EP1753619B1 - Method for producing flexographic printing plates using direct laser engraving - Google Patents

Abstract

Process for the production of flexographic printing plates by means of direct laser engraving by engraving a print relief in the relief-forming layer with the aid of a laser and cleaning the resulting printing plate with a liquid cleaning agent.

Description

The invention relates to a process for the production of flexographic printing plates by direct laser engraving by engraving a printing relief in the relief-forming layer by means of a laser and subsequent cleaning of the printing plate formed with a liquid cleaning agent.

In direct laser engraving for the production of flexographic printing forms, a printing relief is engraved with a laser directly into the relief-forming layer of a flexographic printing element. A subsequent development step as in the conventional process for the production of flexographic printing forms is no longer necessary. The production of flexographic printing plates by direct laser engraving is known in principle, for example US 5,259,311 . WO 93/23252 . WO 02/49842 . WO 02/76739 or WO 02/83418 ,

In direct laser engraving, the relief-forming layer absorbs laser radiation to such an extent that it is removed or at least detached at those points where it is exposed to a laser beam of sufficient intensity. Under the influence of the laser radiation, the material of the relief-forming layer is evaporated on the one hand, on the other hand split into more or less large fragments. In this case, among other things, sticky, organic aerosols with a particle diameter of usually <1 □ m and, in addition, volatile organic substances and possibly dusts are formed. High-performance IR lasers, such as CO ₂ lasers or Nd-YAG lasers, are common for engraving. Suitable apparatus for engraving flexographic printing plates are, for example, in EP 1 162 315 and EP 1 162 316 disclosed.

Typical relief layer thicknesses of flexographic printing plates are usually between 0.4 and 7 mm. The non-printing depressions in the relief amount to at least 0.03 mm in the grid area, significantly more in the case of other negative elements and can assume values of up to 3 mm for thick plates. Already at an engraving depth of only 0.7 mm and an average of 70% erosion, approx. 500 g of material per m ^{2 of} the printing form are removed. Laser direct engraving removes large amounts of material with the laser.

Direct laser engraving equipment has suitable suction devices for receiving the decomposition products. In addition to avoiding contamination of the environment with degradation products, the suction devices should also prevent the in As the engraving is formed, very sticky aerosols deposit again on the printing surface of the plate. Redeposition of aerosols on the surface is highly undesirable because it reduces the quality of the printing relief and, accordingly, can significantly degrade the printed image when printed. This effect naturally makes the more noticeable the finer the respective relief elements are.

Even with very good extraction, however, it can not always be completely prevented that degradation products can deposit on the surface again. This is especially true when engraving very quickly, which is quite desirable for economic reasons.

It has therefore been proposed to refinish the surface of laser-engraved flexographic printing plates after laser engraving with liquid cleaning agents. WO 03/45693 . WO 03/106172 or WO 03/107092 suggest for this purpose to use conventional washout agents for photosensitive flexographic printing elements. As a rule, such washout agents have a good cleaning effect with regard to the degradation products of the layer produced by laser engraving.

However, the use of conventional cleaning agents has the disadvantage that the printing forms swell up in the cleaning agent. After the post-cleaning, the printing form can therefore not be used immediately for printing, but must be carefully dried again before use. This usually takes 2 to 3 hours and is highly undesirable, since this eliminates the time advantage of laser direct engraving compared to the conventional production of flexographic printing plates.

It has therefore also been proposed by the cited documents, in essence aqueous detergents, of EP-A 463 016 disclosed "water-in-oil" emulsions or those of WO 99/62723 disclosed microemulsion cleaning agents of water, alkyl esters of saturated and unsaturated fatty acids and surfactants use. However, these do not always have the desired cleaning effect. Also, some components of substantially aqueous detergents, such as long chain fatty acid alkyl esters, tend to swell flexographic printing forms.

The object of the invention was to provide a process for the production of flexographic printing plates by means of direct laser engraving, in which a liquid cleaning agent for re-cleaning the engraved layer is used, which achieves a very good cleaning effect, but wherein the relief layer still does not swell excessively.

