EP1353802B1 - Method for the production of thermally cross-linked laser engravable flexographic elements and multi-layer composites - Google Patents

Abstract

Laser-engravable flexographic printing elements including a thermally crosslinked, elastomeric, laser-engravable relief-forming layer E are made by producing a multilayer composite which has at least a two-layer composite formed of a depot layer D and an uncrosslinked precursor layer V for the relief-forming layer E which is directly adjacent to the depot layer D. Optionally, the multilayer composite may include further layers, such as support foils or films and/or protective films. The precursor layer V most preferably includes at least one elastomeric binder, and at least one ethylenically unsaturated monomer and, optionally an absorber for laser radiation and/or further additives. The depot layer D most preferably includes at least one elastomeric binder, and at least one thermally decomposing polymerization initiator and, optionally, an absorber for laser radiation and/or further additives. The thermally decomposing polymerization initiators are allowed to diffuse out of the depot layer D into the precursor layer V. If desired the depot layer D may be removed. Thermal crosslinking of the precursor layer V thereby yields the crosslinked elastomeric, laser-engravable, relief-forming layer E.

Description

The invention relates to a method for producing thermally crosslinked, laser-engravable flexographic printing elements, the production of relief printing plates from the laser-engravable flexographic printing elements, and the thermally non-crosslinked flexographic printing elements.

The conventional technique for the production of flexographic printing plates by placing a photographic mask on a photopolymeric recording element, irradiating the Element with actinic light through this mask as well as washing out not polymerized areas of the exposed element with a developer liquid is in increasingly replaced by techniques that use lasers.

In direct laser engraving depressions are engraved with the aid of a sufficiently powerful laser, in particular by means of an IR laser, directly into a suitable elastomeric layer, whereby a relief suitable for printing is formed. For this purpose, large amounts of the material from which the printing relief consists must be removed. For example, a typical flexographic printing plate is between 0.5 and 7 mm thick and the nonprinting depressions in the plate are between 0.3 and 3 mm deep. The technique of direct laser engraving for flexographic printing plate production has therefore improved in recent years with the advent of Laser systems also found economic interest, although the laser engraving of rubber pressure cylinders with CO ₂ lasers is basically known since the late 60s. Thus, the need for suitable laser-engravable flexographic printing elements as a starting material for the production of flexographic printing elements by means of laser engraving has become significantly larger.

In principle, commercially available photopolymerizable flexographic printing elements for the production of flexographic printing plates by means of laser engraving can be used. No. 5,259,311 discloses a method in which, in a first step, the flexographic printing element is photochemically crosslinked by full-surface irradiation and in a second step a printing relief is engraved by means of a laser. However, the sensitivity of such flexographic printing elements to CO ₂ lasers is low.

It has therefore been proposed that the elastomeric layer be engraved by laser is to increase the sensitivity of IR radiation absorbing substances disclosed in EP-A 0 640 043 and EP-A 0 640 044, for example. Such substances as carbon black or certain dyes absorb but also very strong in the UV / VIS range. Flexographic printing elements containing these absorbers contain, therefore, no more or at best in a very thin layer photochemically be networked. Thus, EP-A 0 640 043 discloses the preparation of a soot-containing, elastomeric layer by photocrosslinking. But this layer has only a thickness of 0.076 mm, while the typical thickness of commercially available flexographic printing plates 0.5 to 7 mm.

It has therefore also been proposed to use the elastomeric layer by means of laser is to be engraved to add thermally decomposing polymerization initiators and thermally crosslinking, as disclosed in EP-A 0 640 044. Photocrosslinkable, flexible Printing plates based on thermoplastic elastomers are elegantly using Extrusion and calendering at elevated temperatures using thermal stable photoinitiators produced. However, this manufacturing route is in use thermally decomposing initiators difficult, because of the high working temperatures and because of the high shear in the preparation of the thermally crosslinkable mixture in the extruder can lead to premature crosslinking. Because of the Temperature sensitivity of the crosslinkable mixture are low working temperatures of clearly below 100 ° C required, so that, for example, a processing in one Two-screw extruder precipitates.

The object of the invention is to provide a method for producing laser engravable Flexographic printing plates with thermally crosslinked, elastomeric relief-forming layer provide.

(i) Herstellen eines Mehrschichtverbundes, mindestens umfassend einen Zweischichtverbund aus einer Depotschicht D und einer der Depotschicht D direkt benachbarten unvernetzten Vorläuferschicht V für die reliefbildende Schicht E, und gegebenenfalls weitere Schichten und Träger- und/oder Schutzfolien,
   wobei die Vorläuferschicht V

(a) mindestens ein elastomeres Bindemittel,

(b) mindestens ein ethylenisch ungesättigtes Monomer,

(c) gegebenenfalls einen Absorber für Laserstrahlung, sowie

(d) gegebenenfalls weiteren Additive,
und die Depotschicht D

(e) mindestens ein elastomeres Bindemittel,

(f) mindestens einen thermisch zerfallenden Polymerisationsinitiator,

(g) gegebenenfalls einen Absorber für Laserstrahlung, sowie

(h) gegebenenfalls weitere Additiven,

enthalten,

(ii) Eindiffundieren lassen der thermisch zerfallenden Polymerisationsinitiatoren aus der Depotschicht D in die Vorläuferschicht V,

(iii) gegebenenfalls Entfernen der Depotschicht D, und

(iv) thermische Vernetzung der Vorläuferschicht V zu der elastomeren reliefbildenden Schicht E.

