Printing plate and polymeric coating material for said plate

Abstract

The present invention relates to a coating material for coating metallic or non-metallic printing plates, comprising a liquid starting material that can be polymerized using ultraviolet light to form a polymer matrix, and comprising a filler that can be covalently incorporated into the polymer matrix of the starting material. The filler material is of sub-microscale size, and absorption of IR radiation is provided by the filler material in the starting material, said absorption being higher than absorption without the filler material. The present invention also relates to a printing plate comprising a cylindrical body having a polymer layer applied to at least a portion of the circumferential surface of the body, the polymerization of which is induced by ultraviolet light, characterized in that the polymer layer has sub-microscale filler material, and the filler material in the polymer layer is used to provide higher absorption of infrared radiation than the polymer layer without the filler material.

Description

[Technical field]

[0001] The present invention relates to printing plates and polymeric coating materials for said printing plates. In particular, the present invention relates to polymer nanocomposites as monolayers for printing plates, in particular gravure plates or cylinders, patterning plates or cylinders, embossing plates or cylinders, and letterpress printing plates or cylinders or coating rollers, and inking rollers, such as for flexographic printing, having sufficient tribological properties for the requirements of modern printing.

[0002] In the following text, the term "printing plate" is used as a general term for gravure printing plates, letterpress printing plates or embossing patterning plates, but also includes coating or inking rollers. In particular, gravure printing plates and letterpress printing plates are used for a wide variety of printed materials such as magazines and packaging, while patterning plates are used to emboss relief-like patterns into normally soft surfaces. [Background technology]

[0003] For gravure printing, gravure cylinders are particularly popular, consisting of a metal substrate with a galvanic coating on the outer circumference. The image-forming layer is made of copper, on which a hard chrome layer is applied to protect against wear. The copper surface is engraved, using a mechanical engraver or a laser, to resemble a real printing plate. It has proven effective to form the engraving in the form of small depressions called cells, which are intended to absorb the printing ink during the subsequent printing process and transfer it to the substrate, such as paper or plastic.

[0004] The production of suitable coatings for printing plates, particularly gravure and patterning cylinders, by galvanic processes is costly and requires several manufacturing steps.

[0005] To avoid costly metal galvanization, it has already been considered to coat the metal substrate of the gravure cylinder with a UV-curable polymer layer. UV-curable polymer layers are usually transparent because the UV light required for curing can penetrate through them. If the transparency is reduced by the addition of additives, the penetration depth or energy density of the UV light that penetrates also decreases. As a result, if the layer becomes too thick or the transparency is reduced, polymerization may not be completed and complete curing of the polymer layer may not be achieved.

[0006] Patterning of transparent polymer layers, in particular the introduction of surface patterns, for example in the form of cells or patterns for ink absorption or embossing, can generally only be achieved with the aid of UV lasers. However, UV lasers have the disadvantage that they are expensive to purchase, time-consuming to operate and costly to maintain. In gravure printing, the requirement for rapid patterning of the surface, i.e. rapid introduction to the surface of the printing plate, makes UV lasers suitable only to a limited extent.

[0007] The use of faster, industrially available and cost-effective infrared lasers (IR lasers) with sufficient ablation quality is usually not possible with transparent (polymer) layers, since infrared light is not absorbed by the transparent layer and therefore penetrates through the polymer layer to the (e.g. metal) substrate, where ablation only occurs. As a result, ablation and therefore patterning of the transparent polymer layer surface to produce gravure cells is not feasible.

[0008] Instead of UV curing the polymer layer on the gravure cylinder, it is possible to heat cure it, but this is not effective due to the long tempering times. It should be noted that gravure cylinders are usually made of solid iron or aluminum bodies and are usually designed as thick-walled tubes with or without a welded shaft. Heating such a massive body requires a considerable amount of time.

[0009] Cells commonly used in gravure printing have a maximum depth of, for example, 40 μm. Taking into account the concentricity errors of the cylinders, tolerances in processing and the avoidance of stray light, the minimum layer thickness of the polymer layer is therefore 100 μm. Also, assuming the currently performed gradation within a set of cylinders, a layer thickness of up to 250-300 μm must be ensured. Gradation is understood to mean the gradation of diameters within a set of cylinders, for example, in a printing press with six cylinders, the difference in diameter from the first printing cylinder to the next is usually 0.02 mm. This is to compensate for the stretching or shrinkage of the printing web in unregulated printing presses in order to print the printing image in perfect register on the substrate.

