EP0759582B1 - Method for ink transfer and device and machines for carrying out said method - Google Patents

Description

The invention relates to methods for the transmission of solid or liquid printing ink from an intermediate carrier, for example a transfer cylinder, on another intermediate carrier or on a substrate, such as paper, as well as several Devices and printing machines for carrying out these processes.

To print liquid ink from a cylinder of a printing press transferred to another cylinder or to a substrate in order to be able to do so, it must be based on the effects on the interface based adhesion of the printing ink on the second cylinder or the substrate larger than that on the Be the original cylinder. When transferring takes place however always a split of the liquid film instead, so that a Part of it remains on the original cylinder, and it is practically impossible, only approximately one hundred percent Achieve transfer of liquid ink.

The same problem exists with the transmission from fixed Ink that is in a granular state, z. B. a toner powder. Although they are electrostatic Known transmission techniques with which a Transmission efficiency of a maximum of approx. 95 to 98% achieved is, but this also only in application use non-conductive toner. For production machines with one This is printing performance of many thousands of sheets per hour but not sufficient, because the Cleaning facilities replaced or outside the Printing machine would have to be cleaned.

In an article entitled "Offset Quality Electrophotography "in the journal" Journal of Imaging Science and Technology ", Volume 37, No. 5, September / October 1993, p. 458 (hereinafter with "OQE" are different xerographic techniques specified for the transfer of conductive toner also in high humidity are suitable. One of those techniques is to pressurize the toner onto a substrate transferred and fixed at the same time. Another technique consists of a thermal transfer with two Temperature levels.

There are also combinations of pressure transmission and thermal transmission. Such a combination is on Page 459 of the above publication. The Toner is pressed from a first cylinder onto a Intermediate cylinder and then by thermal transfer transfer a paper between the intermediate cylinder and runs through a hot impression cylinder. In the Transmission by pressure should achieve an efficiency of 95% be, and in the case of thermal transmission such a 100%.

In the journal "The Seybold Report on Publishing Systems ", Volume 24, No. 20, page 20, left column (hereinafter referred to as the "Seybold Report") becomes a Transmission system described in which an image over two Tapes are transferred to the paper. The first tape takes the toner in a distribution corresponding to the printed image on. The image is then transferred to the second tape, the is heated. This ribbon is not hot enough to hold the toner melting, however, causes the toner particles to separate and then transfer the image onto the paper which is preheated, with the picture hot Print roller is fixed. As a result, no subsequent Melting or fixing the toner is required more.

In the first step, when transferring from the first tape to the second volume, but cannot Transmission efficiency of 100X can be achieved. The first Although the tape is coated with Teflon, it is practicing in principle at least low adhesive forces on the toner, so that a transmission efficiency of at least in the first step less than 100% is assumed, similar to that in the magazine "OQE" described technology.

In US 5,110,702 is a method for toner transfer with an intermediate roller or an intermediate volume described. The roller or belt are heated so that at Application of print sticks to a toner image. The sintered toner image is then also transferred to a receiving material by application of heat and pressure. The toner image is heated starting from the surface of the roller or of the tape.

In both of the techniques described above, the toner not completely from the first cylinder or the first band transmitted. Especially with newer ones Printing techniques, e.g. B. that described in the "Seybold Report" Printing technology, however, it is to achieve a flawless Printing, the remaining ink before one rewriting the first volume or the first Remove the cylinder completely. This can be very difficult and be expensive, especially when the printing ink to be reused.

The invention is based on the object To create transmission techniques that are not only one transfer on paper, but also with a transfer on an intermediate carrier a transmission efficiency of always have practically 100%.

In the generic method, in which the Ink in a granular state on an intermediate carrier is liable, the problem is solved in that the printing ink on their facing away from the intermediate carrier Side is melted before continuing on Intermediate carrier or the substrate is transferred.

In one embodiment, a further intermediate carrier has one outer elastic layer, e.g. B. a rubber layer, in the release agent is contained, the release agent being on the surface of the rubber layer is driven when the other subcarrier and that Substrate pressed against each other. The Loss of release agent during operation can be caused by a corresponding feeder can be compensated, or that Release agent is added to the paint so that it is in operation establishes an equilibrium in the release agent guidance.

