EP2748002A1

EP2748002A1 - Method for producing a printing plate for waterless offset printing

Info

Publication number: EP2748002A1
Application number: EP12759664.1A
Authority: EP
Inventors: Gert SIEGER
Original assignee: Individual
Current assignee: Sieger Gert
Priority date: 2011-08-25
Filing date: 2012-08-23
Publication date: 2014-07-02
Anticipated expiration: 2032-08-23
Also published as: KR20140051395A; WO2013026904A1; CN103732409A; US20140208969A1; RU2014104167A; DE102011052991B4; JP2014528856A; EP2748002B1; DE102011052991A1

Abstract

The invention relates to a method for producing a printing plate for waterless offset printing. A method for producing a printing plate for waterless offset printing is proposed, having the following method steps: - providing a substrate; - applying an ink onto the substrate using an inkjet printing technique; and - fixing the applied ink on the substrate. The method is characterized in that the substrate has a surface tension of ≥ 35 mN/m, preferably ≥38 mN/m, and the ink has a surface tension of ≤30 mN/m, preferably ≤25 mN/m, when fixed on the substrate. The ink is applied into substrate regions which should not have printing ink during the offset printing process.

Description

Dr. Gert Sieger

Mendelssohnstrasse 53, 70619 Stuttgart, Germany

Process for producing a printing form for waterless offset printing

The present invention relates to a process for producing a printing form for waterless offset printing.

Offset printing is an indirect lithographic printing process, which has been widely used in various fields since the beginning of the 20th century. In addition to its use in the area of book and newspaper printing, offset printing is used in particular in the area of commercial printing as well as the printing of packaging of all kinds. The fundamental principle of offset printing goes back to developments in lithography, as it was already used at the end of the 18th century. In classical wet offset printing in several mostly photochemical steps printing plates are produced whose surfaces are divided into hydrophilic and hydrophobic areas. In the offset printing machine, water or an aqueous mixture of different auxiliaries, such as, for example, isopropanol, are applied to the printing plates produced in this way with a roller, the so-called dampening unit. The hydrophilic areas of the printing form hold the water or the aqueous mixture, while the hydrophobic areas remain dry. By means of an inking roller, the so-called inking unit, we applied a greasy printing ink on the watered printing form, which repelled from the water-wetted hydrophilic areas and adheres to the dry hydrophobic areas. The so-colored printing form is rolled on a blanket, which then transmits the printed image on the medium to be printed. It is therefore an indirect printing method in which the printed image is not transferred directly from the printing plate to the medium to be printed.

A disadvantage of wet offset printing is that both for the production of the printing form, as well as in the printing process itself by the dampening solution, a variety of excipients are used, which you want to avoid environmental technology.

One approach to avoid these auxiliaries is the waterless offset printing, or dry offset. Here are used as printing plates silicone-coated printing plates in combination with printing inks based on silicone. The silicone-coated printing plate is lipophobic and repels the printing ink. The printed image is applied by means of, for example, laser irradiation on the printing plate by the color-bearing areas of the printing plate are removed from the silicone coating. On the printing form there is a segregation of the ink in the paint components on the one hand and silicone oil on the other hand, wherein the color components adhere to the free of the silicone layer areas of the printing plate. European Patent Application EP 0 672 950 A1 discloses a corresponding printing plate for waterless offset printing, which can be structured accordingly by laser irradiation. For this purpose, a photosensitive layer is applied between a silicone coating and a carrier plate, which leads to a detachment of the silicone layer in the irradiated areas with laser radiation of suitable wavelength. The areas thus exposed are lipophilic, so that the printing ink adheres to the printing form in these areas.

US 4,003,312 discloses a process for producing a master by means of inkjet technology. A master is provided by applying a silicone on a suitable substrate master by means of an inkjet printing device and curing the silicone to an elastomeric state. Alternatively, an inkjet printing device can be used to apply a catalyst on an uncured silicone on a master substrate, whereby the silicone is cured in the areas treated with the catalyst.