[0010] Thus, although UV-curable polymer layers exist, they are transparent and therefore can only be imaged with sufficient quality using a UV laser, while polymer layers that can be patterned with faster infrared lasers are not transparent enough (at least throughout their thickness) and therefore require thermal curing rather than UV curing, which is very time- and energy-intensive.

[0011] An anilox roller filler for variable depth laser ablation is known from DE 101 15 434 A1. The filler is used to fill the cell structure of an anilox roller. After the filler material has hardened in each filled cell, it can be removed by IR laser ablation in the individual cells in order to image the printing plate.

[0012] DE 101 13 927 A1 describes a method for the production of relief printing plates by laser engraving, in which a crosslinkable relief layer is applied to a dimensionally stable carrier.

[0013] EP 1 710 094 A1 also discloses a process for producing a laser-engravable printing substrate.

[0014] Another method is described in EP 1 642 715 A1. Summary of the Invention [Problem to be solved by the invention]

[0015] The invention is based on the object of enabling a simple polymer coating of printing plates which allows reliable production of layers and rapid generation of surface patterns (gravure / letterpress or embossing plates) in conjunction with a sufficient service life and high printing or embossing quality. [Means for solving the problem]

[0016] The object according to the invention is achieved by a printing plate having a polymer coating and by a corresponding coating material for coating metallic or non-metallic printing plates, e.g. metallic or non-metallic cylinders, respectively.

[0017] In particular, a coating material for coating a printing plate is provided, the coating material being: - A liquid starting material that can be polymerized by UV light to form a polymer matrix; - a filler having a sub-microscale size, - the coating material comprises, in addition to the sub-microscale filler, an additional filler; - the sub-microscale fillers are particulate and have a size ranging between 100 nm and 999 nm; - the additional filler is a nanoscale filler comprising filler particles having a nanoscale size in the range between 1 nm and 99 nm; - the sub-microscale filler is a metal oxide coated mica, TiO 2 or (Sn,Sb)O 2 and is composed of at least one metal oxide and / or semi-metal oxide selected from the group consisting of The nanoscale filler is Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 or organometallic particles, - the sub-microscale fillers are capable of being covalently bonded to a polymer matrix of the starting material; the nanoscale fillers are included to improve wear resistance and are capable of being covalently bonded to the polymer matrix of the starting material; The sub-microscale fillers are capable of causing the starting material to absorb infrared radiation that is higher than the absorption without the filler.

[0018] Additionally, a printing plate is provided, the printing plate being as follows: - a substrate; - a polymer matrix including a polymer layer induced to polymerize by ultraviolet light is applied to at least a portion of a surface of a substrate; - the polymer layer comprises sub-microscale fillers; - the polymer layer comprises, in addition to the sub-microscale fillers, an additional filler; - the sub-microscale fillers are particulate and have a size ranging between 100 nm and 999 nm; - the additional filler is a nanoscale filler comprising filler particles having a nanoscale size ranging between 1 nm and 99 nm; - the sub-microscale filler is composed of at least one metal oxide and / or one semi-metal oxide selected from metal oxide-coated mica, TiO2, or (Sn, Sb)O2; The nanoscale filler is Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 or organometallic particles, - the sub-microscale fillers are covalently bonded to a polymer matrix of the polymer layer; - Nanoscale fillers are included to enhance wear resistance and are covalently bonded to the polymer matrix of the starting material. The sub-microscale fillers in the polymer layer cause a higher absorption of infrared radiation than a polymer layer that does not contain a filler.

[0019] therefore, A coating material for coating a printing plate, comprising: a liquid starting material that can be polymerized by ultraviolet light to form a polymer matrix; and a filler that can be covalently bonded to the polymer matrix of the starting material, said filler being capable of being polymerized by ultraviolet light to form a polymer matrix. One of the fillers is submicroscale size, this Coating materials are described in which the filler is capable of causing the starting material to absorb infrared radiation measurably higher than the absorption without the filler.

