EP1217454A2 - Digital printing or copying machine - Google Patents

Abstract

A digital printing or photocopying machine (1) prints on one or both sides of a sheet of paper (11) using a toner and a heated fixing unit (3) to fix the toner on the paper. The paper is fed past the heater by a transport unit (17) which is especially a meshed suction belt (19). The total cross sectional air through-flow area of the apertures (21) is greater than that of the cross-pieces between the apertures (21). The area of each aperture (21) is less than 1 sq mm. The suction belt (19) interface in contact with the substrate (11) is coated with a separation material of low surface energy. The substrate adheres to the suction belt by means of an electrostatic charge generated by friction between the two. The suction belt has a thin coating of silicon oil and is cooled by a radiator located on the return part of the belt loop.

Description

The invention relates to a digital printing or copying machine for one-sided or double-sided printing of a substrate using at least a toner according to the preamble of claim 1.

Machines of the type mentioned here are known. For example, you work after the electrophotographic process, in which a latent electrostatic Image is developed by charged toner particles. These are placed on an image receiving substrate, hereinafter referred to as substrate. After that it will developed and transferred to the substrate fixed image by the toner particles heated and melted. For melting the toner particles frequently used touching processes in which the toner particles come into contact with appropriate facilities, such as hot roles or rollers. The disadvantage is that usually the use of silicone oil is required as a release agent, which prevents the melted from sticking To prevent toner on the heater. Furthermore, the structure that Maintenance and operating costs of these touching heaters complex and therefore costly. Furthermore, that is due to the touching heaters error rate caused relatively high. Nevertheless, such procedures are still common and allow a by pressurization in fixing the toner into the structure of the substrate.

To fix the toner transferred, for example, to paper, are also contactless working heaters and methods known, for example with the help of heat / microwave radiation or with hot air the toner particles be melted.

The contacting and the non-contacting melting processes use, for example, toners whose glass transition temperature (T _G ) is in a range from 45 ° C. to 75 ° C. The glass transition temperature at which the toner - starting from the solid state - begins to soften can be influenced by the choice of raw materials and by the addition of certain additives to the toner. In a fixing device for the toner having at least one heating device, both the toner and the substrate itself are heated. In order to ensure a good fixation of the toner on the substrate, the surface temperature of the substrate must be in the range of the glass transition temperature of the toner or above. The toner already reaches or exceeds the glass transition temperature (T _G ) in the area of the heating device.

Printing and copying machines are known in which the substrate is double-sided is printed, whereby for printing on the front and back either one and the same imaging and transmission device and heating device or a separate imaging and transmission device, and each Heating device can be used. This is used to fix the toner image Substrate often with the help of a conveyor belt on which the substrate rests the at least one image generation and transmission device and the associated one Heater passed by. First, a first toner image transferred to a first substrate side and fixed thereon. Then will transfer and fix a second toner image onto the second substrate side. At the Melting of the second toner image is therefore the first substrate side with the already fixed first toner image on the conveyor belt. The disadvantage here is that during the melting of the second toner image the first toner image can heat up to the point that it becomes soft and to do so tends to stick to the conveyor belt. This can lead to several unwanted ones Effects lead: By sticking it can lead to a substrate jam at the Transfer of the substrate from the conveyor belt to a subsequent part of the Machine come. Furthermore, the appearance of the toner image can vary in the areas in which it is stuck to the conveyor belt. this leads to Image quality problems, for example, the toner image is uneven Shine on. These undesirable effects are reinforced by a pressurization with a heating roller when touching fixing the Toner.

Conveyor belts are known which are designed as a suction belt, ie one Have a number of through openings to which vacuum can be applied the substrate can be sucked in and is thereby held. The famous suction belt has the same disadvantages as a conveyor belt with a closed Support surface.

It is an object of the invention to provide a machine of the type mentioned in the introduction, in which a suction belt for transporting a toner-carrying substrate is provided before, by and / or after the heating device and by the suction belt the appearance and editing of the toner image, or at least only is negligibly changed or impaired, especially a double-sided one Printing a substrate with high quality on the front and Back of the substrate applied toner images is possible.

