CA2138064A1 - Device for producing an erasable printing form for letterpress printing - Google Patents
Device for producing an erasable printing form for letterpress printingInfo
- Publication number
- CA2138064A1 CA2138064A1 CA 2138064 CA2138064A CA2138064A1 CA 2138064 A1 CA2138064 A1 CA 2138064A1 CA 2138064 CA2138064 CA 2138064 CA 2138064 A CA2138064 A CA 2138064A CA 2138064 A1 CA2138064 A1 CA 2138064A1
- Authority
- CA
- Canada
- Prior art keywords
- coating
- printing
- locations
- group
- propellant
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
- B41C1/00—Forme preparation
- B41C1/055—Thermographic processes for producing printing formes, e.g. with a thermal print head
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- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Thermal Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Printing Methods (AREA)
- Printing Plates And Materials Therefor (AREA)
- Rotary Presses (AREA)
- Manufacture Or Reproduction Of Printing Formes (AREA)
Abstract
An expandable material which contains a polymer paste and a propellant and is contained in a layer or in at least one layer in a series of layers arranged on top of one another is used to produce a printing form for a letterpress process, in particular for the flexographic printing process, by raising the locations to be printed. The process can preferably be applied within a printing machine by a coating device having a plurality of applicator units. The printing form which is accordingly produced on the surface of a printing form cylinder can be raised by expansion, e.g., by a laser, at the printing locations corresponding to the image to be printed. At the end of the printing run, the printing form can be removed again at the conclusion of the printing process by an erasing device.
Description
21380~
BACKGROUND OF THE INVENTION
1. Field of the Invention The invention is directed to a printing form for letterpress printing, in particular for flexographic printing.
BACKGROUND OF THE INVENTION
1. Field of the Invention The invention is directed to a printing form for letterpress printing, in particular for flexographic printing.
2. Description of the Prior Art Le~el~ress printing processes include the flexographic printing process which makes use of elastic printing forms, rubber plates or photopolymer printing forms. The elastic printing form enables printing not only upon absorbent substrates such as paper or cardboard, but also on nonabsorbent m~teri~ls such as plastics, films or metal. Flexographic printing forms are also used for in-line v~rni~hing in offset printing machines. For surface v~rnishing with blank portions, cut out rubber blankets are used, although the latter are not suitable for spot v~rni~hing and ornamental v~rni~hing for which flexible photopolymer flexographic printing plates are used as v~rni~hing plates.
Conventional techniques for manufacturing flexographic printing forms include the production of rubber plates which are made from molds. The process step for producing a mold is omitted in the production of photopolymer flexographic printing plates.
Flexographic printing plates are produced by exposing, washing out the non-image regions, subsequent drying and post-exposure or burning-in. Further, there are also laser-engraved rubber plates. These printing processes are known from "Technik des Flexodrucks"
("Flexographic printing technique") (edited: J. Paris), St. Gallen, 1986, second edition.
A:\410~50.APP -2-21380~
Conventional methods for manufacturing printing forms for letterpress printing or particularly for planographic printing are accordingly based on the removal of non-printing areas. The processes often require a plurality of process steps, e.g., production of a mold, or a plurality of photographic steps and are therefore costly.
Expandable coatings are used in various areas of industry, e.g., in the manufacture of textiles, leather, wallpapers, flooring materials and the like. For instance, an expandable polymer, polyvinyl chloride, combined with a propellant (azodicarbonamide) and an activator suitable for the production of a floor covering is known from DE 19 37 474.
A:\410~50.APP 3 213806~
SUMMARY OF THE INVENTION
The object of the present invention is to provide a novel possibility for the use of a letterpress process, in particular the flexographic printing process.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a device and method for producing an erasable letter press printing form on a printing form cylinder. Coating means coat the form cylinder with at least one layer of an expandable coating m~teri~l which contains a polymer paste and a propellant. The coating has printing locations that can be raised, as well as non-printing locations. Image forming means then form an image on the coating and, subsequent to printing, erasing means remove the printing form from the form cylinder.
Pursuant to another embodiment of the invention, heat is applied to the coating m~teri~l to raise the printing locations. An absorbent m~teri~l is contained in the coating m~t.qri~l and the heating means can be provided in the form of either a heatable pin electrode or a laser.
Pursuant to a further embodiment of the invention, an inhibitor is mixed with the coating m~teri~l at the non-printing location so that only the printing locations which do not have the inhibitor are expanded by the application of heat.
In yet another embodiment an activator is mixed with the coating at printing locations so that only the locations where the activator is mixed are expanded by the heat application.
A particular advantage of the invention consists in that a printing form which is produced according to the invention can be used in a varnishing mechanism for producing surface varnishes with blank portions as well as spot varnishes and ornamental varnishes.
A:\4100-50.APP -4-213806~
Such a device can be used inside a printing machine because the form cylinder need not be removed from it.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
A:\4100-SO.APP -5 -213&0~
BRIEF DESCRIPrION OF THE DRAWINGS
Figs. 1 to 4 show expandable layers prior to and after expansion;
Fig. 5 shows a device for producing and erasing a printing form on a form cylinder;
and Fig. 6 shows the layer construction of a printing form on a substrate.
