Printing – Processes – Condition responsive
Reexamination Certificate
1999-06-04
2001-07-10
Hilten, John (Department: 2854)
Printing
Processes
Condition responsive
C101S148000, C101SDIG029, C101S147000
Reexamination Certificate
active
06257144
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention:
The invention relates to a method of metering dampening solution when printing with a printing form for offset printing. In order to achieve a desired printing result when printing with a wet offset printing machine, it has been known to control or regulate the proportion of dampening solution in an emulsion of printing ink and dampening solution to be applied to a printing form. The actual portion or share of dampening solution can be determined with suitable detectors which are directed towards the surface of the printing form. The portion can be determined indirectly by evaluating signals from an image recording device or a densitometer, which are directed toward locations on the printing material which are free of a printed image, the extent of scumming or smearing that occurs being a participant therein. The composition of the emulsion must be set to an optimum value before printing is begun and during the production of first prints, otherwise prints which are not of suitable quality will be produced. The composition of the emulsion is disrupted if printing is interrupted. In order to obtain the desired composition of the emulsion as quickly as possible, it has become known to continue to dampen the printing form or plate for a predefined number of revolutions of the form or plate cylinder after printing has been interrupted. Furthermore, it has become known to set the supply of dampening solution operating again for a predefined number of revolutions of the plate cylinder before printing is continued. Post-dampening after an interruption may last for thirty-two revolutions, for example, whereas predampening before continuing to print may be performed for six revolutions of the plate cylinder. Premoistening may take place initially with a maximum supply rate and be continued with a supply rate that is suitable for continuous printing. In the case of rotary printing machines, premoistening and after or post-moistening may take place on the surface of the printing form or plate or on the surfaces of inking rollers which can be brought into contact with the surface of the printing form or plate. In conventional inking units, bridge rollers are provided, which produce a connection between rollers feeding dampening solution and printing ink (published German Patent Document DE 195 06 639 C2).
The procedure described hereinabove is implemented by control devices, which operate in accordance with a program. A printing machine operator, however, also has the possibility of changing the predampening and after or post-dampening times by manual entry, how the entered numbers of revolutions of the plate cylinder are optimally adapted or matched to the properties of the printing material, the printing image, the material of the printing form or plate, the transfer properties of a transfer cylinder and the properties of ink and dampening solution being determined by the experience of the operator. The operator cannot take into account the frequency and the duration of the interruption, because they are unable to be predicted by him or her.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of metering dampening solution when printing with a wet offset printing plate, which affords a reduction in the number of prints of nonsuitable quality.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of metering dampening solution when printing with a printing form for offset printing, including, with a control device, setting an amount of dampening solution on the surface of the printing form to a predetermined value before starting to print, which comprises, following one interruption in the printing, determining the number of interruptions which have occurred previously in a predefined time interval, and varying in accordance with the number of interruptions the amount of dampening solution supplied to the surface of the printing form during the one interruption.
In accordance with another mode, the method invention includes additionally determining the duration of the interruptions which have occurred previously in a predefined time interval, and increasing the amount of dampening solution supplied to the surface of the printing form during the one interruption, if the duration of the interruptions is increasing.
In accordance with a concomitant mode, the method invention includes applying the dampening solution to the surface of the printing form by rollers, and reducing the speed of one of the rollers timely and more rapidly during the one interruption when the number of interruptions is increasing.
By applying the method according to the invention, the restarting of a wet offset printing machine following an interruption can be optimized. The control system of the printing machine contains stores for pre-set values and parameters which have an influence upon the amount of dampening solution to be used. In offset printing machines, in which the dampening solution is applied to the surface of a printing plate by using a dampening-solution roller that can be brought into and out of contact, i.e., thrown on and thrown off, it is possible to enter the number of revolutions of a plate cylinder during which the dampening-solution roller is to be brought into contact with the printing plate, for the purpose of predampening before restarting the printing, the number of revolutions during which the dampening-solution roller is to remain in contact with the surface of the printing plate for the purpose of after or post-dampening, the speed of the dampening-solution roller during post-dampening, and the number of revolutions of the plate cylinder during which the dampening-solution roller is to apply a maximum amount of dampening solution to the surface of the printing plate when predampening. In the case of multicolor printing, the initial variables of the printing units, entered before printing, may be different, and this may depend, for example, upon the properties of the respective printing ink. The printing inks may have different viscosities and may exhibit a different tendency when mixing with the dampening solution. In addition, it is possible for a special dampening solution to be used in one of the printing units because of the printing ink used therein, and the properties of the dampening solution, for example the different pH thereof, can likewise be taken into account. In order to facilitate the operation of the printing machine, the entered values may be stored in the form of parameter sets, which are called up for use by the operator of the printing machine before printing. In the event of parameter sets being provided, the properties of the printing material, in particular the thickness and the absorption behavior and the area coverage in the printing image, can be taken into account.
The time duration of printing interruptions and production or continuous printing phases, and the number of printing interruptions, are recorded in a further storage or memory. According to the method invention, the values for the number of revolutions of the plate cylinder and the supply rate of the dampening solution during printing interruptions are varied continuously as a function of the number and the duration of the interruptions and, respectively, the duration of production printing phases. In wet offset printing machines, wherein zonal metering of the dampening solution transversely to the transport direction of the printing material is possible, the supply rate can be adapted or set in accordance with the average area coverages of the zones, it being possible to take into account the influence of the metering in one zone on adjacent zones.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method of metering dampening solution when printing with a printing form or plate for offset printing, it is nevertheless not intended to be
Erhardt Stephan
Haaf Franz
Pfeiffer Nikolaus
Greenberg Laurence A.
Grohusky Leslie J.
Heidelberger Druckmaschinen Aktiengesellschaft
Hilten John
Lerner Herbert L.
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