[0020] Thus, the coating material refers to a material that is applied to the outer circumference of a cylinder, in particular a printing cylinder, to form a desired polymer layer thereon. The coating material defined herein is therefore still in an initial liquid state. Only by irradiating with ultraviolet light is polymerization induced and the starting material hardened. The outer surface of the polymer layer can then be patterned or marked or coded with the aid of infrared radiation, in particular by IR laser or NIR laser (near infrared).

[0021] Thus, the starting material is polymerized with UV light and then patterned with IR radiation. During this process, the actual laser ablation (patterning of the surface) is made possible by adding fillers, which increase IR absorption. The fillers, present in the form of particles or pigments, increase the absorption of IR radiation due to their sub-microscale size.

[0022] In particular, it has been proven that near infrared rays with wavelengths of 780 to 3000 nm, particularly up to 1064 nm, are suitable as infrared rays.

[0023] The starting materials can be, for example, UV-curable prepolymers or monomer mixtures based on acrylates of radical UV-curing systems. In this case, the composite layer is composed of multiple multifunctional monomers, oligomers and / or polymers that can be crosslinked by UV radiation curing. In addition, a binder can also be used.

[0024] Sub-microscale fillers are At least one It may be composed of metal oxides and / or semi-metal oxides. Suitable metal oxides are metal oxide coated mica, titanium dioxide, i.e., TiO2, or (Sn, Sb)O2.

[0025] Sub-microscale fillers are in the form of particles that can range in size from 100 nm to 999 nm, which is suitable for absorbing infrared and near infrared radiation.

[0026] In addition to the sub-microscale fillers, the coating material can include additional nanoscale fillers; especially Nanoscale metals in powder form and / or It can be a semi-metal oxide. these are Al2O3, SiO2, TiO2, ZrO2 or organometallic particles It is.

[0027] Sub-microscale and nanoscale fillers can ensure the transmission of ultraviolet light so that the starting material can be fully polymerized. Thus, the filler particles allow the transmission of UV radiation to the extent necessary for UV-induced polymerization. As a result, a complete full cure or full polymerization of the starting material can be achieved to obtain a polymer layer that adheres firmly on the object to be coated.

[0028] In particular, the coating material can be conductive and / or non-electrically charged. It has therefore been surprisingly found that the material does not become electrostatically charged and even discharges. This aspect is advantageous, since solvent-based printing inks are frequently used in printing processes, the processing of which requires a certain level of explosion protection. It is therefore advantageous if discharge or even ignition processes can be avoided. It is in principle possible to make the polymer conductive by adding carbon black. However, this measure impairs the transmission of ultraviolet light and compromises the complete curing of the polymer layer. but,By adding the filler provided in accordance with the present invention, the addition of carbon black is not necessary.

[0029] Coating materials or polymer layers that can be produced from coating materials by UV irradiation can be resistant to the mechanical (abrasive) stresses inherent in the printing process under the influence of highly abrasive and solvent-containing printing inks or coatings. Thus, with the help of coating materials it is possible to produce polymer layers that are permanently resistant to the printing process and meet the tribological requirements during printing.

[0030] A printing plate having a substrate, a polymer layer induced to polymerize by ultraviolet light is applied to at least a portion of a surface of the substrate, the polymer layer being coated with a sub-microscale filler. and nanoscale fillers in the polymer layer. Sub-microscale A printing plate is provided in which the filler causes a higher absorption of infrared radiation than a polymer layer that does not contain the filler.

[0031] The term "printing plate" is understood in this context as a general term for a number of different applications and embodiments. In particular, the term "printing plate" is to be understood as a gravure plate (e.g. a gravure cylinder), a letterpress printing plate (e.g. a letterpress cylinder) or a patterning plate for embossing (e.g. a patterning or embossing cylinder), as well as a coating or inking roller that can be used, for example, in flexographic printing. Gravure and letterpress printing plates can be used for a variety of printed items, such as magazines and packaging, while patterning plates are used to emboss relief-like patterns into normally soft surfaces. Printing plates can be cylindrical or flat.

