Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N1/00—Printing plates or foils; Materials therefor
  • B41N1/12—Printing plates or foils; Materials therefor non-metallic other than stone, e.g. printing plates or foils comprising inorganic materials in an organic matrix
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/02—Engraving; Heads therefor
  • B41C1/04—Engraving; Heads therefor using heads controlled by an electric information signal
  • B41C1/05—Heat-generating engraving heads, e.g. laser beam, electron beam
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/145—Infrared
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/146—Laser beam

Definitions

• the present invention relates to a method for producing flexographic printing plates by means of laser engraving by applying at least one elastomeric relief layer to a dimensionally stable support, the relief layer comprising at least one elastomeric binder and at least one absorber for laser radiation, cross-linking of the relief layer by means of electron radiation in the entire area a minimum total dose of 40 kGy and engraving a print relief into the cross-linked relief layer using a laser.
• the invention further relates to flexographic printing forms which are obtainable by the process.
• Direct laser engraving has several advantages over the conventional production of flexographic printing plates.
• a number of time-consuming process steps such as creating a photographic negative or developing and drying the printing form, can be omitted.
• the flank shape of the individual relief elements can be designed individually using the laser engraving technique. While the flanks of a relief point in photopolymer plates continuously diverge from the surface to the base of the relief, laser engraving can also be used to engrave a flank that falls vertically in the upper area and that widens only in the lower area. Thus, with increasing wear of the plate during the printing process, there is no or at most a low tone value - an increase. Further details on the technique of laser engraving are shown, for example, in "Technique of Flexographic Printing", p. 173 ff., 4th ed., 1999, Coating Verlag, St. Gallen, Switzerland.
• EP-A 640 043 and EP-A 640 044 disclose single-layer or multi-layer elastomeric laser-engravable recording elements for the production of flexographic printing plates.
• the elements consist of "reinforced" elastomeric layers.
• Elastomeric binders in particular thermoplastic elastomers such as SBS, SIS or SEBS block copolymers, are used to produce the layer.
• the so-called reinforcement increases the mechanical strength of the layer in order to enable flexographic printing.
• the reinforcement is achieved either by introducing suitable fillers, photochemical or thermochemical crosslinking or combinations thereof.
• C0 2 lasers with a wavelength of 10640 nm can be used for laser engraving of flexographic printing plates.
• Very powerful C0 2 lasers are commercially available.
• the elastomeric binders that are usually used for flexographic printing plates generally absorb radiation with a wavelength in the range of around 10 ⁇ m. They can thus in principle be engraved with CO 2 lasers (wavelength of 10,640 nm), as disclosed, for example, by US Pat. No. 5,259,311, even if the speed of the engraving is not always optimal.
• the achievable resolution and thus the quality of the printing plate when engraving with C0 2 lasers is limited. In addition to existing physical limits, the beam becomes increasingly difficult to focus with increasing power.
• Solid-state lasers with wavelengths in the range of around 1 ⁇ m can also be used for laser engraving of flexographic printing elements.
• powerful Nd / YAG lasers (wavelength 1064 nm) can be used.
• Nd / YAG lasers have the C0 2 laser The advantage is that due to the significantly shorter wavelength, significantly higher resolutions are possible. In general, however, elastomeric binders of flexographic printing plates do not absorb the wavelength of solid-state lasers, or only do so poorly.
• EP-B 640 043 therefore proposes as a solution to produce a thick layer by casting a multiplicity of thin layers, each followed by photochemical crosslinking of each individual layer.
• this procedure is cumbersome and expensive.
• adhesion between the layers when pouring a new layer onto an already crosslinked layer is often unsatisfactory.
• Laser-engravable flexographic printing elements which have an opaque relief layer can also be produced by casting the layer and then thermally, e.g. crosslinked using monomers and thermal polymerization initiators.
• layers of limited thickness can also be produced by casting, because with increasing layer thickness, layer defects are also increasingly caused when the solvent is evaporated.
• Flexographic printing plates have layer thicknesses of up to 7 mm. Such layer thicknesses can generally only be achieved by repeated pouring on one another if high-quality layers are to be obtained, and the procedure is correspondingly cumbersome and expensive.
