TEST-PRINTING METHOD AND TEST-PRINTING FORM FOR USE IN THE METHOD

Abstract: A test-printing method for a rotary press with a determinable ink coverage, whereby a test-printing form having a first and a second printing area is used, which method comprises determining the ink coverage provided by the rotary press, designing the test-printing form layout to the effect that the ink requirement does not, for any part of the combined first and second printing areas, essentially exceed a predetermined value V, said value V being set in a predetermined relation to the determined ink coverage; and the ink requirement of said second printing area amounts to a value essentially representing the difference between said value V and the ink requirement of said first printing area. A rotary press test-printing form having a layout designed for use in the test-printing method.

Description: Test-printing method and test-printing form for use in the method The present invention relates to a test-printing method for a rotary press that provides a determinable ink coverage, whereby a test-printing form is used to transfer ink onto a substrate, said test-printing form having a layout with a first and a second printing area, and the printing areas are positioned so as to transfer ink onto said substrate consecutively in the rotary press printing direction. The general purpose of most test-printing methods is to check that all parts of the object to be printed are positioned correctly, and to assure that test patches and evaluation areas, such as pictures and images, can be reproduced later on with essentially the same printing result (or provide a predetermined result or response to a specified adjustment of any printing conditions). One problem burdening conventional test-printing methods for rotary presses is that they tend to require a multitude of test-prints or test-printing rotations in order to obtain a result of acceptable stability. This, of course, is very costly, with regard to time as well as other resources. Multi-colour printing processes are particularly burdened with this problem. It would thus be desirable to be able to provide a test-printing method that is not burdened by this problem. Specifically, it would be desirable to be able to provide a test-printing method for rotary presses that produces an acceptably stable result within the run of a comparatively low number of test-printing rotations. A solution to the above problem is provided by the present invention as defined by appended claim 1. More specifically, the present invention relates to a test-printing method of the kind initially described, which method comprises - determining the ink coverage capacity provided by the rotary press and/or printing area coverage to be run on the press; - designing the test-printing form layout to the effect that • the ink requirement does not, for any part of the combined first and second printing areas, essentially exceed a predetermined value V, said value V being set in a predetermined relation to the determined ink coverage; and • the ink requirement of said second printing area amounts to a value essentially representing the difference between said value V and the ink requirement of said first printing area. Rotary presses are generally not designed to provide a fulltone or total ink coverage, i.e. to transfer the full ink amount required to provide the entire printing area with an even ink coating. Although the reasons behind this fact may not be fully known, it is assumed that important factors may be of historic and economic character. The historic component would be that during printing equipment development an ink coverage of 20-30% was found to provide, in most instances, for an acceptable ink transfer, e.g. legible text for newspaper purpose. The economic component would be that higher ink coverages require more extensive ink application systems, involving, for instance, more and/or bigger ink application rolls; this is particularly the case in multicolour printing, specifically image reproductions. The circumstance that rotary presses are generally not designed to provide a fulltone or total ink coverage has, as far as hitherto known, in fact not been taken into account in prior art test-printing methods. Thus, the actually provided ink coverage has been an ignored or forgotten factor, or has, at least subconsciously, been assumed to amount to fulltone ink coverage. Consequently, the probability (or risk) of experiencing instabilities when using prior art test-printing methods is thus rather high, and anyhow not fully controlled. When a test-printing method is not, in contrast to the present invention, adapted to the actual ink coverage provided by the rotary press, the ink transfer during, and over, the printing rotations will fluctuate, producing a number of test prints of varying quality. Conventionally, this is eventually rectified by manually adjusting the ink feed regulators of the rotary press. However, this adjustment does of course take time, and consumes a lot of ink and printing substrate before reaching acceptable levels of process stability. In addition to this, different ink thicknesses are prevailing in the inking system, which can effect ink flow and ink properties, and thus result in a less reproducible system to model, or to reproduce test