DE1671577A1 - Method and device for relief printing - Google Patents

Description

RANK XEROX LIMITED
Rank Xerox House
338, Euston Road
London, NW1
England

MÖHLSTRASSE 22, CALL NUMBER 483921/22

The invention relates to an imaging method, in particular to a relief printing process.

Relief printing or typographic printing is a contact printing process, in which the image surface parts of the printing plate are arranged raised above the flat reference plane of the plate. A paint roller with a common ink is drawn over the surface out of the relief printing plate. Through the sublime training of the image area parts, the ink comes into contact and is deposited on only these parts of the printing plate. The colored image is then transferred directly to a copy sheet, generally by pressure. This type of pushing will commonly referred to as letterpress.

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Although letterpress printing is the classic form of printing and has found widespread use, it also has disadvantages. A very high pressure is generally required to print a relief image area, and a uniform application of the printing ink to the printing areas and, in many cases, a very high relief of the letters in relation to the background areas is necessary. The relief is generally made by a chemical etching process or mechanical engraving to achieve the desired results. In practice, the high pressure used at the edges of the letters results in the well-known "paint splashes ^11. If the printing areas are very small, the pressure is extremely high. If the printing areas are large, the pressure is quite low. This pressure difference requires a large one A further disadvantage of letterpress printing is that the printing inks normally used are viscoelastic and exert considerable pressure on the copy paper when it is peeled from the printing plate In order to overcome some of these difficulties, a printing method was developed in which a rubber-covered cylinder is used as an intermediate element in the transfer of the image from the printing plate to the copy sheet However, the proceedings are still going to take place overnight ile on, an interface is required, which increases the number of image transfers; and the picture quality is deteriorated.

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There has also been proposed a printing method in which the liquid ink by electrostatic lines of force on the Printing area and then transferred from the printing area to the image area. Due to the properties of the substances used however, this procedure is severely restricted. The inks are charged by induction and release their charge as soon as possible they get out of the force field. In addition, the surface tension of the printing ink is generally greater than any effective electrostatic force. It is therefore generally believed that ink transfer is not possible without contact is. In addition, special steps must be taken to control the selective development of the printing area.

A method of making a print with a relief printing plate is designed according to the invention in such a way that the printing surfaces of the relief printing plate with dry developer material are developed and that the developed printing plate with the surface of a one opposite the developer particles different potential leading copy sheet is brought into contact, so that the developing material particles in imagewise Distribution can be transferred to the copy disk.

A device for carrying out this procedure contains according to the Brrinduiif a rotatably mounted pressure plate, one near the Pressure plate parallel to this rotatably mounted dispenser for Applying a charged developer powder to the printing plate, a device for generating an electrical voltage between the surface of the printing plate and the dispenser, the one

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Transfer of the charged developer powder from the dispenser to the relief printing area the pressure plate causes a drive device for rotating the pressure plate and the dispenser and a device for transferring the developer powder from the relief printing surface to the surface of a copy tape.

The invention is described below with reference to the figure, in which, in section, a device for carrying out the invention Procedure is shown.

In the figure, a relief printing plate 1 is shown, which Has the shape of a letterpress cylinder, which consists of raised printing surfaces 2 and recessed non-printing surface parts 3. Near the relief printing plate 1 a rotatable donor electrode 11 is provided with its axis parallel, which consists of a metallic Drum 13 and a semiconductor layer 12 applied thereon. Next to the donor electrode 11 is a development electrode 14 arranged, preferably corresponding to the donor cylinder is curved. The development electrode can be made from a solid sheet, a grid, a group of wires, or a Number of points that are close to the surface of the donor electrode. The development electrode is with the Power source 16 connected. Above the developing electrode 14 and the donor cylinder 11 there is an output container 15, from which a cascading devolatilizer containing electroscopic toner particles is applied to the surface of the donor cylinder is applied. The developer falls between the surface of the dispenser drum and the development electrode 14-, so that it covers practically the entire surface of the dispenser. the

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Particles not held on the surface of the donor electrode fall into container 18, from which they are transferred to the dispensing container 15 can be transferred. The developer 17 preferably consists of finely divided, pigmented electroscopic Particles and a coarser carrier, which is triboelectrically to one of the polarity of the electroscopic Character particles of opposite polarity are charged when they come into frictional contact. The charge of the toner particles can be improved by an optionally provided corona discharge device 21 which has a charge with one polarity on the toner which applies the polarity of the triboelectric generated toner charge corresponds. The development electrode 14 promotes the overall development of the donor surface and carries a voltage between approx. 400 and approx. »1000 volts one of the polarity of the frictionally charged toner particles corresponding polarity.

