EP1381511B1 - Laser engravable flexographic printing elements comprising relief-forming elastomeric layers that contain syndiotactic 1,2-polybutadiene - Google Patents

Abstract

Laser-engravable flexographic printing element comprises a flexible dimensionally stable support bearing a laser-engravable, relief-forming, thermally and/or photochemically crosslinkable elastomer layer in which the binder comprises at least 5 wt.% of syndiotactic polybutadiene (I) with a 1,2-linkage content of 80-100%, a crystallinity of 5-30% and a molecular weight of 20,000-300,000.

Description

The invention relates to laser-engravable flexographic printing elements with relief-forming elastomeric layers containing syndiotactic 1,2-polybutadiene, process for Production of relief printing elements from the laser-engravable 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 non-printing depressions in the plate are between 0.3 and 3 mm deep. The technique of direct laser engraving for the production of flexographic printing forms has therefore also found economic interest in recent years with the advent of improved laser systems, 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 relief printing elements by means of laser engraving has become significantly larger.

WO 93/23252 discloses laser-engravable flexographic printing elements comprising a carrier a laser-engravable, elastomeric layer containing at least one thermoplastic elastomer as a binder and process for the preparation of flexographic printing plates. This is the laser-engravable elastomeric layer thermochemically by heating or photochemically by irradiation with actinic Light amplified and then the printing relief engraved with a laser. When Binder calls the font copolymers of butadiene and styrene, copolymers of Isoprene and styrene, styrene-diene-styrene triblock copolymers such as polystyrene-polybutadiene-polystyrene (SBS), polystyrene-polyisoprene-polystyrene (SIS) or polystyrene-poly (ethylene-butylene) -polystyrene (SEBS). Furthermore, are generally not networked Called polybutadienes and polyisoprenes.

EP-A 0 076 588 discloses photocrosslinkable flexographic printing elements comprising a Mixture of 30 to 70% syndiotactic 1,2-polybutadiene with a degree of crystallinity from 5 to 20%, a content of 1,2-linked units of 85% and a molecular weight above 100,000 g / mol and 70 to 30% cis-1,4-polyisoprene. The printing elements will be exposed imagewise with UV light and by washing the uncrosslinked areas with developed an organic solvent.

US Pat. No. 4,517,278 discloses a flexographic printing plate which is melt-pressed from a photosensitive molding composition, the molding composition containing syndiotactic 1,2-polybutadiene (I) swollen with the solution of an ethylenically unsaturated monomer (II) and a photoinitiator (III). (I) has an average molecular weight of 10,000 to 300,000 g / mol, a content of 1,2-linked polybutadiene units of at least 80% and a degree of crystallinity of 10 to 30%. (II) is an ester of methacrylic acid with a C ₄ -C ₂₀ alkanol and (III) is benzoin or a benzoin alkyl ether. For preparation, pellets of (I) are swollen in a solution of (II) and then melt pressed into 0.1 to 10 mm thick plates. This method is only discontinuous feasible and expensive. The printing plates prepared in the examples require xylene as a leaching agent for development. Shore A hardnesses of 60 to 65 are achieved only with the use of larger amounts of non-crosslinking plasticizers such as vinyl ethers or phthalates. These form melt edges during laser engraving.

Disadvantages of the known binders include the sometimes long exposure times Photochemical crosslinking of the elastomeric relief-forming layers as well as not always satisfactory resolution and sharpness of the engraved printing reliefs.

The object of the invention is improved, laser-engravable flexographic printing elements provide.

The object is achieved by a laser-engravable flexographic printing element according to the present claims, comprising a flexible support an elastomeric relief-forming, laser-engravable, thermal or Photochemically crosslinkable layer containing at least 5% by weight as binder syndiotactic 1,2-polybutadiene containing 1,2-linked butadiene units from 80 to 100%, a degree of crystallinity of 5 to 30% and a mean Molar mass from 20,000 to 300,000 g / mol.

By the term "laser engravable" is meant that the elastomeric relief forming Layer has the property of laser radiation, in particular the radiation of an IR laser, absorb, leaving them in those places where they receive a laser beam is exposed to sufficient intensity, removed or at least replaced. Preferably, the layer is thereby, without first melting, evaporated or thermally or oxidatively decomposed, and their decomposition products in the form of hot Gases, vapors, smoke or small particles from the layer.