1. (1) Eingravieren eines Druckreliefs in die reliefbildende Schicht mit Hilfe eines Lasers, wobei die Tiefe der mit dem Laser einzugravierenden Reliefelemente mindestens 0,03 mm beträgt, sowie
2. (2) Nachreinigen der erhaltenen Druckform mittels eines flüssigen Reinigungsmittels,

wobei das Reinigungsmittel mindestens 50 Gew. %, bezogen auf die Menge aller Komponenten des Reinigungsmittels, einer oder mehrerer Komponenten (A) ausgewählt aus der Gruppe von

• (A1) Lactonen mit 5, 6 oder 7-gliedrigen Ringen,
• (A2) Hydroxymonocarbonsäureestern der allgemeinen Formel R¹-COO-R², wobei R¹ und R² unabhängig voneinander für einen linearen oder verzweigten Alkyl-, Aralkyl-, Aryl- oder Alkylarylrest mit 1 bis 12 C-Atomen stehen und mindestens einer der Reste R¹ bzw. R² mit mindestens einer OH-Gruppe substituiert ist, der Maßgabe, dass die Ester 5 bis 20 C-Atome aufweisen,
• (A3) Alkoxymonocarbonsäureestern der allgemeinen Formel R³-COO-R⁴, wobei R³ und R⁴ unabhängig voneinander für einen linearen oder verzweigten Alkyl-, Aralkyl- oder Alkylarylrest mit 1 bis 12 C-Atomen stehen, und bei dem in mindestens einem der Reste eines oder mehrere, nicht benachbarte, nicht endständige aliphatische Kohlenstoffatome durch ein Sauerstoffatom ersetzt sind und der Rest außerdem noch eine endständige OH-Gruppe aufweisen kann, mit der Maßgabe, dass die Ester 5 bis 20 C-Atome aufweisen,
• (A4) Ketomonocarbonsäureestern der allgemeinen Formel R⁵-COO-R⁶, wobei R⁵ und R⁶ unabhängig voneinander für einen linearen oder verzweigten Alkyl-, Aralkyl- oder Alkylarylrest mit 1 bis 12 C-Atomen stehen, und bei dem in mindestens einem der Reste eines oder mehrere, nicht benachbarte, nicht endständige aliphatische Kohlenstoffatome durch eine Ketogruppe >C=O ersetzt sind, mit der Maßgabe, dass die Ester 5 bis 20 C-Atome aufweisen,
• (A5) Dicarbonsäureestern der allgemeinen Formel R⁷OOC-R⁸-COOR^7' und/oder R⁷COO-R⁸-OOCR^7', wobei R⁷ und R^7' unabhängig voneinander für lineare oder verzweigte Alkylreste mit 1 bis 4 C-Atomen und R⁸ für einen zweiwertigen Kohlenwasserstoff rest mit 2 bis 12 C-Atomen stehen, mit der Maßgabe, dass die Ester 6 bis 20 C-Atome aufweisen, und wobei die Reste R⁷ bzw. R^7' und R⁸ gegebenenfalls noch weitere Substituenten, ausgewählt aus der Gruppe von F, Cl, Br, OH oder =O aufweisen können und/oder optional in den Resten nicht benachbarte C-Atome durch O-Atome ersetzt sein können,
• (A6) Etheralkoholen der allgemeinen Formel R⁹O-(-R¹⁰-O)_nH, wobei n für eine natürliche Zahl von 2 bis 5 steht, R⁹ für H oder einen geradkettigen oder verzweigten Alkylrest mit 1 bis 6 C-Atomen und R¹⁰ für gleiche oder verschiedene Alkylenreste mit 2 bis 4 C-Atomen stehen

umfasst, mit der Maßgabe, dass die Komponenten (A1) bis (A6) jeweils einen Siedepunkt im Bereich von 150°C bis 300°C aufweisen.Accordingly, a process for the production of flexographic printing plates by direct laser engraving has been found, wherein the starting material used is a laser-engravable flexographic printing element, at least comprising a dimensionally stable support and an elastomeric, relief-forming layer having a thickness of at least 0.2 mm, the process being at least the following steps include:

1. (1) Engraving a printing relief in the relief-forming layer by means of a laser, wherein the depth of the relief elements to be engraved with the laser is at least 0.03 mm, as well
2. (2) post-cleaning the printing form obtained by means of a liquid cleaning agent,

wherein the cleaning agent at least 50 wt.%, Based on the amount of all components of the cleaning agent, one or more components (A) selected from the group of

