EP1457324B1 - Method and means for printing a web - Google Patents

Description

The invention relates to a method and a device for printing web-like material according to the preamble of claim 1 or that of claim 18.

For printing web material rotary printing machines are used, which can generally be divided into two groups. In one group, the diameter of the cylinder transferring the print image to the web, hereinafter referred to as "transfer cylinder", is adjusted to the length of the print image such that the outer printing circumference of the cylinder is one image length or more of such image length plus optionally corresponds to a repeat distance. This transfer cylinder is assigned a impression cylinder, around which the web to be printed is guided. Transfer cylinders and impression cylinders run continuously at a constant speed, so that such printing machines have a very high throughput. The disadvantage, however, is that when changing from one print image to another, at least the transfer cylinder must be replaced if the following print image has a different length, because then a transfer cylinder with a different diameter is needed. This has a correspondingly high cost result, especially since the conversion of the machine also takes a certain amount of time. For this reason, such Printing machines suitable only for the production of large quantities of the same print image. However, this condition is not always given.

In the case of the second group of printing machines for printing web-like material, by contrast, the transfer cylinder is designed so that its printing-technically effective peripheral surface can be adapted to different print image lengths without much effort. This can be achieved, for example, in offset printing in that the lateral surface of the transfer cylinder is formed by a rubber blanket, which can be exchanged without difficulty and / or easily adapted to the respective print image length. However, the transfer cylinders of this group are generally designed so that their lateral surface extends over less than 360 °, so that special precautions must be taken to apply the printed images without spacing or only with a small repeat distance on the web. To do this, the web must be positioned after each work cycle for the following work cycle, so as to enable printing with small distances between the individual print images.

So revealed the EP 0018291 an embodiment in which the printing unit has a drive roller which operates independently of the actual printing unit. The same applies to the printing press according to EP 0159225 B1 Although the transfer cylinder is formed fully cylindrical, but also for the positioning of the web requires an additional drive means.

A method and a device according to the preamble of claims 1 and 18 are known from US-A-4 066 016 known.

The invention has for its object to design methods and apparatus of the type described above so that on the one hand in the transition from one print image to another in a short time can be switched to a new image format, with an accurate guidance and positioning of the web to achieve a high Quality of the print images may be possible should. The throughput should at least meet today's usual requirements.

This object is achieved by applying the teaching of claim 1 or of claim 18.

The invention, which belongs to the second group of the types of printing machines explained in the introduction, can be summarized in that the web is driven in the printing station by the printing cylinder and positioned thereat after each printing operation for the following working cycle, the length of the in the range The web portion of the respective printing station is changed in response to the transport speed and direction to compensate for the difference between the preferably uniform speed at which the web enters the printing station and the transport speed and direction respectively transmitted from the printing cylinder to the web. For this purpose, a reciprocating compensation device is provided whose movements are coordinated with the speed and direction of rotation of the printing cylinder.

Since the web wraps around the pressure cylinder driving it, in addition to a precise transfer of the rotation of the printing cylinder on the web a defined and rapid separation of the web from the transfer cylinder is effected after the web had come into contact with this for the purpose of transmitting the printed image. This also promotes the quality of the printed image on the web.

When using a blanket cylinder for the transfer of the printed image on the web, to facilitate setting to a different length of the printed image, the blanket in the circumferential direction of the transfer cylinder may be provided with a portion of lesser thickness, which out of contact with the The web remains, with the pressure technically effective circumferential length of the blanket, which comes into contact with the web, is adjusted depending on the length of the printed image. This can be done continuously. However, the blanket can also be fixed on the lateral surface of the transfer cylinder by means of gluing, wherein its length in the circumferential direction corresponds to the length of the printed image or a multiple thereof. When using a suitable adhesive, it is possible to remove the blanket when changing the format and stick a new blanket on the cylinder.