The relief printing drum 1 is in a weak pressure contact brought with the donor electrode 11. The toner particles are transferred from the surface of the donor electrode to the relief printing areas the printing plate drawn in accordance with the electrical IPeId generated by the power source 21, since the relief printing plate is located near the surface of the donor electrode. The toner particles 17a, which are now on the raised 3? Smile parts 2 of the Relief print plates 1 adhere, come into contact with copy tape 31. This is brought into contact by the roller 51 via the guide roller with the surface of the printing plate 1, for which purpose the mtb of the power source 41 connected ever capable transmission

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role 33 serves. The toner particles are transferred in an image-wise distribution onto the surface of the copy tape 31 by the action of the electric field generated between the conductive transfer roller 33 and the surface of the relief printing plate 1. The potential generated by the current source 41 on the transfer roller with respect to the relief printing plate 1 has a polarity opposite to the charge of the toner particles 17a and is so strong that the attraction of the relief printing plate is overcome and thus a transfer of the toner particles to the copy tape is caused. The transferred toner image is guided over a zwdte! Guide roller 34 to a fixing device, which is shown as a heat fixing device 45 in the I ¹ IgUr. Then, the copy tape provided with the fixed image is fed to the take-up roller 52 via the roller 47.

The surface of the relief printing plate is moved past a cleaning brush 61 which removes any residual toner from the plate surface and prepares the plate for another printing cycle. Also, untransferred toner can easily be recharged to the desired polarity and used again. A drive device 62 is provided for rotating the parallel parts of the device. Although the Spatimingswerfe of the relief printing plate is not; Is tritic, a voltage between approx. 200 and approx. 1500 volts is preferably used with respect to the donor drum, the value actually selected depending on the air gap between the charged toner particles and the relief printing areas of the printing plate. In the embodiment described, the surfaces dex «relief printing plate and the donor electrode have a distance that

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varies between actual contact and a value of approx. 0.08 mm. Optimal results require a voltage difference of approx. 1000 volts with a transmission air gap between actual contact and approx. 0.025 mm.

The relief printing plate used in the present invention may have a cylindrical shape according to the device shown in the figure have or it is designed as a flat printing rotary plate, the relief image having a height difference between the Printing areas and the non-printing areas of 0.025 to approx. 0.8 mm.

Although the development of the donor electrode has been described in connection with a cascading process, which in more detail as illustrated in U.S. Patents 2,618,551 and 2,618,552, other development techniques may be used, for example powder cloud development in US Patents 2,725,305 and 2,918,910 and magnetic brush development in U.S. Patents 2,791 94-9 and 3,015,305. Also Any suitable toner or developer can be used, such as those described in US Pat. Nos. 2,788,288, 3,079 34-2 and Re 25 156 substances described. The toner generally consists made of a synthetic resin, which in the fixed state has the properties required to create a permanent print ' Has. Typical developer powders are styrenic polymers including the substituted styrenes such as those from Pennsylvania Industrial Chemical Corporation available piccolasty resins, phenol-formaldehyde resins, and other resins with similar properties. The development

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Wrapping material particles are selected so that they through the Fields on the surface of the donor electrode are electrostatically attracted and held there by electrostatic attraction will.

Although the surface of the donor electrode is made of a conductive material such as aluminum, brass, steel, copper, nickel, and zinc Compositions of these substances can exist, a conductive substance is preferably coated with a synthetic resin for this purpose Conductivity used to determine the resistance of the electrostatic field as well as the retention of the developer particles to ensure on the electrode surface. Typical semiconducting substances with low electrical conductivity are polyvinyl acetates, Polyvinyl alcohol, cellulose acetate, iithyl cellulose and mixtures thereof. Other suitable substances with a specific

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See resistance of about 10 ohmcm or more can also be used. Typical such materials are cellophane, polystyrene, polytetrafluoroethylene, polyethylene terephthalate, polyethylene-coated papers, polyvinylidene chloride, polyvinyl fluoride and mixtures thereof. Another advantage of using these materials is that the possibility of short circuits is reduced.

Any suitable material can be used for the copy tape for transferring the developed image from the relief plate. It can be an insulator, or it can be partially or fully conductive. Typical materials are polyethylene, polypropylene, polyethylene terephthalate, normal fine paper, ethyl cellulose, cellulose acetate utid Tedlar, a polyvinyl fluoride. Will the relief printing areas

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the printing plate covered with a thin layer of a dielectric material of the type mentioned above, so the developed If desired, the image can also be placed on a conductive surface be transferred, which consists for example of copper, aluminum, zinc or brass, including that in US Pat. No. 5,004 described procedure is applied.