A:\4100-50.APP -6-~13~0~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polymer coatings, in particular thermoplastic polymer coatings such as layer 1 (Fig.
1) on substrate 8, are rendered expandable by the addition of unstable substances 3. These substances decompose accompanied by a marked increase in volume when excited physically or chemically or in particular physically with chemical reinforcement. Raised regions 4 forming the printing areas occur when these substances 3 are excited and subsequently decomposed corresponding to the image to be formed. The unstable substances, henceforth referred to as propellants, are preferably excited by thermal energy. The application of thermal energy for the purpose of forming images can be effected, for example, by means of a laser 5 (Fig. 1, Fig. 3) or by a heatable pin electrode 6 (Fig. 4). For example, CO2 lasers or YAG lasers are used for the purpose of image-oriented expansion. YAG lasers are distinguished by their improved resolution due to their improved focussing ability. However, they require the addition of carbon black particles 7 (Fig. 3). To achieve optimum dispersion and accordingly optimum absorption, the carbon black particles preferably have a diameter of less than 1.0 ~m. However, the addition of carbon black particles 7 can have a negative impact on the ~tt~in~ble degree of expansion. Therefore, it must be decided whether the degree of expansion or the resolution of the image to be printed has the greater importance. But other types of light sources can also be used.
The expandable polymer in layer 1 is polyvinyl chloride, for instance. Generally, a pre-gelated thermal paste, i.e., a thermoplastic polymer, is required. Beside direct application of thermal energy for the purpose of forming images and subsequent decomposition for the purpose of forming images, such polymer coats according to the A:~410~50.APP -7-~1380~
invention can also be expanded by the inhibitor process or the activator process. In the inhibitor process, a stabilizer (kicker) is added to the polymer in addition to a propellant.
The outer surface 10 of the layer 1 (Fig. 1) is coated, corresponding to the locations to be printed, with an inhibitor-containing paste which deactivates the stabilizer and accordingly inhibits expansion at the printed locations. The application of the inhibitor-containing paste corresponding to the image to be formed is effected, e.g., by an ink jet method. The expansion of the coating at the locations to be printed is achieved by applying heat over the entire surface, e.g., by means of infrared radiation. The layer 1 does not expand at the locations printed with the inhibitor, since this inhibitor deactivates the kicker.
In another process, the layer 1 is coated with an activator corresponding to the image area. The activator is applied, e.g., by means of the ink jet method. The pre-gelated propellant-containing thermoplastic paste forming layer 1 is accordingly printed with an activator (kicker) so that the layer will expand to a greater extent at the printed locations than at the non-printed locations when heat is subsequently applied to the entire surface area, e.g., by means of an infrared radiator.
The printing form shown in Fig. 6, which is produced by one of the processes described above, can be made more resistant to mechanical or chemical action, e.g., solvents or abrasion or splitting of pores in the region below the surface 10, by applying a cover layer 9 on top of layer 1 before layer 1 is expanded by heat. The cover layer 9 preferably contains the same binder systems as layer 1, but may also be constructed in a different manner for special printing requirements. An adhesive layer 2 can be arranged between layer 1 and substrate 8 to increase bonding strength.
A \4100 50.APP -8-213~06~
Adhesive layer 2, layer 1 and cover layer 9 can be applied to the substrate 8 by means of known coating techniques. A device for applying the different layers by means of rollers which are rotatably supported in a rotatable drum or cylinder is particularly suitable.
Such a coating device can be advantageously arranged within the printing machine, e.g., within a web-fed printing machine 11 (Fig. 5). The web-fed printing machine 11 has a printing form cylinder 12 which is adjusted relative to an impression cylinder 13 in order to print on a printing stock web 14. Printing ink is applied to the printing form cylinder 12 via a short inking mechanism with a doctor blade 15 and a screen applicator roller 16. At the conclusion of a printing process following the printing run of the printing form arranged on the printing form cylinder 12, this printing form can be removed by an erasing device 17.
There are various possible methods for erasing the printing form, e.g., melting, dissolving or embrittling. For example, the printing form is first softened by applying heat or chemicals and is then removed by means of high-pressure water jets. In another method the printing form is embrittled by cooling and then removed mechanically, e.g., by means of CO2 dry ice jets, which includes bombardment with dry ice pellets.
If the new printing form to be applied has adhesive layer 2, layer 1 and cover layer 9, a coating device 18 with three applicator units 181, 182, 183 is necessary. Each of the individual applicator units 181 to 183 is preferably constructed as a rotatable roller which dips into a container filled with the material of the layer to be applied and can be adjusted relative to the respective surface of the printing form cylinder 12 in order to coat the latter with the material in question. Each applicator unit 181 to 183 in turn is arranged on a rotatable cylinder 180 so that the applicator units 181 to 183 can be adjusted relative to the A:\410~50.APP 9 , 2l3sa64 surface of the printing form cylinder 12 one after the other by rotating the cylinder 180. The applied layer can be dried by a drier 19, e.g., an infrared heat source. If an ink jet applicator device 20 is provided in addition to the applicator units 181 to 183, an activator or an inhibitor can be applied to the outer surface of layer 1 by this ink jet applicator device 20 as described above so that this layer 1 can be expanded subsequently by the drier 19. Instead of expanding layer 1 by the inhibitor method or activator method, this layer 1 can also be expanded at the locations to be printed by means of a laser.