Those using the special syndiotactic 1,2-polybutadiene as a binder produced elastomeric relief-forming layers result in the laser engraving very sharp and high-resolution relief elements. There are no laser engravings Melt edges, but only weak deposits, mechanically or by simple post-treatment with water or alcohol can be removed. Further are the elastomeric relief-forming layers by irradiation with UV-A light extremely fast photocrosslinkable.

The advantages mentioned are already without the concomitant use of additives such as Plasticizers, ethylenically unsaturated, crosslinking monomers or Initiators in the relief-forming elastomeric layers achieved.

(a) 50 bis 99,9 Gew.-%, bevorzugt 60 bis 85 Gew.-% eines oder mehrerer Bindemittel als Komponente A bestehend aus

(a1) 5 bis 100 Gew.-%, bevorzugt 50 bis 85 Gew.-%, syndiotaktischem 1,2-Polybutadien mit einem Gehalt an 1,2-verknüpften Butadien-Einheiten von 80 bis 100 %, einem Kristallinitätsgrad von 5 bis 30 % und einer mittleren Molmasse von 20 000 bis 300 000 g/mol als Komponente A1, und

(a2) 0 bis 95 Gew.-%, bevorzugt 0 bis 50 Gew.-% weiterer Bindemittel als Komponente A2,

   wobei die Summe der Komponenten A1 und A2 100 Gew.-% ergibt,

(b) 0,1 bis 30 Gew.-%, bevorzugt 5 bis 20 Gew.-% vernetzender oligomerer Weichmacher, die reaktive Gruppen in der Hauptkette und/oder reaktive seitenständige und/oder endständige Gruppen aufweisen als Komponente B,

(c) 0 bis 25 Gew.-%, bevorzugt 5 bis 20 Gew.-% ethylenisch ungesättigter Monomere als Komponente C,

(d) 0 bis 10 Gew.-%, bevorzugt 0,1 bis 5 Gew.-% Photoinitiatoren und/oder thermisch zerfallender Initiatoren als Komponente D, und

(e) 0 bis 20 Gew.-%, bevorzugt 0 bis 10 Gew.-% Absorber für Laserstrahlung als Komponente E,

(f) 0 bis 30 Gew-%, bevorzugt 0 bis 10 Gew-% weiterer üblicher Additive als Komponente F.

wobei die Summe der Komponenten A bis F 100 Gew.-% ergibt.The relief-forming elastomeric, laser-engravable layer contains:

(A) 50 to 99.9 wt .-%, preferably 60 to 85 wt .-% of one or more binders as component A consisting of

(a1) 5 to 100 wt .-%, preferably 50 to 85 wt .-%, syndiotactic 1,2-polybutadiene having a content of 1,2-linked butadiene units of 80 to 100%, a degree of crystallinity of 5 to 30 % and an average molecular weight of 20,000 to 300,000 g / mol as component A1, and

(a2) 0 to 95% by weight, preferably 0 to 50% by weight, of further binders as component A2,

the sum of components A1 and A2 being 100% by weight,

(b) 0.1 to 30% by weight, preferably 5 to 20% by weight, of crosslinking oligomeric plasticizers having reactive groups in the main chain and / or reactive pendant and / or terminal groups as component B,

(c) 0 to 25% by weight, preferably 5 to 20% by weight, of ethylenically unsaturated monomers as component C,

(D) 0 to 10 wt .-%, preferably 0.1 to 5 wt .-% of photoinitiators and / or thermally decomposing initiators as component D, and

(e) 0 to 20% by weight, preferably 0 to 10% by weight, of absorber for laser radiation as component E,

(f) 0 to 30% by weight, preferably 0 to 10% by weight, of further customary additives as component F.

wherein the sum of components A to F is 100% by weight.

As component A1, the elastomeric relief-forming layer contains syndiotactic 1,2-polybutadiene containing from 80 to 100% of 1,2-linked butadiene units, a degree of crystallinity of 5 to 30% and an average molecular weight of 20,000 to 300 000 g / mol. The content of 1,2-linked butadiene units is preferably 90 to 95 %, more preferably 90 to 92%, the degree of crystallinity from 10 to 30%, especially preferably 15 to 30% and the average molecular weight of 80,000 to 200,000 g / mol, more preferably from 100,000 to 150,000 g / mol.

As component A2, the elastomeric relief-forming layer optionally contains further Binder. In principle, both elastomeric binder as well as thermoplastic elastomeric 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 also two or more different further binders are used.

