DE2262432A1 - METHOD AND DEVICE FOR TRANSFERRING IMAGES - Google Patents

Description

"Method and device for transferring

• Images "

The invention relates to electrostatic reproduction and more particularly to a method and apparatus by means of the properly readable copy (s) on a desired receiving sheet from a properly readable one electrogranhischen or electrostatic original sheet or member are generated. __

Transfer methods are known in which an electrostatic latent image is formed on the surface of a photoconductive or dielectric recording member. The latent image is made visible by using electroscopic marking particles. The mar- "'309827/1041

Coating particles can be suspended dry or in an insulating • liquid, a so-called carrier liquid be. Such carrier liquids generally have a volume resistivity greater than 10 ^ ohm cm and a dielectric constant of less than 3 x The developed image precipitate is then transferred to a recording member by a surface bearing the image is brought into contact with the surface of a recording member, usually with simultaneous application of a directed electric field. The combination of touch and use of such directed electric field causes at least a portion of the image precipitate to be transferred to the recording member surface.

It is also known to have more than one developed image precipitate to be transferred to a recording member. In the end it is known to form electrostatic latent images using electroscopic marking particles or toners of various kinds Develop colors. This combination enables multicolor images to be formed on the surface of a desired recording member, for example a paper web or a metal surface or the like.

A disadvantage of the previously known transmission method is the need to generate the image on the receiving member as a mirror image of the image to be transmitted per se. Accordingly, if it is necessary that the ultimately transferred image can be read the correct way round, it is necessary that the image as developed on the receiving member, such as an electrophotographic original sheet, be a mirror image. While this is not a particular disadvantage with an office copier, as it optically creates right vray reading or mirror-image (wrong way reading) images that correspond to the original, this can have serious disadvantages when the electrostatic transfer process is used for the production of preliminary proofs for offset lithography

ver · 3 0 9827/1041

119243?

is turned. Such pressure tests are normally carried out Using positive transparencies produced, of which the printing plates are to be made as originals. That An electrostatic latent image is created by exposing the charged surface of an electrophotographic recording device. member is brought into contact with the transparency in a vacuum frame and exposed for a predetermined time. However, since offset printing plates can be read the correct way round, the transparency plates are usually made so that they Correctly readable images result when they are for imaging on a photosensitive member by means of contact exposure are used, the emulsion side of the transparent game in contact with the photo-sensitive surface of the image-wise exposed Oliedes is located. If accordingly such transparencies for the production of electrostatic latent images on electrophotographic pickup members used and the emulsion layer of the transparency is in contact with the surface of the receiving member, the image generated on it can be read the right way round. When such an image is developed and applied to the surface of a recording member is transmitted, it is on the Recording element generated image sr> reversed.

So you have so far the position of the transparent image during the Reverse contact exposure when correct-facing legible transfer copies were required. However, this leads to a Significant reduction in the point size if, as is customary in offset lithography, rasterized transparencies are used will. In special cases this leads to a complete loss of points in areas of great brightness (high-light dots). The image sample produced in this way is therefore not an exact template of the image which is ultimately produced if the same transparencies are used for the production of offset printing plates, in which the mentioned " Points in areas of high brightness (e.g. glossy, Highlights or highlights) can be obtained in a predictable manner.

309827/1041

? In further disadvantage of the known methods mentioned above when used for the production of pre-pressure sample is to limit the types of materials which are suitable as the recording elements using relatively low potentials for image transmission E. The reason for this is the insulating property of the electrophotographic or dielectric recording element and the further need to provide operational protection by covering the voltage application device, for example a roller with a resilient layer of insulating material. This combination limits the volume resistivity of the recording member when it is desired to use relatively low transfer potentials. Accordingly, it has been found that when the transfer potential is limited to 1500 volts or less, the recording member is limited in thickness to about 0.025 cm (0.010 ") or less in the case of a paper web. More insulating members such as plastic films or the like can normally be used as Recording members are not used at all at transmission potentials of this order of magnitude.

The object of the invention is therefore to create a method and a device of the type mentioned at the outset, in which or which removes the limitations previously described in the prior art.

According to the invention, the dots in areas of high brightness can be made to the same extent as in offset plate making although the same transparencies are used and although the one that was finally generated Transmission image can be read the right way round. In addition, enables the transfer method according to the invention a further selection of materials for the recording member can be used without endangering the personnel.

309827/1041.

