quality control code for the publication and preferably the production controller automatically retrieves wastage data to indicate the maximum tolerance for wastage for a particular production run, and preferably ribbons are transferred to a collation station by passage over rollers having air nozzles to form an air cushion to prevent contact of the ribbons with the rollers.
3. A process as claimed in any preceding claim, wherein a centre line of a ribbon is weakened by either application of a jet of water along the line, or alternatively by perforation of the line using a toothed wheel, the selection being dependant on the nature of the paper, and 5 preferably the identifier which is applied to a bundle of sections includes a code indicating the section order within the publication, a code indicating the bundle number, and a code indicating the particular publication, and 10 preferably there is automatic thickness detection of a section after dispensing onto the conveyor from the hopper, said thickness verification being carried out by use of optical sensors.
4. 4. A process substantially as hereinbefore described, 15 with reference to and as illustrated to in the accompanying drawings
5. 5. A publication whenever produced by a process as claimed in any preceding claim.