The object is achieved by a method for producing a laser-engravable flexographic printing element, comprising a thermally crosslinked, elastomeric relief-forming layer E, comprising the steps:

(i) producing a multilayer composite, at least comprising a two-layer composite comprising a depot layer D and an uncrosslinked precursor layer V directly adjacent to the depot layer D for the relief-forming layer E, and optionally further layers and carrier and / or protective films,
wherein the precursor layer V

(a) at least one elastomeric binder,

(b) at least one ethylenically unsaturated monomer,

(c) optionally an absorber for laser radiation, as well

(d) optionally further additives,
and the depot layer D

(e) at least one elastomeric binder,

(f) at least one thermally decomposing polymerization initiator,

(g) optionally an absorber for laser radiation, as well

(h) optionally further additives,

contain,

(ii) allowing the thermally decomposing polymerization initiators to diffuse from the deposit layer D into the precursor layer V,

(iii) optionally removing the deposit layer D, and

(iv) thermally crosslinking the precursor layer V to the elastomeric relief-forming layer E.

In a first step (i), a multi-layer composite, at least comprising one Two-layer composite from the depot layer D and the depot layer D directly adjacent uncrosslinked precursor layer V produced for the relief-forming layer E.

The precursor layer V contains at least one elastomeric binder as a component (A).

As elastomeric binder, all known, including for the production of photopolymerizable flexographic printing plates used are used. In principle, both elastomeric binders and thermoplastic elastomers Binder suitable. Examples of suitable binders are the known ones Triblock copolymers of the SIS or SBS type, which are also fully or partially hydrogenated can. It is also possible to use ethylene / propylene / diene elastomeric polymers, Ethylene / acrylic acid rubbers or elastomeric polymers based on acrylates or Acrylate copolymers are used. Further examples of suitable polymers are in DE-A 22 15 090, EP-A 084 851, EP-A 819 984 or EP-A 553 662. It can It is also possible to use mixtures of two or more different binders.

The type and amount of binder used will be determined by those skilled in the art depending on the desired properties of the printing relief selected. As a rule, the Amount of the binder 50 to 90 wt .-%, preferably 60 to 90 wt .-%, based on the Sum of all components of the precursor layer, ie the sum of components (a) to (D).

The precursor layer contains at least one ethylenically unsaturated monomer as Component (b).

As ethylenically unsaturated monomers can be used in principle those which are also commonly used for the production of photopolymerizable Flexographic printing elements are used. The monomers are said to bind with the binders be compatible and at least one polymerizable, ethylenically unsaturated Have double bond. Suitable monomers generally have a boiling point of greater than 100 ° C at atmospheric pressure and a molecular weight of up to 3,000 g / mol, preferably up to 2,000 g / mol. Particularly advantageous are esters or Amides of acrylic acid or methacrylic acid with mono- or polyfunctional alcohols, Amines, amino alcohols or hydroxy ethers and esters, styrene or substituted Styrenes, esters of fumaric or maleic acid or allyl compounds proved. Examples suitable monomers are butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol diacrylate, Trimethylolpropane triacrylate, dioctyl fumarate and N-dodecylmaleimide. It is also possible to use mixtures of different monomers. As a rule the total amount of the monomers is 5 to 30% by weight, preferably 5 to 20% by weight, based on the sum of components (a) to (d).

The precursor layer may further comprise an absorber for laser radiation as a component (c) included. The precursor layer preferably contains such an absorber.

Suitable absorbers for laser radiation have a high absorption in the range of Laser wavelength on. In particular, absorbers are suitable which have a high absorption in the near infrared, as well as in the longer-wave VIS range of the electromagnetic spectrum exhibit. Such absorbers are particularly suitable for absorbing the radiation from powerful Nd-YAG lasers (1064 nm) and IR diode lasers, which are typically Wavelengths between 700 and 900 nm and between 1200 and 1600 nm exhibit.

Examples of suitable absorbers for the laser radiation are in the infrared spectral range strongly absorbing dyes such as phthalocyanines, naphthalocyanines, Cyanines, quinones, metal complex dyes such as dithiolenes or photochromic dyes.

Further suitable absorbers are inorganic pigments, in particular intensively colored inorganic pigments such as chromium oxides, iron oxides, carbon black or metallic Particle.

Particularly suitable as an absorber for laser radiation are finely divided carbon blacks with a Particle size between 10 and 50 nm.

Furthermore, particularly suitable absorbers for laser radiation are iron-containing solids, in particular intensively colored iron oxides. Such iron oxides are commercially available and are commonly used as color pigments or as pigments for magnetic recording. Suitable absorbers for laser radiation are, for example, FeO, goethite (alpha-FeOOH), akaganeite (beta-FeOOH), lepidocrocite (gamma-FeOOH), hematite (alpha-Fe ₂ O ₃ ), maghemite (gamma-Fe ₂ O ₃ ), magnetite (Fe ₃ O ₄ ) or Berthollide. Furthermore, doped iron oxides or mixed oxides of iron with other metals can be used. Examples of mixed oxides are Umbra Fe ₂ O ₃ xn MnO ₂ or Fe _x Al _(1-x) OOH, in particular various spinel black pigments such as Cu (Cr, Fe) ₂ O ₄ , Co (Cr, Fe) ₂ O ₄ or Cu (Cr, Fe, Mn) ₂ O ₄ . Examples of dopants are, for example, P, Si, Al, Mg, Zn or Cr. Such dopants are usually added in small amounts in the course of the synthesis of the oxides to control particle size and particle shape. The iron oxides can also be coated. Such coatings can be applied, for example, to improve the dispersibility of the particles. These coatings may for example consist of inorganic compounds such as SiO ₂ and / or AIOOH. However, it is also possible to apply organic coatings, for example organic adhesion promoters such as aminopropyl (trimethoxy) silane. Particularly suitable as absorbers for laser radiation are FeOOH, Fe ₂ O ₃ and Fe ₃ O ₄ , very particularly preferably Fe ₃ O ₄ .

The size of the iron-containing, inorganic solids used, in particular the iron oxides, is selected by the person skilled in the art, depending on the desired properties of the recording material. However, solids with an average particle size of more than 10 μm are generally unsuitable. Since iron oxides in particular are anisometric, this information refers to the longest axis. The particle size is preferably less than 1 μm. It is also possible to use so-called transparent iron oxides which have a particle size of less than 0.1 μm and a specific surface area of up to 150 m ² / g.