- ■ 5 -

In accordance with the invention, the developed image deposit is deposited on an electrophotographic or electrostatic basis Original sheet is electrostatically transferred to a surface of an intermediate link and is then further applied to the Image recording member transferred. The desktop of the Intermediate member is conductive, which facilitates both the first and the second transfer step, since the first step the transmission voltages regardless of the electrical Properties of the image recording member can be adjusted can, while the relatively insulating photoconductive original sheet is not used in the second step, so that the Image recording member can have a higher resistance than the known method and the like Transmission potentials is the case. Thus, according to the invention, there is an electrostatic latent image on the surface generated from a photoconductive or dielectric original sheet. The template sheet can be used one or more times as desired be used. The image is, on it by means of "a dry or developed in liquid-dispersed toner of desired color. The developed image is transferred to an intermediate link, which is either metallic or has a metallic surface. The transfer takes place with the help of the electrostatic Transfer procedure. The image thus created is then applied to a surface of the recording member, for example a paper web or a metal surface or a synthetic film or the like. It is It is clear that if the image developed on the original sheet can be read the right way round, that too will ultimately result the image transferred to the recording member surface can be read in the correct direction.

To explain further details of the present invention, reference is made to the accompanying drawings.

Shown ^are:. ■

309827/1041

Pig. 1 An illustration of the method steps according to the method according to the invention, and

2 shows a preferred embodiment of a system,

which are used to carry out the invention Procedure suitable.

1 shows a carrier member 1 which has an electrostatically chargeable layer 2 on its surface, on which an electrostatic latent image 3 has been produced. Fig. Ib shows the electrostatic latent image after development using electroscopic marking particles ¹ I. In Fig. 1c, the developed receiving member is placed on a conductive support member 7. A first receiving member 5 is brought into contact with the developed surface 2 of the receiving member. The contact is ensured by means of the application of a conductive roller 6 with simultaneous application of a transfer voltage, whereby the electroscopic marking J ¹ are transferred to the surface of the first receiving member. 5 In FIG. 1d, the first receiving element 5 is placed on a sliding support 7 with the image side up. A second receiving member is brought into contact with the image-bearing surface of the first receiving member 5 under the influence of an electric field to transfer the marking particles H from the first receiving member 5 to the surface of the second receiving member 8 ai.

In Fig. 2 is a preferred system for carrying out the invention Procedure illustrated. Fig. 2a shows the use of the device for carrying out the first transfer process, while Fig. 2b shows the use of the device for Execution of the second transfer process reproduces. According to Fig. 2a, a conductive drum 11 is in contact arranged with a conductive roller 12. The conductive roller carries a relatively compliant one on its outer surface semiconducting layer 13. A receiving member 14, which on

30 9827/1OA1

. _7th 2252432

one side carries a developed image, which is made up of electroscopic There is marking particles 15, is introduced into the nip between the drum 11 and the roller 12, whereby the image precipitate 15 is closed to the drum 11 ". is. The drum 11 is grounded. The positive high voltage is applied to the roller 12 simultaneously with the rotation of the roller 11 in applied in the direction shown, whereby the image deposit 15 is transferred to the surface of the drum 11.

In Fig. 2b the second transfer process is illustrated, in which the application of a negative high voltage to the roller 12 causes the transfer of an image deposit 15 from the surface of the drum 11 on the surface of a second receiving member 16 causes.

It should be noted that the polarities shown relate to the transfer of electroscopic marking particles which are attracted to a negative polarity and repelled by a positive polarity. In such cases in which electroscopic marking particles are opposite If polarities are used, the transmission polarities must be reversed from those shown.

It is also noted that other mechanical devices can be made suitable for use in accordance with the basic principles of the invention. Several ', such devices are in the following for example as these are particularly suitable.

Example 1 :

A metallic drum was made with a circumference slightly exceeding the maximum length of the images to be transferred. For example, if the maximum sheet size is about 21 "30" (53 »5 cm 76.5 cm), the diameter was the

309827-041

Drum about 17.8 cm (7 ^W ) and its length about 80 cm (31 "). Drive wheels were provided at each end of the drum, the pitch circle diameter of which was equal to the drum diameter. The drum was made of aluminum with a grained Outer surface. A compliant (resilient) support member was prepared having racks along each edge that matched the pitch of the drive wheels on the drum. A pin alignment arrangement was provided at one end of the compliant support. The racks were arranged so that that the polished surface of the drum came into contact with the surface of the compliant carrier. The compliant carrier was a sheet of synthetic polyurethane rubber having a thickness of about 0.32 cm (1/8 "). The top surface of the resilient support was positioned to contact the polished drum surface, while the bottom surface of the support was bonded to a sheet of metal. The bare surface of the drum was isolated from the metal plate bonded to the lower surface of the resilient support. Drive means were provided to move the drum in relation to the carrier, the rack and pinion arrangement holding the drum and carrier in alignment with one another. The drive mechanism could be activated to rotate the drum while the axis of the drum was in a fixed position, thereby causing the resilient support to move in a direction perpendicular to the axis of the drum. Alternatively, the resilient carrier could be held in a fixed position and the drum moved across the surface of the carrier by engaging the pinions with fixed racks. Means were also provided for applying a directional electric field between the drum and the compliant support. Drum or resilient carrier could be grounded depending on your choice.