To solve the problem, a digital printing or copying machine is proposed, having the features of claim 1. It includes at least a fixing device for fixing toner image transferred to a substrate serves. The toner image can be single or multi-colored. In connection with The present invention also includes at least one "toner image" understood a coating having a toner layer. For example, the substrate be an arc or a continuous path, for example made of Paper or cardboard. To fix the preferably dry toner on this becomes the substrate on a heating device, which is part of the fixing device is passed by. To feed the substrate to the heater, on the heater to pass and / or for further transport from the heating device to a subsequent part of the machine is at least one transport device provided that has at least one suction belt that has a number of has through openings which can be acted upon by vacuum. The invention Printing and or copying machine is characterized in that the Mesh belt, preferably in the manner of a close-meshed sieve or Network, is formed. If the substrate is printed on both sides and on a first toner image is already fixed on a first substrate side, the substrate lies with its underside having the already fixed first toner image on the Sieve or mesh on, while a second toner image melted on the substrate top becomes. The first toner image may melt when the second one melts Possibly heat the toner image to such an extent that it may become soft or pasty, but does not become liquid. Because of the negative pressure of the sieve or net, the substrate is attracted to the sieve or net, so that the surface structure of the sieve or mesh is reflected in the soft virtually imprints the first toner image. The fact that the through openings and the Bridges between the through openings according to the invention are or are so small have such a small width is the change in the surface structure the first toner image as a result of the screen structure being pressed in is only so small that it is preferred by a viewer with the naked eye not, but at least hardly recognizable. Through the suction belt according to the invention So the image quality, especially the gloss of the while fixing of the second toner image, the first toner image coming into contact with the suction belt not in the visible area or only in a very small amount Dimensions changed. The suction belt can also be used for safe, wrinkle-free guidance the substrate, especially at high transport speeds, are guaranteed, especially if the transport route before, through and after the heating device in several independently drivable transport sections is divided, in each of which the subsequent transport section is somewhat driven faster than the previous transport section and others, organs driving the substrate, e.g. a touching heating roller, something leads. A resulting, slowed relative speed of the substrate compared to the suction belt is due to the structure of the invention harmless, in particular if, as provided for in a development of the invention, the suction tape is designed as a wide, endless and seamless fabric tape is that with a particular advantage a homogeneous temperature distribution in the Area of the entire substrate and a constant structure of the suction belt guaranteed in this area.

In a preferred embodiment it is provided that the total cross-sectional flow area the through openings are larger, preferably significantly larger, than the total area of the webs between the through openings. Thereby it is ensured that the majority of the area of the second toner image does not Has contact with the suction belt and is therefore completely unaffected by it. The through openings of the sieve or net preferably have one Diameter that is less than 1.0 mm. The smallest diameter of the through openings can be a few micrometers.

Adhesion of the first toner image located on the underside of the substrate to avoid on the suction belt, at least that with the substrate in Contacting surface of the suction tape coated with a release material his. The soft first toner image does not stick to the release material, so that the substrate can be safely separated from the suction belt. As For example, a Teflon coating can be used for the release material. Alternatively, it can be provided that the entire screen or net from the Separating material exists. Additionally or alternatively, the suction belt can be used with a thin layer of a "release agent", for example silicone oil.

According to a development of the invention, it is provided that at least those with surface of the suction tape coming into contact with the substrate with a material is coated that has a low surface energy. Thereby the adhesive forces of the first soft due to the melting of the second toner image Toner image on the suction belt only low, so that here too a safe Separation between suction belt and substrate is possible. A substrate jam or Problems with the transfer of the substrate from the suction belt to a subsequent one Part of the machine, for example on a shelf, can therefore be practically excluded become. Alternatively, the entire suction belt can of course also be used be made from the material having a low surface energy.

Furthermore, an embodiment of the machine is preferred in which at least a cooling device for cooling the suction belt is provided. With help the cooling device, the suction belt is cooled to the extent that the Suction belt coming into contact first toner image that is on the bottom of the Substrate is located during the melting of the substrate top located second toner image is not melted again. Preferably so much heat is extracted from the first toner image via the cooled suction belt, that the toner layer of the first toner image does not become soft. This leaves the Image quality of the first toner image is completely unaffected by the fixing process of the second toner image.