An intermediate carrier is understood to mean a device which has a surface on which a printed image in the form a color distribution, transported and is then dismantled again, e.g. B. a rotating Transfer cylinder or one rotating around a cylinder Ribbon, the color transfer optionally to another Intermediate carrier or on a substrate.

With the fixed color transfer, d. H. a transfer by melting, the Ink is mostly solid, a transmission efficiency of practically 100% reached.

When melting a granular printing ink from the outside First, the color particles are caused to separate another tack. Second, the adhesion of the ink not melted on the intermediate carrier enlarged since it is only on the outer surface of the Color layer takes place while the printing ink on the Intermediate carrier facing side still only individual points is liable to the intermediate carrier. Therefore can contiguous islands of color on the intermediate carrier detach easily and completely. Third, it does Melting of the printing ink from the outside a stronger adhesion on the subsequent intermediate carrier or the substrate, which ensures the complete transfer of the ink is additionally ensured.

Unlike the one known from the "Seybold Report" The process does not become the solid printing ink according to the invention from the inside, but on the outside melted. While the known technique is peeling off makes the intermediate carrier more difficult, they remain required release forces unchanged in the invention small, and moreover the liability on the target carrier improved. Therefore takes place in the inventive method the transfer process in more reliable than the known one in several respects Method. One achieves with low construction and Energy expenditure a transfer efficiency of 100%, where those for transfer to a substrate such as paper required contact forces are low, so that the paper is spared.

This does not only apply if the printing ink is directly on one Substrate is transferred as paper, which is the transfer supported by its strong capillary action, but also in the case of a multi - stage procedure in which the Ink over another intermediate carrier on the Substrate to be transferred. The full transfer a latent developed on a first intermediate carrier Image on a second intermediate carrier and from this on a substrate places opposite demands on both processes. First, the affinity of the ink for the second Intermediate carrier compared to the first intermediate carrier dominate, then the affinity of the printing ink for Dominate substrate over the second intermediate carrier. The The second intermediate carrier must first be the printing ink accept and then return it. Since according to the Invention the replacement of the ink from the first Intermediate carrier after development is facilitated you need a smaller one on the second intermediate beam Affinity as if the detachment is not supported to the color completely towards the second intermediate carrier transfer. The low adhesive forces on the second Intermediate carriers make it easier to print the ink afterwards completely transfer to the substrate.

If the transfer to the substrate Melting process applied, so needed one for the transfer and the final fixing altogether much less thermal energy than known ones Techniques where the ink is heated by heating the Intermediate carrier or melted by preheating the paper becomes. The paper does not dry out during printing and will spared.

The use of a release agent is particularly advantageous with an intermediate carrier in the form of a Rubber transfer cylinder that holds the liquid ink on transfers a substrate. An elastic, e.g. B. made of rubber or a similar material existing layer of Transfer cylinder, which is for a uniform Color transfer to an uneven substrate surface can nestle without exerting excessive pressure, also serves as a carrier for the release agent that is in the preferred embodiment is silicone oil. The Absorption capacity of the elastic layer for the release agent can be due to diffusion and / or penetration of the Release agent based in micropores of the elastic layer. When the elastic layer is pressed against the substrate, the silicone oil is expelled so that the printing ink of the surface of the transfer cylinder is rejected. At the same time, the printing ink gets into the substrate surface driven in so that a particularly simple way residue-free ink transfer is achieved.

Due to the high transmission efficiency Simplified designs for multi-color presses possible.

The melting in the different embodiments or heat sources used for fixing can e.g. B. Be infrared emitters that the radiation on the Bundle the intermediate carrier or the substrate. The place on the Intermediate carrier on which the radiation is focused should as close as possible to the point of transfer of the Printing ink on the further intermediate carrier or the substrate Lying, so on the way to the transfer point if possible little heat flows onto the intermediate carrier or the printing ink does not need to be heated much more than it is for the transfer is required.