• many carrier films no longer have adequate dimensional stability at the temperatures of the thermal crosslinking.
• the object of the invention was therefore to provide a method for producing flexographic printing plates in which the printing relief is engraved by means of a laser in relief layers which contain absorbers for laser radiation, and also in which thicker layers and any other layers that may be present can be crosslinked in a single operation.
• an elastomeric layer which comprises at least one elastomeric binder and at least one absorber for laser radiation, is first applied to a dimensionally stable carrier.
• the relief layer is opaque.
• suitable dimensionally stable supports include films made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate, polyamide or polycarbonate, preferably PET or PEN films.
• Conical or cylindrical tubes made of the said materials, so-called sleeves, can also be used as supports.
• Glass fibers or dressing materials made of glass fibers and suitable polymer materials are also suitable for sleeves.
• Metallic carriers are generally not suitable for carrying out the method because they heat up too much under electron radiation, which should not preclude their use in special cases.
• the dimensionally stable support can optionally be coated with an adhesive layer for better adhesion of the relief layer.
• the relief layer comprises at least one elastomeric binder.
• binders are only limited insofar as relief layers suitable for flexographic printing have to be obtained. Suitable binders are selected by the person skilled in the art depending on the desired properties of the relief layer, for example with regard to hardness, elasticity or color transfer behavior.
• Suitable elastomers essentially include
• the first group includes those elastomeric binders that have ethylenically unsaturated groups.
• the ethylenically unsaturated groups can be crosslinked using electron beams.
• Such binders are, for example, those which contain copolymerized 1,3-diene monomers such as isoprene or butadiene.
• the ethylenically unsaturated group can act as a chain building block of the polymer (1, incorporation), or it can be bound to the polymer chain as a side group (1, 2 incorporation).
• Examples include natural rubber, polybutadiene, polyisoprene, styrene-butadiene rubber, nitrile-butadiene rubber, acrylate-butadiene rubber, acrylonitrile-isoprene rubber, butyl rubber, styrene-isoprene rubber, polynorbornene rubber or Ethylene propylene diene rubber (EPDM) called.
• natural rubber polybutadiene, polyisoprene, styrene-butadiene rubber, nitrile-butadiene rubber, acrylate-butadiene rubber, acrylonitrile-isoprene rubber, butyl rubber, styrene-isoprene rubber, polynorbornene rubber or Ethylene propylene diene rubber (EPDM) called.
• EPDM Ethylene propylene diene rubber
• thermoplastic elastomeric block copolymers of alkenyl aromatics and 1,3-dienes include thermoplastic elastomeric block copolymers of alkenyl aromatics and 1,3-dienes.
• the block copolymers can be either linear block copolymers or radial block copolymers. Usually, these are three-block copolymers of the ABA type, but it can also be a two-block polymer of the AB type, or those with several alternating elastomeric and thermoplastic blocks, e.g. B. ABABA. Mixtures of two or more different block copolymers can also be used. Commercial three-block copolymers often contain certain proportions of two-block copolymers.
• the diene units can be 1, 2 and / or 1, 4-linked.
• Both block copolymers of styrene-butadiene and of the styrene-isoprene type can be used. They are commercially available, for example, under the name Kraton ® . We can also use thermoplastic elastomeric block copolymers with end blocks made of styrene and a statistical styrene-butadiene middle block, which are available under the name Styrof lex ® .
• binders with ethylenically unsaturated groups include modified binders in which crosslinkable groups are introduced into the polymeric molecule by grafting reactions.
• the second group includes those elastomeric binders which have functional groups which can be crosslinked by means of electron beams. These are preferably lateral functional groups. However, they can also be groups that are integrated into the polymer chain. Examples of suitable functional groups include -OH, -NH, -NHR, -NCO, -CN, -COOH, -COOR, -CONH 2 , -CONHR, -C0-, -CHO or -S0 3 H, where R is generally aliphatic and called aromatic residues. Protic functional groups such as -OH, -NH, -NHR, -COOH or -S0 3 H have proven to be particularly advantageous for the production of flexographic printing plates by means of electron beam crosslinking and laser engraving.