In a preferred embodiment, the cooling device is on the opposite side of the substrate Side of the suction belt arranged - in the substrate transport direction seen - in front of the fixing device or within the fixing device. The cooling device can thus, for example, be opposite the heating device be arranged so that the suction belt directly at the point in the fixing device is cooled, on which the second toner image is melted becomes.

According to a development of the invention, it is provided that the substrate flat side of the suction belt coming into contact a defined, depending a desired gloss of the fixed toner selected surface roughness having. The surface structure of the suction belt, which is due to excessive heating of the toner image imprinted on it determines the gloss of the toner image. The smoother the surface of the suction belt, the smoother it is also the surface of the toner image sucked onto the suction belt and so on higher its gloss. In this embodiment, the surface structure is embossed of the suction belt in the already fixed toner image is just desired, so that a defined, uniform and, above all, simple way reproducible gloss is adjustable. This can control the melting process at least for the first toner image. Preferably is the suction belt of an electrostatic in this embodiment Suction belt formed. Conversely, if desired, the suction belt instead be equipped with an antistatic element to prevent the Avoid substrates and favor delivery and handover.

The suction belt according to the invention can, for example, be made of coated metal, coated polyamide or Teflon. The suction belt coating or the material from which the suction tape is made is preferably wear-resistant and has only a low surface energy. Preferably on the suction tape is a thin layer of a "release agent", for example silicone oil applied.

This is used to set a defined surface roughness of the suction belt for example, sandblasted or impact deformed. The diameter of the on the Suction belt thrown processing material, such as the sand in the Case of sandblasting, determines the roughness of the suction belt.

An embodiment of the machine can provide that the heating device has at least one microwave resonator through which the suction belt is guided is. The microwave resonator applies this to the suction belt flat-lying substrate with microwave radiation, which means that on the Top of the substrate located toner image is melted. By means of the Suction belt can guide the substrate exactly along the transport path be guaranteed.

It remains to be noted that the front of the substrate - depending on the view - can form both the top and the bottom, that is, the first toner image can be on the front or back of the substrate. The same applies accordingly to the second toner image.

Further advantageous embodiments result from the remaining subclaims.

In particular, according to a further development of the invention, for those who are also more independent Protection is claimed and that mentioned above the suction belt essentially consists of a fabric, whereby "tissue" is to be understood in general and in a broad sense and in particular also includes, for example, knitted goods or the like and not just one woven goods. It is advantageous that the suction belt comprises a fabric, which extends uniformly across the entire width and is therefore uniform Forms a base for the entire substrate.

The fabric of the suction belt is preferably endless and seamless as a closed one Loop made, for example, as a section of a seamless one Hose or stocking.

The fabric can preferably consist of polyester and, for example, an antistatic element and / or comprise a stiffening element, both in the form of a Yarn or melt thread more or less incorporated into the fabric could be. Here, a stiffening element in the transverse and / or longitudinal direction of the suction belt.

A further development of the invention provides that at least one guide element is arranged on the suction belt, preferably two parallel to each other running guide ribs along the underside of the suction belt are in with guide grooves in a drive shaft of the suction belt Stand in engagement and the suction belt slips in the transverse direction, i.e. in Prevent axial direction of the drive shaft. The guide ribs can, for example consist of a rubber-like, bendable material, so that the Bends of the suction belt can follow like a belt.

Fig. 1

eine schematische Darstellung eines Ausschnittes aus einem ersten Ausführungsbeispiel einer erfindungsgemäßen Druck- oder Kopiermaschine in einem Längsschnitt,

Fig. 2

einen Ausschnitt aus einem zweiten Ausführungsbeispiel im Längsschnitt und

Fig. 3

den Ausschnitt gemäß Fig. 2 in der Draufsicht.

Exemplary embodiments from which further inventive features can also result, but to which the scope of the invention is not limited, are shown in the drawing. Show it:

Fig. 1

2 shows a schematic illustration of a detail from a first exemplary embodiment of a printing or copying machine according to the invention in a longitudinal section,

Fig. 2

a section of a second embodiment in longitudinal section and

Fig. 3

the section of FIG. 2 in plan view.