• (A1) lactones with 5, 6 or 7-membered rings,
• (A2) Hydroxymonocarbonsäureestern the general formula R ¹ -COO-R ² , wherein R ¹ and R ^{2 are} independently a linear or branched alkyl, aralkyl, aryl or alkylaryl radical having 1 to 12 carbon atoms and at least one of Radicals R ¹ or R ² is substituted by at least one OH group, with the proviso that the esters have 5 to 20 C atoms,
• (A3) alkoxymonocarboxylic esters of the general formula R ³ -COO-R ⁴ , where R ³ and R ⁴ independently of one another are a linear or branched alkyl, aralkyl or alkylaryl radical having 1 to 12 C atoms, and in which at least one the radicals of one or more, non-adjacent, non-terminal aliphatic carbon atoms are replaced by an oxygen atom and the radical may additionally also have a terminal OH group, with the proviso that the esters have 5 to 20 C atoms,
• (A4) Ketomonocarbonsäureestern the general formula R ⁵ -COO-R ⁶ , wherein R ⁵ and R ^{6 are} independently a linear or branched alkyl, aralkyl or alkylaryl radical having 1 to 12 carbon atoms, and in which in at least one the radicals one or more, non-adjacent, non-terminal aliphatic carbon atoms are replaced by a keto group> C = O, with the proviso that the esters have 5 to 20 carbon atoms,
• (A5) dicarboxylic acid esters of the general formula R ⁷ OOC-R ⁸ -COOR ^{7 '} and / or R ⁷ COO-R ⁸ -OOCR ^7' , where R ⁷ and R ^{7 '} independently of one another represent linear or branched alkyl radicals having 1 to 4 C Atoms and R ^{8 are} a divalent hydrocarbon radical having 2 to 12 C atoms, with the proviso that the esters have 6 to 20 C atoms, and wherein the radicals R ⁷ or R ^{7 '} and R ⁸ optionally still further substituents selected from the group of F, Cl, Br, OH or = O may have and / or optionally non-adjacent C atoms in the radicals may be replaced by O atoms,
• (A6) Ether alcohols of the general formula R ⁹ O - (- R ¹⁰ -O) _n H, where n is a natural number from 2 to 5, R ^{9 is} H or a straight-chain or branched alkyl radical having 1 to 6 C atoms and R ^{10 are} identical or different alkylene radicals having 2 to 4 carbon atoms

with the proviso that the components (A1) to (A6) each have a boiling point in the range of 150 ° C to 300 ° C.

More specifically, the following is to be accomplished for the invention:

The starting material for carrying out the process according to the invention is a laser-engravable flexographic printing element which, in a manner known in principle, comprises at least one dimensionally stable support and an elastomeric, relief-forming layer having a thickness of at least 0.2 mm, preferably at least 0.3 mm and more preferably at least 0.5 mm. As a rule, the thickness is 0.5 to 3.0 mm.

The dimensionally stable carrier may be in a manner known in the art to polymer or metal foils, or else to cylindrical sleeves made of metals or polymeric materials. The latter are used for the production of round printing plates, also called sleeves.

The relief-forming layer can be obtained in a manner known in principle by crosslinking a crosslinkable layer comprising at least one elastomeric binder and components suitable for crosslinking, for example ethylenically unsaturated monomers and suitable initiators. The crosslinking can be carried out, for example, photochemically. Furthermore, optional absorbers for laser radiation, such as Carbon black, and / or plasticizers and other auxiliaries such as dyes, dispersing aids or the like can be used.

Laser-engravable flexographic printing elements are known in principle. Laser-engravable flexographic printing elements may comprise only one relief-forming layer or several identical, similar or different structures. Details of the construction and the composition of laser engravable flexographic printing elements are, for example, in
WO 93/23252 . WO 93/23253 . US 5,259,311 . WO 02/49842 . WO 02/76739 or
WO 02/83418 discloses, to which reference is expressly made at this point.

The inventive method is not limited to the use of very specific flexographic printing elements as the starting material. However, the advantages of the process are particularly evident in such laser-engravable flexographic printing elements, whose relief-forming layer essentially comprises hydrophobic binders in a manner known in principle. Examples of such elastomeric binders include natural rubber, polybutadiene, polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile-butadiene rubber, acrylate-butadiene rubber, butyl rubber, styrene-isoprene rubber, polynorbornene rubber, polyoctenamer, ethylene-propylene Diene rubber (EPDM) or styrene-butadiene or styrene-isoprene type thermoplastic elastomeric block copolymers, such as SBS or SIS block copolymers, or star-shaped styrene-butadiene and / or styrene-isoprene block copolymers.