The electrophotographic template was thereby in operation manufactured to load a photoconductive receiving member,

309827/1041

exposed and the electrostatic latent image thus formed in a dry or liquid-dispersed toner of the desired color has been developed. It has been found desirable to have toners dispersed in liquid to be used in the production of color prints. However, the method and the device is also suitable for dry transfer. The master sheet with the developed The picture was made on the resilient support and on the registry pins aligned. In this state the drum is at the end of the path and free of stop pins. If, as usual, the receiving member photoconductive zinc oxide as Contains photosensitive material, the photoconductor is in front negatively charged after exposure. The toner for the image deposit is positively charged. In these cases a directed Field applied for transmission by giving the drum a negative polarity and the compliant carrier a positive polarity is allocated, with either the drum or the carrier additionally being earthed, if desired. The transmission potential is usually in the range of 200 to 2000 volts, but / L can be higher or lower in some cases depending on the value of the toner properties. To effect the transfer of the image deposit from the original to the drum, the drum is rolled over the carrier by the aforementioned drive means simultaneously with the aforementioned directed electric field is switched on.

The original sheet is then removed from the carrier and the Image recording sheet placed in the appropriate orientation on the carrier. The directed field is reversed simultaneously with switching on the drive device again to precipitate the image from "the drum surface onto the imaging sheet transferred to. The process becomes more different using different templates with image precipitates Colors repeated to obtain a colored print on the image recording member. In some cases you can alternatively transfer all colored toner deposits onto the drum and simultaneously add several toner deposits

309827/1041

3 ammeη be transferred back to the image recording member. This alternative requires the use of toners with a balanced electrophoretic "^ received".

Example 2:

In this example, two drums were used in addition to the compliant support member. The dielectric bearing the image Original was set in alignment with the upper drum and the transfer to the lower drum, which was metallic and was in contact with the upper drum. The imaging sheet was in registration on the compliant Carrier arranged. Using the electrical conditions already mentioned above for Example 1, the image was transferred from the photoconductive original to the drum and subsequently from the drum to the imaging sheet transmitted in one go. This device enables the image recording sheet to be in a fixed position on the Carrier remains during the entire multicolor transfer process. When wet transferring liquid developed However, images have been found to be particularly advantageous in short the upper part of the surface of the image recording member at least partially dry before each subsequent transfer step after the first pair.

Example 3 ;

In this example two rollers were also used, but without a resilient carrier. The two drums were side by side in a substantially common horizontal position Arranged level and held aligned with one another. In addition, alignment pins are provided on a drum, while the other has a smooth polished surface. The first drum can also be advantageous Have a resilient surface, such as an outer layer of semiconducting synthetic polyurethane rubber. During operation, the original sheet carrying the image is

_ n _ 2252432

arranged directed on the first drum. The two Drums are brought into contact with each other simultaneously with the application of the aforementioned directional electric field rotated to achieve the transfer of the image deposit to the polished surface of the second drum. That Original sheet is then removed and the imaging sheet is placed in alignment on the surface of the first drum. The directional field is reversed and the drums are rotated to transfer the image precipitate from the surface of the second drum onto the image recording sheet to effect. The process is repeated as many times as desired to obtain the desired multi-color print.

example U:

No drums are used in this example. A support link is used which is curved in only one direction, that is, the support member is a segment of a cylinder of a relatively large radius, such as about 61 to 1590 cm (2 to 50 feet) or more. This curved support member surface may be in the form of a stainless steel plate or an aluminum-coated polyester resin film or the like, with the necessary support. A roller is provided to come into contact with the curved Porter to kick. This roller is relatively small in diameter, for example about 3 »8 cm (½"). It is preferably coated with a resilient semiconducting layer of the type described above. Alignment means are provided at one end of the curved support member. During operation, the original sheet bearing the image is aligned placed on the curved support with the image bearing surface in contact with the support. That Directional electric field is applied while the roller is moving to establish contact between the. both surfaces to reach. If desired, the original sheet can immediately after passing through the roller out of contact with the curved carrier plate are brought. Before, the fore,

309827 / 10A1

Layer sheet taken away and an image recording sheet aligned laid down and the directed electric field reversed. At the same time there is a second pass of the roller, to effect the transfer of the image precipitate to the image recording member. The process can be repeated as many times as required for making a multicolor reproduction on the image recording sheet.

example 5 '

In this example, the first drum according to example 3 is replaced by a flexible roller according to example k . A pin alignment device is also provided over the nip between the two rollers. This apparatus operates in a manner similar to that of Example 3 and essentially the same as that of the embodiment of FIG.

