Patent Application
20090294038
This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 025 285.9, filed May 27, 2008; the prior application is herewith incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method and an apparatus for transferring a transfer layer adhering to a carrier film because of a release layer, under the action of pressure, to flat material at least partly coated with an adhesive.
More specifically, the invention relates to a method for transferring a transfer layer of a transfer film from a carrier film of the transfer film to a printing material. The method includes applying adhesive to at least some areas of the printing material in an applicator, leading the printing material, together with the transfer film, through a transfer nip in a transfer unit, transferring the transfer layer to the printing material in the transfer nip, during the transfer, moving the transfer film through the transfer nip at a first speed, being substantially equal to a speed of the printing material, when no transfer is taking place, moving the transfer film through the transfer nip at a second speed being lower than the first speed, and accelerating the transfer film to the first speed and braking the transfer film to the second speed by adjusting front guide elements disposed before the transfer nip and/or rear guide elements disposed after the transfer nip.
Additionally, the invention relates to a film transfer apparatus, including an applicator for applying an adhesive, at least in some areas, to a printing material led through the applicator, a transfer unit disposed downstream of the applicator and having a transfer nip for transferring a transfer layer of a transfer film from a carrier film of the transfer film to the printing material, at least in some areas, a supply roll for providing the transfer film, a take-up roll for accommodating used transfer film, and adjustable guide elements disposed before and/or after the transfer nip to match a speed of movement of the transfer film, at least from time to time, to a speed of the printing material in the transfer nip.
Generic film transfer apparatuses are used in the finishing of printed products, for example in order to produce gloss effects. The machines can be subdivided into hot embossing film machines and cold film embossing machines. In the latter, the transfer layer is only transferred to the flat material, i.e. to a printing material such as a sheet, under pressure but not additionally under the action of heat. As a rule, in cold film transfer apparatuses, i.e. cold film transfer devices having a printing unit which is placed upstream of the transfer apparatus, adhesive is printed, so that there remains on the sheet a printed image of adhesive which, within a film transfer unit, is able to pull a corresponding transfer layer off the transfer film, so that the transfer layer adheres to the sheet in some areas. In that case, the transfer layer can be transferred partially in the transfer nip under the action of pressure, substantially in the areas to which adhesive has been applied.
The problem with that film transfer technique is that the transfer film has to be moved at the same speed as the printing material during the transfer and that, as a rule, only small areas on the printing material are to be covered with the transfer layer. In particular, a transfer cylinder involved in the transfer nip often has a so-called channel, in which a printing blanket can be fixed. In the region of that channel, no transfer of the transfer layer through the use of pressure can be carried out. Therefore, the process should always be controlled in such a way that the printed material dips into the transfer nip between the transfer cylinder and an impression cylinder when the channel cannot be in the area of the printing material. Other areas, in which transfer film is transported through the transfer nip without being used, are areas in which no transfer layer is to be transferred to the printing material.
In order to use the transfer film better and to reduce the consumable materials, provision is made, for example according to European Patent EP 0 932 501 B1, corresponding to U.S. Pat. No. 6,491,780, to move the transfer film through a pair of dancer rolls, which are moved cyclically at the same cycle rate as the channel of the transfer cylinder, so that the transfer film is braked to a speed of zero, for example, in the area of the channel. For that purpose, the two dancer rolls are coupled to each other in such a way that a transfer film web which is stored by a first, front dancer from the supply roll, which continues to move, is simultaneously released to the take-up roll by a second, rear dancer. In that way, a certain constancy of the web tension in the area of the supply and take-up rolls can be ensured. For that purpose, in order to spare the transfer film, both dancers are moved in coupled fashion in a braking direction. In that case, the film can in particular also be pulled back out of the transfer nip.
A problem occurs with such apparatuses with synchronized dancers when the transfer cylinder is enclosed by the transfer film and has rotated to such an extent that the transfer film before the transfer nip can already dip into the channel while the transfer film after the transfer nip is still set completely on the transfer cylinder and wrapped around the latter. A dancer roll which is disposed downstream of the transfer nip sees nothing of the channel already acting on the film, as a result of the transfer cylinder being set on the impression cylinder. However, a dancer roll which is provided upstream of the transfer nip already “notices” that the channel is present. The front and rear dancer rolls are substantially decoupled from each other by the transfer nip. While the web tension remains constant in the area of the rear dancer roll, it is already decreasing on the side of the front dancer roll.
