EP0076905A2 - Flat-bed printing method - Google Patents

Abstract

The invention relates to printed products which have been obtained by the planographic printing process by transferring printing inks to a printing material by means of a lithographic printing plate, and a corresponding planographic printing process. There are printing inks, which mainly contain water as a solvent and / or dispersant, and printing plates, the information-bearing, i.e. H. printing surfaces are hydrophilic and the non-printing surfaces are hydrophobic.

Description

The invention generally relates to printed products which have been obtained by the planographic printing process by transferring printing inks to a printing material by means of a lithographic printing plate, and to a process for their production.

A well-known printing process is offset printing. In recent years, offset printing has gained considerable economic importance. In offset printing, the incompatibility of water and oil is used to divide a homogeneous oil-based ink film on a printing plate into the corresponding information fields.

The offset printing plates have the properties of being water-friendly in the non-information-carrying areas and being oil-friendly in the information-carrying areas. In the course of the printing process, the plate is completely wetted with a water film (wash water), then it is colored with the oil-based printing ink. The hydrophilic areas wetted by water cannot be wetted by the hydrophobic oil paint. This creates a colored one on the printing plate Print image, which is transferred to the substrate via a roller mechanism.

The main advantages of offset printing are the simple, cheap and very quick to produce print carrier, the possibility to create printing plates directly with the help of electronic data processing and the possibility of four-color wet-on-wet printing.

The highly viscous printing inks used in offset printing require repeated rolling out in order to achieve an absolutely uniform ink film across the entire width of the printing press. Inking units of offset printing presses have up to 30 rollers, between which the pasty printing inks are rolled out. Because of this long and intensive rolling, it is not possible to use low-boiling solvents, as is customary in gravure printing, but only high-boiling solvents, since otherwise the printing ink dries on the inking rollers and the ink flow would be disturbed.

In practice, high-boiling mineral oils and vegetable oils that are hydrophobic and water-insoluble are used as solvents.

The use of high-boiling mineral oils as a solvent in offset printing inks has considerable disadvantages. The drying either takes too long because the mineral oils take a long time to penetrate the paper surface (knocking away) and are hampered by the water in the paper, or it increases to an economically sensible level (150 to 160 ° C) when the drying temperature is increased ) drying out and curling of the paper, so that the subsequent further processing steps such as cutting, collating and binding are considerably more difficult. Also used for drying e.g. consumed a considerable amount of energy in web offset.

During printing, offset printing and mixing water are mixed, i.e. an emulsion is formed. This process is advantageous in itself because the resulting consistency of the printing ink only enables economical four-color wet-on-wet printing. As is known to the person skilled in the art, the pre-printed inks are prevented from being lifted off from the printing material by the reprinting printing units by the emulsification of water. On the other hand, this process has the disadvantage that it takes a certain time when starting up a printing press to adjust the ink-water balance. It is therefore quite possible that a total of 5 to 10% of a print run will be produced as waste when starting up a printing machine and when it is switched off and on again.

In order to avoid this disadvantage, attempts have been made to emulsify the water into the printing ink as early as during production. Despite intensive propagation, this has not been able to assert itself, since these printing inks are often unstable. There is a separation of oil and water, and there is no need for a separate dampening unit on the printing press, since the amount of water is also not adjustable and cannot be adapted to the paper or the printed object. It should be noted that conventional printing inks can absorb about 10 to 30% water on the printing press in the printing unit.

In addition to the conventional offset printing described, the so-called waterless offset printing is known. In this process, attempts are made to use special printing plates, in which the ink-bearing layers are hydrophobic, and the non-ink-bearing layers have been made extremely repellent by means of silicone coating, without printing with washing water with conventional offset printing inks.

Despite intensive processing, this printing process has not been able to gain widespread acceptance on the market because Four-color wet-on-wet printing presents problems similar to those of conventional letterpress printing. This applies in particular to pluck-sensitive papers.

It is an object of the invention to avoid the disadvantages of the prior art and to specify printed products and a process for their production in which the use of high-boiling organic solvents can largely be dispensed with while maintaining the advantages of offset printing. Furthermore, the high losses when starting up a printing press and when printing is interrupted are to be avoided.

Surprisingly, it has now been found that instead of the greasy printing inks in the case of planographic printing, aqueous printing inks can be used if the corresponding printing plates are produced in such a way that the printing surfaces are hydrophilic and the non-printing surfaces are hydrophobic. Aqueous printing inks are known per se. So far, however, they have only been used in gravure and flexographic printing. Despite the long-known disadvantages of greasy printing inks, it has so far not become known to use aqueous printing inks in a planographic printing process. It was surprising that good results can be obtained without using grease and water rejection when using aqueous inks.