The thickness of the applied expandable paste depends on the desired raising of m~teri~l The raising of the m~teri~l must correspond to the standard relief depth in flexographic printing which is at least 0.39 mm to a maximum of 3.5 mm. Relief depths of 0.39 to 1.10 mm are standard for printing smooth surfaces. In very uneven printing stock such as corrugated cardboard, relief depths of 3.0 to 3.5 mm are standard. Commercial propellants have minimum grain sizes of approximately 10 ~m and expansion factors of 20 to 200 ml/g. Accordingly, it is possible to raise the material by roughly three to six times the application thickness of the pre-dried material. Consequently, in order to achieve differences in height between the printing locations and non-printing locations on the outer surface 10 of layer 1 amounting to approximately 0.8 mm, which is standard for flexographic printing, an average thickness of 200 ~m of the pre-dried material is necessary.
To produce the layer 1, the coating contains one or more polymer film formers as chief components. These film formers are expanded by adding suitable propellants. The m~teri~l properties of film formers and propellants must be carefully matched to enable the greatest and most uniform possible expansion of the propellant and accordingly of the A:\4100-SO,APP - 10-21380~
coating. Thermoplastics such as polyvinyl chloride, polyolefins, ethylene/vinyl acetate copolymers, polystyrene, polyamide, acrylonitrile/butadiene/styrene copolymers or thermoplastic elastomers (plastics) or elastomers (rubber) are preferably used for the coating according to the invention. In addition to the desired favorable image-forming and printing characteristics, another characteristic of these polymer groups is that they can easily be erased by the device 17 by melting, dissolving or embrittling.
Propellants are added to these coating materials in a proportion to the total coating compound such that the excited expansion of the coating achieves a uniform printing form height conventional for flexographic printing. To produce finely structured printing areas with optimum stability of the expanded areas, the distribution and particle size of the propellant is a very important. The smaller the gas bubbles in the coating, the tighter and more stable the binder mesh. The distribution of the propellant must therefore be very uniform and very fine particulate propellants with particle diameters between 5,um and 10 ~m are preferably used.
Suitable propellants are, in particular, solid chemical propellants, e.g., azodicarbonamide, azoisobutyrodinitrile, toluenesulfonhydrazide and 4,4'-oxybisbenzenesulfohydrazide. Such organic propellants based on hydrazides and azo compounds are exothermic.
Inorganic propellants such as sodium hydrogen carbonate or ammonium carbonate in combination with weak organic acids, e.g., citric acid, react endothermally. Therefore, the exothermic organic propellants are particularly suitable for the present invention. The proportion of propellant in the coating material is between 1% and 25 % .
A:\4100-50.APP
213~0~
In the activator method, an activator (kicker) is additionally added to the coating m~teri~l. Suitable activators are compounds of lead, zinc and cadmium such as PbO, ZnO, cadmium oxide, cadmium acetate and/or isophorone diamine and/or dodecylamine.
Normally, 0.5% to 5% stabilizer is added.
For the inhibitor method, inhibitors such as fumaric acid, maleic acid, oxalic acid, hydroquinone, thiourea, trimellitic anhydride or methyl ethyl ketone are used in combination with azodicarbonamide. The use of such substances is known, e.g., from DE 19 37 474, GB
2 076 005 or DE 30 43 202.
Moreover, additional additives can be added to the coating material. For example, carbon black increases sensitivity to lasers, since it absorbs the laser light very well within a wide range of wavelengths. Depending on the type of laser used, the carbon black content can fluctuate within a range of 0.1% to 10%. The wavelength absorption in the coating material and accordingly the propellant decomposition can be accurately controlled in a point-by-point manner by adding carbon black. Comparison between the laser source 5 in Fig. 3 and the pin electrode 6 in Fig. 4 shows that the relief 4a achieved for the printing areas with excitation by means of laser light is much steeper than the relief 4b produced by heating with the pin electrode 6. In the latter case, the heat acts on the surface of the layer so that heat is uniformly distributed in every direction by heat conduction in the layer 1. With the use of laser 5, the thermal excitation acts uniformly in the entire irradiated region given optimal distribution and concentration of the absorbent m~teri~l, e.g., carbon black particles.
Excitation of the propellant by heat conduction is minimi7ed when using laser light. Because of this, steeper relief edges 4a and more uniform pore sizes result from the propellant. This A:\4100-50 APP -12-213~0~
in turn leads to advantageous characteristics of the expanded coating with respect to stability and resolution capacity.
Furthermore, the layer 1 can also contain other inorganic fillers which increase the mechanical stability of the porous expanded regions. l~tçri~l~ which improve the surface characteristics of the printing form are added to improve receptivity to ink.
A printing form produced according to this principle can be used for letterpress processes other than the flexographic printing process if m~teri~l~ having the required hardness are used.