Further suitable as absorber for laser radiation ferrous compounds Ferrous metal pigments. Particularly suitable are acicular or rice-kernel-shaped Pigments with a length between 0.1 and 1 μm. Such pigments are as Magnetic pigments known for magnetic recording. In addition to the iron can Also, other dopants such as Al, Si, Mg, P, Co, Ni, Nd or Y may be present or the ferrous metal pigments may be coated therewith. Iron metal pigments are surface oxidized to protect against corrosion and consist of an optionally doped Iron core and an optionally doped iron oxide shell.

At least 0.1% by weight of absorber with respect to the sum of all components (a) to (d), used. The amount of added absorber is determined by the skilled person depending on the respective desired properties of the laser-engravable flexographic printing selected. In this In the context, the person skilled in the art will consider that the added absorbers are not only 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. in the As a rule, therefore, more than 20% by weight of the absorber for laser radiation is the sum all components of the laser-engravable elastomeric layer unsuitable. Preferred is the amount of the laser radiation absorber is 0.5 to 15% by weight and more preferably 0.5 to 10 wt .-%.

The precursor layer V may optionally contain further additives as component (d) for adjustment contain the desired properties of the relief layer. Other additives are Plasticizers, fillers, dyes, compatibilizers or dispersing aids. The amount of such further constituents should, however, as a rule be 20% by weight, preferably 10 wt .-%, based on the sum of the components (a) to (d), not exceed.

The depot layer D also contains an elastomeric binder as component (e). It the same elastomeric binders can be used, which are also used in the Precursor layer can be used, are preferred in precursor and Depotschicht the used the same elastomeric binder.

The depot layer D contains at least one thermally decomposing polymerization initiator as component (f).

Suitable polymerization initiators are in principle all thermal initiators suitable for the radical polymerization are used, such as peroxides, hydroperoxides or Azo compounds.

The selection of suitable initiators is of particular importance for carrying out the process according to the invention. Suitable thermal initiators decompose only in the final step of the process according to the invention, the thermal crosslinking, with high reaction rate in radicals. They are largely thermally stable in the preceding process steps of melting, mixing, extruding and calendering or casting from solution or dispersion, evaporation of the solvent and lamination. The term "substantially thermally stable" in this context means that the initiators decompose at most slowly in the course of carrying out these steps of the process according to the invention, that crosslinking of the layer and / or the mixture by polymerization can take place only to a minor extent. The thermal stability of an initiator is usually given by the temperature of the 10 h half-life 10 ht _1/2 , ie the temperature at which 50% of the original amount of initiator has decomposed into free radicals after 10 h. Further details can be found in "Encylopedia of Polymer Science and Engineering", Vol. 11, pp. 1ff., John Wiley & Sons, New York, 1988.

Initiators which are suitable in particular for carrying out the process according to the invention usually have a 10 ht _1/2 of at least 60 ° C., preferably of at least 70 ° C. Particularly suitable initiators have a 10 ht _1/2 of 80 ° C to 150 ° C.

Examples of suitable initiators include certain peroxyesters, such as t-butyl peroctoate, t-amyl peroctoate, t-butyl peroxy isobutyrate, t-butyl peroxymaleic acid, t-amyl perbenzoate, Di-t-butyl diperoxyphthalate, t-butyl perbenzoate, t-butyl peracetate or 2,5-di (benzoylperoxy) -2,5-dimethylhexane, certain diperoxyketals such as 1,1-di (t-amylperoxy) cyclohexane, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane or ethyl 3,3-di (t-butylperoxy) butyrate, certain dialkyl peroxides such as di-t-butyl peroxide, t-butyl cumene peroxide, Dicumole peroxide or 2,5-di (t-butylperoxy) 2,5-dimethylhexane, certain diacyl peroxides such as dibenzoyl peroxide or diacetyl peroxide, certain t-alkyl hydroperoxides such as t-butyl hydroperoxide, t-amyl hydroperoxide, pinane hydroperoxide or cumene hydroperoxide. Also suitable are certain azo compounds such as 1- (t-butylazo) formamide, 2- (t-butylazo) isobutyronitrile, 1- (t-butylazo) cyclohexanecarbonitrile, 2- (t-butylazo) -2-methylbutanenitrile, 2,2'-azobis (2-actoxypropane), 1,1'-azobis (cyclohexanecarbonitrile), 2,2'-azobis (isobutyronitrile) or 2,2'-azobis (2-methylbutanenitrile).

The concentration of the thermally decomposing initiators in the depot layer depends according to the thickness of the depot layer relative to the thickness of the laser-engravable, relief-forming elastomeric layer.

Usually, the concentration of the thermally decomposing polymerization initiators is after diffusion and before thermal crosslinking in the Precursor layer about 1 to 5 wt .-%, preferably about 2 to 3 wt .-%, based on the Sum of all the components then present in the precursor layer. The thickness of the Depot layer is usually half to 1/30 of the total thickness of Precursor layer and depot layer taken together, for example 1/10 of Total thickness of both layers. Thus, the concentration of thermally decomposing Polymerization initiators in the depot layer double to 30 times the desired Concentration of the polymerization after diffusion into the Precursor layer, for example, at a layer thickness of the deposit layer of 1/10 of Total layer thickness of both layers 20 to 30 wt .-%, based on the sum of Components (e) to (h).

The total thickness of relief-forming elastomeric layer D or precursor layer V and Depot layer D is generally 0.4 to 7 mm.

The depot layer may optionally contain an absorber for laser light as component (g) contain. Suitable absorbers are the absorbers previously mentioned as component (c) in the quantities indicated there. The depot layer then contains an absorber when it is according to an embodiment of the method according to the invention during the Laser engraving on the printing side of the flexographic printing element remains and together is laser-engraved with the relief-forming layer E.