Particularly preferred are styrene-butadiene type binders in combination with larger amounts of a suitable plasticizer, such as
WO 03/106172 disclosed.

In method step (1) of the method according to the invention, a printing relief is engraved into the laser-engravable layer in a manner known in principle by means of a laser. In particular, they can be IR lasers, for example CO ₂ or Nd / YAG lasers. It may be apparatuses that work only with a laser beam or with multiple. It is preferably an apparatus with a so-called "rotating cylinder". Such apparatuses are known in principle. Their structure and functioning are, for example, in EP-A 1262 315 .
EP-A 1 262 316 or WO 97/19783 shown. Details are in particular in
EP-A1 262 315 , Pages 14 to 17 are shown.

The depth of the elements to be engraved depends on the total thickness of the relief and the type of elements to be engraved and is determined by the person skilled in the art according to the desired properties of the printing form. The depth of the engraved relief elements is at least 0.03 mm, preferably at least 0.05 mm - is called here the minimum depth between individual halftone dots. Printing plates with too low relief depths are generally unsuitable for printing by means of flexographic printing technology because the negative elements are filled with printing ink. Individual negative points should usually have greater depths; for those of 0.2 mm diameter, a depth of at least 0.07 to 0.08 mm is usually recommended. For weggravierten surfaces is recommended a depth of more than 0.15 mm, preferably more than 0.3 mm and more preferably more than 0.4 mm. The latter is of course only possible with a correspondingly thick relief.

The degradation or decomposition products of the relief-forming layer should be extracted as well as possible during the engraving of the relief. This can be particularly advantageous in our still unpublished application
DE 103 55 991.4 described apparatus are used for suction. Of course, however, other suction devices can be used.

After engraving the relief layer, the printing plate obtained, or its surface, is subsequently cleaned in process step (2) using a liquid cleaning agent.

According to the invention, the cleaning agent comprises at least 50% by weight of one or more components (A), the amount being based on the sum of all components of the cleaning agent. The components are one or more components selected from the group of components (A1) to (A6).

The component (A1) is lactones with 5, 6 or 7-membered rings, which may optionally also be further substituted, for example by
OH groups. Preference is given to γ-butyrolaton, δ-valerolactone or ε-caprolactone.

Component (A2) is hydroxymonocarboxylic acid ester of the general formula R ¹ -COO-R ² . R ¹ and R ² hereby independently of one another represent a linear or branched alkyl, aralkyl, aryl or alkylaryl radical having 1 to 12 C atoms,
where at least one of the radicals R ¹ and / or R ^{2 is} at least one additional OH group having. Furthermore, the total number of all carbon atoms of hydroxymonocarboxylic esters is from 5 to 20.

Examples of linear or branched alkyl radicals include methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, t-butyl, 1-pentyl, 1-hexyl, 2-ethyl 1-hexyl, 1-octyl, 1-decyl or 1-dodecyl groups. They are preferably linear alkyl groups.

Aralkyl groups are, in a known manner, aryl-substituted alkyl groups. Examples include a benzyl or phenylethyl group. An aryl radical may be, for example, a phenyl group. Alkylaryl radicals are, in a known manner, alkyl-substituted aryl radicals. For example, it may be a 4-alkylphenyl radical, in particular a 4-methylphenyl radical.

R ¹ and R ^{2 are} preferably, independently of one another, linear or branched alkyl radicals having 1 to 6 C atoms.

The number of OH groups is selected by the skilled person depending on the desired properties of the cleaning agent. Usually, the components (A2) have 1 to 4 OH groups, preferably 1 or 2 and particularly preferably an OH = group.

The components (A2) are preferably hydroxymonocarboxylic acid esters whose radicals R ¹ and R ² are alkyl groups, more preferably linear alkyl groups. The OH groups can be arranged both vicinally and terminally on the alkyl group. The OH groups are preferably arranged terminally or in the □ -position.

Examples of suitable hydroxymonocarboxylic esters include in particular esters of lactic acid H ₃ CCH (OH) -COOR ^{2 '} , where R ^2' is a straight-chain or branched alkyl group having 2 to 6 C atoms and esters of the general formula R ¹ COOCH ₂ CH ₂ OH. Other examples include glycolic acid esters
HO-CH ₂ COOR ^{2 '} or 3-hydroxybutyric acid ester CH ₃ -CH (OH) CH ₂ COOR ^2' in particular the respective ethyl esters.