prints with different printing machines. It should be noted that the present invention is not restricted to be applied only on rotary presses providing less than fulltone ink coverage; a person skilled in the art would ap- preciate that the present invention should be effective also in the case of rotary presses providing fulltone ink coverage. One important teaching of the present invention is that the test- printing method should, in contrast to prior art methods, be elaborated based on the actual ink coverage that can be provided by the rotary press. The specific ink coverage providable by the rotary press to be used in the method can be determined in a number of ways. It should be noted that in the present context, the term "determine the ink coverage" comprises all means of obtaining this information, regardless of information source. The ink coverage providable by the rotary press may be known by the manufacturer or supplier, particularly if indeed it was consciously designed to provide less than total or fulltone coverage, and thus be possible to communicate to the op- j erator or end-user performing the test-printing. If this information for some reason would not be available, a person skilled in the art would be able to determine said specific ink coverage by examining the rotary press, e.g. with regard to certain physical dimensions, such as the roll diameters, and the ink(s) to be used in the method, e.g. with regard to ink formulation and rheological properties. Once the specific ink coverage has been established, the test-print form layout is to be designed based on this information. Within the scope of the present invention, this can be done in a number of ways, depending, among other things, on the purpose of the test- printing. According to a first embodiment of the present method, aiming at quickly providing stable test-printing conditions, the layout of the test-printing form is designed to have a first area, below referred to as the "analysis area", which is provided to be used iorper se known methods for analysing or evaluating test prints. Said analysis area is designed so that, with regard to each individual spot or process colour ink, no part of said analysis area has an ink requirement exceeding said rotary press specific ink coverage. This can be done, for instance, by measuring the object, i.e. all of the images, pictures, and patches that are to make up the analysis area, e.g. by means of a densitometer, in order to establish if any part thereof, with regard to any of the spot or process colours to be used, would require more ink than can be supplied, under stable conditions, by the rotary press in view of the specific ink coverage it can provide. If so, the object is adjusted in order to decrease the ink requirement of that part, with a corresponding decrement of the ink requirement also being made of all the other parts of the object. This can be done, for instance, by shrinking the dimensions, and thus the surface area, of the object, decreasing the ink film thickness, decreasing the colorant content of the ink, or a combination thereof, and simultaneously making the corresponding adjustment of the other spot or process colours, if any. Once the analysis area has been adjusted accordingly, the test-print form layout should be provided with a second area, below referred to as the "compensation area", the purpose of which is primarily to receive an ink amount, for each individual spot or process colour ink, corresponding to the difference between the ink amount supplied by the rotary press, when printing at its specific ink coverage level under stable condi- tions, and the ink amount used by the analysis area. Thus, for each individual spot or process colour, the compensation area could be regarded as an "inverse" or "negative" in relation to the analysis area. Accordingly, in this embodiment of the invention, the value V essentially equals the rotary press specific ink coverage. The result is that the rotary press, essentially from the outset of the test-printing session, is adjusted to supply, for each rotation of the test- printing, all of the spot or process colour inks at a stable or rapidly controllable rate along and across the printing direction of the web or sheets to be printed. By means of the present method, systematic errors in the test results due to different specific ink coverage provided by different rotary presses can be essentially eliminated. As long as the above conditions apply, any other printing parameter may be varied in order to provide the desired printing result. According to another embodiment of the present method, the test-printing form layout is designed according to the above first embodiment, except that the analysis area is designed to have an ink requirement deviating, in a controlled way, from the rotary press specific ink coverage, and/or the compensation area is designed to receive an ink amount, for each individual spot or process colour ink, that deviates, in a controlled way, from the difference between the ink amount supplied by the rotary press, when printing at its specific ink coverage level under stable conditions, and the ink amount used by the analysis area. Accordingly, in this embodiment of the invention, the value V essentially deviates from the rotary press specific ink coverage. This