According to the invention, an expandable m~tçri~l which contains a polymer paste and a propellant and is contained in a layer 1 or in at least one layer 1 in a series of layers 9, 1, 2 arranged on top of one another is used to produce a printing form for a letterpress process, in particular for the flexographic printing process, by raising the locations to be printed. The process can preferably be applied within a printing machine 11 by means of a coating device 18 having a plurality of applicator units 181 to 183. The printing form which is accordingly produced on the surface of a printing form cylinder 12 can be raised by expansion, e.g., by means of a laser 20, at the printing locations corresponding to the images to be printed. After concluding the printing run, the printing form can be removed again at the conclusion of the printing process by means of an erasing device 17.
The printing form which can be produced and erased according to the invention can also be used in particular on a printing form cylinder 12 of a varnishing mechanism which is constructed in the manner of the device shown in Fig. 5. The final printing mechanism of a A:\410~50.APP -13 -- ~1380S~
printing machine for direct or indirect printing of a web or sheet of printing stock is used as the varnishing mechanism.
A varnishing mechanism with a printing form cylinder for selective varnishing which varnishes only a certain proportion of the surface of printing stock, e.g., in folding cardboard, is known from DE 39 06 648 Al.
The varnishing mechanism according to the invention which has the devices shown in Fig. 5, the coating device 18, erasing device 17, and a laser 20 for forming images, is suitable for producing a surface varnishing with blank portions as well as for spot v~rni~hing and ornamental v~rni~hing.
The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims.
A:\4100-50.APP - 14-
Conventional techniques for manufacturing flexographic printing forms include the production of rubber plates which are made from molds. The process step for producing a mold is omitted in the production of photopolymer flexographic printing plates.
Flexographic printing plates are produced by exposing, washing out the non-image regions, subsequent drying and post-exposure or burning-in. Further, there are also laser-engraved rubber plates. These printing processes are known from "Technik des Flexodrucks"
("Flexographic printing technique") (edited: J. Paris), St. Gallen, 1986, second edition.
A:\410~50.APP -2-21380~
Conventional methods for manufacturing printing forms for letterpress printing or particularly for planographic printing are accordingly based on the removal of non-printing areas. The processes often require a plurality of process steps, e.g., production of a mold, or a plurality of photographic steps and are therefore costly.
Expandable coatings are used in various areas of industry, e.g., in the manufacture of textiles, leather, wallpapers, flooring materials and the like. For instance, an expandable polymer, polyvinyl chloride, combined with a propellant (azodicarbonamide) and an activator suitable for the production of a floor covering is known from DE 19 37 474.
A:\410~50.APP 3 213806~
SUMMARY OF THE INVENTION
The object of the present invention is to provide a novel possibility for the use of a letterpress process, in particular the flexographic printing process.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a device and method for producing an erasable letter press printing form on a printing form cylinder. Coating means coat the form cylinder with at least one layer of an expandable coating m~teri~l which contains a polymer paste and a propellant. The coating has printing locations that can be raised, as well as non-printing locations. Image forming means then form an image on the coating and, subsequent to printing, erasing means remove the printing form from the form cylinder.
Pursuant to another embodiment of the invention, heat is applied to the coating m~teri~l to raise the printing locations. An absorbent m~teri~l is contained in the coating m~t.qri~l and the heating means can be provided in the form of either a heatable pin electrode or a laser.
Pursuant to a further embodiment of the invention, an inhibitor is mixed with the coating m~teri~l at the non-printing location so that only the printing locations which do not have the inhibitor are expanded by the application of heat.
In yet another embodiment an activator is mixed with the coating at printing locations so that only the locations where the activator is mixed are expanded by the heat application.
A particular advantage of the invention consists in that a printing form which is produced according to the invention can be used in a varnishing mechanism for producing surface varnishes with blank portions as well as spot varnishes and ornamental varnishes.
A:\4100-50.APP -4-213806~
Such a device can be used inside a printing machine because the form cylinder need not be removed from it.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
A:\4100-SO.APP -5 -213&0~
BRIEF DESCRIPrION OF THE DRAWINGS
Figs. 1 to 4 show expandable layers prior to and after expansion;
Fig. 5 shows a device for producing and erasing a printing form on a form cylinder;
and Fig. 6 shows the layer construction of a printing form on a substrate.
A:\4100-50.APP -6-~13~0~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polymer coatings, in particular thermoplastic polymer coatings such as layer 1 (Fig.
1) on substrate 8, are rendered expandable by the addition of unstable substances 3. These substances decompose accompanied by a marked increase in volume when excited physically or chemically or in particular physically with chemical reinforcement. Raised regions 4 forming the printing areas occur when these substances 3 are excited and subsequently decomposed corresponding to the image to be formed. The unstable substances, henceforth referred to as propellants, are preferably excited by thermal energy. The application of thermal energy for the purpose of forming images can be effected, for example, by means of a laser 5 (Fig. 1, Fig. 3) or by a heatable pin electrode 6 (Fig. 4). For example, CO2 lasers or YAG lasers are used for the purpose of image-oriented expansion. YAG lasers are distinguished by their improved resolution due to their improved focussing ability. However, they require the addition of carbon black particles 7 (Fig. 3). To achieve optimum dispersion and accordingly optimum absorption, the carbon black particles preferably have a diameter of less than 1.0 ~m. However, the addition of carbon black particles 7 can have a negative impact on the ~tt~in~ble degree of expansion. Therefore, it must be decided whether the degree of expansion or the resolution of the image to be printed has the greater importance. But other types of light sources can also be used.