Similar effects also occur when the channel is already set with its rear edge on the impression cylinder.
Different web tensions therefore arise on both sides whenever the front and rear dancer rolls are decoupled from each other. In addition, there is a general dip in the web tension on both sides when the channel is located in the area of the transfer nip.
It is accordingly an object of the invention to provide an intermittent film drive and method, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which avoid web tension changes to the greatest possible extent.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for transferring a transfer layer of a transfer film from a carrier film of the transfer film to a printing material. The method comprises applying adhesive to at least some areas of the printing material in an applicator; leading the printing material, together with the transfer film, through a transfer nip in a transfer unit; transferring the transfer layer to the printing material in the transfer nip; during the transfer, moving the transfer film through the transfer nip at a first speed, being substantially equal to a speed of the printing material; when no transfer is taking place, moving the transfer film through the transfer nip at a second speed being lower than the first speed; accelerating the transfer film to the first speed and braking the transfer film to the second speed by adjusting front guide elements disposed before the transfer nip and/or rear guide elements disposed after the transfer nip; and moving the front and/or rear guide elements asynchronously in relation to one another.
Therefore, in the method according to the invention, the transfer film is accelerated to the first speed and braked to the second speed through the use of adjustments of front guide elements which are provided before the transfer nip and rear guide elements which are provided following the transfer nip, with the first speed being the speed of the printing material and the second speed being the speed which the transfer film is intended to assume in the channel.
In this method according to the invention, then, guide elements, which can be provided in particular before and/or after the transfer nip, are moved asynchronously in relation to one other in order to at least reduce web tension fluctuations of the transfer film as it passes through the transfer nip. This asynchronous control is intended in particular to lead to a time-offset movement. As a result of the asynchronous control of the guide elements, even in the case of guide elements decoupled from one another, such as dancers, for example, the web tension can be kept virtually constant on both sides of the transfer nip, independently of each other. The asynchronous control includes an at least partly time-offset and/or different movement of the guide elements.
In accordance with another mode of the invention, in order to firstly maintain the web tension which is changed by an only partial effect of the channel, and to subsequently maintain the web tension which is impaired by the overall effect of the channel, the invention provides for the front and rear guide elements for respectively accelerating and braking the transfer film to be moved with two mutually different respective accelerations in respective acceleration and braking directions.
In this case, provision is in particular made for the front guide elements firstly to be accelerated highly and then less highly and for the rear guide elements firstly to be accelerated less highly and then highly. This acceleration profile is provided in order to brake the transfer film. In particular, provision can also be made in this case for an acceleration profile in the form of splice functions to be provided, in which the individual successive splice functions have lower and higher accelerations in relation to each other.
If the film is to be accelerated from a braked state to the speed of the printing material again, provision is made in this case for the front guide elements firstly to be accelerated highly and then less highly, while the rear guide elements are firstly accelerated less highly and then highly. In this case, the action of the edges of the channel is taken into account in each case. In order to avoid overswings, provision can also be made for the speed of the printing material firstly to be exceeded during the acceleration of the film, and then to have to be compensated through a corresponding negative acceleration through the use of the rear and front guide elements.
In accordance with a further mode of the invention, it is possible for the transfer film to be drawn back out of the transfer nip between the braking and the acceleration of the transfer film, through a further movement of the guide elements in the braking direction. In this way, even more film can be spared than solely by stopping the film.
In accordance with an added mode of the invention, in order to correspondingly take the times at which the channel acts on the rear and front guide elements into account, provision is made for the front guide elements to be accelerated in the braking direction with an acceleration and for the rear guide elements to be likewise accelerated in the braking direction later with a time offset with an acceleration, with the acceleration of the rear guide elements being lower than the acceleration of the front guide elements.