The invention therefore relates to printed products which have been obtained by the planographic printing process by transferring printing inks to a printing material by means of a lithographic printing plate, characterized in that printing inks which predominantly contain water as solvents and / or dispersing agents and printing plates whose information-carrying, i.e. printing areas are hydrophilic and the non-printing areas are hydrophobic.

The invention also relates to a planographic printing process in which printing inks are transferred to a printing material by means of a lithographic printing plate. The process according to the invention is characterized in that printing inks, which predominantly contain water as a solvent and / or dispersing agent, and printing plates, the information-carrying, i.e. printing surfaces are hydrophilic and the non-printing surfaces are hydrophobic.

The printing inks to be used according to the invention contain color pigments and / or soluble dyes, binders which fix the pigments on the printing material surface, other auxiliaries such as waxes, defoamers, disinfectants and thickeners which are used by other fields of activity, for example aqueous printing inks for gravure or flexographic printing or are known from the field of aqueous lacquers and paints. Both dispersions and water-soluble binders can be used as binders.

The printing inks mainly contain water as a solvent and / or dispersant. In addition to water, they can contain a minor amount of organic solvents that are completely or partially miscible with water. Small quantities of petroleum fractions can only be used as aids. It should be noted here that the printing ink retains its watery character.

Printing inks which correspond to the aqueous printing inks of gravure or flexographic printing but which have a higher viscosity than these can advantageously be used.

As with other printing inks, natural and synthetic waxes, polyethylene, etc. are suitable as auxiliaries for improving the lubricity. In some cases, partial fluorination of the auxiliaries improves the abrasion resistance.

Inorganic or organic substances, in particular soluble or swellable substances, are used as thickeners. Among others, the following are known: alginates, starch, cellulose and their derivatives, e.g. Cellulose ester or cellulose ether. Mineral bodies, which swell with polar solvents, act in the same way.

All known coloring components, for example organic and inorganic color pigments, preferably directly from water pastes, and dyes soluble in water or in solvents are suitable for coloring. These products are known from other areas of printing and painting technology.

The printing inks to be used according to the invention are produced by known processes. So you can e.g. incorporate pigments, pigment preparations or predispersed pigments into the aqueous binder solution or mixture with stirrers and dispersers.

To carry out the method according to the invention, printing plates are advantageously used whose non-printing surfaces are coated with silicone rubber and whose information-bearing surfaces are metal surfaces or hydrophilic plastic surfaces. For example, printing plates such as are used for so-called waterless offset printing are suitable.

For better printability, i.e. to improve the ink repellency of non-printing areas e.g. on printing plates coated with silicone rubber, additions of additives containing silicone groups are useful. These can be dispersed silicone oils or water-soluble silicone derivatives.

The transfer of the printing inks from the inking unit of the printing press to the substrate can be done directly or via an intermediate carrier. A blanket cylinder known from offset printing can serve as the intermediate carrier. In general, an offset printing machine known per se can advantageously be used, the dampening system of which has been removed or deactivated. If necessary, the inking unit of the printing press is reduced, ie all the rollers that are not necessary for inking are removed. This counteracts the faster evaporation of water compared to high-boiling mineral oils. It is also possible to encapsulate the inking unit for this purpose.

In an advantageous embodiment of the method according to the invention, the printing inks are transferred to a printing plate cylinder and from there via a rubber blanket cylinder to the printing material via an anilox roller, which has a doctor blade, via an ink transfer roller arranged downstream of the anilox roller.

The anilox roller advantageously works as an immersion roller, i.e. it protrudes into an ink tray.

Instead of a single ink transfer roller, two or more ink transfer rollers working in parallel can also be used. It is essential, however, that the ink transfer rollers each work directly with the anilox roller and with the printing plate cylinder and not several rollers are connected in series.

In an advantageous embodiment of the method according to the invention, the anilox roller works as an immersion roller, i. H. it protrudes into the ink supply. The printing inks can of course also be applied to the doctor roller in another known manner, for example by brushing.

In the method according to the invention, the disadvantages of the mechanical sensitivity of a rubber film forming a color film are avoided by using a rastered metal roller. It is also more resistant to bending and can be scraped off precisely by using grid bars produced by etching or engraving as support elements.