The induction transfer method is used in which the relief printing plate is coated with a thin dielectric layer with a Thickness between approx. 0.0025 and approx. 0.25 mm, preferably between approx. 0.02 and 0.038 mm, can be covered with any suitable insulating material with a specific resistance of the order of magnitude

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10 ' ohm cm, for example Krylon, an acrylic ester resin from Krylon Inc., Viken, a vinyl plastic from Chemical Rubber Co., Mylar, a polyethylene terephthalmic resin from EI duPont de Nemours & Co., Inc., polyethylene, Polypropylene and other similar thermoplastics and their combinations. Furthermore, any suitable thermosetting synthetic resin can be used, for example phenolic resins such as phenol-formaldehyde, halibto-fformaldehyde resins, melamine resins, alkyd resins and the various epoxy resins. The preferred thickness of the coating is determined by the fields generated.

If the printing surface is covered with a thin coating of a poorly conductive one or semiconducting material with a specific resistance in the range of approx. 1o "to 10 ^ ohmcm, any suitable composition can be used for this purpose. "Typical semiconductors of this type are polyvinyl acetates, polyvinyl

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alcohols, cellulose acetate, ethyl cellulose and various dielectric Substances that are doped with conductive additives. Such additives are Staybelite, an amine resin treated with nigrosine and VYNS, a vinyl chloride acetate resin treated with Rhodamine B and combinations thereof. The strength of this coating is through determines the generated fields and lies in a range similar to the dielectric coating of the induction transmission process is. Optimal results are obtained with fabrics whose special

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fischer resistance is approximately 10 Ohmcm. It is regarded as a consequence of the semiconducting coating that the generation of strong fields as well as the charge density at the sharp edges of the letters, as they are generally present, are markedly reduced, so that the time required for the image transfer is too short to allow a so-called " Developing agent expansion "to generate when the copy tape comes into contact with the characters.

Although a heat fixing device has been mentioned for fixing, any other suitable fixing method can also be used, for example the action of vapors, the treatment of the developed image with a regulated amount of heat, as shown, spraying the toner image with an adhesive film to form a coating or applying a plastic sheet to the Surface of the transferred image.

The following examples serve to further illustrate the present invention, but they are not intended to restrict the basic concept of the invention. Parts and percentages are by weight unless otherwise stated.

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Example I.

A sheet of 3aryt paper, paper coated with BaSO ^, is passed through a cassette method using an electrode to dusted to a thickness of 30 microns with an even layer of toner particles made of polystyrene, the The interaction between paper and toner is such that the toner particles assume a negative electrical charge. the Charge on the surface of the toner particles is improved by the particles are further exposed to a negative ion spray generated by a coronal device. A letter field a pressure plate, which carries a voltage of approx. +1000 volts in relation to the dispenser surface, is close to the grounded dispenser brought closer, i.e. up to a distance of approx. 0.025 mm. Mach the separation of the pressure plate from the dispenser is located a negative image on the donor paper while the toner particles are transferred as a positive image on the relief types of the printing plate. The thus dusted letter surface is then with brought into contact with a transfer sheet, a negative Voltage of approx. 1000 volts compared to the earthed paper backing on the printing plate. The toner particles are off the printing plate transferred to the surface of the transfer paper in a distribution corresponding to the relief image of the printing plate.

Example II

The letter field of a relief printing plate is developed according to the method described in Example I with the difference that that the relief surface was previously coated with a layer of polyethylene terephthalate up to a thickness of approx. 30 microns.

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After the subsequent transfer of the toner particles to the characters, the thus dusted plate is -on a > Voltage of approx. -600 volts through a corona discharge device after which the particles were placed on an aluminum copy sheet are transferred by bringing this into contact with the grounded pressure plate that carries the charged toner particles will. The method is more fully described in U.S. Patent J004 860. The toner particles are transferred onto the aluminum substrate in an image-wise distribution.

Example III

The letter field of a relief printing plate is made according to the method in Example I developed the method described with the difference that previously a coating of a composition of 100 grams Toluene, 30 grams of Staybelite and 0.15 grams of kigrosine with a Thickness of approximately 50 microns is applied. The rest of the steps of the procedure correspond to the steps mentioned above. The results obtained are similar to those from Example I, whereby the picture quality is a bit better.