Since today usually printing inks are used, which cure under the action of UV rays, it is expedient to assign the UV lamp to the printing cylinder such that the printed image is exposed to the effect of UV rays as early as possible after its formation on the web, so the color hardens as quickly as possible and the web, after it has expired from the printing cylinder, can be deflected as soon as possible, so as to keep the construction of the printing station compact.

It may be expedient to cool the web after it has passed the UV lamp. This can be done in a simple manner already during the passage of the printing cylinder, which may be designed for this purpose as a cooling roller. In any case, if possible, the procedure should be such that the web does not undergo any heating due to the UV irradiation, which could lead to unacceptable stretching or shrinkage of the web. This is particularly important if the web is made of plastic and / or several printing stations are arranged one behind the other, through which the web, as usual in multi-color printing, is passed.

Fig. 1

im Schema die Seitenansicht einer Druckmaschine mit mehreren Druckstationen,

Fig. 2

im Schema die Seitenansicht einer Druckstation in größerem Maßstab,

Fig. 3A-C

jeweils einen stark vereinfachten Ausschnitt aus Fig. 2 in noch größerem Maßstab in drei während eines Arbeitszyklus aufeinanderfolgenden Positionen der zusammenwirkenden Teile,

Fig. 4

die Seitenansicht eines Transferzylinders, teilweise im Schnitt.

In the drawing, two presently preferred embodiments of the invention are shown. Show it

Fig. 1

in the diagram the side view of a printing machine with several printing stations,

Fig. 2

in the diagram the side view of a printing station on a larger scale,

Fig. 3A-C

each a much simplified section Fig. 2 on an even larger scale in three consecutive positions of the interacting parts during one cycle of operation,

Fig. 4

the side view of a transfer cylinder, partly in section.

In the Fig. 1 illustrated printing machine (10) is used for printing web-like material (12), which withdrawn from a first roller (14) and in the direction indicated by the arrow (16) general transport direction by four in this transport direction (16) successively arranged printing stations I - IV is guided, which have substantially the same structure. After printing, the web (12) is wound on a second roller (18).

Each printing station (I-IV) is provided with a printing unit (20) and the means for transporting, positioning and guiding the web to be printed (12) in the region of the respective printing station. The web runs at a constant feed rate V ₁ in the respective printing station. According to the embodiment Fig. 1 the printing stations are designed as roller printing units, whereas in Fig. 2 illustrated printing unit is designed as a short printing unit. Both types of printing unit are applicable and incidentally familiar to those skilled in the art, so that they are not explained in detail here.

Each printing unit is provided with a transfer cylinder (22) which has a substantially cylindrical base body (24) and a releasably mounted support for the print image to be transferred from the transfer cylinder (22) to the web (12). In the embodiment shown in the drawing, the carrier is a blanket, namely a blanket, so the transfer cylinder hereinafter referred to as blanket cylinder (see. Fig. 4 ), referred to as. The blanket cylinder (22) is associated with a printing cylinder (26) to which the web to be printed (12) via a compensation device (28) is supplied. The latter has a non-driven roller (30), which is supported by a carriage (34) which is arranged in the direction of the arrows (36, 38) linearly back and forth. The web (12) is formed over the roll (30) to form a first loop (39) having two parallel web sections and another, likewise non-driven, but stationary roll (42) over which the web moves in the direction of the web Pressure cylinder (26) is deflected, fed to the printing unit, in which the guided by the printing cylinder web with the lateral surface of the blanket cylinder for the purpose of transferring the printed image comes into contact with the web.

From the printing cylinder (26), the web (12) runs out of the printing station (10) to form a second loop (41) via a second roller (32) of the compensation device (28) and a further stationary deflection roller (44) Running direction (16) behind the second compensating roller (32) again has a constant pull-out speed V ₁ , which is equal to the feed speed V _{1 in} front of the stationary guide roller (40), which is arranged in front of the first roller (30) of the compensation device (28).