The depot layer may optionally contain further additives as component (h) for adjusting the Properties of the depot layer such as plasticizers, fillers, dyes, compatibilizers or dispersing agents in amounts of up to 20 wt.%, Preferably until to 10% by weight.

The preparation of the two-layer composite from depot layer D and precursor layer V can be done in different ways. In general, not the two-layer composite but this is in the context of a multi-layer composite manufactured, which comprises the two-layer composite and next to other layers, carriers and / or Protective films used in laser-engravable flexographic printing elements or in general Flexographic printing elements are conventional includes. Usually, the multi-layer composite by a dimensionally stable carrier film on one side and by a peelable Protective film on the other side or also limited by two protective films. Between a depot layer D and coated with this carrier film can be usual adhesive layer be present. The printing side of the elastomeric, laser-engravable relief-forming layer or optionally also an overlying, laser-engravable deposit layer D can be used to improve the upper layer Have printing properties. A peelable protective film can be made with a detackifying layer Be coated (release layer). These multi-layer composites will be by processing appropriately pre-coated foils according to one of the below described method of calendering, lamination, casting or pressing produced.

Suitable dimensionally stable carriers S are plates and films of metals such as steel, Aluminum, copper or nickel or of plastics such as polyethylene terephthalate (PET), Polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyamide, polycarbonate, if appropriate, also fabrics and nonwovens, such as glass fiber fabric and composite materials made of glass fibers and plastics. As a dimensionally stable carrier come above all dimensionally stable carrier films such as polyester films, in particular PET or PEN foils in question. The thickness of the carrier film is generally 75 to 225 microns. The carrier film may be coated with an adhesive layer A.

The multilayer element may have a thin top layer T on the precursor layer V or the laser-engravable depot layer D include. Through such a top layer can essential parameters for the printing behavior and color transfer, such as roughness, Abrasiveness, surface tension, surface tack or solvent resistance be changed on the surface, without the typical characteristics of the Printing form such as hardness or elasticity are influenced surface properties and layer properties can therefore be independent of each other be changed to achieve an optimal print result. The composition the upper class is limited only insofar as the laser engraving is underneath the laser-engravable layer may not be affected and the Upper layer with this together must be removable. The upper class should be thin be opposite to the laser-engravable layer. As a rule, the thickness exceeds the Upper layer not 100 microns, preferably the thickness is between 1 and 80 microns, especially preferably between 3 and 10 microns. Preferably, the upper layer itself should be good be laser engravable.

Optionally, the multilayer element can also be a non-laser-engravable underlayer U which is located between the carrier and the laser-engravable layer. With Such sublayers can be the mechanical properties of the relief printing plates be changed without affecting the relief typical properties of the printing form. Furthermore, the multi-layer element optionally against mechanical damage be protected by a, for example made of PET protective film P, based on the uppermost layer, and each before engraving with lasers must be deducted. The thickness of the protective films is generally 75 to 225 microns.

The protective film can be coated with a "release layer" R.

The thickness of the entire multilayer element is generally 0.7 to 7 mm.

The shaping of the precursor layer of one of the components (a) to (d) containing Mixture may be before, during or after contacting the precursor layer V or the mixture with the depot layer D done.

In one embodiment of the method according to the invention is the Two-layer composite of D and V by extruding a melt containing the Components (a) to (d), and calendering of this melt between a first film and a second film is produced, wherein at least one film with the depot layer D is coated. Only one or both foils can be coated with the depot layer D. be between depository layer D and film can be present more layers. Preferably, only one film is coated with a depot layer. The other slide can also be coated with other layers. It can also coextrude several layers be, for example, the precursor layer V and an overlying Upper class T.

With the method according to the invention is a preparation of the thermally crosslinkable Flexographic printing elements also by conventional twin-screw extrusion and calendering the crosslinkable layer possible. This method offers the advantage of being low Thickness tolerances are maintained, the mixture of components during the Extrusion process takes place and layer thicknesses> 1 mm are available.

In a further embodiment of the method according to the invention is the Two-layer composite of D and V by laminating one with the depot layer D. coated first film on a coated with the precursor layer V second film produced. Between depot layer D and first film or between precursor layer V and second film may be further layers.

In a further embodiment of the method according to the invention is the Two-layer composite of D and V by applying a moldable mixture, solution or dispersion containing the components (a) to (d) on a film associated with the Depot layer D is coated, and optionally produced subsequent drying. The two-layer composite can by applying a moldable melt and then pressing or by pouring the solution or dispersion and then Drying be prepared. It can also be poured several layers on top of each other be, for example, the precursor layer V and then a top layer T.

In a second step (ii), the thermally decomposing polymerization initiators from the deposit layer D in the precursor layer V diffuse, preferably until they are homogeneously distributed in the precursor layer V. The diffusion of the Polymerization initiators can by simply storing the multilayer elements over a period of 1 to 100 days, preferably 3 to 14 days. The Diffusion can also occur at elevated temperature, for example 30 to 80 ° C, which significantly shortens the storage time required. For example, shortened the time of storage of 7 days by raising the temperature to 80 ° C to 3 to 8 Hours.

Optionally, the depot layer D is removed in a third step (iii). This will be the depot layer D, for example by delamination, following the indiffusion removed from the precursor layer. This should be the adhesion between precursor layer V and deposit layer D less than 1 N / 4 cm, preferably less than 0.5 N / 4 cm.

It concludes as a fourth step (iv) the thermal crosslinking of the precursor layer V to the elastomeric, laser-engravable relief-forming layer E. The thermal crosslinking is achieved by heating the multilayer element to temperatures of generally 80 to 220 ° C, preferably 120 to 200 ° C over a period of 2 to 30 min performed.