The most suitable for bundling are lasers, their Radiation is converted into heat at the point of impact. By suitable choice of radiation wavelength can be achieved that the radiation from the ink with a higher Efficiency and with the intermediate carrier or the substrate is absorbed at a lower efficiency, so that the Intermediate carrier and the substrate heated as little as possible become. An even more targeted warming is possible with the help of a Arrays of lasers or laser diodes possible in according to the transferred print image in order to heat only the positions carrying the ink. The necessary to generate such a heating pattern Information is from the control of the Printheads known. With a corresponding resolution of the laser diode array can perform pixel-perfect heat transfer be carried out, and with the help of the gray value information the respective ink layer thickness can be taken into account. As a result, the heat input can be dimensioned so that the Ink when transferring to paper regardless of other parameters have the same temperature everywhere and reliable color transfer is guaranteed.

Further features and advantages of the invention result from the subclaims and from the following description several embodiments and from the drawing on the Reference is made.

Fig. 1

eine Prinzipskizze eines Druckwerks für Festfarbenübertragung;

Fig. 3

eine Prinzipskizze eines Druckwerks mit einer zweistufigen Farbübertragung, nämlich einer Kombination aus einer Festfarben- und einer Flüssigfarbenübertragung;

Fig. 5

eine Prinzipskizze einer Mehrfarben-Druckmaschine mit zweistufiger Farbübertragung;

Fig. 6

eine Prinzipskizze einer weiteren Mehrfarben-Druckmaschine mit zweistufiger Farbübertragung;
und

Fig. 7 und 8

verschiedene Wärmequellen, die für die Ausführungsbeispiele von Fig. 1, 3, 5, 6 geeignet sind.

In it show:

Fig. 1

a schematic diagram of a printing unit for solid color transfer;

Fig. 3

a schematic diagram of a printing unit with a two-stage color transfer, namely a combination of a solid color and a liquid color transfer;

Fig. 5

a schematic diagram of a multicolor printing machine with two-stage color transfer;

Fig. 6

a schematic diagram of another multicolor printing machine with two-stage color transfer;
and

7 and 8

different heat sources that are suitable for the exemplary embodiments of FIGS. 1, 3, 5, 6.

In Fig. 1 are a printing unit with a Transfer cylinder 1, a schematically shown Inking unit 2 and an impression cylinder 3 and a Substrate 4 shown. Opposite the surface of the Transfer cylinder 1 between the inking unit 2 and the A heat source 5 is arranged on the substrate 4 and opposite the printed side of the substrate 4 is a heat source 6 arranged.

In operation of the printing unit shown in Fig. 1, the Transfer cylinder 1 and the impression cylinder 3 in the directions indicated by arrows while one is not drawn transport device in succession Substrates 4 in the direction of the arrow between the Transfer cylinder 1 and the impression cylinder 3 through promotion.

On the inking unit 2, ink particles 7 become one achieving the corresponding distribution on the print image Transfer cylinder 1 applied. The color particles 7 are shown in the figure as balls of equal size, in the Practice shaped irregularly. While the color particles 7 be transported further by the transfer cylinder 1, they are from the heat source 5 directed at it from the outside melted so that coherent islands of color 8 arise. The ink adheres to the ink islands 8 as still before just selectively on the transfer cylinder 1, like shown schematically. As long as this is selective Liability does not change significantly, is the intensity of the Melting is not critical. It is essential that the plasticity in the color islands 8 increases from the inside out, their outer surface has not yet completely melted should. Due to the glassy melting behavior of Common solid colors can meet these conditions relatively easy to meet.

Between the transfer cylinder 1 and the Impression cylinder 3, the substrate 4 on the Transfer cylinder 1 pressed, the printing ink on the Substrate 4 is transferred. Since the ink is on your from side melted away from the transfer cylinder 1 has been, the color islands 8 are contiguous and easily transferred to the substrate 4. Therefore, the Contact forces between the substrate 4 and the Transfer cylinder 1 can be kept small. Subsequently the printing ink is fixed using the heat source 6, in many cases, it is sufficient that the color islands 8 on the Warm the surface to smooth it. Alternatively or in addition, the substrate 4 before passing through the Transfer cylinder 1 by a not shown Facility to be preheated.