In accordance with an additional mode of the invention, in order to ensure a constant web tension irrespective of the guide elements on the supply roll, provision is made for a front feed to be provided in the area of the film web guidance before the front guide elements and for the drive speed of a supply roll and a take-up roll for providing the transfer film to be controlled as a function of the drive speed of the front feed. In this way, it is possible to ensure, as opposed to an apparatus without intermittent drive, that the intermittent drive speed is predefined not by the transfer nip but in the front feed, to which the drives of the supply and take-up rolls are then accordingly controlled.
In accordance with yet another mode of the invention, in order to maintain the web tension on the take-up roll, a rear feed, which is intended to move more quickly than the front feed, is provided in the area of the rear guide elements.
In accordance with yet a further mode of the invention, provision is made for the guide elements to be dancers which each have an individual drive. The drives drive the dancers asynchronously, at least from time to time, so that at least web tension changes after and before the transfer nip because of a channel of the transfer cylinder are reduced.
With the objects of the invention in view, there is also provided a film transfer apparatus, comprising an applicator for applying an adhesive, at least in some areas, to a printing material led through the applicator. A transfer unit disposed downstream of the applicator has a transfer nip for transferring a transfer layer of a transfer film from a carrier film of the transfer film to the printing material, at least in some areas. A supply roll provides the transfer film, a take-up roll accommodates used transfer film, and adjustable guide elements are disposed before and/or after the transfer nip to match a speed of movement of the transfer film, at least from time to time, to a speed of the printing material in the transfer nip. At least one drive asynchronously drives the adjustable guide elements.
Therefore, in the apparatus according to the invention, at least one drive is provided for the asynchronous drive of the adjustable guide elements. In this way, the guide elements can react independently of one another to the different web tension changes before and after the transfer nip.
In accordance with another feature of the invention, a control device is provided in order to activate the drives asynchronously, so that at least a time offset of the movement sequences of the guide elements is achieved and the web tension can be kept as constant as possible by this activation of the drives of the guide elements. In this case, the control device can be driven in accordance with a predefined control system or it can itself control the guide elements as a function of measured web tensions in the area of the guide elements or measure the web tension and further parameters and accordingly set up a learning curve relating to changing the possible asynchronous activations of the drives.
In accordance with a further feature of the invention, in particular, the control device should activate the drives in such a way that the guide elements for braking or accelerating the transfer film are in each case driven with at least two different accelerations.
In accordance with an added feature of the invention, both the take-up roll and the supply roll are mounted on a friction shaft, front and rear feeds are provided in the regions of the respective front and rear guide elements and the take-up roll and/or the supply roll are driven by a drive which sets the drive speed as a function of the speed of the front feed.
In this way, control of the drive speeds of the take-up and supply rolls in accordance with the speed of movement of the printing material, is no longer necessary.
In accordance with an additional feature of the invention, the guide elements are simply dancer rolls.
In accordance with a concomitant feature of the invention, further guide elements are provided which lead the transfer film around a transfer cylinder with a wrap angle a preferably being an angle of more than 10 degrees. In this way, as opposed to substantially tangential guidance of the transfer film through the transfer nip, a large amount of space, in which further apparatuses can be provided, can be made available in the area of the transfer nip.
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 embodied in an intermittent film drive and method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly, to
The transfer nip 3 is formed by a transfer cylinder 5 and an impression cylinder 4. The transfer film 2 is unwound from a supply roll 7 and pulled by a front feed 9 in the direction of the transfer nip 3. In this case, the supply roll 7 is located on a non-illustrated friction shaft and is driven at a speed which is lower than a speed of a printing material 21. The supply roll 7 is driven by the friction shaft. The transfer film 2 is pulled off the supply roll 7 by the front feed 9, with rolls of the front feed 9 being driven at a higher speed than the friction shaft of the supply roll 7. However, the front feed 9 is always still operated at a lower speed than the speed of the printing material 21.
The unwound transfer film 2 is guided over a front guide element in the form of a front dancer 13 of an intermittent drive module 11 and over further deflection rollers 6 through the transfer nip 3 in such a way that it forms a wrap angle a with the transfer cylinder 5 (see
The printing material 21 is led through the transfer nip 3 over the impression cylinder 4 together with the transfer film 2. During the transfer of a non-illustrated transfer layer, the transfer film 2 and the printing material 21 are at the same speed.