The laser-engravable flexographic printing elements produced according to the invention serve as Starting material for the production of relief printing plates. The method includes that First, the protective film - if any - is deducted. In the following process step (v) becomes a printing relief in the recording material by means of a laser engraved. Advantageously, picture elements are engraved in which the flanks of the picture elements first drop off vertically and only in the lower part of the picture element broaden. As a result, a good Versockelung the pixels is still lower Tonwertzunahme reached. But it can also differently shaped flanks of the pixels engraved.

Laser engraving is particularly suitable for CO ₂ lasers having a wavelength of 10,640 nm, but also Nd-YAG lasers (1064 nm) and IR diode lasers or solid-state lasers, which typically have wavelengths between 700 and 900 nm and between 1,200 and 1,600 nm , However, it is also possible to use lasers with shorter wavelengths, provided the laser has sufficient intensity. For example, it is also possible to use a frequency-doubled (532 nm) or frequency-tripled (355 nm) Nd-YAG laser or else an excimer laser (for example 248 nm). The image information to be engraved is transmitted directly from the lay-out computer system to the laser apparatus. The lasers can be operated either continuously or pulsed.

The relief layer is very completely removed by the laser, so that an intense Post-cleaning is usually not necessary. If desired, the obtained Pressure plate but still to be cleaned. By such a cleaning step are detached, but may not yet completely from the disk surface removed removed layer components. As a rule, simple wetting with water completely adequate.

In one embodiment of the method for the production of relief printing plates is the Deposit layer D itself laser-engravable and lies on the printing side of the flexographic printing element before, with the relief in the depot layer D, which is a laser light absorbing Contains material, and the underlying relief-forming elastomeric layer E engraved.

The invention also relates to multi-layer composites according to claims 7-10, comprising the Two-layer composite of depot layer D and uncrosslinked precursor layer V.

(I) eine Trägerfolie S,

(II) gegebenenfalls eine Haftschicht A,

(III) eine haftende Depotschicht D,

(IV) eine Vorläuferschicht V,

(V) eine Oberschicht T,

(VI) gegebenenfalls eine Release-Schicht R, und

(VII) eine abziehbare Schutzfolie P

auf, worin D und V nach Anspruch 1 definiert sind. In one embodiment, the multilayer element according to the invention in the order (I) - (VII)

(I) a carrier film S,

(II) optionally an adhesive layer A,

(III) an adhesive portfolio layer D,

(IV) a precursor layer V,

(V) a top layer T,

(VI) optionally a release layer R, and

(VII) a peelable protective film P

in which D and V are defined according to claim 1.

(I) eine Trägerfolie S,

(II) eine Haftschicht A,

(III) eine Vorläuferschicht V,

(IV) eine lasergravierbare Depotschicht D, und

(V) eine abziehbare Schutzfolie P

auf, worin D und V nach Anspruch 1 definiert sind.In a further embodiment, the multilayer composite according to the invention in the order (I) - (V)

(I) a carrier film S,

(II) an adhesive layer A,

(III) a precursor layer V,

(IV) a laser-engravable depot layer D, and

(V) a peelable protective film P

in which D and V are defined according to claim 1.

(I) eine Trägerfolie S,

(II) eine Haftschicht A,

(III) eine Vorläuferschicht V,

(IV) eine nicht haftende, entfernbare Depotschicht D, und

(V) eine auf D gut haftende Schutzfolie P

auf, worin D und V nach Anspruch 1 definiert sind.In a further embodiment, the multilayer composite according to the invention in the order (I) - (V)

(I) a carrier film S,

(II) an adhesive layer A,

(III) a precursor layer V,

(IV) a non-adherent, removable depot layer D, and

(V) a protective film P well adhering to D.

in which D and V are defined according to claim 1.

(I) eine abziehbare Schutzfolie P,

(II) gegebenenfalls eine Release-Schicht R,

(III) eine Oberschicht T,

(IV) eine Vorläuferschicht V,

(V) eine nicht haftende, entfernbare Depotschicht D, und

(VI) eine abziehbare Schutzfolie P

auf, worin D und V nach Anspruch 1 definiert sind.In a further embodiment, the multilayer composite according to the invention in the order (I) - (VI)

(I) a peelable protective film P,

(II) optionally a release layer R,

(III) a top layer T,

(IV) a precursor layer V,

(V) a non-adherent, removable depot layer D, and

(VI) a peelable protective film P

in which D and V are defined according to claim 1.

The non-adherent, removable depot layer D may be prior to thermal crosslinking be removed without a significant influence on the surface quality occurs. For this purpose, the binders in D are chosen so that the adhesion of D in uncrosslinked Condition to V is less than 1 N / 4 cm, preferably less than 0.5 N / 4 cm.

The invention is explained in more detail by the following examples.

Examples General experimental method:

After successive uniform metering of binder and other ingredients a conventional, designated flexographic printing plate in a twin-screw extruder (ZSK 53, Werner & Pfleiderer) was the homogeneous melt or moldable mixture discharged through a slot die.

The supported peroxide deposit layers D1 and D2 were attached to a dimensionally stable film, so that the deposited peroxide deposit layer could form a layer composite during calendering with the elastomeric melt or with the moldable elastomeric mixture.

After a defined waiting time for the distribution of Peroxidanteilen by diffusion into the later pressure element forming layer V of the layer composite D1 / V or separated from the peroxide depot layer pressure element-forming layer E under the specified conditions completely or partially crosslinked to the layer E.

In this context, a layer composite is understood to be the direct contact between the pressure element-forming layer V and at least one peroxide deposit layer D1 or D2 , if this contact has persisted for at least the duration of the combination process, but otherwise independent of a fixed period of contact after the unification process.

Measurements to check the quality of the crosslinking:

To check the crosslinking quality of the two-layer composite depending on from the further treatment, swelling and extraction in toluene were determined. Furthermore, breaking stress and elongation at break were measured by a tensile strain measurement (Universal tester from Zwick).