The expandable polymer in layer 1 is polyvinyl chloride, for instance. Generally, a pre-gelated thermal paste, i.e., a thermoplastic polymer, is required. Beside direct application of thermal energy for the purpose of forming images and subsequent decomposition for the purpose of forming images, such polymer coats according to the A:~410~50.APP -7-~1380~
invention can also be expanded by the inhibitor process or the activator process. In the inhibitor process, a stabilizer (kicker) is added to the polymer in addition to a propellant.
The outer surface 10 of the layer 1 (Fig. 1) is coated, corresponding to the locations to be printed, with an inhibitor-containing paste which deactivates the stabilizer and accordingly inhibits expansion at the printed locations. The application of the inhibitor-containing paste corresponding to the image to be formed is effected, e.g., by an ink jet method. The expansion of the coating at the locations to be printed is achieved by applying heat over the entire surface, e.g., by means of infrared radiation. The layer 1 does not expand at the locations printed with the inhibitor, since this inhibitor deactivates the kicker.
In another process, the layer 1 is coated with an activator corresponding to the image area. The activator is applied, e.g., by means of the ink jet method. The pre-gelated propellant-containing thermoplastic paste forming layer 1 is accordingly printed with an activator (kicker) so that the layer will expand to a greater extent at the printed locations than at the non-printed locations when heat is subsequently applied to the entire surface area, e.g., by means of an infrared radiator.
The printing form shown in Fig. 6, which is produced by one of the processes described above, can be made more resistant to mechanical or chemical action, e.g., solvents or abrasion or splitting of pores in the region below the surface 10, by applying a cover layer 9 on top of layer 1 before layer 1 is expanded by heat. The cover layer 9 preferably contains the same binder systems as layer 1, but may also be constructed in a different manner for special printing requirements. An adhesive layer 2 can be arranged between layer 1 and substrate 8 to increase bonding strength.
A \4100 50.APP -8-213~06~
Adhesive layer 2, layer 1 and cover layer 9 can be applied to the substrate 8 by means of known coating techniques. A device for applying the different layers by means of rollers which are rotatably supported in a rotatable drum or cylinder is particularly suitable.
Such a coating device can be advantageously arranged within the printing machine, e.g., within a web-fed printing machine 11 (Fig. 5). The web-fed printing machine 11 has a printing form cylinder 12 which is adjusted relative to an impression cylinder 13 in order to print on a printing stock web 14. Printing ink is applied to the printing form cylinder 12 via a short inking mechanism with a doctor blade 15 and a screen applicator roller 16. At the conclusion of a printing process following the printing run of the printing form arranged on the printing form cylinder 12, this printing form can be removed by an erasing device 17.
There are various possible methods for erasing the printing form, e.g., melting, dissolving or embrittling. For example, the printing form is first softened by applying heat or chemicals and is then removed by means of high-pressure water jets. In another method the printing form is embrittled by cooling and then removed mechanically, e.g., by means of CO2 dry ice jets, which includes bombardment with dry ice pellets.
If the new printing form to be applied has adhesive layer 2, layer 1 and cover layer 9, a coating device 18 with three applicator units 181, 182, 183 is necessary. Each of the individual applicator units 181 to 183 is preferably constructed as a rotatable roller which dips into a container filled with the material of the layer to be applied and can be adjusted relative to the respective surface of the printing form cylinder 12 in order to coat the latter with the material in question. Each applicator unit 181 to 183 in turn is arranged on a rotatable cylinder 180 so that the applicator units 181 to 183 can be adjusted relative to the A:\410~50.APP 9 , 2l3sa64 surface of the printing form cylinder 12 one after the other by rotating the cylinder 180. The applied layer can be dried by a drier 19, e.g., an infrared heat source. If an ink jet applicator device 20 is provided in addition to the applicator units 181 to 183, an activator or an inhibitor can be applied to the outer surface of layer 1 by this ink jet applicator device 20 as described above so that this layer 1 can be expanded subsequently by the drier 19. Instead of expanding layer 1 by the inhibitor method or activator method, this layer 1 can also be expanded at the locations to be printed by means of a laser.
The thickness of the applied expandable paste depends on the desired raising of m~teri~l The raising of the m~teri~l must correspond to the standard relief depth in flexographic printing which is at least 0.39 mm to a maximum of 3.5 mm. Relief depths of 0.39 to 1.10 mm are standard for printing smooth surfaces. In very uneven printing stock such as corrugated cardboard, relief depths of 3.0 to 3.5 mm are standard. Commercial propellants have minimum grain sizes of approximately 10 ~m and expansion factors of 20 to 200 ml/g. Accordingly, it is possible to raise the material by roughly three to six times the application thickness of the pre-dried material. Consequently, in order to achieve differences in height between the printing locations and non-printing locations on the outer surface 10 of layer 1 amounting to approximately 0.8 mm, which is standard for flexographic printing, an average thickness of 200 ~m of the pre-dried material is necessary.