[0032] The substrate, which essentially determines the printing plate, can be designed accordingly to be cylindrical or planar. In the case of a cylindrical substrate, the surface carrying the polymer layer can accordingly be the circumferential surface of the substrate.

[0033] In this case, the substrate is generally made of a metal such as iron or aluminum, but it is also possible to use plastics, glass fiber composites, carbon fiber composites, elastomers, etc. as the substrate material.

[0034] The printing plate or printing cylinder is coated with the coating material specified above, and then polymerized by exposure to ultraviolet light. Thus, the coating material represents the initial state, and the polymer layer on the printing plate represents the final state. This polymer layer is the same as that described in the present application. Scope of the invention They are also called nanocomposites.

[0035] After application to the substrate and after polymerization, the polymer layer can be mechanically finished, for example by grinding, polishing, turning, milling, turn-milling, etc. In this way, the dimensional accuracy and - for example in the case of printing cylinders - the roundness can be improved with the polymer layer applied on the outside.

[0036] Cell, relief and letterpress patterns can be generated on the surface of a polymer layer by NIR (near infrared) radiation. In particular, a pattern in the form of depressions, so-called cells, can be generated on the surface of a polymer layer using a NIR laser. Ink is then introduced into these cells during the actual gravure printing process and transferred to the substrate.

[0037] The polymer layer may be opaque prior to exposure to NIR radiation, whereby exposure to NIR radiation may induce a color change in the polymer layer, which may refer, for example, to a change from "opaque light" to "opaque dark" or vice versa, although other color changes are also possible.

[0038] This is useful, for example, for the above-mentioned identification (eg marking or also coding), since a dark marking is easily recognizable. In addition, it is also possible to change the color tone depending on the material used.

[0039] A color change in the polymer layer can already be produced by near infrared radiation of lower intensity than that required for the production of the cell pattern. Thus, while mechanical or laser ablation is not possible with lower intensity NIR radiation, a color change can already be produced. This can be used, for example, to introduce marks or codes into the polymer layer, thus marking or coding the entire printing plate or the entire printing cylinder.

[0040] Markings or coding applied with the aid of low intensity near infrared radiation can contain machine readable data, allowing the finished printing plates to be processed automatically.

[0041] In addition to doping with sub-microscale fillers, the polymer layer may also have doping with nanoscale fillers, which may improve the wear resistance of the polymer layer, thereby achieving a longer life or longer operation of the printing cylinder during printing operations.

[0042] Additional nanoscale fillers are particularly suitable for improving wear resistance. These are Al2O3, SiO2, TiO2, ZrO2 or organometallic particles. Metal and / or semi-metal oxides It is.

[0043] A method for producing a printing plate using the above coating material includes the following steps. The process of applying a coating material to the surface of the printing plate precursor. - A process in which the coating material is hardened by polymerization under UV irradiation to form a polymer layer. - irradiating the polymer layer with near infrared radiation to form a surface pattern in the polymer layer.

[0044] Prior to irradiating the polymer layer with light, as a further manufacturing step, the surface of the cured polymer layer can be machined by a suitable manufacturing process (e.g., turning, grinding, milling, turn-milling) to achieve the required surface quality. This step is optional and can be omitted if the coating quality is sufficient for the subsequent printing step.

[0045] Certain aspects of the invention and various embodiments are summarized below.

[0046] As explained above, according to the present invention, sub-microscale fillers composed of metal or semi-metal oxides are added to polymers, which increase the absorption of NIR radiation for laser micropatterning, but at the same time allow the transmission of UV radiation to the extent necessary for UV-initiated polymerization.

[0047] The near-infrared additive (sub-microscale filler) used causes a color change when a certain near-infrared radiation density is received. In addition, the additive absorbs near-infrared radiation well, improving the processability of near-infrared lasers.

[0048] The laser-machined cells that are ablated onto the surface are evident on the surface of the polymer layer as a color change.

[0049] It is also possible to change the color tone without ablating the surface using lower near-infrared laser power.