The relative percentage increase of the measured values compared to a equivalent elastomeric single layer without the composite with a peroxide depot layer ("Raw layer") is considered as a measure of the quality of crosslinking.

Comparative Example A1

100 parts by weight of an unexposed nyloflex® FAH printing plate based on SIS block copolymers as binder (Kraton® D-1161NU from Shell), hexanediol diacrylate and dimethacrylate as monomers, oligobutadiene, PE wax and stabilizer were used in a Haake laboratory kneader at an initial temperature of 150 ° C and a rotational speed of 160 min ^-1 for a period of 10 minutes kneaded. The melt temperature settled to a constant 166 ° C, and the torque reached a plateau at about 2 Nm. The toluene extraction ratio of the kneaded mixture is 100%.

Comparative Example A2

97 parts by weight of the unexposed nyloflex® FAH printing plate from Comparative Example A1 were kneaded in a Haake kneader at an initial temperature of 150 ° C and a rotational speed of 160 min ^-1 for one minute. Without interrupting the kneading process then 3 parts by weight of dicumyl peroxide were added. Within less than a minute, the melt temperature rises from 163 ° C to 175 ° C and the torque increases to about 12 Nm. If the kneading process is continued for a total duration of 10 minutes, torque and temperature decrease again, the melt becomes grainy and inhomogeneous. The toluene extraction content of the kneaded mixture is only 36%.

Comparative Example B1

The constituents of the printing plate formulation described in Example 1 of EP-A 0 326 977 were kneaded in a Haake kneader at an initial temperature of 150 ° C. and a rotational speed of 160 min ^-1 for a period of 10 minutes. The melt temperature settled to a constant 180 ° C and the torque reached a plateau at about 7 Nm. The toluene extraction ratio of the kneaded mixture is 100%.

Comparative Example B2

97 parts by weight of the printing plate formulation described in Example 1 of EP-A 0 326 977 were kneaded in a Haake kneader at an initial temperature of 150 ° C. and a rotational speed of 160 min ^-1 for a period of one minute. Without interrupting the kneading process then 3 parts by weight of dicumyl peroxide were added. Within less than a minute, the melt temperature rises from 176 ° C to 188 ° C and the torque increases to about 20 Nm. If the kneading process is continued for a total duration of 10 minutes, torque and temperature decrease again, the melt becomes grainy and inhomogeneous. The toluene extraction content of the kneaded mixture is only 32%.

example 1

A peroxide depot adhesive layer D1 was prepared as follows: 80 g of a styrene-isoprene-styrene block copolymer (Kraton® D-1161NU from Shell) was dissolved in 185 ml of toluene at 110 ° C. After cooling the solution to 60 ° C, 20 g of dicumyl peroxide was added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C for 3 hours.

An oxygen-poor melt was produced from the components of a nyloflex® FAH printing plate by the above-mentioned method.
The two-layer composite D1 / V was then produced by calendering the depot layers described, wherein a commercially available PET film was used as the second dimensionally stable carrier.

Example 1a (comparative example )

The resulting two-layer composite of peroxide Depothaftschicht and elastomeric Pressure element forming layer was stored for one week at room temperature.

Example 1b

The two-layer composite D1 / V from example 1a was heated to 160 ° C. after one-week storage for a period of 20 minutes in a normal air atmosphere.

Example 1c

After storage for one week, the two-layer composite D1 / V from example 1a was first heat-treated at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Example 2

Another peroxide depot adhesive layer D1 was prepared as follows: 80 g of a styrene-butadiene / styrene-styrene block copolymer (Styroflex® BX 6105, BASF) were dissolved in 150 ml of toluene at 110 ° C. After cooling the solution to 60 ° C, 20 g of dicumyl peroxide were added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C. for 3 hours.

An oxygen-poor melt was made from the components of a nyloflex® FAH Pressure plate after the o.g. Process produced.

The two-layer composite D1 / V was then produced by calendering the described depot layers, wherein a commercially available PET film was used as the second dimensionally stable carrier.

Example 2a (comparative example )

The resulting two-layer composite of peroxide Depothaftschicht and elastomeric Pressure element forming layer was stored for one week at room temperature.

Example 2b

The two-layer composite D1 / V from Example 2a was heated to 160 ° C. after one-week storage for a period of 20 minutes in a normal air atmosphere.

Example 2c

After storage for one week, the two-layer composite D1 / V from example 2a was first heat-treated at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Example 3

A peroxide depot release layer D2 was prepared as follows: 80 g of a polyamide hot melt adhesive (Macromelt® 6208, Henkel) was dissolved in a mixture of 90 ml of toluene and 90 ml of 1-propanol at 95 ° C. After cooling the solution to 60 ° C, 20 g of dicumyl peroxide was added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C. for 3 hours.

An oxygen-poor melt was made from the components of a nyloflex® FAH Pressure plate after the o.g. Process produced.

The two-layer composite D2 / V was then classified by calendering Depot layer produced, as a second dimensionally stable carrier is a commercial PET film was used.

Example 3a (comparative example )

The resulting two-layer composite of peroxide depot release layer and elastomeric Pressure element forming layer was stored for one week at room temperature.

Example 3b

The two-layer composite D2 / V from Example 3a was separated after one-week storage, that is, the depot release layer D2 was removed from the precursor layer. The peroxide-containing precursor layer V was heated to 160 ° C for a period of 20 minutes in a normal air atmosphere.

Example 3c

The two-layer composite D2 / V from Example 3a was separated after one-week storage, that is, the depot release layer D2 was removed from the precursor layer. The peroxide-containing precursor layer V was first annealed at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Example 4

Another peroxide depot adhesive layer D1 was prepared as follows: 64 g of an ethylene-propylene-diene terpolymer (Buna EP G-KA 8869, Bayer) and 6 g of an aliphatic ester plasticizer (Plastomoll® DNA, BASF) were dissolved in 260 ml of toluene at 110 ° C solved. After cooling the solution to 60 ° C, 30 g of dicumyl peroxide was added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C. for 3 hours.