Although the above examples contain specific conditions and substances, all of the typical substances mentioned above can be used with similar results. In addition to the erfindungSGemfißen steps further steps] can ode "Abfandermren _t as desired u2 ⁱ ch _i ^ eiührt been Beinpd (* ^c: wci i:..... O kaun dj c i; it toner provided kt ■ Irfdruckplatte begin rji ; an exercise. ^ trafvun ^ ßband Jn Leir-uhi-uiii ;; net avenge to be before do-- ÜL-crtrar; uno of the toner particles a volJ iiiiindig; Tiorührun · -:. · π.ύ der, "· au - "= ? λι b (-v ;. ^; · · .'r / _; n. ? AlsUtzllch '.- ^.: 'ir..C'i.ve; 1: cf iitofie in de ¹¹ hvx r-rr ^ r- '} rV ; ■ <\ ^ , - \ η ^Ύ

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Developing material particles, the relief printing plate or the transfer surfaces be included, which is an enhancing, synergetic or otherwise have a beneficial effect on the properties of the process according to the invention. For example, can additives that increase the conductivity of the respective substance may be present within the insulating material layers.

On the basis of the invention, those skilled in the art are able to develop further developments that are based on the basic idea of the invention be included.

Claims (3)

- VY - - T67T577 P_a__t_e_n_t_a_n_s_ £ _r_ü_c_h_e 1. A method for producing a print with an intaglio printing plate, characterized in that the printing surfaces (2) of the relief printing plate (1) are developed with dry developer particles (17) and that the developed printing plate (1) with the surface of a one opposite the developing agent particles ( 17) different potential leading Kopieblattss is brought into contact (31), so that the Entwicklerstoffteilchen (17) is transmitted i ⁿ imagewise distribution to the copy sheet (31). 2. The method according to claim 1, characterized in that the rotogravure printing plate (1) a PiIm applied before development contains a dielectric insulating material. 3. The method according to claim 2, characterized in that the dielectric 9 15 a specific resistance of 10 to 10 Ohmcm owns. 4. Method according to one of the preceding claims, characterized in that the relief printing plate (1) is developed in that the printing surfaces (2) are brought close to the surface of a donor electrode (11) which is covered with a layer Elei "GrosLopischer toner particles (17) isn dusted, and daii st / iaehen Selieidruckplabfce (1) and Spendereiektrods (11) an electrical field is :: · arzanrt so that -lie toner particles (17)"'he ^r, represents Spexidereiektroie ( 11) aiii "the Druo ^ flUchon (2) the LiDliei'druckulatte (1) transmitter. We> dsu, K, \ ^r η vl ah. cn η also An. ρϊτλΙι - '! ,! vl · ...-: ":!: cr.:'.?oic.unai·, duü; iic Si ^ li-ji d :: a: ikp! λι; ¹ : ·! (Λ) ;. ·. ; ί 1Ί: ϊ ..in, -):, !! -. ··, _u · _.; n ·. ¹ '- (11; Θΐΐϋη Aba band from ü inJü-iV · 3.VG ,, in uaber. Ui 9 t fl β / (j J ij H BATH ORIGINAL 6. The method according to claim 4 or 5 »characterized in that the The donor electrode (11) consists of a conductive base (13) with a thin semiconductor layer (12) applied over it. 7. Device for performing the method according to one of the claims 1 to 6, characterized by a rotatably mounted pressure plate (1), by one close to the pressure plate (1) parallel to it Drehbayfeelagerten dispenser (11) for applying a loaded Developer powder (17) on the printing plate (1) by a device (21) for generating an electrical voltage between the surface of the printing plate (1) and the dispenser (11), the one Transfer of the charged developer powder (17) from the dispenser (11) on the relief printing surface (2) of the printing plate (1) caused by a drive device (62) for rotating the pressure plate (1) and the dispenser (11), and by means (33, 41) for over-transforming of the developer powder (17a) from the relief printing area (2) onto the surface of a copy tape (31) 3. Device according to claim 7 »characterized in that the pressure Plate (1) and the dispenser (11) are arranged so that they are less at the point of the superior of the developer powder (17) a distance of 0.076 mm from each other. 9 «Device ave claim 7 or 6, characterized in that i'er nor the Spencer (11) is an Entvrichrunirsc'lekoroae (1 ^)," - υ ^ ecrd.net 10. Establishment r.ccli claim% da-'Iuron gekei-nsr-jehnci, deii the «Spei: rcr (11) from an i.eii -: ü.b_ron. ür:; erl;.: ^ '"Ii") v.,. \: (une: · - öM-iuJ auf-fcebraehter: uiJm copy 1 V, 0 f. Fc $ /: \ -H - Blank page