The uniform ink-absorbing depressions over the entire width of the anilox roller ensure a uniform color, regardless of the different ink consumption at different locations on the print motif. This also complies with the standardization in offset printing. With the previous inking units, the coloring cannot be kept constant during the printing process.

Special requirements for higher or lower ink layer thicknesses, e.g. B. for rougher papers, can be met by exchanging for deeper or flatter etched anilox rollers.

By tempering the anilox roller, even better ink guidance can advantageously be achieved, since the ink viscosity no longer changes due to temperature influences. In conventional long inking units, the inking unit heats up due to internal friction and through many splitting processes of the inks, which causes the inks to become less viscous during the print run. This changes the ink transfer and the ink layer thickness in the print image. Waste can only be avoided by carefully regulating the color scheme by the printer.

To further reduce or completely avoid stenciling, the printing plate cylinder and the ink transfer roller advantageously have the same through knife on. It is particularly advantageous if the anilox roller and the blanket cylinder also have the same diameter as the printing plate cylinder and the ink transfer roller.

The invention also relates to the use of predominantly aqueous printing inks in a planographic printing process and printing inks for carrying out the process, which are characterized in that they contain inorganic and / or organic pigments, binders and, as a solvent and / or dispersant, essentially water and a viscosity of 10 to 250 Pa s, advantageously from 20 to 50 Pa s, measured at 23 C by means of a plate and cone viscometer of the Ferranti-Shirley type.

The printing inks according to the invention advantageously contain silicone oil and / or water-soluble silicone derivatives.

The invention also relates to a planographic printing press for performing the method with an inking unit, a lithographic printing plate cylinder and a blanket cylinder, which is characterized in that the information-carrying, ie. H. printing surfaces are hydrophobic and the inking unit has an anilox roller, which rests on a doctor blade, and an ink transfer roller arranged between the anilox roller and the printing plate cylinder.

The anilox roller of the dipping roller advantageously projects into an ink tray.

To reduce or avoid stenciling, the printing plate cylinder and the ink transfer roller advantageously have the same diameter. Particularly advantageously, the anilox roller and the blanket cylinder have the same diameter as the printing plate cylinder and the ink transfer roller.

In order to achieve a good printing result, the non-printing surfaces of the printing plate cylinder are advantageously coated with silicone rubber and the information-bearing, ie. H. printing surfaces are metal surfaces or hydrophilic plastic surfaces.

The following advantages are achieved by the invention:

A short inking unit with only a few splitting points for the ink considerably reduces the evaporation rate of the volatile components compared to conventional inking units with their many rollers. This is why colors can be used that contain the fast evaporating water that shoots away into the paper. All physical drying processes, i.e. H. Throwing away into the paper, evaporation of the water in the web offset heatset or by IR emitters in the sheetfed offset are much quicker than with the slowly kicking or evaporating mineral oils of conventional inks.

A major advantage of the invention is the reduction in stenciling due to the short inking unit and the continuous renewal of the ink film by the anilox roller.

The temperature in the web offset heatset drying ovens can be significantly reduced, depending on the machine speed, substrate and ink layer thickness. This enables considerable energy savings. The papers dry out less and therefore remain dimensionally stable. H. they do not absorb any water from the environment after drying and no longer "grow" after processing or storage. Under favorable conditions, these inks can even be dried in web offset with IR emitters. These limit cases depend on paper, printing speed and ink layer thickness. In contrast to non-polar conventional oil-based offset inks, the water-based inks also respond to high-frequency dryers.

The invention is explained in more detail below on the basis of exemplary embodiments. The figure shows a section through a planographic printing machine.

The planographic printing machine has an inking unit (13), a printing plate cylinder (3), a blanket cylinder (11) and an impression cylinder (9). The printing substrate (10) runs between the blanket cylinder (11) and the impression cylinder (9). The inking unit (13) consists of an anilox roller (1) which bears a doctor blade (2) and an ink transfer roller (4) which is arranged between the anilox roller (1) and the printing plate cylinder (3). The anilox roller (1) protrudes into the ink tray (8). As the figure shows, all rollers or cylinders have the same diameter.