An oxygen poor melt was described in Patent No. EP 326977 Components of an EPDM-based printing plate layer (binder: Buna EP G-KA 8869, Bayer) after the o.g. Process produced.

The two-layer composite D1 / V was then produced by calendering the described depot layers, wherein a commercially available PET film was used as the second dimensionally stable carrier.

Example 4a (comparative example )

The resulting two-layer composite of peroxide Depothaftschicht and elastomeric Pressure element forming layer was stored for one week at room temperature.

Example 4b

The two-layer composite D1 / V from example 4a was heated to 160 ° C. after storage for one week for a period of 20 minutes in a normal air atmosphere.

Example 4c

After storage for one week, the two-layer composite D1 / V from example 4a was first heat-treated at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Example 5

Another peroxide depot adhesive layer D1 was prepared as follows: 64 g of a cyclic rubber (Vestenamer® 6213, Creanova) and 6 g of an aliphatic ester plasticizer (Plastomoll® DNA, BASF) were dissolved in 150 ml of toluene at 110 ° C. After cooling the solution to 60 ° C, 30 g of dicumyl peroxide was added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C. for 3 hours.

An oxygen poor melt became part of a flexographic printing plate formulation as described in EPDM No. EP 326977 (binder: Buna EP G-KA 8869, Bayer) after the o.g. Process produced.

The two-layer composite D1 / V was then produced by calendering the described depot layers, wherein a commercially available PET film was used as the second dimensionally stable carrier.

Example 5a (comparative example )

The resulting two-layer composite of peroxide Depothaftschicht and elastomeric Printing element-forming layer was stored for one week at room temperature.

Example 5b

The two-layer composite D1 / V from example 5a was heated to 160 ° C. after storage for one week for a period of 20 minutes in a normal air atmosphere.

Example 5c

After storage for one week, the two-layer composite D1 / V from Example 5a was first heat-treated at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Example 6

This example illustrates the applicability of the principle in pigmented systems, which is not continuous due to the strong absorption of the pigment in the UV range can be crosslinked photochemically:

Another peroxide depot adhesive layer D1 was prepared as follows: 80 g of an ethylene-propylene-diene terpolymer (Buna EP G-KA 8869, Bayer AG) were dissolved in 260 ml of toluene at 110.degree. After cooling the solution to 60 ° C, 20 g of dicumyl peroxide was added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C. for 3 hours.

A pigmented elastomeric pressure element-forming layer V was prepared as follows: 87% by weight of an ethylene-propylene-diene terpolymer (Buna EP G-KA 8869, Bayer AG) and 13 wt .-% of a basic carbon black (Printex® A, Degussa Huels) were in a Haake lab kneader pre-compounded. The precompound was subsequently in so much Toluene solved that a 25 weight percent solution was formed in toluene. The way prepared solution was so by means of a laboratory knife on a PET protective film applied so that after evaporation of the solvent, a dry layer thickness of about 800 microns was obtained.

The two-layer composite D1 / V was then produced by laminating the depot layer described.

Example 6a (comparative example )

The resulting two-layer composite of peroxide depot and pigmented elastomeric pressure element forming layer was at room temperature for one week stored.

Example 6b

The two-layer composite D1 / V from example 6a was heated to 160 ° C. after storage for one week for a period of 20 minutes in a normal air atmosphere.

Example 6c

After storage for one week, the two-layer composite D1 / V from Example 6a was first heat-treated at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Example 7

This example also illustrates the applicability of the principle in pigmented Systems that are not due to the strong absorption of the pigment in the UV range can be crosslinked photochemically throughout:

Another peroxide depot layer D1 was prepared as follows: 80 g of Kraton® D-1161 NU were dissolved in 190 ml of toluene at 110 ° C. After cooling the solution to 60 ° C, 20 g of dicumyl peroxide was added and stirring was continued until the solution was clear and homogeneous (about 1 hour). The solution thus prepared was applied by means of a laboratory knife in different thicknesses on a PET protective film. The resulting layers were then dried at room temperature for one day and finally at 35 ° C. for 3 hours.

A pigmented elastomeric pressure-element-forming layer V was prepared as follows: 88.6% by weight of components of a nyloflex® FAH printing plate and 11.4% by weight of a basic carbon black (Printex® A, Degussa-Huels) were dissolved in a Haake Laborkneter pre-compounded. The precompound was then dissolved in enough toluene to form a 40% by weight solution in toluene. The solution prepared in this way was applied to a PET protective film by means of a laboratory knife in such a way that, after evaporation of the solvent, a dry layer thickness of about 800 μm was obtained.
The two-layer composite D1 / V was then produced by laminating the depot layer described.

Example 7a (comparative example )

The resulting two-layer composite of peroxide depot and pigmented elastomeric pressure element forming layer was at room temperature for one week stored.

Example 7b

The two-layer composite D1 / V from Example 7a was heated at 160 ° C. for one week after storage for a period of 20 minutes in a normal air atmosphere.

Example 7c

After storage for one week, the two-layer composite D1 / V from Example 7a was first heat-treated at 80 ° C. for 3 hours and then heated to 160 ° C. for a period of 20 minutes in a normal air atmosphere.