The transfer cylinder 5 has a non-illustrated printing blanket which is clamped over a channel 20. The channel 20 is also provided in order to be able to accommodate possible grippers on the side of the impression cylinder 4.
When a front edge 113 of the channel 20 comes into the transfer nip 3, web tension between the dancer 13 and the transfer nip 3 collapses. During the transfer of a transfer layer to the printing material 21, the sum of the speed of the front feed 9 and of the front dancer 13 gives the speed of the printing material 21. For this reason, the dancer 13 is moved in an acceleration direction 18 along a path which is identified by a double arrow 16. As a result of contact made between the front edge 113 of the channel 20 and the impression cylinder 4, the front dancer 13 is decoupled from the rear dancer 12. In order then to compensate for the diminishing web tension, provision is made for the front dancer 13 to be driven by a motor 15 in such a way that it is firstly accelerated highly in a braking direction 19. In this way, a constant web tension is achieved in this area. For this purpose, a control device 22 acts appropriately on the motor 15 of the front dancer 13. Once the channel 20 is completely in the area of the transfer nip 3, the dancer 13 is moved in the braking direction 19 with a lower acceleration, so that the transfer film 2 comes to a standstill or is pulled back.
When the channel 20 is “seen” for the first time by the dancer 12, the rear dancer 12 is firstly accelerated in the braking direction 19 with a lower acceleration in order to compensate for this dip and later accelerated with a higher speed, so that a standstill of the transfer film 2 can be achieved. For this purpose, too, the control device 22 is connected to the motor 14 of the rear dancer 12.
The sheet 2 which is treated in this way can then be transported onward through the printing press, i.e. through the film transfer apparatus, so that it is moved to a further adjoining printing unit 103, which once more has a press nip 109, that is formed by a blanket cylinder 110 and an impression cylinder 111. The printing unit 103 additionally has an inking unit 112. The sheet 21 to which a transfer layer has been applied can then be overprinted conventionally in the printing unit 103.
The influence of the different positions of the channel 20 from the sections 1 to 6 of
Before the front edge 113 of the channel 20 dips into the transfer nip 3, as in the illustration in section 1 of
Once the front edge 113 dips into the transfer nip 3 then, as is illustrated in graph 201, there is a dip in the web tension on the front dancer 13. As is illustrated in graph 200, from this instant the film web speed should also be reduced. In order to reduce the film web speed and at the same time to compensate for the web tension loss, the front dancer 13 according to graph 202 is accelerated in the braking direction 19 with a high acceleration aT1,1. The rear dancer 12 still sees substantially no dip in the web tension but should also reduce the film web speed. It is therefore accelerated in the braking direction 19 with a lower acceleration aT2,1. This acceleration of the rear dancer 12 is offset slightly in time with respect to the acceleration of the front dancer 13.
In the illustration in section 2 of
The accelerations described above always also relate substantially to the intermediate areas illustrated between the sections 1 to 6.
As is shown in the illustrations in sections 2 and 3 of
As can be seen in the illustration in section 4 of
According to
In
The graph 201 shows the course 204 of the web tension before the transfer nip and a course 205 of the web tension after the transfer nip, firstly as would be present without any compensation by the accelerations to compensate for the web tension changes through the use of the front and rear dancers 13, 12 and, secondly with reduced web tension changes in accordance with dashed lines 206, 207 as would be present for a front web tension area 206 and for a rear web tension area 207 with compensation.
As can be seen, as a result of the superimposition of the simple acceleration for the intermittent drive with an acceleration to reduce the web tension through the use of the front and rear dancers 12, 13, as is illustrated in graph 202, the web tensions 206, 207 are reduced sharply before and after the transfer nip 3.
As a result of using friction shafts in the supply and take-up rolls 7, 8, it is of course also possible to use a plurality of partial film webs of the transfer film 2 beside one another. If each partial film web is assigned an individual front and/or rear feed 9, 10, these partial film webs can also be driven intermittently independently of one another, depending on the subject.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 025 285.9 | May 2008 | DE | national |