DE 19500486 AI discloses a photosensitive lithographic printing plate which does not require moistening water. The printing plate comprises an aluminum support on which a primer layer, a photosensitive layer, and a silicone rubber layer are applied, the aluminum surface having an average roughness R _a of 0.2 to 0.8 μm and a whiteness of 0.10 to 0, 35 has.

EP 1046497 A1 discloses a method of making a lithographic printing plate comprising the step of spreading a novolak resin on a hydrophilic surface of a lithographic base in a predetermined pattern.

US 2006/0188813 A1 discloses a hydrophilic film on a master, which is obtainable by heat or light induced curing of a composition comprising at least two five- or six-membered hydrophilic ring structures. The compound can be applied by means of inkjet technology on the surface.

The waterless offset process offers the advantage that emission of the dampening solution, as occurs in wet offset printing, is avoided. In addition, it is possible to produce finer raster on the medium to be printed. As a rule, this results in a low start-up waste (eg 20 sheets instead of 200) since the printing form does not first have to be correspondingly moistened with moisture. Also, a more precise printout of the halftone dots, a better fine drawing and a lower dot gain are achieved. In the printing machine itself can be dispensed with a dampening unit, which significantly reduces the design effort. This also reduces the maintenance of the printing presses. By dispensing with fountain solution can over it In addition, a corrosion of metal colors are avoided, which increases the color fastness of the print.

A disadvantage of the waterless offset printing technique, however, is that the printing plates are more expensive than in the wet offset method. The printing plates used are also scratch-sensitive and, after their development (exposure), only difficult to correct. With previously used ink jet process for the production of printing plates can not be achieved sufficient resolutions to produce high quality prints. Also, the achievable durability of the printing plates thus produced is significantly limited, so that they can be used only for printing very small runs. It is therefore an object of the present invention to provide a method for the production of printing plates for waterless offset printing, with which it is possible to overcome the disadvantages known from the prior art and in particular to manufacture printing plates more cost-effectively.

This object is achieved by a method according to claim 1. Embodiments of the method can be found in the subclaims and the following description.

It is thus a process for producing a printing form for the waterless

Offset printing proposed, comprising the method steps:

- Providing a support plate;

- Applying an ink to the support plate by inkjet technique;

Fixing the applied ink on the support plate,

which is characterized in that the support plate has a surface tension> 35 mN / m, preferably> 38 mN / m and the ink has a surface tension <30 mN / m, preferably <25 mN / m in the state fixed to the support plate and the ink is applied in the areas of the carrier plate, which should bear no ink in offset printing. By fiction, contemporary method, it is possible in an advantageous manner to produce printing plates for waterless offset printing quickly and inexpensively. By means of a suitable ink jet device, such as an ink jet printer, it is possible with the method according to the invention to create print templates in a data processing system and transfer them directly to a printing plate to provide a printing plate.

According to the invention, it is provided that the printing plate is produced in such a way that the area of the carrier plate which should not bear any color as a printing form in the printing process, be provided by means of inkjet technology with a coating which is sufficiently lipophobic to reject the ink, while not coated areas of the support plate are sufficiently lipophilic that ink adheres. Thus, according to the invention, a negative of the printed image is applied to the carrier plate by coating the non-color-bearing background of the printing plate.

Surprisingly, it has been found that support plates with a surface tension of> 35 mN / m are suitable for safely carrying printing inks, while inks which have a surface tension <30 mN / m in the fixed state reject printing inks with sufficient certainty. It has thus surprisingly been found that a difference in the surface tension between the ink-bearing areas and the ink-repellent areas of the printing form of> 5 mN / m is sufficient to produce a printed image in waterless offset printing.

In one embodiment of the method according to the invention, at least the surface of the carrier plate consists of a material from the group consisting of aluminum, aluminum alloys, steel, polycarbonate, polyester and polyolefin. The surface is to be understood as the area of the carrier plate which comes into contact with the printing ink in the printing process. According to the invention, the carrier plate can be a composite structure which consists of a base carrier on which a material of the above mentioned group is applied. For example, it may be provided that a polycarbonate layer is applied to a base carrier made of sheet steel. Preferably, it is provided that the carrier plate consists of only one material.