To produce the layer 1, the coating contains one or more polymer film formers as chief components. These film formers are expanded by adding suitable propellants. The m~teri~l properties of film formers and propellants must be carefully matched to enable the greatest and most uniform possible expansion of the propellant and accordingly of the A:\4100-SO,APP - 10-21380~
coating. Thermoplastics such as polyvinyl chloride, polyolefins, ethylene/vinyl acetate copolymers, polystyrene, polyamide, acrylonitrile/butadiene/styrene copolymers or thermoplastic elastomers (plastics) or elastomers (rubber) are preferably used for the coating according to the invention. In addition to the desired favorable image-forming and printing characteristics, another characteristic of these polymer groups is that they can easily be erased by the device 17 by melting, dissolving or embrittling.
Propellants are added to these coating materials in a proportion to the total coating compound such that the excited expansion of the coating achieves a uniform printing form height conventional for flexographic printing. To produce finely structured printing areas with optimum stability of the expanded areas, the distribution and particle size of the propellant is a very important. The smaller the gas bubbles in the coating, the tighter and more stable the binder mesh. The distribution of the propellant must therefore be very uniform and very fine particulate propellants with particle diameters between 5,um and 10 ~m are preferably used.
Suitable propellants are, in particular, solid chemical propellants, e.g., azodicarbonamide, azoisobutyrodinitrile, toluenesulfonhydrazide and 4,4'-oxybisbenzenesulfohydrazide. Such organic propellants based on hydrazides and azo compounds are exothermic.
Inorganic propellants such as sodium hydrogen carbonate or ammonium carbonate in combination with weak organic acids, e.g., citric acid, react endothermally. Therefore, the exothermic organic propellants are particularly suitable for the present invention. The proportion of propellant in the coating material is between 1% and 25 % .
A:\4100-50.APP
213~0~
In the activator method, an activator (kicker) is additionally added to the coating m~teri~l. Suitable activators are compounds of lead, zinc and cadmium such as PbO, ZnO, cadmium oxide, cadmium acetate and/or isophorone diamine and/or dodecylamine.
Normally, 0.5% to 5% stabilizer is added.
For the inhibitor method, inhibitors such as fumaric acid, maleic acid, oxalic acid, hydroquinone, thiourea, trimellitic anhydride or methyl ethyl ketone are used in combination with azodicarbonamide. The use of such substances is known, e.g., from DE 19 37 474, GB
2 076 005 or DE 30 43 202.
Moreover, additional additives can be added to the coating material. For example, carbon black increases sensitivity to lasers, since it absorbs the laser light very well within a wide range of wavelengths. Depending on the type of laser used, the carbon black content can fluctuate within a range of 0.1% to 10%. The wavelength absorption in the coating material and accordingly the propellant decomposition can be accurately controlled in a point-by-point manner by adding carbon black. Comparison between the laser source 5 in Fig. 3 and the pin electrode 6 in Fig. 4 shows that the relief 4a achieved for the printing areas with excitation by means of laser light is much steeper than the relief 4b produced by heating with the pin electrode 6. In the latter case, the heat acts on the surface of the layer so that heat is uniformly distributed in every direction by heat conduction in the layer 1. With the use of laser 5, the thermal excitation acts uniformly in the entire irradiated region given optimal distribution and concentration of the absorbent m~teri~l, e.g., carbon black particles.
Excitation of the propellant by heat conduction is minimi7ed when using laser light. Because of this, steeper relief edges 4a and more uniform pore sizes result from the propellant. This A:\4100-50 APP -12-213~0~
in turn leads to advantageous characteristics of the expanded coating with respect to stability and resolution capacity.
Furthermore, the layer 1 can also contain other inorganic fillers which increase the mechanical stability of the porous expanded regions. l~tçri~l~ which improve the surface characteristics of the printing form are added to improve receptivity to ink.
A printing form produced according to this principle can be used for letterpress processes other than the flexographic printing process if m~teri~l~ having the required hardness are used.
According to the invention, an expandable m~tçri~l which contains a polymer paste and a propellant and is contained in a layer 1 or in at least one layer 1 in a series of layers 9, 1, 2 arranged on top of one another is used to produce a printing form for a letterpress process, in particular for the flexographic printing process, by raising the locations to be printed. The process can preferably be applied within a printing machine 11 by means of a coating device 18 having a plurality of applicator units 181 to 183. The printing form which is accordingly produced on the surface of a printing form cylinder 12 can be raised by expansion, e.g., by means of a laser 20, at the printing locations corresponding to the images to be printed. After concluding the printing run, the printing form can be removed again at the conclusion of the printing process by means of an erasing device 17.
The printing form which can be produced and erased according to the invention can also be used in particular on a printing form cylinder 12 of a varnishing mechanism which is constructed in the manner of the device shown in Fig. 5. The final printing mechanism of a A:\410~50.APP -13 -- ~1380S~
printing machine for direct or indirect printing of a web or sheet of printing stock is used as the varnishing mechanism.
A varnishing mechanism with a printing form cylinder for selective varnishing which varnishes only a certain proportion of the surface of printing stock, e.g., in folding cardboard, is known from DE 39 06 648 Al.
The varnishing mechanism according to the invention which has the devices shown in Fig. 5, the coating device 18, erasing device 17, and a laser 20 for forming images, is suitable for producing a surface varnishing with blank portions as well as for spot v~rni~hing and ornamental v~rni~hing.