The invention is first explained in more detail with reference to FIG. 1. This shows in schematic representation of a detail from the first embodiment a digital printing or copying machine 1, namely a fixing device 3, the for fixing a toner on a substrate 11, for example paper sheets, serves.

The fixing device 3 has a heating device, which here is a first Microwave resonator 5 and a second microwave resonator 7 are formed. The microwave resonators 5, 7 are - in the transport direction 9 of the substrate 11 seen - arranged a short distance apart. The construction and the function of the microwave resonators 5, 7 is basically known, so that in the following is only briefly discussed. The microwave resonators 5, 7 each have a slot-shaped opening 13 and 15 through which the transport path of the substrate 11 runs. Inside the openings 13, 15 the substrate 11 is exposed to microwave radiation, causing a on the substrate top transferred toner image is melted and with the Substrate 11 connects.

Around the substrate 11 along the transport path through the microwave resonators 5, 7 to pass through, a transport device 17 is provided, which at least A suction belt 19 has a number of through openings 21 is provided. The suction belt 19 is, according to the invention, of a close-meshed Sieve formed. This preferably extends across the entire substrate width Extending suction belt 19 is designed here as an endless belt and via guide rollers 23, 25, 27 and 29 out. The guide rollers 23, 25 are arranged that the intermediate suction belt section was intended to be parallel to each other Horizontal runs. As can be seen from the figure, the is between the Guide rollers 23 and 25 located suction belt section through the openings 13, 15 of the microwave resonators 5, 7 out.

A magnetron 31, which is used for supply, is arranged in the interior of the suction belt loop the microwave resonators 5, 7 are used with microwave radiation. Further suction boxes 33 and 35 are provided, which the microwave resonators 5, 7 - in Seen substrate transport direction - are upstream or downstream. The Suction boxes 33, 35, which extend over the entire width of the suction belt 19 can, are connected to a vacuum source, not shown, by means of which via the through openings 21 in the suction belt 19 air between the substrate 11 and the suction belt 19 can be sucked off, as indicated by arrows 37. As a result, the substrate 11 is held securely on the suction belt 19.

In the embodiment shown in the figure, each of the microwave resonators 5, 7 a suction box 39 is integrated, which consists of one in the bottom of the transport path of the substrate 11 part of the microwave resonator arranged vacuum chamber 41, which is used to vacuum the between the guide rollers 23, 25 lying suction tape section has an opening.

The opening is by means of a perforated plate 43, which consists for example of Teflon, covered. The vacuum chambers 41 are connected to one another via a connecting channel 45 and via a common connecting duct 47 with a blower 49 connected to apply pressure to the vacuum chambers 41.

About the function of the fixing device 3: The substrate 11 is one of the fixing device 3 upstream part of the machine 1 transferred to the suction belt 19 and flat on the suction belt section located between the guide rollers 23, 25 hung up as shown in the figure. The toner image to be fixed is on the substrate top 51. On the substrate bottom 53 there is another first toner image that was already on the in a previous fixing process Substrate 11 is fixed. By moving the suction belt 19 in the transport direction 9, the substrate 11 is successively through the slit-shaped openings 13, 15 of the microwave resonators 5, 7 guided and with microwave radiation acts, whereby the toner image located on the substrate top 51 is melted and fixed. In the area of the suction boxes 33, 35 and the microwave resonators 5, 7 or their vacuum chambers 41 the substrate 11 is sucked onto the suction belt 19. After the substrate 11 the Has left the effective range of the microwave resonators 5, 7, it will be in the range the guide roller 25 separated from the suction belt 19 and to a subsequent one Part of machine 1 transferred. The suction of the between the guide rollers 23, 25 located suction belt section is also used for stabilization of the suction belt 19.

The fixing device 3 described in Figure 1 is characterized by a compact Building on. In another embodiment, not shown, is provided that the heating device for melting the toner image only comprises a microwave resonator. Alternatively, one can also be used as a heating device Radiation device are used, which the toner image with electromagnetic Radiation, for example in the UV range and / or infrared range. Alternatively or additionally, the toner image can also be used with hot air or Steam is applied to melt it. It is also conceivable that the Heating device, for example at least one heatable heating roller or roller which mechanically contacts the toner image to melt it.