• binders include acrylate rubbers, ethylene-acrylate rubbers, ethylene-acrylic acid rubbers or ethylene-vinyl acetate rubbers and their partially hydrolyzed derivatives, thermoplastic elastomeric polyurethanes, sulfonated polyethylenes or thermoplastic elastomeric polyesters.
• elastomeric binders which have both ethylenically unsaturated groups and functional groups.
• examples include copolymers of butadiene with (meth) acrylates, (meth) acrylic acid or acrylonitrile, and also copolymers or block copolymers of butadiene or isoprene with functionalized styrene derivatives, for example block copolymers of butadiene and 4-hydroxystyrene.
• Unsaturated thermoplastic elastomeric polyesters and unsaturated thermoplastic elastomeric polyurethanes are also suitable.
• the third group of elastomeric binders includes those which have neither ethylenically unsaturated groups nor functional groups.
• examples include ethylene / propylene elastomers, ethylene / 1-alkylene elastomers or products obtained by hydrogenating diene units, such as SEBS rubbers.
• elastomeric binders can of course also be used, which may be binders from only one of the groups described in each case, or mixtures of binders from two or all three groups.
• the possible combinations are only limited insofar as the suitability of the relief layer for flexographic printing must not be negatively influenced by the binder combination.
• a mixture of at least one elastomeric binder which has no functional groups and at least one further binder which has functional groups can advantageously be used.
• the amount of the elastomeric binder or binders in the relief layer is usually 40% by weight to 99% by weight, based on the sum of all constituents, preferably 50 to 95% by weight, and very particularly preferably 60 to 90% by weight.
• the relief layer further comprises at least one absorber for laser radiation.
• Mixtures of different absorbers for laser radiation can also be used.
• Suitable absorbers for laser radiation have a high absorption in the range of the laser wavelength.
• absorbers are suitable which have a high absorption in the near infrared and in the longer-wave VIS range of the electromagnetic spectrum.
• Such absorbers are particularly suitable for absorbing the radiation from power strong Nd-YAG lasers (1064 nm) and IR diode lasers, which typically have wavelengths between 700 and 900 nm and between 1200 and 1600 nm.
• Suitable absorbers for laser radiation in the infrared spectral range are highly absorbent dyes such as phthalocyanines, naphthalocyanines, cyanines, quinones, metal complex dyes such as dithiolenes or photochromic dyes.
• Suitable absorbers are inorganic pigments, in particular intensely colored inorganic pigments such as chromium oxides, iron oxides, iron oxide hydrates or carbon black.
• Finely divided soot types with a particle size between 10 and 50 nm are particularly suitable as absorbers for laser radiation.
• the laser absorbers mentioned also have a high absorption in the UV and VIS range of the electromagnetic spectrum and are accordingly intensely colored.
• the relief layers which contain these absorbers are therefore generally opaque or at least largely opaque and therefore no longer fully photochemically crosslinkable.
• the sum of all components' of the laser-engraved relief-activatable layer are related to at least 0.1 wt .-% absorber. Employed. The amount of absorber added is chosen by the person skilled in the art depending on the properties of the relief layer desired in each case.
• the person skilled in the art will also take into account that the absorbers added not only influence the speed and efficiency of the engraving of the elastomeric layer by laser, but also other properties of the flexographic printing element, such as, for example, its hardness, elasticity, thermal conductivity or ink acceptance. As a rule, therefore, more than 40% by weight of absorbers are unsuitable for laser radiation with regard to the sum of all components of the laser-engravable elastomer layer.
• the amount of the absorber for laser radiation is preferably 1 to 30% by weight and particularly preferably 5 to 20% by weight.
• the elastomeric relief layer can optionally also comprise low-molecular or oligomeric compounds which can be crosslinked by means of electron radiation.
• Oligomeric compounds generally have a molecular weight of not more than 20,000 g / mol.
• Low molecular weight and oligomeric compounds are referred to below as monomers for the sake of simplicity.
• monomers can be added to increase the rate of crosslinking, if this is desired by the person skilled in the art.
• elastomeric binders from groups 1 and 2 the addition of monomers for acceleration is generally not absolutely necessary. In the case of Group 3 elastomeric binders, the addition of monomers is generally advisable, although this is not absolutely necessary in any case.