In Fig. 3 are a printing unit with a first Transfer cylinder 30, a second Transfer cylinder 31, an inking unit 32 and one Impression cylinder 33 and a substrate 34 are shown. Opposite the surface of the first transfer cylinder 30 between the inking unit 32 and the second Transfer cylinder 31, a heat source 35 is arranged, and opposite the surface of the second Transfer cylinder 31 between the first Transfer cylinder 30 and the substrate 34 is one Heat source 36 arranged. The second transfer cylinder 31 has a rubber jacket 37 containing silicone oil.

In operation of the printing unit shown in Fig. 3, the first transfer cylinder 30, the second Transfer cylinder 31 and the impression cylinder 33 in the directions indicated by arrows while one is not drawn transport device in succession Substrates 34 in the direction of the arrow between the second Transfer cylinder 31 and the impression cylinder 33 through promotion.

On the inking unit 32, ink particles 38 corresponding to one latent printed image, which is based on an unspecified Way of a schematically illustrated write head 39 is generated on the first transfer cylinder 30 applied. Transfer of the ink to the second Transfer cylinder 31 is carried out in the same way as in FIG Connection with Fig. 1 described. The second Transfer cylinder 31 is the printing ink by means of Heat source 36 and / or by heating the Transfer cylinder 31 completely melted and then transferred to the substrate 34.

In the arrangement shown in FIG. 3, it is also possible to to do without a release agent when the paint transfer from the second transfer cylinder 31 to the substrate 34 is also carried out analogously to Fig. 1, that is by Melting on the outside using the heat source 36, while the inside of the ink on the Transfer cylinder 31 is quenched. The due to the previous melting increased liability on the second transfer cylinder 31 is essential by the greater liability on the substrate 34 at least made up for. In this case too, there is complete color transfer possible, if necessary supported by suitable additional measures, such as preheating the substrate 34. Instead of the combination shown in Fig. 3 from a Solid color and liquid color transfer will be one two-stage transmission of more or less fixed Printing ink realized.

5, four first transfer cylinders 50, one second transfer cylinder 51, an impression cylinder 52 and a substrate 53 are shown. The first four Transfer cylinders 50 are one behind the other on the circumference of the second transfer cylinder 51 arranged, and on the circumference each first transfer cylinder 50 are each one Inking unit 54 and a write head 55 are arranged. Besides, is one at the circumference of each transfer cylinder 50, 51 Heat source arranged.

5 rotate during operation of the printing unit first transfer cylinder 50, the second Transfer cylinder 51 and the impression cylinder 52 in the directions indicated by arrows while one is not drawn transport device in succession Substrates 53 in the direction of the arrow between the second transfer cylinder 51 and the impression cylinder 52 through promotion.

The printing inks are essentially as in Connection with Fig. 3 described transmitted, with one revolution of the second Transfer cylinder 51 transfer all four inks become.

6, a first transfer cylinder 60, a second transfer cylinder 61, an impression cylinder 62 and a substrate 63 are shown. The scope of the second Transfer cylinder 61 is four times the size of the first transfer cylinder 60. On the circumference of the first Transfer cylinders 60 are four inking units 64 and one Print head 65 arranged. Besides, everyone is on the scope Transfer cylinders 60, 61 each have a heat source arranged.

In the operation of the printing unit shown in Fig. 6, the first transfer cylinder 60, the second Transfer cylinder 61 and the impression cylinder 62 in the directions indicated by arrows while one is not drawn transport device in succession Substrates 63 in the direction of the arrow between the second Transfer cylinder 61 and the impression cylinder 62nd through promotion.

The printing inks are essentially as in Connection with Fig. 3 described transmitted, with each revolution of the Transfer cylinder 60 an ink on the Transfer cylinder 61 is transferred.

As can be seen from FIGS. 5 and 6, these result Embodiments with multicolor printing presses two-stage color transfer, where several Transmission cylinder can be saved.

For the embodiments described in the above heat sources used come e.g. B. infrared heater in Consideration. Further, particularly suitable heat sources are in Connection with Fig. 7 and 8 described.