It is noted that the metallized or metallic intermediate transfer member can also be in the form of a suitable and aligned continuous tape or web held on a feed roll and onto a take-up roll is convicted. Such a tape or web can be made of metal or a polyester resin film or be the like, one side of which is covered with a layer made of aluminum or another metal. The travel of such a belt or path can be provided by arranging suitable guide rollers so that the various transfer functions at certain Adjustment positions are met along the way to work.

It is also noted that the intermediate transmission member is normally reusable and usually needs to be cleaned between transfer sequences. This purification can be done by bringing the surface of the intermediate transfer member into contact with a wiper which is moistened with toner carrier liquid. A rotating brush can also be used.

309827/1041

Further paper guiding means and sheet separating means can also be used in each of the exemplary embodiments. where possible. The process can be automated to the greatest possible extent in this way.

In case of doubt, all of the features described and / or shown here are on their own or in any meaningful combination essential to the invention. Ira rest is sought protection for the what is objectively protectable.

Patent claims:

309827/1041

Claims (1)

Patent claims: Electrostatic process for the reproduction of Print templates, characterized by the following steps: Making an electrostatic latent image on the dielectric surface of an electrostatically chargeable. Recording member, developing the electrostatic latent image by attracting electro-conical marking particles, transferring the electroscopic mark kierungspartikel through to a first receiving surface simultaneous provision of the touch and a directed electrostatic field of a certain "polarity" around the transmission the marking particles on the first receiving surface to assist in transferring the electroscopic marking particles from the first receiving surface to a second receiving surface by simultaneously providing a touch and a directional electrostatic field a certain polarity in order to transfer the marking particles to the second receiving surface, and fixing the electroscopic marking particles on the second receiving surface. 2. The method according to claim 1, characterized in that that the number of the process steps is repeated several times and each time with a different color is performed. 3. The method according to claim 1 or 2, characterized in that that the developer contains electrostatic particles in an electrically insulating carrier liquid are suspended. Ί. Method according to one of Claims 1 to 3, characterized characterized that the developer elekfcro- 309827/1041 static particles in an electrically insulating liquid contains, and that a series of individual but successively different color images successively on the first or second receiving surface are applied, and that before each subsequent application of developer the surface of the imaging member at least partially prior to further transfer is dried. 5. The method according to any one of claims 1 to 4, characterized characterized in that a developer is applied to the first receiving surface by means of a field of one polarity is transmitted, and that. the first receiving surface is then applied with an opposite polarity, to repel the developer and knock it down on the second receiving surface. 6. The method according to any one of claims i to 5 * marked that a first application of electroscopic marking particles to the first receiving surface is made with particles of a selected color, and that then, in a second step, marking particles of a different color are applied to the first receiving surface to form an overprint, and that the two dyes thus deposited are then transferred to the second receiving surface and be fixed there. ■ 7. The method according to claim 6, d a d u r c h g e k e η η -> indicates that the first receiving surface receives at least one further dye in the same way and all deposited dyes then on the second receiving surface be transmitted. · 8. The method according to claim 6 or 7, d a d u r c h characterized in that the developer marking particles suspended in an insulating carrier liquid 309827/1041 Contains the use of fixing agents, and that before each dye application the first receiving surface in each case the application of a developer layer is at least partially dried. 9. The method according to any one of claims 1 to 8, characterized characterized in that the electroscopic marking particles a selected color onto a first receiving surface and from there onto a second receiving surface are transferred, after which marker points of a second selected but different color on one first receiving surface and then as an overprint on the second receiving surface are applied, whereby a Two-color image is created. 10. The method according to claim 9 »characterized in that that the method steps at least once more to produce an image with at least three colors are executed. 11. The method according to claim 9 or 10, characterized in that that the developer using marker particles suspended in an insulating carrier liquid of fixatives contains, and that before any dye application to the second receiving surface, each previously applied developer layer at least partially dried will. 12. The method according to any one of claims 1 to 11, characterized characterized in that the first reception is a Roller is on which the electroscopic marking particles can be applied from the dielectric surface by sandwiching the member with the dielectric surface Receiving roller and a pressure roller is carried out, which presses the member on the first receiving roller that a field of one 309827/1041 Polarity is applied between the rollers to transfer the electrostatic marking particles to the first receiving roller, that a sheet which forms a second receiving member is then passed between the rollers while a field of opposite polarity is passed between the rollers, whereby the electroscopic marking particles are transmitted from the first receiving element to the second receiving element. 309827/1041