This option is used in connection with the exemplary embodiment according to Figures 2 and 3 still come back.

In addition, it can be provided that the suction belt 19 is not shown Cooling device is assigned, which serves to cool the conveyor belt. The Cooling device can for example be arranged inside the suction belt loop be and the suction belt, for example, in its return area cool between rollers 25, 27, 29 and 23.

The toner mentioned in connection with the present invention can be a liquid or dry toner.

In the second, in Figures 2 and 3, once in a longitudinal section and once in the plan view, illustrated embodiment, there is at least one Suction belt 19 of the transport device 17 made of a woven, meshed fabric. The same or corresponding components are shown in FIGS. 2 and 3 the same reference numerals as in Figure 1.

The transport device 17 described with reference to the figures can be both the Feeding the substrate to the heater also serve to substrate to pass the heating device and for further transport of the substrate to a subsequent part of the printing or copying machine 1. Everything becomes clearly that the transport device 17 alternatively only the feed of the substrate can serve for the heating device, for this purpose the at least a suction belt of the transport device in front of the heater to the The beginning of the transfer line is returned. According to a further variant it is provided that the transport device only the substrate past the heater, feeding the substrate and its further transport from the heating device to a subsequent part the machine is carried out with the help of at least one further transport device. According to a third embodiment variant, it is provided that the transport device 17 exclusively for the further transport of the substrate from the heating device to a subsequent part of the machine. Of course can the at least one transport device 17 can also be configured such that with the aid of which the substrate 11 is fed to the heating device, on the heating device passed over and / or transported further by the heating device.

The use of the respective suction belt 19 and those indicated above possible subdivisions of the transport route can in particular also be made dependent on the type of heating device used.

For example, it would be possible to use a suction belt in a microwave heating device 19 according to the embodiment of Figure 1 to use To transport substrate through the heater, while for example Transport and to bridge the path between the toner inking units or a transport section according to the actual printing units and the heating device of the embodiment of Figures 2 and 3 are taken could.

On the other hand, for example, for transport before, through and after a heating device with a touching, pressure-exerting heating roller a continuous one Transport section according to the second embodiment from the figures 2 and 3 can be taken alone. Other subdivisions and combinations are conceivable.

Figures 2 and 3 show a extending over a transport section Transport device 17 with lateral housing parts 55. As in the enlarged Section IIIa indicated, the suction belt 19 is a mesh fabric with tight Through openings 21 are formed. The suction belt 19 is by means of a drive shaft 57 driven and tensioned by means of a tension shaft 59. It runs endlessly and seamlessly around these waves 57, 59 um. The drive shaft 57 is by means of a motor 61 driven. To guide it on the drive shaft 57 points the suction tape 19 has raised guide ribs running along its underside of the edges 63 on the guide grooves of the drive shaft, not shown 57 are engaged. The completion of the transport device 17 in the transport direction 9 forms an outlet plate 65 for the delivery or transfer of the transported Substrate 11.

The patent claims submitted with the application are proposed without prejudice for obtaining further patent protection. The applicant reserves the right to add more, so far only in the description and / or To claim drawings disclosed combination of features.

Back-references used in subclaims indicate the further development of the subject matter of the main claim by the features of the respective subclaim; they are not to be understood as a waiver of the achievement of independent, objective protection for the combinations of features of the related subclaims.
The exemplary embodiments are not to be understood as a restriction of the invention. Rather, numerous changes and modifications are possible within the scope of the present disclosure, in particular such variants, elements and combinations and / or materials, which, for example, by combining or modifying individual ones in conjunction with and described in and in the general description and embodiments and the claims Features or elements or method steps contained in the drawings can be found by the person skilled in the art with regard to the solution of the task and lead to a new object or to new method steps or method step sequences by means of combinable features.