The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims.
A:\4100-50.APP - 14-
Claims (36)
1. A device for producing an erasable letterpress printing form on a printing form cylinder, comprising: coating means for coating the form cylinder with at least one layer of an expandable coating material which contains a polymer paste and a propellant, the coating having printing locations that can be raised as well as non-printing locations; image forming means for forming an image on the coating; and erasing means for removing the printing form from the form cylinder.
2. A device according to claim 1, and further comprising means for applying heat to the printing locations on the material so that the printing locations are raised.
3. A device according to claim 2, wherein the coating material contains an absorbent material, the heating means including a heatable pin electrode arranged and adapted to cause the coating material to expand.
4. A device according to claim 3, wherein the absorbent material is carbon black.
5. A device according to claim 2, wherein the coating material contains an absorbent material, the heating means including a laser arranged and adapted to cause the coating material to expand.
6. A device according to claim 5, wherein the laser is one of a YAG laser and a CO2 laser.
7. A device according to claim 5, wherein the absorbent is carbon black.
8. A device according to claim 1, wherein the coating means includes a cylinder and a plurality of applicator units rotatably mounted on the cylinder for applying the coating material to the printing form cylinder.
9. A device according to claim 2, wherein an inhibitor is mixed with the coating material at the non-printing locations so that only the printing locations where the inhibitor is not mixed in are expanded by applying heat to an entire outer surface of the coating.
10. A device according to claim 2, wherein an activator is mixed with the coating material at the printing locations so that only the printing locations where the activator is mixed in are expanded by applying heat to an entire outer surface of the coating.
11. A device according to claim 1, wherein the coating material is one of a thermoplastic, a thermoplastic elastomer and an elastomer.
12. A device as defined in claim 11, wherein the coating material is formed of a thermoplastic chosen from the group consisting of polyvinyl chloride, polyolefins, ethylene-vinyl-acetate copolymers, polystyrene, polyamide and acrylonitrile-butadiene-styrene copolymers.
13. A device according to claim 1, wherein the coating material contains an organic propellant.
14. A device according to claim 13, wherein the organic propellant is selected from the group consisting of azodicarbonamide, azoisobutyrodinitrile, toluenesulfonhydrazide and 4, 4'-oxybisbenzenesulfohydrazide.
15. A device according to claim 1, wherein the coating material contains an inorganic propellant.
16. A device according to claim 15, wherein the inorganic propellant is selected from the group consisting of sodium hydrogen carbonate and ammonium carbonate in combination with a weak organic acid.
17. A device according to claim 16, wherein the weak organic acid is citric acid.
18. A device according to claim 9, wherein the inhibitor is one of the group consisting of fumaric acid, maleic acid, oxalic acid, hydroquinine, thiourea, trimellitic anhydride and methyl ethyl ketone.
19. A device according to claim 10, wherein the activator is a compound of one of, lead, zinc and cadmium.
20. A device according to claim 19, wherein the activator compound is one of the group consisting of lead oxide, zinc oxide and cadmium oxide.
21. A device according to claim 19, wherein the compound is at least one of the group consisting of cadmium acetate, isophorone diamine and dodecylamine.
22. A method for any one of surface varnishing with blank portions, spot varnishing and ornamental varnishing, comprising the steps of: providing a form cylinder; coating the form cylinder with at least one layer containing an expandable material which contains a polymer paste and a propellant, said material varnishing locations that can be raised and non-varnishing locations; forming an image on the coating; and erasing the vanishing form from the cylinder.
23. A method for producing an erasable letter press printing form on a printing form cylinder, comprising the steps of: coating the form cylinder with at least one layer containing an expandable coating material that includes a polymer paste and a propellant, the material coating having printing locations that can be raised and non-printing locations; and applying heat to the coating surface to expand and raise the printing locations.
24. A method according to claim 23, and further comprising the step of mixing an inhibitor with the coating material at the non-printing locations so that only the printing locations where the inhibitor is not mixed in are expanded by applying heat to the outer surface of the coating.
25. A method according to claim 23, and further comprising the step of mixing an activator with the coating material at the printing locations so that only the printing locations where the activator is mixed in are expanded by applying heat to the outer surface of the coating.
26. A method according to claim 23, wherein the coating step includes coating the form cylinder with a material selected from the group consisting of thermoplastic, thermoplastic elastomers and elastomers.
27. A method according to claim 26, wherein the material is a thermoplastic from the group consisting of polyvinyl chloride, polyolefins, ethylene-vinyl acetate copolymers, polystyrene, polyamide and acrylonitrile-butadiene-styrene copolymers.
28. A method according to claim 23, wherein the coating step includes coating the form cylinder with a material containing an organic propellant.
29. A method according to claim 28, wherein the organic propellant is selected from the group consisting of azodicarbonamide, azoisobutyrodinitrile, toluenesulfonhydrazide and 4, 4'-oxybisbenzenesulfohydrazide.
30. A method according to claim 23, wherein the coating step includes coating the form cylinder with a material containing an inorganic propellant.
31. A method according to claim 30, wherein the inorganic propellant is selected from the group consisting of sodium-hydrogen carbonate and ammonium carbonate in combination with a weak organic acid.