• monomers can also be used to control the crosslinking density in the course of electron beam curing and to set the desired hardness of the crosslinked material. Depending on the type and 'amount of added low molecular weight compounds or tere closer WEI networks are obtained.
• the known ethylenically unsaturated monomers can be used as monomers, which can also be used for the production of conventional photopolymer flexographic printing plates.
• the monomers should be compatible with the binders and have at least one ethylenically unsaturated group. They shouldn't be volatile.
• the boiling point of suitable monomers is preferably not less than 150 ° C.
• Amides and esters of acrylic acid or methacrylic acid with monofunctional or polyfunctional alcohols, amines, aminoalcohols or hydroxyethers and esters, styrene or substituted styrenes, esters of fumaric or maleic acid or allyl compounds are particularly suitable.
• Examples include butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol diacrylate, trimethylol propane triacrylate, dioctyl dodecylate, dioctyl fumarate.
• monomers which have at least one functional group which is crosslinked under the influence of electron beam curing.
• the functional group is preferably a protic group. Examples include -OH, -NH 2 , -NHR, -COOH or -S0 3 H. With particular preference it is also possible to use di- or polyfunctional monomers in which terminal functional groups are connected to one another via a spacer.
• Such monomers include dialcohols such as, for example, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, diamines such as, for example, 1,6-hexanediamine, 1,8-hexanediamine, dicarboxylic acids such as, for example, oxalic acid, Malonic acid, adipic acid, 1, 6-hexanedicarboxylic acid, l, 8-0c-tanedicarboxylic acid, 1, 10-decanedicarboxylic acid, phthalic acid, terephthalic acid, maleic acid or fumaric acid.
• dialcohols such as, for example, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol
• diamines such as, for example, 1,6
• Monomers can also be used which have both ethylenically unsaturated groups and functional groups.
• ⁇ -hydroxyalkyl acrylates such as ethylene glycol mono (meth) acrylate, 1,4-butanediol mono (meth) acrylate or 1,6-hexanediol mono (meth) acrylate.
• Mixtures of different monomers can of course also be used, provided that the properties of the relief layer are not negatively influenced by the mixture.
• the amount of added monomers is 0 to 30% by weight, based on the amount of all constituents of the relief layer, preferably 0 to 20% by weight.
• the elastomeric relief layer can furthermore also comprise additives and auxiliary substances such as, for example, dyes, dispersing agents, antistatic agents, plasticizers or abrasive particles.
• additives and auxiliary substances such as, for example, dyes, dispersing agents, antistatic agents, plasticizers or abrasive particles.
• the amount of such additives should generally not exceed 20% by weight with respect to the amount of all components of the elastomeric relief layer of the Au drawing element.
• the elastomeric relief layer can also be constructed from several relief layers. These elastomeric sub-layers can be of the same, approximately the same or different material. Composition.
• the thickness of the elastomeric relief layer or all of the relief layers together is generally between 0.1 and 7 mm, preferably 0.4 to 7 mm.
• the thickness is suitably chosen by the person skilled in the art depending on the intended use of the flexographic printing form.
• the flexographic printing element used as the starting material can optionally still have an upper layer with a thickness of not more than 100 ⁇ m.
• the composition of such an upper layer can be selected with a view to optimum printing properties such as ink transfer, while the composition of the relief layer underneath is selected with a view to optimum hardness or elasticity.
• the thickness is preferably 5 to 80 ⁇ m and particularly preferably 10 to 60 ⁇ m.
• the upper layer must either itself be laser-engravable or at least be removable together with the relief layer underneath in the course of the laser engraving. It comprises at least one polymeric binder, which does not necessarily have to be elastomeric. It can also comprise an absorber for laser radiation or else monomers or auxiliaries.
• the starting material for the process can be produced, for example, by dissolving or dispersing all components in a suitable solvent and pouring them onto a support.
• a suitable solvent for example, a suitable solvent for a support.
• several layers can be cast onto one another in a manner known in principle. Since work is carried out wet-on-wet, the layers bond well together. An upper layer can also be poured on.