As component B, the elastomeric relief-forming layer contains crosslinking oligomers Plasticizers, the main chain reactive groups and / or reactive pendants and / or terminal groups. Suitable plasticizers are, for example Polybutadiene oils, polyisoprene oils, allyl citrates and other allyl groups synthetic plasticizers having a viscosity of 500 to 150,000 mPas at 25 ° C, the may have functional end groups such as OH groups.

Preferred crosslinking oligomeric plasticizers are the polybutadiene oils mentioned and polyisoprene oils. These preferably have a viscosity of 500 to 100,000 mPas, more preferably from 500 to 10,000 mPas at 25 ° C. Suitable, for example Polybutadiene oils of the companies Chemetall, Hüls and Elf Atochem. These have one Molecular weight of about 1000 to about 3000 g / mol, a content of 1,2-linked Units of often 40 to 50%, often only about 20% or 1%, a flashpoint from 170 ° C to 300 ° C and a viscosity of 700 to 100,000 mPas at 25 ° C on.

By using the crosslinking acting oligomeric plasticizer Smelting during laser engraving avoided particularly efficiently. Furthermore, a achieved particularly good color transfer of the printing relief layers, for example with water-based or alcohol-based inks or UV-curable inks.

As component C, the elastomeric relief-forming layer optionally contains ethylenically unsaturated monomers. The ethylenically unsaturated monomers are advantageous, but not necessary, since the elastomeric relief-forming layer also in their Absence can network. The monomers should be compatible with the binders and at least one polymerizable, ethylenically unsaturated double bond. Suitable monomers generally have a boiling point of more 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 of suitable monomers are Butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, isobornyl methacrylate, Isodecyl methacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol diacrylate, trimethylolpropane triacrylate, Dioctyl fumarate and N-dodecylmaleimide. It can also be mixtures of different Monomers can be used.

As component D, the elastomeric relief-forming layer optionally contains Photoinitiators and / or thermally decomposing initiators. The presence of Photoinitiators is not necessary, but advantageous because the elastomeric relief-forming Layer can be photochemically crosslinked even in the absence of photoinitiators. If the elastomeric relief-forming layer to be thermally crosslinked, then the Presence of thermally decomposing initiators in amounts of 0.1 to 5 wt .-%, based on the sum of components A to F, generally required. The elastomeric relief-forming layer can also be crosslinked photochemically and thermally be as component D photoinitiators and / or thermally decomposing Initiators may be included.

Suitable photoinitiators are benzoin or benzoin derivatives, such as methylbenzoin or Benzoin ethers, benzil derivatives such as benzil ketals, acylarylphosphine oxides, acylarylphosphinic acid esters and multinucleated quinones without being limited to the list. Preference is given to using those photoinitiators which have a high absorption between Have 3 00 and 450 nm.

Suitable thermally decomposing initiators are, for example, 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 (tamylperoxy) 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, dicumyl 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 for example 1- (t-butylazo) formamide, 2- (t-butylazo) isobutyronitrile, 1- (t-butylazo) cyclohexanecarbonitrile, 2- (t-butylazo) -2-methylbutanenitrile, 2,2'-azobis (2-acetoxypropane), 1,1'-azobis (cyclohexanecarbonitrile), 2,2'-azobis (isobutyronitrile) or 2,2'-azobis (2-methylbutanenitrile).

As component E, the elastomeric relief-forming layer may contain absorbers for laser radiation. The presence of the absorbers is advantageous, but not necessary, if the binders already absorb laser radiation of a suitable wavelength, for example that of a CO ₂ laser. Suitable absorbers for laser radiation have a high absorption in the range of the laser wavelength. 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. Such absorbers are particularly suitable for absorbing the radiation of high-performance Nd-YAG lasers (1064 nm) and of IR diode lasers, which typically have wavelengths between 700 and 900 nm and between 1200 and 1600 nm.

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

As component F, the elastomeric relief-forming layer may contain further additives. Further additives are non-crosslinking plasticizers, fillers, dyes, compatibilizers or dispersing agent.

The flexographic printing elements according to the invention have the usual layer structure and consist of a flexible dimensionally stable support, optionally an elastomeric Underlayer, one or more elastomeric relief-forming, laser-engravable layers, wherein the different layers can be connected by adhesive layers, and one optionally with a detackifying layer (release layer) coated protective film.