In a further embodiment of the method according to the invention it can be provided that the carrier plate is pretreated before the application of the ink to change the surface roughness. In particular, it is provided that the surface roughness R _{a of} the support plate is set to less than 1 μιη. The roughness is determined according to EN ISO 25178. By setting a corresponding roughness is ensured that the ink has a sufficient adhesive strength in the fixed state on the support plate to ensure a sufficient longevity of the printing form. A sufficient longevity is regarded as a lifetime of> 100,000 printed copies per printing form.

To set a corresponding surface roughness and / or surface tension of the carrier plate, it may be provided in one embodiment of the invention that the carrier plate is pretreated by means of pickling, etching, corona treatment or plasma treatment.

The application of the ink to the carrier plate can be carried out in the process according to the invention by means of known ink-jet techniques. For example, it may be provided that the ink is applied in the CIJ process (continuous ink-jet process) or in the DOD process (drop-on-demand process). CIJ printers are known in the field of industrial printing. In this case, the ink jet exits via a nozzle from a printhead, wherein the jet modulates via a piezoelectric transducer behind the outlet nozzle in order to achieve a uniform drop in the ink drop. The emerging drops are electrostatically charged via an electrode and then pass through a deflection field built up by a further electrode, within which they are deflected as a function of their charge. Deflecting method and multi-deflecting method is distinguished. Ink drops not needed for printing are collected and returned to the ink circuit.

In contrast, in the DOD process, only the ink drop leaves the nozzle that is actually to be applied as a printed image. Here one differentiates the technology, with which the ink drops are ejected. In bubble jet printers, the required ink drops are created by means of a heating element which heats the ink. This explosively forms a vapor bubble, which presses an ink drop from the nozzle by its pressure. Depending on the type of vapor bubble generation, a distinction is made between sideshooter systems and edgeshooter systems. In piezo printers, a piezoceramic element is deformed by applying an electrical voltage to press ink through a die by the change in shape. The drop size can be controlled by the applied electrical pulse.

According to a preferred embodiment of the inventive method, the ink is applied to the carrier plate with a dot density of> 1200 dpi, preferably> 2400 dpi.

After application to the carrier plate, the ink is fixed. This can be done by air drying. However, it may also be provided in one embodiment of the method according to the invention that the ink is fixed after application to the support plate by means of UV radiation and / or thermal radiation. This advantageously allows rapid fixation of the ink.

According to a further embodiment of the inventive method, it may be provided that the ink comprises a silicone, a polyisoprene and / or fluoroplastic, in particular a poly (dimethylsiloxane). In addition, the ink may include adjuvants such as solvents, surface tension adjusting agents in the fixed state, and / or fixing agents. In a further embodiment of the method according to the invention, the ink used is an UV-curing ink. It may be provided that the ink is free-radical curing or cationic curing. Radical curable inks use unsaturated resins having reactive groups that cause a crosslinking reaction via free radicals. In general, these are acrylated resins or monomers having acrylic acid groups (acrylic acid esters). In addition to the acrylates, other compounds with reactive double bonds, such as unsaturated polyester resins and vinylic monomers such as styrene can be crosslinked via this mechanism. Upon irradiation of UV light, photoinitiators contained in the ink spontaneously decompose into free radicals and initiate a chain reaction for the polymerization. The result is a three-dimensionally crosslinked, insoluble and solid structure of macromolecules. This happens in seconds or fractions of a second, so that immediately after hardening a resilient film is created.

For cationically curing UV inks curing takes place after a different reaction mechanism. The resin base is an oxirane group-containing compound. As an initiator, an acid is used, which is activated only by the exposure. The resin component is usually a cycloaliphatic epoxy resin. The protons of the acid cause opening of the epoxide ring and initiate polymerization with continued chain growth. By combining epoxy resins with polyols, the film properties of the fixed ink can be advantageously adjusted to the requirements of the invention.