The FIGS. 3A to 3C and 4 can be seen that the blanket cylinder (22) has a cutout (48) in which two conventional clamping devices (49) (49) ( Fig. 4 ) are arranged, on each of which one end of the blanket (50) is fixed so that it is stretched over the circular-arc-shaped peripheral portion of the blanket cylinder (22) and insofar forms its lateral surface. At the in Figs. 3A to 3C the embodiment shown in the drawing extends the lateral surface forming and in one revolution of the blanket cylinder (22) in contact with the on the impression cylinder (26) out Web (12) coming and thus printing effective portion of the blanket (50) over about 280 °, this corresponds to the largest possible print image length, because the blanket (50) has the largest printing technology length in the circumferential direction, which is a difference between a circumference of 360 ° and the peripheral portion of the cutout (48) represents.

However, since the printing unit for different print image lengths in the direction of the web (12) should be usable without having to use blanket cylinder with different diameters, it is expedient, the blanket (50) in its supported by the circular arc-shaped peripheral portion of the blanket cylinder area with a longitudinal Partial section (52) to provide lesser thickness, as in Fig. 4 is shown, wherein only the longitudinal portion (51), which has a normal thickness, is effective in terms of printing technology, so comes into contact with the web (12). By contrast, the portion of lesser thickness (52) does not come into contact with the web (12) guided over the printing cylinder (26) during rotation of the blanket cylinder (22) and is thus ineffective in printing technology.

The adaptation of the blanket cylinder (22) to the respective print image length is carried out by appropriate selection or adjustment of the blanket (50). When changing the print image, for example, of a length according to the embodiment of Figs. 3A to 3C to a shorter length according to the embodiment of Fig. 4 Thus, another blanket could be mounted, which is provided with a correspondingly sized portion (52) of lesser thickness. But it is also possible to use a blanket, which has the maximum possible length in the circumferential direction for the contact with the web (12) required thickness, but also in one piece with an additional section, z. B. with the thickness of the portion (52) of Fig. 4 is in any case out of contact with the web (12), wherein such a blanket according to the respective printing requirements according to the blanket cylinder (22) is to be installed and adjusted.

With respect to the embodiments shown in the drawing, this would mean that in the arrangement according to Figs. 3A to 3C the portion (52) of lesser thickness would be completely wrapped or otherwise housed in the tensioner located in the cutout (48). On the other hand is in the execution according to Fig. 4 the printing blanket is arranged so that a part of its lesser thickness section is located on the surface of the blanket cylinder (22) such that the blanket (50) turns out of contact with the web (14) in one circumferential area of the blanket cylinder (22). which corresponds to the sum of the arcuate portion of the cutout (48) and the arcuate portion of the blanket portion (52) of lesser thickness. In this case, a part of the section which has the thickness required for contact with the web would be wrapped in one of the clamping devices (49). Preferably, the portion (52) of lesser thickness of the blanket is arranged in the direction of rotation (54) behind the cutout (48) following it.

The course of the printing process and the functions of the parts acting together are described below with reference to Figs. 3A to 3C and 4 explains:

In the position according to Fig. 3A is located in the direction of the arrow (54) continuously rotating blanket cylinder (22) approximately in a position at the beginning of the actual printing process, in which in the direction of rotation (54) in front of the cutout (48) located beginning region of the blanket forming blanket (50) with the guided around the pressure cylinder (26) track (14) has just come into contact. The web is fed continuously via the guide roller (40) at a constant speed V ₁ of, for example, 30 m / min. The peripheral speed of blanket cylinder (22) and impression cylinder (26) and thus the running speed However, V _{2 of} the web (12) in the region of these two cylinders are larger, for example 35 m / min.

Fig. 3B shows an intermediate stage during the printing process, in the course of which a printed image is applied to the web (12) which is approximately the length of the circumference of the blanket cylinder (22) minus the peripheral portion which corresponds to the cutout (48).