The flexographic printing elements according to the invention comprise a flexible, dimensionally stable Carrier. Examples of suitable flexible dimensionally stable supports for laser engravable Flexographic printing elements are plates, films as well as conical and cylindrical tubes made of metals such as steel, aluminum, copper or nickel or of plastics such as Polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate, Polyamide, polycarbonate, if appropriate also fabrics and nonwovens, such as glass fiber fabric and composite materials, e.g. made of glass fibers and plastics. As dimensionally stable Carriers are above all dimensionally stable carrier films, such as polyester films, for example. in particular PET or PEN films in question.

Of particular advantage are flexible metallic carriers that are so thin that they are around Pressure cylinder can be bent. On the other hand, they are also dimensionally stable and so thick that the wearer in the production of the laser-engravable element or the Assembly of the finished printing plate on the printing cylinder is not kinked.

On the support, optionally on an elastomeric sublayer, the elastomeric relief-forming, laser-engravable layer defined in claim 1, before.

The elastomeric relief-forming, laser-engravable layer may also have a multilayer structure be. These laser-engravable, crosslinkable partial layers can be of the same, approximately same or of different material composition. Such a multilayer construction, especially a two-layered construction, is sometimes advantageous because thereby surface properties and layer properties independently can be optimized to achieve an optimal print result. The For example, a laser-engravable flexographic printing element may be a thin laser-engravable one Upper layer whose composition in terms of optimal Color transfer was selected while the composition of the underlying Layer was selected for optimum hardness or elasticity.

The thickness of the elastomeric relief-forming, laser-engravable layer or all As a rule, relief-forming layers together are between 0.1 and 7 mm. The Thickness is determined by the person skilled in the art according to the intended use of the printing plate selected.

The laser-engravable flexographic printing elements according to the invention can optionally be further Include layers. For example, between the carrier and the or laser-engravable layer (s) have an elastomeric sublayer that is not must necessarily be laser engravable. With such a lower layer, the mechanical properties of the relief printing plates are changed without the Properties of the actual printing relief layer are influenced. the serve the same purpose so-called elastic substructures, which are based on the laser-engravable layer opposite side of the dimensionally stable support are located.

Further layers may be adhesive layers which overlay the carrier Connect layers or different layers with each other.

Furthermore, the laser-engravable flexographic printing element against mechanical Damage caused by, for example, made of PET protective film which is located on the uppermost layer, and each one before the Engraving with lasers is removed. The protective film may be used to facilitate peeling also be siliconized or provided with a suitable Entklebeschicht.

The laser-engravable flexographic printing element, for example, by solving or Disperse all components in a suitable solvent and pour on one Carriers are produced. In multilayer elements can in a conventional manner and several layers are poured on top of each other. Alternatively, the Single layers, for example, poured onto temporary support and the layers then be joined together by laminating. Especially Photochemically crosslinkable systems can be extruded and / or calendered getting produced. This technique can in principle also for thermally crosslinkable systems be used, provided that only those components are used in the Do not cross-link the process temperature yet.

From the laser-engravable flexographic printing elements according to the invention by thermal and / or photochemical crosslinking of the elastomeric relief-forming layer and engraving a printing relief obtained relief printing elements.

(i) thermische oder photochemische Vernetzung der elastomeren reliefbildenden Schicht des erfindungsgemäßen Flexodruckelements, und

(ii) Eingravieren des erfindungsgemäßen druckenden Reliefs in die vernetzte, elastomere reliefbildende Schicht mittels eines Lasers.

The invention thus also provides a method according to claims 4 or 5 for producing a relief printing element with the steps

(i) thermal or photochemical crosslinking of the elastomeric relief-forming layer of the flexographic printing element according to the invention, and

(Ii) Engraving the printing relief of the invention in the crosslinked, elastomeric relief-forming layer by means of a laser.

The elastomeric relief-forming, laser-engravable layer is photochemical and / or thermally crosslinkable. The photochemical crosslinking is carried out in particular by Irradiate with shortwave visible or longwave ultraviolet light. Naturally, however, radiation of higher energy, such as short-wave UV light or X-radiation, or - with appropriate sensitization - also longer-wave light in principle suitable. In particular, electron radiation is also suitable for crosslinking.

With the laser-engravable flexographic printing elements according to the invention are particularly realized low irradiation times for photochemical crosslinking. This can According to the invention only 10 s to 5 min against 5 to 30 min using Materials according to the prior art amount.