In order to preclude disturbing influence of oxygen, it may be particularly preferred according to the invention for the ink to be applied to the carrier plate in an inert gas atmosphere, for example in a nitrogen, carbon dioxide, helium or argon atmosphere. This can preclude adverse oxidation reaction of the inks or the support surface with atmospheric oxygen, thereby improving the adhesion of the ink to the support plate, which in turn results in durability the pressure plate and the pressure to be reached with this increased number of copies. On the other hand, an increased resolution can be achieved by reducing or suppressing the oxidation reactions induced by atmospheric oxygen, since an oxidatively induced fraying of the image dot edges can be avoided. Inert gas atmosphere in the sense of the present invention means that the oxygen concentration in the working atmosphere is <5 vol., Preferably <1 vol., Particularly preferably <0.5 vol.%.

In a further preferred embodiment of the invention, it is provided that at least the ink application takes place in a low-moisture atmosphere in order to exclude disturbing influences of any residual moisture. Low moisture means in the context of the invention that the water content in the working atmosphere is <1 vol., Preferably <0.5 vol., Particularly preferably <0.1 vol .-%.

In particular, it may be provided according to the invention that the ink is applied in a dry inert gas atmosphere with a residual moisture content <0.1% by volume. Furthermore fiction, according to it may be provided that the above-described optional adjustment of the surface roughness R _{a of} the support plate to less than 1 μιη in an inert gas atmosphere, in particular dry inert gas atmosphere. It is particularly preferred that a moisture and / or acidic material contact of the support plate between the setting of the surface roughness and the application of the ink is avoided. In the process according to the invention, for example, in the ink applied to the carrier plate, a silicone, in particular a poly (dimethylsiloxane), a polyisoprene, in particular a poly-2-methyl-1,3-butadiene, or mixtures thereof, can be used as binder. To reduce the surface energy, for example, in the ink applied to the support plate, a silicone oil, a fluorine surfactant, a fluoroplastic, in particular a perfluoroalkoxylalkane and / or a perfluorooctanesulfonate, a silicone, in particular a poly (dimethylsiloxane), a polyisoprene, in particular a poly-2-methyl-1,3-butadiene or a mixture thereof. As the solvent, for example, in the ink applied to the support plate, a short-chain hydrocarbon, N-methyl-2-pyrrolidone, toluene or a mixture thereof may be contained. As the dye, for example, in the ink applied to the support plate, a triphenylmethane, a (4- (4,4'-bis (dimethylaminophenyl) benzhydryliden) cyclohexa-2,5-dien-1-ylidene) dimethyl ammonium chloride or a mixture of these be.

According to a further embodiment of the invention, a coloring agent is added to the ink. This makes it possible to supply the printing form after its preparation of a visual inspection to detect any errors.

The invention will be further described by embodiments and figures, without the idea according to the invention being limited to these examples.

Fig. 1 shows schematically a manufacturing method according to the invention;

Fig. 2 shows a fiction, prepared according to printing;

Fig. 3 shows a fiction, prepared according to printing form with applied thereto

Ink; and

Fig. 4 shows the printed image produced with a printing form according to the invention.

Fig. 1 shows schematically a manufacturing method according to the invention for producing a printing form 100 for waterless offset printing. On a support plate 200, an ink 200 is applied by means of an ink jet device 400. According to the invention, the carrier plate 200 has a surface tension> 35 mN / m. As the material for the support plate 200, for example, aluminum, an aluminum alloy, steel, a polycarbonate, a Polyester, or serve a polyolefin. It may also be provided that the carrier plate 200 has a composite structure in which a coating is applied to a support layer, which has a surface tension in the inventive area. In order to change the surface tension of the carrier plate 200 to the voltage value provided according to the invention, the carrier plate 200 may be subjected to a suitable surface treatment before the ink 300 is applied thereto. Examples of corresponding surface treatments are pickling, etching, corona treatment or plasma treatment. The ink droplets 310 are applied in the areas of the carrier plate 200, which should not carry any color in later offset printing. To avoid any reactions of the ink 300 with atmospheric oxygen, it may be provided that the application of the ink 300 to the carrier plate 200 in a protective gas atmosphere, such as nitrogen or argon, takes place.