LIST OF REFERENCE NUMBERS

1

Copying or printing machine

3

fixing

5

1.Mikrowellenresonator

7

2.Mirkrowellenresonator

9

transport direction

11

substratum

13

opening

15

opening

17

transport device

19

suction belt

21

Through openings

23

leadership

25

leadership

27

leadership

29

leadership

31

magnetron

33

suction box

35

suction box

37

arrow

39

suction box

41

Vacuum chamber

43

perforated plate

45

connecting channel

47

connecting channel

49

fan

51

top

53

bottom

55

casing

57

drive shaft

59

clamping shaft

61

engine

63

guide rib

65

outlet plate

Claims (22)

Digital printing or copying machine (1) for one-sided or double-sided printing of a substrate (11) using at least one toner, with at least one fixing device (3) for fixing the toner on the substrate (11), the fixing device (3) at least one Has heating device for melting the toner, and with at least one transport device (17) for feeding the substrate (11) to the heating device, passing the heating device and / or for further transport from the heating device, the transport device (17 ) has at least one suction belt (19) which is provided with a number of through openings (21) and can be subjected to negative pressure, characterized in that the suction belt (19) is meshed. Printing or copying machine according to claim 1, characterized in that the total cross-sectional flow area of the through openings (21) is larger, preferably significantly larger, than the total area of the webs between the through openings (21). Printing or copying machine according to one of the preceding claims, characterized in that the through openings (21) each have a diameter which is less than 1.0 mm. Printing or copying machine according to one of the preceding claims, characterized in that at least the surface of the suction belt (19) coming into contact with the substrate (11) is coated with a separating material. Printing or copying machine according to one of the preceding claims, characterized in that at least the surface of the suction belt (19) which comes into contact with the substrate (11) is coated with a material which has a low surface energy. Printing or copying machine according to one of the preceding claims, characterized in that the adhesion of the substrate to the suction belt (19) is brought about by electrostatic charging of the substrate and / or the suction belt and / or as a result of friction between the substrate and the suction belt. Printing or copying machine according to claim 4, characterized in that the suction belt is coated with a thin layer of a release agent, in particular with silicone oil. Printing or copying machine according to one of the preceding claims, characterized by at least one cooling device for cooling the suction belt. Printing or copying machine according to one of the preceding claims, characterized in that the cooling device is arranged on the side of the suction belt (19) opposite the substrate (11). Printing or copying machine according to one of the preceding claims, characterized in that the flat side of the suction belt (19) which comes into contact with the substrate (11) has a defined surface roughness selected as a function of a desired gloss of the fixed toner. Printing or copying machine according to one of the preceding claims, characterized in that the heating device has at least one microwave resonator (5, 7) through which the suction belt (19) is guided. Printing or copying machine according to one of the preceding claims, characterized in that the suction belt (19) consists essentially of a fabric. Printing or copying machine according to one of the preceding claims, in particular according to claim 12, characterized in that the suction belt (19) is manufactured endlessly as a closed loop. Printing or copying machine according to one of the preceding claims, characterized in that the suction belt (19) is essentially made of polyester. Printing or copying machine according to one of the preceding claims, characterized in that the suction belt (19) has at least one antistatic element. Printing or copying machine according to claim 12 and 15, characterized in that the antistatic element is incorporated as a yarn in the fabric. Printing or copying machine according to one of the preceding claims, characterized in that the suction belt (19) has at least one stiffening element. Printing or copying machine according to claim 12 and 17, characterized in that the stiffening element is a melting thread. Printing or copying machine according to one of the preceding claims, characterized in that the suction belt (19) has at least one guide element running in the circumferential direction. Printing or copying machine according to claim 19, characterized in that raised guide ribs (63) are provided as guide elements along the underside of the suction belt (19). Printing or copying machine according to claim 20, characterized in that the guide ribs (63) can be brought into engagement with guide grooves in a drive shaft (57) for the suction belt (19). Printing or copying machine according to one of Claims 1 to 10 or 12 to 21, characterized in that the heating device comprises at least one heating roller, under which the suction belt (19) can be moved faster than the peripheral rolling speed of the heating roller, the heating roller being on the toner supporting substrate (11) can be pressed and the substrate (11) can be driven by its rolling movement in the transport direction (9) of the suction belt (19) in such a way that the substrate (11) remains behind the suction belt (19) at a lower relative speed or lags behind.

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