As soon as in the course of further rotation of the blanket cylinder in the direction of the arrow (54), the transfer of the respective print image is completed and the blanket (50) out of contact with the web (14), that is about the position according to Fig. 3C The controlled according to a program drive the printing cylinder is controlled such that initially the rotation in the direction of arrow (56) delayed and after reaching the value zero, a rotation of the printing cylinder (26) in the opposite direction, ie in the direction of the arrow (58) takes place, so that the web (12), which is out of contact with the blanket cylinder during this phase, between the impression cylinder (26) and the guide roller (30) runs in the opposite direction. After the web has been moved a sufficient distance in the opposite direction, the rotation of the printing cylinder in the direction of the arrow (58) is retarded to zero, in order immediately thereafter to rotate the impression cylinder (26) back in the direction of the arrow (56) let and bring to the rotational speed which corresponds to the peripheral speed of the blanket cylinder (22). This rotational speed of the printing cylinder (26) in the direction of the arrow (56) is reached at the latest by the time in which the blanket (50) of the cylinder (22) for applying the next printed image according to Fig. 3A comes back in contact with the train (12). In the manner described above, a positioning of the web takes place relative to the blanket cylinder (22) rotating continuously in the direction of the arrow (54), so that the next printed image without or only a small distance from that in the preceding Working cycle applied print image can be transferred to the web.

The above-described sequence of rotational movements of the printing cylinder (26) correspond to the linear movements of the compensation carriage (34). During the first phase of the working cycle in which printing takes place, the carriage (34) controlled with respect to its movements is moved with the two freely rotatable rollers (30, 32) in the direction of the arrow (38) so as to assist at the speed V ₁ continuously fed web (12) to shorten the distance between the compensation roller (30) and the guide roller (42), whereby additional sheet material in the area between the compensation roller (30) and counter-pressure roller (26) is made available to an increase in the web speed in the region between the roller (30) and the impression cylinder (26) to eg 35 m / min comes and thus the resulting speed of the web (12) of the printing speed, ie the peripheral speed of the two cylinders (18 and 26) equivalent. Since the printing speed is constant, the movement of the compensation slide in the direction of the arrow (38) also takes place during the printing process at a constant speed V ₃ . The latter can be with the equation V _3/2 = V ₂ - are expressed _V1.

Once the blanket cylinder (22) the position according to Fig. 3C has reached, in which the cylinder (22) or its blanket (50) out of contact with the web (12), the carriage (34) in accordance with the now beginning delay of the rotation of the printing cylinder (26) in the direction of the arrow (56 ) is moved in the direction of the arrow (38) at a corresponding decreasing speed until the speed of the web (12) between deflection roller (42) and pressure cylinder (26) becomes smaller than the speed V ₁ with which the path of the compensation roller (30) is supplied.

As soon as this occurs, the carriage (34) is displaced in the direction of the arrow (36), the speed of the carriage (34) in this direction decreasing the rotational speed of the printing cylinder (26) in the direction of the arrow (56) and then reversing the rotation correspondingly increases in the direction of the arrow (58).

The execution of the next cycle presupposes that the rotation of the printing cylinder 26 in the direction of the arrow 58 and the corresponding counter-movement of the web 12 are brought to zero by a correspondingly programmed deceleration, and then the impression cylinder is returned in the direction of of the arrow (56) is accelerated to the printing speed with simultaneous entrainment of the web (12), wherein the compensation carriage (34) performs corresponding movements - during the deceleration phase a movement with decreasing speed in the direction of the arrow (36) and during the subsequent acceleration in Counter direction (56) a movement in the direction of the arrow (38). The latter occurs when the speed of the web (12) is greater than the speed V ₁ at which the web is fed. This movement in the direction of the arrow (38) takes place, as already mentioned, at a substantially constant speed as soon as the web (12) has been brought to the speed required for printing, which corresponds to the circumferential speed of blanket cylinder (22) and impression cylinder (26) ,

This operating state must have occurred by the time at which the blanket (50) according to Fig. 3A again comes in contact with the web (12) carried by the printing cylinder (26) and the next cycle of operation begins, during which printing cylinder (26) and slide (34) is rotated or displaced at a constant speed.