[0050] Therefore, the coating material and the resulting polymer layer can also be cured in thick films by UV light. At the same time, however, the polymer layer is opaque due to the sub-microscale fillers, so processing with NIR lasers (e.g. pulsed laser sources) is possible without the radiation passing through the polymer material. Rather, the NIR radiation binds to the surface of the polymer layer, allowing ablation. For this process, pulsed NIR ultrashort pulse (USP) lasers can be used in particular.

[0051] The color change on the gravure cylinder occurs at the imaged surface in relation to the material removal that has taken place. Similarly, at low laser powers, color changes can occur without material removal.

[0052] As a result, the laser-processed typeface becomes clearly visible on the material's surface and can be advantageously used for identification or for the insertion of (machine) data. For example, the non-destructive color change can be used for marking with a QR code for print cylinder recognition systems or for storing required data such as the polymer (starting material) batch number, production date, diameter, roughness, UV curing process, order number (service house), brand identification, etc.

[0053] This type of marking can be used as a zero point for precise registration of the gravure cylinders of the printing units, for machine presetting (by transferring the data directly to the press by a scanner), or to visually identify the printing cylinders, the latter previously only possible with the aid of optical aids such as a microscope.

[0054] Especially with the addition of nanoscale fillers, this material is sufficiently wear-resistant to scraper-ink-substrate prevalent systems, such as gravure printing. It is worth mentioning that this combination represents a suitable tribological system, especially since gravure printing requires a very homogeneous non-printing surface that is wear-resistant to scraper, substrate and ink.

[0055] These and other advantages and features are illustrated below by way of example with reference to FIG. [Brief description of the drawings]

[0056] [Figure 1] 1 shows a schematic cross section through a printing cylinder functioning as a printing plate having a polymer layer according to the present invention.

[0057] In FIG. 1, a cylindrical substrate 1 is shown, which may be made of metal, non-metal or plastic. This substrate 1 is the actual printing cylinder that serves as a printing plate and can be installed in a printing press, for example as a gravure cylinder. Based on the example of FIG. 1, the invention will be described with reference to the gravure printing process. Similarly, the invention can also be applied in letterpress printing processes, as well as patterning and embossing plates. The substrate may also be made of plastic, glass fiber composite, carbon fiber composite, elastomer or a combination thereof.

[0058] On the cylindrical periphery of the substrate 1, a polymer layer 2 is applied, which is based on a nanocomposite in which various fillers are incorporated. The polymer layer 2 is essentially composed of an acrylate or acrylate mixture that is curable by UV light. Furthermore, fillers 3 are introduced into the polymer layer 2. The fillers 3 are in particular sub-microscale fillers whose particles or pigments are in the size range between 100 nm and 999 nm. These fillers, as already explained above in the general section, serve to improve the absorption of infrared radiation and thus improve the laser ablation.

[0059] 1 further shows an ultraviolet light source 4 capable of generating ultraviolet radiation 5. The ultraviolet radiation 5 serves in particular to polymerize the flowable starting material, i.e. in particular an acrylate or acrylate mixture, underlying the polymer layer 2 and thus to produce and harden the polymer layer 2.

[0060] Further shown in figure 1 is a NIR laser 6 (infrared laser) capable of generating near infrared radiation 7. The NIR laser 6 may be a USP (ultrashort pulse) laser.

[0061] Infrared radiation 7 impinging on the polymer layer 2 can be used to create cells 8 in the surface of the polymer layer 2 in the form of depressions which are supposed to receive the actual printing ink in a subsequent gravure process.

[0062] The cells 8 can have different shapes and cross sections. For example, the inlet cross section of the cells can be, for example, square, rectangular, rhomboid, triangular or circular. Other shapes are also possible. From this inlet cross section, the cells 8 extend in depth or into the material, where again different shapes are possible.

[0063] In letterpress printing, the printing ink is therefore not introduced into the cells 8 in the usual way, but is applied to the printing dots or to the left surface. In embossing, a relief is formed in the surface, which is then pressed into the carrier material.

[0064] In Fig. 1 the UV light source 4 and the NIR laser 6 are shown side by side. However, for logical reasons they can be arranged in different devices or processing stations. In particular, a processing station can be provided for producing the polymer layer 2 on the substrate 1. The printing cylinder thus produced can then be mechanically finished in an additional station, not shown, in order to smooth the surface of the polymer layer 2 and improve its roundness. Here, for example grinding, turning, polishing, milling, turn-milling etc. are suitable.