The thermal crosslinking is generally by heating the Flexographic printing element to temperatures of generally 80 to 220 ° C, preferably 120 to 200 ° C over a period of 2 to 30 minutes causes.

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 eximer lasers (eg 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 treatment with water or methanol completely sufficient.

The invention is further illustrated by the following examples

Examples 1-6 and Comparative Examples A and B

Starting Materials: Kraton® D-1161 SIS block copolymer from Kraton Polymers (binder) Kraton® D-1102 SIS block copolymer from Kraton Polymers (binder) JSR RB 810 Syndiotactic 1,2-polybutadiene with 90% 1,2-units, a degree of crystallinity of about 15% and an average molecular weight of about 120,000 g / mol of JSR (binder) Lithene® PH Oligomeric polybutadiene oil with an average molecular weight of about 2600 g / mol of Chemetall GmbH (plasticizer) lauryl (crosslinking monomer) 1,6-hexanediol diacrylate (crosslinking monomer) 1,6-hexanediol (crosslinking monomer) Plastomoll® DNA diisononyl Lucirin® BDK Benzil dimethyl ketal from BASF AG (photoinitiator) dicumylperoxide (thermal initiator) Kerobit® TBK 2,6-Di-tert-butyl-p-cresol from Raschig (stabilizer) Printex® A finely divided carbon black from Degussa-Hüls (laser radiation absorbing material) toluene (Solvent)

example 1

124 g of JSR RB 810, 16 g of Lithene PH, 16 g of lauryl acrylate, 2.4 g of Lucirin® BDK and 1.6 g Kerobit® TBK are dissolved at 110 ° C in 240 g of toluene. The obtained homogeneous solution is cooled to 70 ° C and with the help of a doctor blade so on several transparent PET films applied that a homogeneous dry film thickness of 1.20 mm each is obtained. The layers thus prepared are first for 18 hours at 25 ° C and finally dried at 50 ° C for 3 hours. Then the dried ones Layers each laminated on an equal piece of a second PET film. To For one day storage, the layer is photochemically crosslinked as explained below and characterized as described below.

Example 2

By analogy with the method described in Example 1, layers are produced with which Difference is that 116 g of JSR RB 810, 24 g of Lithene PH, 16 g of lauryl acrylate, 2.4 g of Lucirin® BDK and 1.6 g of Kerobit® TBK are dissolved at 110 ° C. in 240 g of toluene.

Example 3

By analogy with the method described in Example 1, layers are produced with which Difference that 116 g JSR 810, 16 g Lithene PH, 16 g lauryl acrylate, 8 g Hexanediol diacrylate, 2.4 g Lucirin® BDK and 1.6 g Kerobit® TBK at 110 ° C in 240 g Toluene are dissolved.

Example 4

By analogy with the method described in Example 1, layers are produced with which Difference that 108 g of JSR RB 810, 16 g of Lithene PH, 24 g of hexanediol divinyl ether, 8 g Hexanediol diacrylate, 2.4 g Lucirin® BDK and 1.6 g Kerobit® TBK at 110 ° C in 240 g Toluene are dissolved.

Example 5

By analogy with the method described in Example 1, layers are produced with which Difference is that 92 g JSR RB 810, 32 g Kraton® D-1161, 16 g Lithene PH, 8 g Lauryl acrylate, 8 g hexanediol diacrylate, 2.4 g Lucirin® BDK and 1.6 g Kerobit® TBK 110 ° C dissolved in 240 g of toluene.

Example 6

108.8 g JSR RB 810, 16 g Plastomoll® DNA, 16 g Lithene PH and 1.6 g Kerobit® TBK and 16 g of Printex® A in a laboratory kneader at a given temperature kneaded at 100 ° C for 15 minutes.

The compound thus obtained (158.4 g) is dissolved at 110 ° C in 240 g of toluene. After this Cool the solution to 60 ° C and add 1.6 g of dicumyl peroxide. To Homogenization by stirring, the resulting solution using a doctor blade so applied to several transparent PET films that a homogeneous dry film thickness each of 1.20 mm is obtained. The layers thus produced become dried first for 18 hours at 25 ° C and finally for 3 hours at 50 ° C. Subsequently, the dried layers are each on an equal piece of a laminated second PET film. After a storage period of one day, the layer becomes 15 Thermally crosslinked at 160 ° C and characterized as described below.