• the individual layers can be cast onto temporary supports, for example, and the layers can then be joined together by lamination. After casting, a cover film can optionally be applied to protect against damage to the starting material.
• thermoplastic elastomeric binders are used with very particular advantage for the process according to the invention, and the production takes place in a known manner by extrusion between a carrier film and a cover film or a cover element followed by calendering, such as for example from EP-A-084 851 disclosed. In this way, thick layers can also be produced in a single operation. Multi-layer elements can be produced by means of coextrusion.
• the relief layer is cross-linked by means of electron radiation. If the flexographic printing element still has a protective film, this should generally be removed before networking. However, this is not mandatory in every case, especially when crosslinking using electron beams.
• Irradiation with electrons can take place both inline directly after the continuous production of the relief layer, e.g. immediately after calendering. Irradiation with electrons can, however, also advantageously take place in a separate process step.
• the flexographic printing element used as the starting material is irradiated with electron radiation as evenly as possible.
• the entire surface of the flexographic printing element should be irradiated absolutely uniformly, although in practice there will always be certain fluctuations. However, larger fluctuations should be avoided.
• the flexographic printing element should be placed as flat as possible on the base.
• the flexographic printing elements are generally irradiated only from the top of the elements. However, the invention naturally also includes the procedure for irradiating the element from the top and from the bottom.
• the maximum radiation dose is determined by the person skilled in the art depending on the desired properties, such as hardness or restoring force of the flexographic printing plate. As a rule, however, it is not recommended to use more than 200 kGy for networking and it is particularly preferred to use no more than 150 kGy for networking. A total dose for radiation of 60 to 120 kGy has proven effective.
• the energy of the electron radiation is determined by the person skilled in the art depending on the thickness and composition of the flexographic printing element.
• the energy of the electron beam is decisive for the maximum penetration depth of the electron beam into the relief layer.
• the relief layers used according to the invention which contain an absorber for laser radiation, it has generally proven useful to use electron beams with an energy of at least 2 MeV.
• Irradiation with electrons can be carried out in such a way that the entire dose is administered in a single irradiation process.
• the dose rate should be as high as possible in order to achieve the shortest possible radiation times.
• it must not be so high that the flexographic printing element heats up too much, because otherwise the dimensional stability of the flexographic printing element could be impaired. Heating to over 80 ° C should be avoided.
• it is regularly advantageous to use particularly temperature-stable carrier films, such as those made of PEN.
• the radiation is usually carried out in air, but the radiation can of course also be carried out in special cases under protective gases such as argon or nitrogen. If desired, the plates to be irradiated can also be encapsulated to exclude air.
• the total dose of electron radiation is distributed over two or more partial doses.
• the partial doses can be of the same size or different sizes, the electron beams can have the same energy or different energy or the same or a different dose rate.
• the individual partial doses can follow one another directly. However, they can also advantageously be interrupted for radiation breaks of the same length or of different lengths. The radiation can be interrupted only briefly or longer. Irradiation breaks of more than 60 min between the individual doses should, however, be avoided. Irradiation breaks between 1 and 30 minutes have proven effective.
• the energy of the electron radiation is the same or approximately the same for all administered partial doses.
• a radiation break is taken after each partial dose.
• Irradiation is preferably carried out with a relatively high dose rate, as a result of which the relief layer heats up considerably. Temperatures of more than 100 ° C should be avoided.
• the relief layer can react and cool off again during the pauses in irradiation.
• the energy of the electron radiation in at least one of the partial doses administered is different from that of the other partial doses.
• the energy of the electron beams of the partial doses administered first can be selected such that the flexographic printing element is cross-linked in the entire depth of the relief, while the energy of the electron beams of the last partial dose administered is dimensioned such that only a thin layer on the Surface is further cross-linked.
• a flexographic printing plate can thus be obtained which has a relatively soft lower layer and a harder upper layer by comparison.
• the energy of the electron beams can also be different for all partial doses, which means that different cross-linking profiles are also possible. For example, one can start with the partial dose at which the electron beams have the highest energy and then reduce the electron energy with each further partial dose. In this way, a flexographic printing plate can be obtained in which the crosslink density of the relief layer gradually increases from the carrier film to the printing surface.