Example:

40 parts by weight of an aqueous emulsion of an alkali-soluble acrylate polymer having a solids content of 40% by weight, 20 parts by weight of propylene glycol, 4 parts by weight of triethanolamine, 4 parts by weight of a 35% strength methyl silicone oil emulsion, 4 parts by weight . Parts of mineral oil with a boiling range of 190 - 250 ° C and 8 parts by weight of starch ether mixed together. 20 parts by weight of an aqueous pigment dough containing 45% by weight of copper phthalocyanine pigment were added to this mixture. The mass was dispersed on a three-roller to form a homogeneous printing ink.

An offset printing machine according to the figure was used as the printing machine. A commercially available silicone-coated printing plate was used as the printing plate.

It was printed on coated offset paper. The result was prints of excellent quality.

Claims (22)

1. Printed products that have been obtained by the planographic printing process by transferring printing inks to a printing material by means of a lithographic printing plate, characterized in that printing inks, which predominantly contain water as a solvent and / or dispersant, and printing plates, the information-carrying, d. H. printing areas are hydrophilic and their non-printing areas are hydrophobic. 2. Flat printing method, in which printing inks are transferred to a printing material by means of a lithographic printing plate, characterized in that printing inks, which predominantly contain water as a solvent and / or dispersant, and printing plates, the information-carrying, d. H. printing surfaces are hydrophilic and the non-printing surfaces are hydrophobic. 3. The method according to claim 2, characterized in that printing inks are used which correspond to the aqueous printing inks of gravure or flexographic printing, but have a higher viscosity than this. 4. The method according to claim 2 or 3, characterized in that printing plates are used, the non-printing surfaces are coated with silicone rubber. 5. The method according to claim 2 to 4, characterized in that printing plates are used, the information-bearing surfaces are metal surfaces or hydrophilic plastic surfaces. 6. The method according to claim 2 to 5, characterized in that printing inks are used which contain an addition of silicone oil or water-soluble silicone derivatives. 7. The method according to claim 1 to 6, characterized in that the transfer of the printing inks from the inking unit of the printing press to the printing material takes place via an intermediate carrier. 8. The method according to claim 7, characterized in that a known offset printing machine is used, the dampening system has been removed or put out of function. 9. The method according to claim 7, characterized in that the printing inks via an anilox roller (1), which rests on a doctor blade (2), via an ink roller arranged downstream of the anilox roller (4) on a printing plate cylinder (3) and from this via a blanket cylinder ( 11) are transferred to the printing material (10). .0. Method according to claim 9, characterized in that the anilox roller (1) projects as an immersion roller into an ink tray (8). .1. Method according to claim 9 or 10, characterized in that the printing plate cylinder (3) and the ink transfer roller (4) have the same diameter. .2. Method according to claims 9 to 11, characterized in that the anilox roller (1) and the blanket cylinder (11) have the same diameter as the printing plate cylinder (3) and the ink transfer roller (4). 13. Use of predominantly aqueous printing inks in a planographic printing process. 14. Printing inks for performing the method according to claim 2 to 12, characterized in that they contain inorganic and / or organic pigments, binders and as a solvent and / or dispersant essentially water and a viscosity of 10 to 250 Pa s at 23 ° C. exhibit. 15. Printing inks according to claim 14, characterized in that they have a viscosity of 20 to 50 Pa s. 16. Printing inks according to claim 4 or 15, characterized by a content of silicone oils and / or water-soluble silicone derivatives. 17 planographic printing machine for performing the method according to claim 2 to 12 with an inking unit, a lithographic printing plate cylinder and a blanket cylinder, characterized in that the information-carrying, d. H. printing surfaces of the printing plate cylinder (3) are hydrophilic and the non-printing surfaces are hydrophobic and the inking unit (13) has an anilox roller (1) - which rests on a doctor blade (2) and one between the anilox roller (1) and the printing plate cylinder (3) arranged ink transfer roller (4). 18 planographic printing machine according to claim 17, characterized in that the anilox roller (1) protrudes as a dipping roller in an ink tray (8). 19. Planographic printing machine according to claim 17 or 18, characterized in that the printing plate cylinder (3) and the ink transfer roller (4) have the same diameter. 20. Planographic printing machine according to claim 17 to 19, characterized in that the anilox roller (1) and the blanket cylinder (11) have the same diameter as that of the printing plate cylinder (3) and the ink transfer roller (4). 21. Flat printing machine according to claim 17 to 20, characterized in that the non-printing surfaces of the printing plate cylinder (3) are coated with silicone rubber. 22. Flat printing machine according to claim 17 to 21, characterized in that the information-carrying, i.e. printing surfaces of the printing plate cylinder (3) are metal surfaces or hydrophilic plastic surfaces.

Images