Comparative Example A

124 g Kraton® D-1161, 16 g Lithene® PH, 16 g lauryl acrylate, 2.4 g Lucirin® BDK and 1.6 g Kerobit® TBK are dissolved at 110 ° C in 240 g toluene. The obtained homogeneous Solution is cooled to 70 ° C and with the help of a doctor blade so on several transparent PET films applied that a homogeneous dry film thickness of each 1.20 mm is obtained. The layers thus produced are first for 18 Hours at 25 ° C and finally dried for 3 hours at 50 ° C. Be connected the dried layers each on an equal piece of a second PET film concealed. After a storage period of one day, the layer is photochemically after the crosslinked and characterized as described below.

Comparative Example B

Analogous to the method described in Comparative Example A layers with the difference that 124 g Kraton® D-1161, 16 g Lithene® PH, 16 g Lauryl acrylate, 2.4 g Lucirin® BDK and 1.6 g Kerobit® TK at 110 ° C in 240 g toluene be solved.

Networking Photochemical crosslinking

The photochemical crosslinking of the example layers described was with a nyloflex® F III platesetter of BASF Drucksysteme GmbH made by first the transparent PET protective film was removed and then for the respective duration the exposure series was irradiated with UVA light over the entire surface without vacuum.

Thermal networking

For thermal crosslinking, the transparent PET protective film was first removed and then the layer for the duration of the crosslinking at the selected temperature heated without inertization.

Duration of networking

• Reißkraft und Reißdehnung bei optimaler Vemetzungsdauer (mit Zugdehnungsmessgerät Typ 1435, Zwick GmbH & Co.)
• Härte nach DIN 53505 in °Shore A (mit Härtemessgerät Typ U 72/80E, Heinrich Bareiss Prüfgerätebau GmbH)

The layers obtained from the examples and comparative examples were each photochemically or thermally crosslinked in steps of one minute of crosslinking time. By mechanical measurements on a tensile strain gauge Type 1435 (Zwick GmbH & Co.) was the exposure time at which the breaking stress was maximum, determined as optimal Vemetzungsdauer t _opt and crosslinked for all examples and comparative examples, a non-crosslinked layer with this optimum crosslinking time. From the thus crosslinked layers and the corresponding uncrosslinked layers as a reference, the following properties were determined:

• Tensile strength and elongation at break with optimum duration of setting (with tensile strain gauge type 1435, Zwick GmbH & Co.)
• Hardness according to DIN 53505 in ° Shore A (with durometer type U 72 / 80E, Heinrich Bareiss Prüfgerätebau GmbH)

The crosslinking conditions (optimal crosslinking time t _opt and crosslinking type) and the measured values obtained are summarized in Table 1. Example no crosslinking method Vemetzungsbedingungen tensile force
[MPa] elongation at break
[%] mech. hardness
[° Shore A] t _opt [min] kind U V U V U V A photochemically 5 UVA 1.4 3.6 2000 1000 <30 32 B photochemically 5 UVA 2.8 8.5 1040 1080 47 59 1 photochemically 1 UVA 5.2 4.0 1230 250 50 62 2 photochemically 1 UVA 4.5 3.3 1150 250 48 60 3 photochemically 1 UVA 4.3 3.3 1130 100 48 68 4 photochemically 1 UVA 6.1 10.8 1130 760 46 66 5 photochemically 1 UVA 2.9 7.1 1000 250 44 67 6 thermal 5 160 ° C 4.7 6.1 700 590 50 64

Laser engraving experiments:

For the laser engraving experiments, a laser system with rotating outer drum was used (Meridian Finesse, ALE), which was equipped with a CO ₂ laser with 250 W output power. The laser beam was focused to a diameter of 20 μm. The flexographic printing elements to be engraved were taped to the drum and the drum was accelerated to 250 rpm.

To evaluate the laser engraving result, the letter A (font Helvetica, font size 24 pt) as a positive engraved in the cross-linked material. The Resolution was 1270 dpi. To assess the quality was a section of the Engraved letter A through a light microscope at 32x magnification Photographed. Furthermore, two lines of 20 μm width were spaced apart engraved of 20 microns in the respective material. From the negative line pairs were made by scanning electron micrographs.

For both elements (letter A and negative line pair) were each 3 features graded on a grading scale of 1-5.