32. A method according to claim 31, wherein the weak organic acid is citric acid.
33. A method according to claim 24, wherein the step of mixing an inhibitor with the coating material includes mixing an inhibitor selected from the group consisting of fumaric acid, maleic acid, oxalic acid, hydroquinine, thiourea, trimellitic anhydride and methyl ethyl ketone.
34. A method according to claim 25, wherein the step of mixing an activator with the coating material includes mixing a compound of one of lead, zinc and cadmium.
35. A method according to claim 34, wherein the activator compound is one of the group consisting of lead oxide, zinc oxide and cadmium oxide.
36. A method according to claim 34, wherein the compound is at least one of the group consisting of cadmium acetate, isophorone diamine and dodecylamine.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19934342954 DE4342954C2 (en) | 1993-12-16 | 1993-12-16 | Method for producing and deleting an erasable high-pressure mold, device for carrying out the method and its use |
| DEP4342954.8 | 1993-12-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2138064A1 true CA2138064A1 (en) | 1995-06-17 |
Family
ID=6505201
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2138064 Abandoned CA2138064A1 (en) | 1993-12-16 | 1994-12-14 | Device for producing an erasable printing form for letterpress printing |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH07195654A (en) |
| CA (1) | CA2138064A1 (en) |
| DE (1) | DE4342954C2 (en) |
| FR (1) | FR2713985B1 (en) |
| GB (1) | GB2284788B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19961867A1 (en) | 1999-12-22 | 2001-06-28 | Roland Man Druckmasch | Device for the production of printing forms |
| DE10009688B4 (en) * | 2000-02-29 | 2004-11-25 | Rotec-Hülsensysteme GmbH & Co. KG | Sleeve with a shrinkable sleeve core, and method for its production |
| DE10031915A1 (en) * | 2000-06-30 | 2002-01-10 | Heidelberger Druckmasch Ag | Compact multi-beam laser light source and interleaved scanning line method for exposure of printing plates |
| DE10039822A1 (en) * | 2000-08-09 | 2002-02-21 | Koenig & Bauer Ag | Method and device for treating reimageable printing forms or printing form cylinders in printing machines |
| DE10063987A1 (en) | 2000-12-21 | 2002-07-18 | Oce Printing Systems Gmbh | Device and method for cleaning a print carrier before each print cycle |
| DE10355996A1 (en) * | 2003-11-27 | 2005-06-30 | Stork Prints Austria Gmbh | Process for the production of flexographic printing plates by means of laser engraving as well as suitable apparatus |
| DE102005046863A1 (en) * | 2005-09-30 | 2007-06-14 | Man Roland Druckmaschinen Ag | printing form |
| GB2479715A (en) * | 2010-04-12 | 2011-10-26 | Genevieve Cast Browne | Laser etching puff binder |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3654864A (en) * | 1970-01-16 | 1972-04-11 | Energy Conversion Devices Inc | Printing employing materials with variable volume |
| US3703362A (en) * | 1972-01-17 | 1972-11-21 | Minnesota Mining & Mfg | Presensitized light-sensitive letterpress printing makeready |
| US3779761A (en) * | 1972-01-17 | 1973-12-18 | Minnesota Mining & Mfg | Presensitized light-sensitive letterpress printing makeready |
| US3995554A (en) * | 1974-06-03 | 1976-12-07 | Xerox Corporation | Process for preparing resilient blown imaged printing masters |
| DE3249837C2 (en) * | 1982-04-08 | 1988-06-01 | Gao Gesellschaft Fuer Automation Und Organisation Mbh, 8000 Muenchen, De | Multilayered identity card which can be used as a printing block |
| JPS6237186A (en) * | 1985-08-12 | 1987-02-18 | Hitachi Cable Ltd | Printing by ink jet printer and ink therefor |
| DE3911932A1 (en) * | 1989-04-12 | 1990-10-25 | Krause Biagosch Gmbh | Rotary printing machine - with built in preparatory facility to produce printing cylinders |
| DE3941303C1 (en) * | 1989-12-14 | 1990-12-13 | Man Roland Druckmaschinen Ag, 6050 Offenbach, De | |
| DE4235242C1 (en) * | 1992-10-20 | 1993-11-11 | Roland Man Druckmasch | Erasable print form |
-
1993
- 1993-12-16 DE DE19934342954 patent/DE4342954C2/en not_active Expired - Fee Related
-
1994
- 1994-12-08 GB GB9424815A patent/GB2284788B/en not_active Expired - Lifetime
- 1994-12-14 CA CA 2138064 patent/CA2138064A1/en not_active Abandoned
- 1994-12-15 JP JP31220794A patent/JPH07195654A/en active Pending
- 1994-12-15 FR FR9415110A patent/FR2713985B1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE4342954C2 (en) | 1998-01-22 |
| GB9424815D0 (en) | 1995-02-08 |
| GB2284788B (en) | 1997-07-16 |
| JPH07195654A (en) | 1995-08-01 |
| GB2284788A (en) | 1995-06-21 |
| DE4342954A1 (en) | 1995-06-22 |
| FR2713985B1 (en) | 1996-11-08 |
| FR2713985A1 (en) | 1995-06-23 |
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