The above-described movements of impression cylinder (26) and compensation slide (34) have the function, the web (12) position so that, in spite of the presence of the cutout (48) and optionally the portion of lesser thickness (52) of the blanket (50), the printed images to be applied sequentially on the web (12) are in close contact with each other or optionally with a small clearance can be applied to each other, which is substantially smaller than the path length in radians, during which the blanket cylinder (22) or the blanket (50) out of contact with the web (12).

The above-described changes in the speed and direction of rotation of the printing cylinder (26) also have the result that the web (12) also runs with correspondingly different running speeds and running directions from the printing cylinder (26). So that the web (12) is fed at a constant speed to the device following in the direction of transport, for example the next printing station, the web (12) running from the printing cylinder (26) is guided over the second compensating roller (32). The two parallel sections of the web (12), which form the compensation roller (32) loop looping around (41) thus undergo the same changes in length as the compensating roller (30) looping of the incoming web depending on the rotational movement of the printing cylinder (26) , but with opposite signs. Thus, the web (12) with the same constant pull-out speed V _{1 runs} out of the respective printing unit (20), with which it is also fed to the printing unit.

As in the embodiment according to the Figs. 3A to 3C the blanket cylinder (22) or its blanket (50) during the entire rotation of the position according to Fig. 3A - Start of printing - up to the position according to Fig. 3C - End of the printing process - is in contact with the web (12), is for the positioning of the web (12) only the time available to the blanket cylinder (22) needed to move in the direction of the arrow (54) in the course of rotation from the position according to Fig. 3C in those according to Fig. 3A from which the next working cycle begins.

In contrast, when a blanket is used, which, like that in the embodiment according to Fig. 4 has a partial peripheral portion (52) of lesser thickness which does not come into contact with the web to be printed, the period during which the blanket cylinder (22) is not in contact with the web corresponds to a longer circumferential distance than in one embodiment according to the Figs. 3A to 3C since the contact between the blanket cylinder (22) and the web (12) is terminated at the moment in which the step (60) ( Fig. 4 ) separating the two regions of different thickness of the blanket (50), passes the location of the printing cylinder (26) at which the blanket is normally in contact with the web (12). This means that normally in an embodiment in which the printing-effectively effective length of the blanket (50) extends over the entire area of the transfer cylinder with the exception of the cutout (48), less time is available for positioning the web (12) for the following working cycle is available than in an embodiment in which a portion of the blanket has such a small wall thickness that it remains out of contact with the web.

On the other hand, a constant duration of a working cycle, irrespective of the length of the printed image to be applied, that is, a constant rotational speed of the blanket cylinder independent of the print image length, has the consequence that the speed V ₁ at which the web (12) is introduced into the respective printing station is higher at a greater length of the printed image than the smaller length of the same, since the supplied per unit time web length is greater for a longer print image than for a shorter print image. This has the consequence that with decreasing print image length because of the lower Feed speed V _1, the difference between the feed speed V ₁ on the one hand and the print speed on the other hand increases and thus the speed at which the compensation slide (34) must be moved during the printing process increases with decreasing print image length and thus more time for the positioning of the web between two successive printing operations, since more time is required for the acceleration and deceleration phases in positioning when acceleration and deceleration do not exceed certain maximum values.

Since the drive of the web (12) in the printing station in both directions by the impression cylinder (26), the angle at which the web (14) wraps around the impression cylinder (26), should not fall below a certain minimum size, so as to slip avoid and achieve the highest possible accuracy of movement of the web (14) relative to the blanket cylinder (22). The size of the required wrap angle, which is about 180 ° in the illustrated embodiments, can be determined at any time by appropriate experiments. To achieve the desired accuracy, it is also advantageous for the drive of the printing cylinder (26) and optionally the blanket cylinder (22) each to use a torque motor that drives the shaft of the respective cylinder with correspondingly high accuracy without gear or other mechanical intermediate links, so Also, the space required for the drive is low.