7 schematically shows a transfer cylinder 70, a Substrate 71, which is transported in the direction of the arrow, and a laser 72 for externally melting ink, the from the transfer cylinder 70 to the substrate 71 is transmitted. The laser 72 is e.g. B. a Carbon dioxide laser, its radiation along the dashed line Line in the gap between the transfer cylinder 70 and the substrate 71 where it is absorbed by the ink and is converted into heat. At the pointed converging Surfaces of transfer cylinder 70 and substrate 71 finds multiple reflections towards the Transfer point instead, so the radiant energy is very is brought close to the transfer point. The Radiation is evenly spread over the lens or mirror Length of the gap is distributed, and / or it is along the Length of the transfer cylinder 70 a plurality of lasers 72 intended.

At least in the case of those described above The radiation is transferred by melting bundled as much as possible, d. H. as narrow as possible linear region along the transfer cylinder 70 concentrated. This also applies to a case in which the radiation is not directly supported by reflection the gap between the transfer cylinder 70 and the Substrate 71 is directed, but a (as small as possible) Piece in front of the transfer point. With the help of A linear radiation area can be lasered with reach a width in the micrometer range, so that the Printing ink passing the irradiation area only very much radiation energy is briefly applied. Thereby ensures that the ink is actually only on warmed their outer surface and thus only on the Surface is melted.

When using a carbon dioxide laser, the radiation definitely absorbed by the ink. polymers Dyes also absorb short-wave light, so that z. B. ND-YAG lasers can also be used. The Short-wave light has the advantage of targeting the individual Color islands are heated on the transfer cylinder 70 can, with maximum protection of the substrate 71 and minimal Heating of the transfer cylinder 70. The latter aspect is particularly important when the transfer cylinder 70 is a Development cylinder is the one at a warming on the Transfer point must then be cooled again to ensure proper development.

An embodiment for a targeted heating of the Color islands, the uniform heating of printing ink enables both with locally different Distribution as well as with different thickness, will be explained with reference to Fig. 8.

8 schematically shows a transfer cylinder 80 a Substrate 81, which is transported in the direction of the arrow, and a Laser diode array 82 for external melting of printing ink, from the transfer cylinder 80 to the substrate 81 is transmitted. The laser diode array 82 extends lengthwise the length of the transfer cylinder 80, being close to Transfer cylinder 80 and as close to the Transfer point is arranged on the substrate 81.

The laser diode array 82 is controlled by a control device 84 driven by a not shown Printing machine computer the same image information including the grayscale values received by the Print heads of the printing unit are fed. The Control device 84 under-controls laser diode array 82 Taking into account the time offset so that the Color layer on the transfer cylinder 80 accordingly their area distribution and their respective thickness with heat is supplied.

In this way it can be achieved that the printing ink in Moment of transfer from transfer cylinder 80 has the same temperature everywhere on the substrate 81. Except for the warmth on the short way to the Transfer point from the printing ink to the Transfer cylinder 80 flows, takes Transfer cylinder 80 no heat.

Targeted heating is most accurate when the Pixel resolution of the laser diode array 82 is equal to that Printhead resolution is. Instead of an array with single controllable laser diodes in pixel spacing can, for. B. also a single, continuously radiating laser with one scanning mirror and a switchable filter used become.

A structure similar to that of the laser diode array 82 and driven laser diode array 83 can behind the Transfer point may be arranged over the substrate 81. The Laser diode array 83 smoothes or fixes the on the substrate 81 transferred ink evenly according to your Distribution on the substrate 81 without this directly is heated.

Instead of the laser diode array 82, one or several continuously operating lasers are used z. B. carbon dioxide laser, which the on the substrate 81st Irradiate transferred ink linearly, similar to described in connection with the transfer cylinder 70. Due to the short-term exposure to radiation when walking past the substrate 81 becomes the ink on its surface melted, which is generally sufficient for fixing, however prevents too much moisture from the paper exit.

All heating methods described above can the laser wavelength and the composition of the printing ink be coordinated so that the printing ink with is heated to the highest possible efficiency, while at the same time the transfer cylinder or the paper is heated as little as possible. That way it dries Paper not out.

Instead of the laser diode array 82, one or several continuously operating lasers are used z. B. carbon dioxide laser, which the on the substrate 81st Irradiate transferred ink linearly, similar to described in connection with the transfer cylinder 70. Due to the short-term exposure to radiation when walking past the substrate 81 becomes the ink on its surface melted, which is generally sufficient for fixing, however prevents too much moisture from the paper exit.