[0065] Only then, in the "patterning" process step, can the printing cylinder be introduced into a station in which a NIR laser 6 is present in order to generate cells 8 and thus the printing pattern (printing plate) on the surface of the polymer layer 2.

[0066] Furthermore, a marking field 9 is shown on the surface of the polymer layer 2. As explained above, it is possible to use low intensity infrared light to only cause a color change in the polymer layer 2, without laser ablation, i.e. without surface patterning. This makes it possible to create a marking field 9 in which coded information, such as a QR code, can be stored.

[0067] Only by irradiating the material with more intense infrared light 7 can actual cells 8 be produced by laser ablation. EXAMPLES

[0068] Below are various examples of nanocomposite production.

[0069] Example 1. 56g Ebecryl 837, 14g Sartomer SR 494, 1.75g ​​DYNAS Y A 250 ml solution of LAN VTMO and 64 mg maleic acid dissolved in 0.64 g water is stirred in a stirring vessel. Then, while continuing to stir, 5-40 m% of Almal nanopowder is added to this mixture within 120 min and stirred for another 3 h. 2.6 g of DYNAS Y After addition of LAN VTMO and 5.2 g of Iriotec 8210 the mixture is stirred for a further 3 hours.

[0070] Example 2. 23g Ebecryl 1290, 46.4g Sartomer SR 494, 12.5g DYNAS Y A 250 ml solution of LAN VTMO and 460 mg maleic acid dissolved in 4.6 g water is stirred in a stirring vessel. Then, while continuing to stir, 5-40 m% of Almal nanopowder is added to this mixture within 120 min and stirred for another 4 h. 2.8 g of DYNAS Y After addition of LAN VTMO and 5.6 g of Iriotec 8210 the mixture is stirred for a further 3 hours.

[0071] Example 3. 56g Ebecryl 837, 14g Sartomer SR 494, 1.35g DYNAS Y A solution of 250 ml of LAN VTMO and 48 mg of maleic acid in 0.48 g of water is stirred in a stirring vessel. Then, with stirring, 5-20 m% of ZrO2 nanopowder is added to the mixture within 120 minutes. Stirring is continued for another 3 hours, after which 3.0 g of Sartomer SR 297 is added to the mixture. 2.6 g of DYNAS Y After addition of LAN VTMO and 5.2 g of Iriotec 8210 the mixture is stirred for a further 3 hours.

Claims

1. The base and a polymer layer applied to at least a portion of the surface of the substrate and polymerized by ultraviolet light; the polymer layer comprises sub-microscale fillers; the polymer layer comprises additional fillers in addition to the sub-microscale fillers; The sub-microscale fillers are particulate and have a size range of 100 nm to 999 nm; the additional filler is a nanoscale filler comprising filler particles having a nanoscale size in the range between 1 nm and 99 nm; The sub-microscale fillers are metal oxide coated mica, TiO 2 or (Sn, Sb)O 2 At least one metal oxide and / or semi-metal oxide selected from The nanoscale filler is Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 or organometallic particles, the sub-microscale fillers are covalently bonded to a polymer matrix of a starting material for forming the polymer layer; the nanoscale filler is included to improve wear resistance and is covalently bonded to the polymer matrix of the starting material; The sub-microscale filler contained in the polymer layer increases infrared absorption rate compared to a polymer layer not containing a filler, the polymer layer is opaque prior to exposure to NIR radiation; A printing plate characterized in that the color tone of said polymer layer can be changed by exposure to NIR radiation.

2. 2. The printing plate of claim 1, wherein the polymer layer is mechanically finished after application to a substrate and polymerization.

3. 3. The printing plate according to claim 1, wherein a cell pattern or a relief pattern can be created by irradiating the surface of the polymer layer with NIR radiation.

4. 4. The printing plate according to claim 1, wherein the change in color tone for introducing a marking or coding into the polymer layer is already effected by NIR radiation of lower intensity than the NIR radiation required for the generation of a cell pattern.

5. The printing plate of claim 4 , wherein the marking or coding comprises machine readable data.

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