FIG. 2 schematically shows a printing plate 100 produced according to the invention. On a carrier plate 200, after being fixed or cured, the applied ink forms regions 320 which have a surface tension <30 mN / m, while the regions not covered with ink 210 have a surface tension> 35 mN / m. In the later printing process, area 210 carries color while areas 320 reject color. The fixing of the ink 300 can be done, for example, thermally or by UV irradiation. Likewise, depending on the ink 200 used, it may be provided that it is fixed or cured by air drying.

3 shows the schematic representation of a printing form 100 to which printing ink has been applied. The ink is accepted by the printing form in the region 500, while the region 320 covered by fixed or cured ink repels the ink. In the subsequent offset printing, the ink-bearing areas are transferred to the blanket cylinder of the printing machine, which then transmits the printed image to the medium to be printed. FIG. 4 shows schematically a medium 600 printed with a printing plate produced in the method according to the invention. The ink-bearing region 500, as described in FIG. 3, was first transferred from the printing plate to a blanket cylinder and then to the medium to be printed.

Claims

claims

1. A method for producing a printing form (100) for waterless offset printing, comprising the method steps:

- Providing a support plate (200);

- applying an ink (300) to the carrier plate (200) by means of inkjet technology;

Fixing the applied ink (300) on the support plate,

characterized in that the carrier plate (200) has a surface tension of> 35 mN / m, preferably> 38 mN / m, and the ink (300) has a surface tension of <30 mN / m, preferably <25 in the state fixed to the carrier plate (200) mN / m and the ink (300) in the areas of the support plate (200) is applied, which should bear no ink in offset printing.

2. A method according to claim 1, wherein at least the surface of the carrier plate (200) is made of a material selected from the group consisting of aluminum, aluminum alloys, steel, polycarbonate, polyester and polyolefin.

A method according to any one of the preceding claims, wherein the support plate (200) is pretreated prior to application of the ink (300) to change the surface roughness.

4. The method according to claim 3, wherein the carrier plate has an average surface roughness R _a below 1 μιη.

5. The method according to any one of claims 3 or 4, wherein the carrier plate (200) is pretreated by means of pickling, etching, corona treatment or plasma treatment.

6. The method according to any one of the preceding claims, wherein the ink (300) after application to the carrier plate (200) by means of UV radiation and / or

Heat radiation is fixed.

7. The method according to any one of the preceding claims, wherein the ink is a silicone, in particular a poly (dimethylsiloxane), a polyisoprene, in particular a poly-2-methyl-l, 3-butadiene, an acrylate, a silicone oil, a fluorosurfactant, a fluoroplastic , a bisacylphosphine oxide, a benzophenone, a perfluoroalkoxyalkane

Perfluorooctanesulfonate, a triphenylmethane, (4- (4,4'-bis (dimethylamino-phenyl) -benzhydrylidene) cyclohexa-2,5-dien-1-ylidene) -dimethylammonium chloride, an N-methyl-2-pyrrolidone, a short-chain hydrocarbon, and / or toluene.

8. The method according to any one of the preceding claims, wherein the application of the ink (300) on the carrier plate (200) takes place in an inert gas atmosphere.

9. The method according to claim 8, wherein the application of the ink (300) to the

Carrier plate in an atmosphere with an oxygen content <5 vol .-% is done.

10. The method according to any one of claims 8 and 9, wherein the application of the ink (300) on the support plate in an atmosphere with a moisture content <1 vol.

A method according to any one of claims 8 to 10, wherein moisture and / or oxygen contact of the support plate between the adjustment of the surface roughness and the application of the ink (300) is avoided.

12. The method according to any one of the preceding claims, wherein the ink (300) with a dot density of> 1200 dpi, preferably> 2400 dpi is applied to the carrier plate (200).

A method according to any one of the preceding claims, wherein a coloring agent is added to the ink (300).

14. Printing form (100), produced by a method according to one of claims 1 to 13.