The same applies to the drive of the compensation slide (34), for which a linear motor can be provided, which causes a precise movement of the compensation carriage, for example, depending on a program. In addition, it may also be advantageous to control or regulate the movements of the compensation carriage as a function of the web tension. For an accurate guide of Path relative to the transfer cylinder, the maintenance of a constant web tension is essential. Consequently, it is possible to proceed in such a way that the web tension is preferably measured continuously and, when deviating from a desired value, the drive of the compensation carriage is influenced, for example, by small control steps in such a way that the setpoint voltage is restored. Influencing the speed of the compensation carriage as a function of the web tension could superimpose the program according to which the movement of the carriage is controlled. However, it is very small in size, and will normally be substantially the same in terms of the speed and direction of movement of the web with the parameters provided by the program.

In order to achieve the greatest possible accuracy of the alignment of the web (12) to the blanket cylinder (22) can also be moved so that the web (12) is provided with markings, which are detected by at least one photocell (62), and the drive for the Pressure cylinder (26) is controlled or regulated in response to the position defined by the registration mark position of the web. This may optionally be done in addition to a drive controlling program. It is also possible to also control the drive for the blanket cylinder (22) using such registration marks, optionally in addition to a program controlling the blanket cylinder, by controlling during the time in which the transfer cylinder is not in contact with the web, the circumferential position of the blanket cylinder is aligned in small steps for each subsequent printing process to the web. However, the influencing of the rotational speed of the blanket cylinder caused by such control steps is so small that the deviation possibly caused thereby from the predetermined constant rotational speed of the blanket cylinder with respect to the duration of the working cycle is negligible.

The above-described possibility of additional regulation of the web transport by markings, which are detected by photocells or other devices and indicate the position of the web, is particularly useful when an already provided with printed images web is reprinted, the newly applied print images to the already must be aligned on the web printed images. This is the case, for example, in multicolor printing.

In view of the fact that predominantly printing inks are used which cure under the action of UV rays, a device (64) is assigned to the printing cylinder (26) ( Fig. 2 ), by means of which the printed web is exposed to irradiation by UV light. This ensures that the ink is substantially dry when the web (12) from the printing cylinder (26) expires. In this way, it is possible to deflect the web (12) in the direction shortly behind the driving pressure cylinder (26) via the compensation roller (32) to obtain the shortest possible railway lines.

Since the web (12) undergoes a certain heating due to the UV irradiation, the printing cylinder (26) is provided with at least one cooling channel (66) through which a cooling medium, for example water, flows. The cooling of the web avoids unacceptable shrinkage and / or stretching caused by heating of the web, which could also affect the accuracy with which the web is aligned with the blanket cylinder. The cooling of the web in order to avoid undue heating may be particularly important if, as in the embodiment according to Fig. 1 , The web is passed through several successively arranged printing stations, each of which is provided with a UV lamp. However, the cooling may also be effected by other means, for example by a cooling air flow being blown against the printed web.

When referring to the "print image" which is applied to the web, this may also be a partial print image in the sense that a plurality of partial print images are applied to the web at the same location in order to produce an overall print image as is the case with multi-color printing, for example.

Although the invention is explained above essentially in connection with the offset method, the invention is also applicable to other printing and decoration methods. Thus, the invention can also be used in high-pressure printing, for example flexographic printing and gravure printing and in rotary screen printing, but also in embossing, in particular hot embossing, without the above enumeration being complete. In all cases, the web to be decorated is to be positioned in one phase of a work cycle so that the successive applied print images have no or only a small distance from each other, the adjustment to different image lengths preferably by appropriate adjustment of the feed speed V ₁ . In all cases, the transfer cylinder, regardless of the print image length in its pressure-technically effective lateral surface have a constant diameter.