embodiment may be useful for studying various proper- ties of the rotary press as such and/or any used spot or process colour ink, or printing substrate. In a specific embodiment, the value V essentially exceeds the rotary press specific ink coverage. Although the analysis area and the compensation area are arranged to transfer ink onto the substrate consecutively in the rotary press printing direction, the order of said areas is of less importance. Thus, the compensation area may be positioned to transfer ink prior to the analysis area during a rotation, just as well as the opposite order. Said areas may also be individually divided, so that, for instance, a first semi-part of the analysis area is printed first, then a first semi-part of the compensation area, then the second semi -part the analysis area, and so on. The present invention is applicable to any kind of rotary press printing, such as for instance various forms of offset printing, flexographic printing, intaglio printing, digital printing, electrocoagulation printing, and rotogravure printing. In a preferred embodiment, offset printing is used. Although the present invention is applicable to monochrome printing, it is par- ticularly useful when applied to multi-colour printing, such as for instance when using any of the common CMYK (Cyan, Magenta, Yellow, blacK), PMS (Pantone Matching System), HSB (Hue, Saturation, Brightness), RGB (Red, Green, Blue), or CIE LAB models. There is no need for any specific printing order of the inks on the substrate, any order may be chosen. The inventive method may be applied when printing on sheets, continuous webs, as well as on any other suitable forms of substrate. One or more sides of the substrate can be printed, either separately or simultaneously. Any suitable printing substrate may be used in the present method, such as pa- per, board, paperboard, plastic, textile, but in a preferred embodiment, the printing substrate is paper. The present invention may comprise one or more tests for various printing characteristics, such as for instance tests relating to printing substrate properties such as strength, delamination, propensity, etc., and/or mottling, ghosting, gloss, registration, colour gamut, visual response etc. Certain tests that can be applied within the scope of the present invention are disclosed in US-A-4,852,485, US-A-5,010,820, and US-A-5, 122,977. The ink requirements can be determined by any suitable method, such as for instance the method disclosed in US-A-5, 825,986. The present invention also relates to a rotary press test-printing form that can be used in the inventive test-printing method, said test-printing form having a layout consisting of a first and a second printing area in the same rotational coverage capacity V of the printing press and/or printing area coverage to be run on the press, said printing areas being positioned so as to transfer ink onto a substrate consecutively in the rotary press printing direction, which test-printing form layout is designed to the effect that • the ink requirement does not, for any part of the combined first and second printing areas, essentially exceed a predetermined value V; and • the ink requirement of said second printing area amounts to a value essentially representing the difference between said value V and the ink requirement of said first printing area. Said areas may be individually divided in two or more parts, so that, for instance, a first semi-part of the first area is arranged to be printed first, then a first semi-part of the second area, then the second semi-part the first area, and so on. The present test-printing form may be designed for any kind of rotary press printing, such as for instance various forms of offset printing, flexographic printing, intaglio printing, digital printing, electrocoagulation printing, and rotogravure printing. In a preferred embodiment, the test-printing form is designed for offset printing. Below, for the purpose of illustration only, a specific embodiment of the present invention is disclosed with reference to the appended drawings, in which Fig. 1 is a schematic side view of an offset printing press, in which a test-printing form according to the present invention is used; Fig. 2 shows the offset printing press from above; and Fig. 3 shows the layout of one embodiment of the test-printing form according to the present invention. In Fig. 1, ink is fed from the ink feeding and regulation system 1 onto the test-printing form 2, which is attached to a printing form cylinder 3. Said system 1 comprises a number of ink supply rolls for applying the ink onto the test-printing form 2, and a number of ink feeding regulators (not shown) positioned at even distances along the axis of the cylinders. Water is also supplied by system 1 onto the test-printing form 2, according to conventional offset printing technology. Ink from system 1 adheres to hydrophobic areas of test-printing form 2, whereas not to the wet hydrophilic areas. As the printing form cylinder 3 rotates, the surface of test-printing form 2 is brought into contact with rubber blanket cylinder 4, whereby the ink adhered to test-printing form 2, or at least a substantial part thereof, is transferred onto its rubber surface. Finally, ink is transferred from rubber blanket cylinder 4 onto the substrate, in