• flexographic printing elements can also be stacked one above the other to increase the efficiency.
• a printing relief is engraved into the layer crosslinked by means of electron radiation by means of a laser.
• Image elements are advantageously engraved in which the flanks of the image elements initially drop vertically and only widen in the lower region of the image element. This achieves a good base of the pixels with a slight increase in tone value.
• flanks of the image points configured differently can also be engraved.
• IR lasers are particularly suitable for laser engraving.
• lasers with shorter wavelengths can also be used, provided the laser is of sufficient intensity.
• a frequency-doubled (532 nm) or frequency tripled (355 nm) Nd-YAG laser can also be used, or eximer lasers (e.g. 248 nm). If required for material removal, absorbers for laser radiation that have been adapted to the laser wavelength must be used.
• a C0 2 laser with a wavelength of 10640 nm can be used for laser engraving.
• Lasers with a wavelength between 600 and 2000 nm are used particularly advantageously.
• Nd-YAG lasers (1064 nm), IR diode lasers or solid-state lasers can be used.
• Nd / YAG lasers are particularly preferred for carrying out the method according to the invention.
• the image information to be engraved is transferred directly from the lay-out computer system to the laser apparatus.
• the lasers can either be operated continuously or pulsed.
• the flexographic printing plate obtained can be used directly. If desired, the flexographic printing plate obtained can still be cleaned. Such a cleaning step removes layer components which have been detached but which may not yet be completely removed from the plate surface.
• simple treatment with water, water / surfactant or alcohols is completely sufficient.
• the method according to the invention can be in a single product! - Onsgang be carried out in which all process steps are carried out in succession.
• the method can advantageously also be interrupted after method step (b).
• the networked, laser-engravable recording element can be assembled and stored and can only be further processed at a later time by means of laser engraving to form a flexographic printing plate or a flexosleeve. It is advantageous to use the flexographic printing element e.g. To protect with a temporary cover film, for example made of PET, which of course has to be removed before laser engraving.
• the adhesion between the carrier film and the relief layer is also significantly improved.
• the thermal load on the flexographic printing element in the course of crosslinking can be significantly reduced or almost completely avoided in comparison with thermal crosslinking. This leads to Flexographic printing forms with significantly improved dimensional stability and thus significantly better print quality.
• a relief layer was produced with a binder with ethylenically unsaturated groups. The following components were used for the relief layer.
• Binder, additives and absorbers for laser radiation were mixed in a laboratory kneader at a melt temperature of 150 ° C.
• the laser radiation absorber was homogeneously dispersed.
• the compound thus obtained was dissolved in toluene together with the monomer at 80 ° C., cooled to 60 ° C. and poured onto an uncoated, 125 ⁇ m thick PET film. After drying for 24 hours at room temperature and drying for 3 hours at
• the relief layer obtained (layer thickness 900 ⁇ m) was laminated at 30 60 ° C. onto a second, 125 ⁇ m thick PET film coated with adhesive lacquer. The element was stored at room temperature for 1 week before further treatment.
• a relief layer with a binder mixture with ethylenically unsaturated groups was produced. The following components were used for the relief layer.
• Binder, additives and absorbers for laser radiation were mixed in a laboratory kneader at a melt temperature of 170 ° C. After 15 minutes the laser radiation absorber was homogeneously dispersed. The compound thus obtained was dissolved in toluene together with the monomers at 80 ° C., cooled to 60 ° C. and poured onto an uncoated, 125 ⁇ m thick PET film. After airing for 24 hours at room temperature and drying for 3 hours at 60 ° C., the relief layer obtained (layer thickness 800 ⁇ m) was laminated onto a second, adhesive-coated, 175 ⁇ m thick PET film. The element was stored at room temperature for 1 week before further treatment.
• a relief layer was produced using a binder with ethylenically unsaturated groups by means of extrusion and subsequent calendering between a cover film and a carrier film. The following components were used for the relief layer.
• the components were mixed intensively in a twin-screw extruder at a melt temperature of 140-160 ° C., extruded through a slot die and then calendered between a cover film and a carrier film.
• the thickness of the Relief layer was 860 ⁇ m.
• the element was stored at room temperature for 1 week before further treatment.