Table 1 below gives the results of Comparative Examples A1 and A2 and Examples 1, 2, 3 and 6. Example no. Base layer thickness [μm] Depot layer thickness [μm] Extract content of toluene [%] Breaking stress [MPa] Elongation at break [%] evaluation A1 / / 100 0.1 105 crosslinked A2 / / 36 nb nb networked, degradation 1a 800 100 100 0.2 125 crosslinked 2a 780 120 100 0.2 125 crosslinked 3a 805 95 100 0.2 130 crosslinked 6a 800 120 0.2 378 crosslinked 1b 800 100 8th 2.0 100 crosslinked 2 B 780 120 8th 1.5 60 networked 3b 805 95 9 2.4 110 networked 6b 800 120 18 0.8 125 networked 1c 800 100 8th 2.2 110 networked 2c 780 120 8th 1.7 80 networked 3c 805 95 8th 4.3 170 networked 6c 800 120 6 2.4 310 networked

It can be clearly seen that the samples b) and c) by the thermal treatment were crosslinked, due to the low levels of toluene extract and the strong Increased breaking stress is proved. In contrast, the only stored samples remained uncrossed. Likewise, a reference sample (Comparative Example A1), which remained without Known initiator was uncrosslinked. An identical sample (Comparative Example A2), the whereas, during the kneading process, the initiator was added, crosslinked immediately within less than 1 minute. The crosslinked polymer was degraded in the kneader destroyed and inhomogeneous.

Table 2 below gives the results of Comparative Examples B1 and B2 and Examples 4, 5 and 7. Example no. Base layer thickness [μm] Depot layer thickness [μm] Extract content of toluene [%] Breaking stress [MPa] Elongation at break [%] evaluation B1 / / 100 0.1 140 crosslinked B2 / / 32 nb nb networked, degradation 4a 820 80 100 <0.1 75 crosslinked 4a 770 130 100 <0.1 70 crosslinked 5a 790 110 100 0.1 330 crosslinked 7a 800 70 100 0.1 150 crosslinked 4b 820 80 20 1.7 630 networked 4b 770 130 20 1.7 735 networked 5b 190 110 20 0.7 250 networked 7b 800 70 13 2.1 90 networked 4c 820 80 28 1.5 685 networked 4c 770 130 13 1.7 900 networked 5c 790 110 18 0.7 145 networked 7c 800 70 3 4.3 130 networked

It can be clearly seen that the samples b) and c) by the thermal treatment crosslinked, which is due to the low levels of toluene extract and the strong Increased breaking stress is proved. In contrast, the only stored samples remained uncrossed. Likewise, a reference sample (Comparative Example B1), which remained without Known initiator was uncrosslinked. An identical sample (Comparative Example B2), the while the initiator was added during the kneading process, crosslinked immediately within less than 1 minute. The crosslinked polymer was degraded in the kneader destroyed and inhomogeneous.

Claims (10)

1. A process for the production of a laser-engravable flexographic printing element comprising a thermally crosslinked, elastomeric, laser-engravable, relief-forming layer E, having the following steps:

   (i) production of a multilayer composite at least comprising a two-layer composite consisting of a depot layer D and an uncrosslinked precursor layer V for the relief-forming layer E which is directly adjacent to the depot layer D, and optionally further layers, support foils or films and/or protective films,
      where the precursor layer V comprises

   (a) at least one elastomeric binder,

   (b) at least one ethylenically unsaturated monomer,

   (c) optionally an absorber for laser radiation, and

   (d) optionally further additives,
   where the depot layer D comprises

   (e) at least one elastomeric binder,

   (f) at least one thermally decomposing polymerization initiator,

   (g) optionally an absorber for laser radiation, and

   (h) optionally further additives,

   (ii) allowing the thermally decomposing polymerization initiators to diffuse out of the depot layer D into the precursor layer V,

   (iii)if desired removal of the depot layer D, and

   (iv) thermal crosslinking of the precursor layer V to give the crosslinked, elastomeric, laser-engravable, relief-forming layer E.
2. A process as claimed in claim 1, characterized in that the two-layer composite consisting of D and V is produced by extruding a melt comprising components (a) to (d), and calendering this melt between a first film or foil and a second film or foil, where at least one film or foil is coated with the depot layer D.
3. A process as claimed in claim 1, characterized in that the two-layer composite consisting of D and V is produced by laminating a first film or foil coated with the depot layer D onto a second film or foil coated with the precursor layer V.
4. A process as claimed in claim 1, characterized in that the two-layer composite consisting of D and V is produced by applying a moldable mixture, solution or dispersion comprising components (a) to (d) onto a film or foil coated with the depot layer D, and if necessary subsequently drying the composite.
5. A process for the production of a relief printing plate comprising steps (i) to (iv), as defined in one of claims 1 to 4, and the additional step

   (v) engraving of a printing relief into the thermally crosslinked, elastomeric, relief-forming layer E by means of a laser.
6. A process as claimed in claim 5, wherein the depot layer D is located on the printing side of the flexographic printing element, and the relief is engraved into the depot layer D, which comprises a material which absorbs laser light, and the underlying elastomeric, relief-forming layer E.
7. A multilayer composite comprising, in the sequence (I) - (VII),

   (I) a support foil or film S,

   (II) optionally an adhesive layer A,

   (III) an adherent depot layer D,

   (IV) a precursor layer V,

   (V) a top layer T,

   (VI) optionally a release layer R,

   (VII) a removable protective film P, wherein D and V have the definitions given in claim 1.
8. A multilayer composite comprising, in the sequence (I) - (V),

   (I) a support foil or film S,

   (II) an adhesive layer A,

   (III) a precursor layer V,

   (IV) a laser-engravable depot layer D,

   (V) a removable protective film P, wherein D and V have the definitions given in claim 1.
9. A multilayer composite comprising, in the sequence (I) - (V),

   (I) a support foil or film S,

   (II) an adhesive layer A,

   (III) a precursor layer V,

   (IV) a non-adherent, removable depot layer D,

   (V) a removable protective film P, wherein D and V have the definitions given in claim 1.
10. A multilayer composite comprising, in the sequence (I) - (VI),

    (I) a removable protective film P,

    (II) optionally a release layer R,

    (III) a top layer T,

    (IV) a precursor layer V,

    (V) a non-adherent, removable depot layer D,

    (VI) a removable protective film P, wherein D and V have the definitions given in claim 1.