this case a continuous paper web 5 passing through the nip between rubber blanket cylinder 4 and an impression cylinder 6 in the direction indicated by the arrows. As seen in Fig. 2, the layout of test-printing form 2 comprises a first area 7 and a second area 8. Area 7 is the analysis area, and area 8 is the compensation area, in accordance with the present invention. Thus, during one rotation of rubber blanket cylinder 4, a length of the continuous paper web 5 corresponding to the distance between one dotted line and the next dotted line is passed through the nip between rubber blanket cylinder 4 and impression cylinder 6, producing one analysis image area 9 and one compensation image area 10, corresponding to analysis area 7 and compensation area 8, respectively, on the layout of test-print- ing form 2. The sample layout in Fig. 3 is designed for waterless offset. It is an A3 format lay-out adapted for an A2 sized printing press, which uses two of the A3:s side by side. The test palette of interest, in this case a colour gamut and ICC/CMS profiling image, is placed in the upper part of the A3 sheet, while the lower part of the lay-out is used for compensation pur- poses to enable the use of so-called linear inking control knifes in the press, i.e. all of the ink feeding regulators being set to one and the same value. Test-image areas are also inserted into the compensation area, i.e. the lower half of the lay-out (big white squares with black spots). Compensating negatives of those images (big black squares with white spots), trapping and process colour spots (light grey), dot gain spots (white) and compensation areas (dark grey) are also displayed in the lower part of the lay-out. The test printing form was designed for 40% ink coverage for each process ink (CMYK sequence) in four colour sheet-fed offset printing (for a half A2 sized printing area), where it can be run with optimally linear inking knifes. It should be understood that the disclosed embodiment should not be regarded as limiting the scope of the present invention; the same applies to all other embodiments disclosed or suggested in the present application.

Claims: Claims 1. A test-printing method for a rotary press providing a determinable ink coverage, whereby a test-printing form is used to transfer an ink onto a substrate, said test-printing form having a first and a second printing area, said printing areas being positioned so as to transfer ink onto said substrate consecutively in the rotary press printing direction, characterised in that the test-printing method comprises - determining the ink coverage capacity provided by the rotary press and/or printing area coverage to be run on the press; - designing the test-printing form layout to the effect that • the ink requirement does not, for any part of the combined first and second printing areas, essentially exceed a predetermined value V, said value V being set in a predetermined relation to the determined ink coverage; and • the ink requirement of said second printing area amounts to a value essentially repre- senting the difference between said value V and the ink requirement of said first printing area. 2. A test-printing method according to claim 1, characterised in that said value V essentially equals the determined ink coverage provided by the rotary press. 3. A test-printing method according to claim 1, characterised in that the rotary press is an offset printing press. 4. A test-printing method according to claim 1, characterised in that the test- printing method is a multi-colour printing method. 5. A test-printing method according to claim 4, characterised in that the multicolour printing method is based on the CMYK model. 6. A test-printing method according to claim 1, characterised in that the substrate is paper or paper board. 7. A test-printing method according to claim 1, characterised in that the test- printing method comprises at least one test relating to materials consumed during printing. 8. Rotary press test-printing form having a layout designed for use in the test-printing method according to any preceding claim, said layout consisting of a first and a second printing area in the same rotational coverage capacity V of the printing press and/or printing area coverage to be run on the press, said printing areas being positioned so as to transfer ink onto a substrate consecutively in the rotary press printing direction, characterised in that the test-printing form is designed to the effect that • the ink requirement does not, for any part of the combined first and second printing areas, essentially exceed a predetermined value V; and • the ink requirement of said second printing area amounts to a value essentially repre- senting the difference between said value V and the ink requirement of said first printing area. 9. Rotary press test-printing form according to claim 8, characterised in that the first and/or the second area is/are divided in two or more separate parts. 10. Rotary press test-printing form according to claim 8, characterised in that the test-printing form is designed for offset printing.

Inventors: NORDSTROEM JAN-ERIK P, NORDSTROEM, JAN-ERIK, P.
Applicants: NORDSTROEM JAN ERIK P, SVENSKA TRAEFORSKNINGSINST, NORDSTROEM, JAN-ERIK, P., STFI
Application year: 2000
Main classification: B41F3
IPC codes: B41F7