LIST OF REFERENCE NUMBERS

10

press

12

train

14

First role

16

arrow

18

Second role

20

printing unit

22

Blanket cylinder

24

body

26

pressure cylinder

28

compensator

30

compensation role

32

compensation role

34

carriage

36

arrow

38

arrow

39

First loop

40

leadership

41

Second loop

42

idler pulley

44

idler pulley

46

leadership

48

neckline

49

tensioning device

50

blanket

51

Printable subsection of 50

52

Partial section of lesser thickness of 50

54

direction of rotation

56

direction of rotation

58

direction of rotation

60

step

62

photocell

64

UV lamps

66

cooling channel

Claims (32)

1. Method for printing a web (12), wherein printing images are successively applied from a transfer cylinder (22) to this web within a printing station (I - IV) and the web (12) is moved towards the printing station (I - IV) at a feeding speed and the speed at which the web is moved within the printing station during the printing operation is higher than the feeding speed, and after the printing operation the movement of the web in the printing station is changed in order to position the web relative to the transfer cylinder, which is not in contact with said web during a part of a full revolution of 360°, for the next printing operation, wherein the web (12) is driven by a printing cylinder (26) associated to the transfer cylinder (22), the outer surface area of the printing cylinder being partially wrapped by the web, and wherein the change of the movement of the web for the purpose of positioning the web for the respective next printing operation is effected by a corresponding change of the rotation of the printing cylinder (26), characterized in that course of the web (12) in the at least one printing station (I - IV) is adjusted ) by a first compensation device (30, 32) arranged in the running direction of the web for a reciprocating movement upstream of the printing cylinder, in dependence of the rotary movement of the printing cylinder (26) for compensating the difference between the feeding movement of the web (12) and the movements transmitted by the printing cylinder (26) to the web.
2. Method according to claim 1, characterized in that the course of the web (12) in the at least one printing station (I - IV) is adjusted by a second compensation device (30, 34), in dependence of the rotary movement of the printing cylinder (26) for compensating the differences between the discharging movement of the web (12) and the movements transmitted by the printing cylinder (26) to the web.
3. Method according to claim 1, characterized in that the change of the course of the web (12) is effected through a corresponding change of length of at least one loop (39) in the web and in dependence of the rotary movement of the printing cylinder (26) and that said first loop (39) is arranged in the transfer direction of the web upstream of the printing cylinder (26).
4. Method according to claim 2, characterized in that the change of the course of the web (12) is effected through a corresponding change of length of at !east a second loop (41) in the web and in dependence of the rotary movement of the printing cylinder (26) and that the second loop (41) arranged in the transfer direction of the web downstream of the printing cylinder is adjusted for achieving a constant discharging speed of the web, which discharging speed may correspond to the feeding speed V₁ of the same.
5. Method according to claim 1, characterized in that the printing image is applied to the web (12) by means of a transfer cylinder (22) designed as a rubber cloth cylinder.
6. Method according to claim 5, characterized in that in the circumferential direction of the rubber cloth cylinder (22) said rubber cloth (50) is provided with a segment (52) of lesser thickness that remains out of contact with the web (12) and that the typographically effective circumferential length (51) of the rubber cloth (50), which comes into contact with the web, is adjusted in dependence of the length of the printing image.
7. Method according to claims 3 and 4, characterized in that the two compensation devices are jointly operated for changes of the two loops (39, 41) arranged in the running direction of the web upstream and downstream respectively of the printing cylinder (26).
8. Method according to claim 1, characterized in that the printed web (12) passing over the printing cylinder (26) is subject to UV radiation for drying the printing dye.
9. Method according to claim 8, characterized in that the printed web (12) is cooled through the printing cylinder (22) which is designed as a cooling cylinder.
10. Method according to claim 1, characterized in that driving control of the printing cylinder (26) takes place in dependence of a program.
11. Method according to claim 1, characterized in that driving control of the printing cylinder (26) takes place in dependence of the position of the web (12).
12. Method according to claim 1, characterized in that driving control of the transfer cylinder (22) takes place during the time in which the transfer cylinder is out of contact with the web (12), in dependence of the position of the web.