All heating methods described above can the laser wavelength and the composition of the printing ink be coordinated so that the printing ink with is heated to the highest possible efficiency, while at the same time the transfer cylinder or the paper is heated as little as possible. That way it dries Paper not out.

LIST OF REFERENCE NUMBERS

1

transfer cylinder

2

inking

3

Impression cylinder

4

substratum

5

heat source

6

heat source

7

color particles

8th

color Islands

30

first transfer cylinder

31

second transfer cylinder

32

inking

33

Impression cylinder

34

substratum

35

heat source

36

heat source

37

mackintosh

38

color particles

39

Stylus

50

first transfer cylinder

51

second transfer cylinder

52

Impression cylinder

53

substratum

54

inking

55

Stylus

60

first transfer cylinder

61

second transfer cylinder

62

Impression cylinder

63

substratum

64

inking

65

Stylus

70

transfer cylinder

71

substratum

72

laser

80

transfer cylinder

81

substratum

82

laser diode array

83

laser diode array

84

control device

Claims (9)

1. Method of transferring ink from an intermediate carrier to a further intermediate carrier or to a substrate, the ink adhering to the intermediate carrier in a granular state, characterized in that on its side facing away from the intermediate carrier (1; 30; 31; 50; 60), the printing ink is caused to begin to melt before it is transferred to the further intermediate carrier (31; 51; 61) or the substrate (4; 34).
2. Device for implementing the method according to Claim 1, having a first intermediate carrier, which is arranged adjacent to an inking unit, and a second intermediate carrier, which is arranged such that it touches the first intermediate carrier and a substrate transported through a printing machine, characterized in that a heat source (35) is arranged opposite a surface of the first intermediate carrier (30) which extends between the inking unit and the second intermediate carrier (31), and in that a heat source (36) is also arranged opposite a surface of the second intermediate carrier (31), extending between the first intermediate carrier (30) and the substrate (34), and/or the second intermediate carrier (31), on its side facing the ink, is permeable to a release agent.
3. Printing machine having a plurality of inking units for implementing the method according to Claim 1, characterized by a plurality of first intermediate carriers (50), which are each arranged adjacent to one of the inking units (54), and a second intermediate carrier (51), which is arranged such that it touches all the first intermediate carriers (50) and a substrate (53) transported through the printing machine, a heat source being arranged opposite a surface of the second intermediate carrier (51) which extends between the first intermediate carrier or carriers (50) and the substrate (53), and/or the second intermediate carrier (51), on its side facing the ink, being permeable to a release agent.
4. Printing unit having a plurality of inking units for implementing the method according to Claim 1, characterized by a first intermediate carrier (60) adjacent to which the inking units (64) are arranged, and a second intermediate carrier (61), which is arranged such that it touches the first intermediate carrier and a substrate (63) transported through the printing machine, a heat source being arranged opposite a surface of the second intermediate carrier (61) which extends between the first intermediate carrier or carriers (60) and the substrate (63), and/or the second intermediate carrier (61), on its side facing the ink, being permeable to a release agent.
5. Device or printing machine according to one of Claims 2 to 4, characterized in that the intermediate carrier or carriers is or are in each case a rotating transfer cylinder (1; 30; 31; 50; 51; 60; 61) or a belt circulating around a cylinder.
6. Device or printing machine according to Claim 5, characterized in that in each case an impression cylinder (3; 33; 52; 62) is mounted opposite that side of the substrate on which the surface of a rotating transfer cylinder or circulating belt rolls.
7. Device or printing machine according to one of Claims 2 to 6, characterized in that the heat source (5; 6; 35; 36) is designed in such a way that it focuses radiation onto the intermediate carrier (1; 30; 31) or the substrate (4).
8. Device or printing machine according to Claim 7, characterized in that the heat source is a laser (72) or an array (82, 83) of lasers or laser diodes.
9. Device or printing machine according to Claim 8, characterized in that the laser (72) or the array (82, 83) of lasers or laser diodes is or are connected to a control device (84), which generates control signals which correspond to the distribution of the ink on the intermediate carrier (70, 80) or the substrate (71, 81).

Images