1: Keine Unregelmäßigkeiten oder Ausbrüche

2: Nur vereinzelt Wellenbildung oder Ausbrüche

3: Wiederholte Ausbrüche und Deformationen mit geringer Amplitude

4: Zahlreiche Unregelmäßigkeiten, Ausbrüche, Verformungen

5: Keine randscharfen Abschnitte vorhanden, Konturen nicht erkennbar

RS edge sharpness (sharpness of the surface edges)

1: No irregularities or outbreaks

2: Only occasional wave formation or breakouts

3: Repeated outbreaks and small amplitude deformations

4: Numerous irregularities, breakouts, deformations

5: No sharp edges available, contours not visible

1: Tiefen scharf begrenzt, gleichförmige Flanken

2: Tiefen leicht deformiert, Flanken schwach gefurcht

3: Wiederholte Deformationen der Tiefen, Flanken gefurcht oder verschwommen

4: Tiefen häufig deformiert, Flanken unregelmäßig und stark gefurcht

5: Keine Tiefendefinition, Tiefen zugesetzt oder uneinheitlich verschmolzen

TD depth definition (shape and uniformity of relief depths)

1: Depths sharply defined, uniform flanks

2: Depths slightly deformed, flanks slightly frayed

3: Repeated deformations of the depths, flanks ragged or blurry

4: Depths often deformed, flanks irregular and severely scared

5: No depth definition, depths added or mixed inconsistently

1: Keine Ablagerungen auf der Oberfläche erkennbar

2: Wenige Ablagerungen auf der Oberfläche, nur einzelne Partikel

3: Wiederholte Ablagerungen und Rückstände

4: Zahlreiche Ablagerungen und Rückstände, Verklumpungen und Anhäufungen

5: Oberfläche durchgehend verschmutzt, zerschmolzen, überhäuft mit Ablagerungen

OG surface quality (quality of the relief surface)

1: No deposits visible on the surface

2: Few deposits on the surface, only single particles

3: Repeated deposits and residues

4: Numerous deposits and residues, clumps and accumulations

5: Surface contaminated throughout, melted, littered with deposits

Figures 1.1 - 1.8 and 2.1 - 2.8 show the underlying evaluation photographic and scanning electron micrographs.

Fig. 1.1

eine fotografische Aufnahme des "A"-Auschnitts - Beispiel 1

Fig. 1.2

eine fotografische Aufnahme des "A"-Auschnitts - Beispiel 2

Fig. 1.3

eine fotografische Aufnahme des "A"-Auschnitts - Beispiel 3

Fig. 1.4

eine fotografische Aufnahme des "A"-Auschnitts - Beispiel 4

Fig. 1.5

eine fotografische Aufnahme des "A"-Auschnitts - Beispiel 5

Fig. 1.6

eine fotografische Aufnahme des "A"-Auschnitts - Beispiel 6

Fig. 1.7

eine fotografische Aufnahme des "A"-Auschnitts - Vergleichsbeispiel A

Fig. 1.8

eine fotografische Aufnahme des "A"-Auschnitts - Vergleichsbeispiel B

Fig. 2.1

eine REM-Aufnahme des Negativlinienpaars - Beispiel 1

Fig. 2.2

eine REM-Aufnahme des Negativlinienpaars - Beispiel 2

Fig. 2.3

eine REM-Aufnahme des Negativlinienpaars - Beispiel 3

Fig. 2.4

eine REM-Aufnahme des Negativlinienpaars - Beispiel 4

Fig. 2.5

eine REM-Aufnahme des Negativlinienpaars - Beispiel 5

Fig. 2.6

eine REM-Aufnahme des Negativlinienpaars - Beispiel 6

Fig. 2.7

eine REM-Aufnahme des Negativlinienpaars - Vergleichsbeispiel A

Fig. 2.8

eine REM-Aufnahme des Negativlinienpaars - Vergleichsbeispiel B

Show it:

Fig. 1.1

a photograph of the "A" cut - Example 1

Fig. 1.2

a photograph of the "A" cut - Example 2

Fig. 1.3

a photograph of the "A" cut - Example 3

Fig. 1.4

a photographic image of the "A" cut - Example 4

Fig. 1.5

a photographic image of the "A" cut - Example 5

Fig. 1.6

a photographic image of the "A" cutout - Example 6

Fig. 1.7

a photograph of the "A" cut - Comparative Example A

Fig. 1.8

a photograph of the "A" cut - Comparative Example B

Fig. 2.1

a SEM image of the negative pair - Example 1

Fig. 2.2

a SEM image of the negative pair - Example 2

Fig. 2.3

a SEM image of the negative pair - Example 3

Fig. 2.4

a SEM image of the negative pair - Example 4

Fig. 2.5

a SEM image of the negative-pair - Example 5

Fig. 2.6

a SEM image of the negative pair - Example 6

Fig. 2.7

a SEM image of the negative pair - Comparative Example A

Fig. 2.8

a SEM image of the negative pair - Comparative Example B

Table 2 summarizes the assessments of the above characteristics and the arithmetic mean of all the characteristics. Example no. Letter a
according to Fig. 1. x Negative line pair
according to Fig. 2. x average
about all features RS TD OG RS TD OG 1 2 2 1 1 1 2 1.5 2 1 1 2 1 2 1 1.3 3 1 2 1 2 3 3 2.0 4 2 1 2 2 3 2 2.0 5 1 1 2 2 3 2 1.8 6 1 3 2 3 4 3 2.7 A 5 5 5 5 5 4 4.8 B 4 3 4 5 4 4 4.0

Based on the assessed characteristics, the superior quality of the Laser engraving produced relief elements in flexographic printing elements based on syndiotactic 1,2-polybutadiene (examples) compared to conventional Recognize flexographic printing elements (comparative examples). In all invention examples can finest relief elements as the negative-line pairs shown in high quality be imaged. Furthermore, the quality of larger engraved relief elements, as shown by way of example on the section of the letter A, in the case of flexographic printing elements Basis of syndiotactic 1,2-polybutadiene significantly better, as strong melting phenomena or avoid material deposits on the printing surface become.

Claims (5)

1. A laser-engravable flexographic printing element comprising an elastomeric, relief-forming, laser-engravable, thermally and/or photochemically crosslinkable layer comprising

   (a) from 50 to 99.9% by weight of one or more binders as component A, consisting of

   (a1) from 5 to 100% by weight of syndiotactic 1,2-polybutadiene having a content of 1,2-linked butadiene units of from 80 to 100%, a degree of crystallinity of from 5 to 30% and a mean molecular weight of from 20,000 to 300,000 g/mol as component A1, and

   (a2) from 0 to 95% by weight of further binders as component A2,

   where the sum of components A1 and A2 gives 100% by weight,

   (b) from 0.1 to 30% by weight of crosslinking, oligomeric plasticizers which contain reactive groups in the main chain and/or reactive pendant and/or terminal groups as component B,

   (c) from 0 to 25% by weight of ethylenically unsaturated monomers as component C,

   (d) from 0 to 10% by weight of photoinitiators and/or thermally decomposable initiators as component D,

   (e) from 0 to 20% by weight of absorbers for laser radiation as component E, and

   (f) from 0 to 30% by weight of further conventional additives as component F,

   where the sum of components A to F adds up to 100% by weight.
2. A laser-engravable flexographic printing element as claimed in claim 1, wherein component B is selected from the group consisting of polybutadiene oils, polyisoprene oils and allyl-containing plasticizers, which may contain functional end groups, having a viscosity of from 500 to 150,000 mPas at 25°C.
3. A laser-engravable flexographic printing element as claimed in claim 2, wherein component B is a polybutadiene oil having a viscosity of from 500 to 100,000 mPas at 25°C.
4. A process for the production of a relief printing element, comprising the steps of

   (i) thermal or photochemical crosslinking of the elastomeric, relief-forming layer of a flexographic printing element as defined in one of claims 1 to 3, and

   (ii) laser engraving of a printing relief into the crosslinked, elastomeric, relief-forming layer.
5. A process for the production of a relief printing element, comprising the steps of

   (i) thermal or photochemical crosslinking of the elastomeric, relief-forming layer of a flexographic printing element comprising an elastomeric, relief-forming, laser-engravable, thermally and/or photochemically crosslinkable layer comprising as binder, at least 5% by weight of syndiotactic 1,2-polybutadiene having a content of 1,2-linked butadiene units of from 80 to 100%, a degree of crystallinity of from 5 to 30% and a mean molecular weight of from 20,000 to 300,000 g/mol and

   (ii) laser engraving of a printing relief into the crosslinked, elastomeric, relief-forming layer.

Images