13. Method according to claim 1, characterized in that driving control of the compensation devices takes place in dependence of the tension of the web (12).
14. Method according to claim 1, characterized in that the web wraps the printing cylinder (26) over at least 180°.
15. Method according to claim 1, characterized in that the printing cylinder (26) is driven by a torque motor.
16. Method according to claim 1, characterized in that the compensation devices (30, 32, 34) are driven by a linear motor.
17. Method according to claim 1, characterized in that several printing stations (I - IV) are arranged one behind the other and that the web is transported continuously through all printing stations from a feeding device to a discharge device for the web (12) also operating in a continuous fashion and that a tension of the web suitable for the web material is maintained between the web feeding device and the web discharging device over the entire length of the web.
18. Means for printing a web (12), wherein said means is provided with at least one printing station (I - IV) which comprises a transfer cylinder (22) and a printing cylinder (26) for the web and wherein in the at least one printing station printing images are successively applied from the transfer cylinder (22), which is not in contact with the web during a part of a complete revolution of 360°, to this web, wherein the web (12) is transferred in the at least one printing station by the printing cylinder (26), of which the outer surface area is partly wrapped by the web and wherein the drive of the printing cylinder (26) can be controlled in such a manner that the web (12) can be positioned relative to the transfer cylinder (22) for each following printing operation, characterized in that the at least one printing station (I - IV) is provided with a first compensation device (30, 32) redirecting the web and arranged upstream of the printing cylinder for reciprocating in dependence of the rotary movement of the printing cylinder (26) in such a way that the web forms at least a first loop (39), the length of which may be varied in dependence of the movement of the compensation device.
19. Means according to claim 18, characterized in that the at least one printing station (I - IV) is provided with a second compensation device (32, 34) redirecting the web (12) and arranged downstream of the printing cylinder (26) capable of reciprocating in dependence of the rotary movement of the printing cylinder (26) in such a way that the web forms at least a second loop (41), the length of which may varied in dependence of the movement of the compensation device.
20. Means according to the claims 18 and 19, characterized in that the first and the second compensation device each comprise at least one compensation roller (30, 32) and both compensation rollers (30, 32) are supported by a common carriage (34) capable of reciprocating in dependence of the rotary movement of the printing cylinder (26).
21. Means according to claim 18, characterized in that the transfer cylinder (22) is provided with an exchangeable carrier (50) for the printing image to be transferred to the web.
22. Means according to claim 21, characterized in that the carrier (50) is designed as a rubber cloth.
23. Means according to claim 22, characterized in that the rubber cloth (50) is provided in the circumferential direction of the cylinder (22) with a segment (52) of lesser thickness that remains out of contact with the web (12) and that the typographically effective circumferential segment (51) of the rubber cloth (50), which comes into contact with the web, is adjustable in dependence of the length of the printing image.
24. Means according to claim 18, characterized in that the printing cylinder (26) has associated to it a UV radiation device (64) for the printed web (12).
25. Means according to claim 18, characterized in that the printing cylinder (26) is provided with a cooling device (66).
26. Means according to claim 18, characterized in that the drive for the printing cylinder (26) is designed as torque motor.
27. Means according to claim 18, characterized in that the drive for the tranfer cylinder (22) is designed as torque motor.
28. Means according to claim 18, characterized in that the drive for the printing cylinder (26) is controllable in dependence of the position of the web.
29. Means according to claim 18, characterized in that the drive for the compensation device is designed as a linear motor.
30. Means according to claim 18, characterized in that the drive for the transfer cylinder (22) is controllable in dependence of the position of the web.
31. Means according to claim 18, characterized in that the drive for the compensation device is controllable in dependence of the tension of the web.
32. Means according to claim 18, characterized in that several printing stations (I - IV) are arranged one behind the other and that a feeding device, in which the web to be printed is paid off from a supply roller, and discharge device, in which the printed web is rolled up on a supply roller after passing the printing stations (I - IV), are provided.

Images