• a relief layer with a binder with ethylenically unsaturated groups was produced by extrusion and then calendering between a cover film and a carrier film. The following components were used for the relief layer.
• the components were mixed intensively in a twin-screw extruder at a melt temperature of 140-160 ° C., extruded through a slot die and then calendered between a cover film and a carrier film.
• the thickness of the relief layer was 850 ⁇ m.
• the element was stored at room temperature for 1 week before further treatment.
• Electron irradiation equipment (nominal output approx. 150 kW) was used for networking, which can generate electron beams with electron energies of 2.5 - 4.5 MeV.
• the transport of the elements to be electron-irradiated through the zone of electron irradiation was carried out by means of vertically freely suspended aluminum pallets, which were connected to a guided conveyor belt via a movable suspension, so that the aluminum pallets could be conveyed evenly through the zone of electron irradiation by controlling the conveyor belt speed.
• the elements to be crosslinked were exposed under vacuum in a F Ill exposure unit from BASF Drucksysteme GmbH for a specific, predetermined time.
• the protective film of the elements in question was first removed and then a transparent, UV-permeable detackification film was placed on the element to be irradiated in order to prevent the element surface from sticking to the vacuum film. After covering the element to be irradiated with the vacuum film and switching on the vacuum, the element was irradiated over the entire area with UV light for the specified period of time.
• Example 1 A total of 6 elements according to Example 1 were used, of which 1 element was retained as a reference (Sample No. 0). The energy of the electron radiation was approximately 3.0 MeV. A successive series of irradiations was carried out with 5 identical partial doses, each with 20 kGy. The waiting time between 2 partial doses was 20 minutes each. After each partial dose, one element was removed from the radiation circuit, the others were turned through 180 ° before the next partial dose was administered.
• the following table shows the properties of the flexographic printing element obtained as a function of the radiation dose.
• Example 2 A total of 9 elements according to Example 2 were used, of which 1 element was retained as a reference (sample No. 0). The energy of the electron radiation was approximately 3.0 MeV. There was a successive radiation series with 8 partially. carried out different partial doses. The partial doses were successively 23, 22, 22, 35, 42, 30, 30 and 29 kGy. The waiting time between 2 partial doses was 20 minutes each. One element was removed from the radiation circuit after each partial dose, and the rest were turned through 180 ° before the next partial dose was administered.
• the following table shows the properties of the flexographic printing elements obtained as a function of the radiation dose.
• Example 3 A total of 9 elements according to Example 3 were used, of which 1 element was retained as a reference (sample no. 0). The energy of the electron radiation was approximately 3.0 MeV. A successive series of irradiations with 8 partly different partial doses was carried out. The partial doses were successively 23, 22, 22, 35, 42, 30, 30 and 29 kGy. The waiting time between 2 partial doses was 20 minutes each. After each partial dose, one element was removed from the radiation circuit, the rest were turned through 180 ° before administration of the next partial dose.
• the following table shows the properties of the flexographic printing element obtained as a function of the radiation dose.
• Example 4 A total of 6 elements according to Example 4 were used, of which 1 element was retained as a reference (sample No. 0). A series of irradiations with UVA light was carried out as described above with the following individual irradiation times: 1, 5, 15, 30, 60 min.
• the following table shows the properties of the flexographic printing element obtained as a function of the UVA exposure time.
• a test motif consisting of solid surfaces and various line elements was engraved in the respective flexographic printing element.
• a list of the engraved line elements is in the following
• the quality of the laser-engraved flexographic printing elements was assessed with the aid of a light microscope, which has a device for measuring distances or heights and depths. For this purpose, the engraving depth was measured using the full-area engraved area. Furthermore, the finest line element was determined, in which the engraved individual lines were still completely separated from one another under the microscope. The individual lines were assessed as being completely separated from one another if the surface of the positive line elements remaining between the negative lines had a width of at least 5 ⁇ m and this surface had the same height up to a difference of 20 ⁇ m as the non-engraved areas before the positive full surface. In this type of assessment, a low number of the number of the finest line element still displayed consequently means good engraving quality, while a high number corresponds to a lower resolution and thus a poorer engraving quality.

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