Component (A3) is alkoxymonocarboxylic acid esters of the general formula R ³ -COO-R ⁴ . R ³ and R ⁴ are each independently a linear or branched alkyl, aralkyl or alkylaryl radical having 1 to 12 C atoms, wherein at least one of the radicals of one or more, non-adjacent, non-terminal aliphatic carbon atoms are replaced by oxygen atoms. In other words, the radicals have one or more ether groups. The total number of all carbon atoms of the alkoxymonocarboxylic acid esters is 5 to 20.

The term "non-terminal" refers to the particular moiety alone, i. that neither a terminal aliphatic carbon atom nor the aliphatic C atom attached directly to the ester group should be substituted by O.

The number of ether groups is chosen by the skilled person depending on the desired properties of the cleaning agent. Usually, however, the components (A3) have not more than 4 ether groups, preferably 1 to 3 and particularly preferably 1 or 2. If several ether groups are present in one group, these are preferably separated from one another by at least 2 C atoms.

The ether groups containing radicals may also have a terminal OH group.

Preferably, only one of the two radicals R ³ or R ^{4 has} ether groups, more preferably R ⁴ .

Examples of suitable alkoxymonocarboxylic acid esters include 2-ethoxyethyl acetate and 2-butoxyethyl acetate.

In a further preferred embodiment of the invention, R ⁴ is a polyoxyalkylene group which is obtainable in a manner known in principle by alkoxylation of a carboxylic acid R ³ COOH with ethylene oxide and / or propylene oxide and / or butylene oxide. The terminal OH group can also be etherified, for example to a methoxy, ethoxy, propoxy or butoxy.

Examples of suitable components (A3) having polyoxyalkylene groups include compounds of the general formula R ³ COO- (CH ₂ CH ₂ O) _k H, R ³ COO- (CH ₂ CH ₂ O) _k CH ₃ , R ³ COO- (CH ₂ CH (CH) ₃ O) _k H or - (CH ₂ CH (CH) ₃ O) _k CH ₃ , where n is 2 or 3 and R ^{3 is} a straight-chain or branched alkyl radical having 2 to 6 C atoms.

Component (A4) is ketomonocarboxylic acid ester of the general formula R ⁵ -COO-R ⁶ . R ⁵ and R ⁶ hereby independently of one another represent a linear or branched alkyl, aralkyl or alkylaryl radical having 1 to 12 C atoms, where at least one of the radicals of one or more, non-adjacent, non-terminal aliphatic carbon atoms is protected by a keto group C = O are replaced. Furthermore, the total number of carbon atoms of the ketomonocarboxylic acid esters is 5 to 20.

The number of keto groups is chosen by the skilled person depending on the desired properties of the cleaning agent. Usually, however, the components (A4) have not more than 4 keto groups, preferably 1 or 2 and more preferably only one keto group.

It is preferable that the component (A4) to keto esters of the general formula R ^{5 'is} -CO-CH ₂ -COOR ^6, wherein R ^5' is a linear or branched alkyl, aralkyl or alkylaryl radical having from 1 to 10 C atoms, preferably a linear or branched alkyl radical having 1 to 6 carbon atoms. More preferably, R ^{5 '} is a methyl group. In R ⁶ , the preferred compound is a linear or branched alkyl radical having 1 to 6 C atoms, for example an ethyl group.

In (A5) are esters of the general formula R ⁷ OOC-R ⁸ -COOR ^{7 '} and / or R ⁷ COO-R ⁸ -OOCR ^7' . R ⁷ and R ^{7 '} are hereby independently of one another linear or branched alkyl radicals having 1 to 4 C atoms and R ^{8 is} a divalent hydrocarbon radical having 2 to 12 C atoms. The esters have 6 to 20 carbon atoms. In other words, they are diesters derived either from dicarboxylic acids or from dialcohols. The total number of all carbon atoms of the dicarboxylic acid esters is 6 to 20.

R ⁷ and R ^{7 '} are hereby independently of one another linear or branched alkyl radicals having 1 to 4 carbon atoms. Examples include methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or t-butyl. Preference is given to methyl, ethyl and 1-propyl radicals, and methyl radicals are particularly preferred.

R ⁸ is a divalent hydrocarbon radical with 2 to 12 C atoms. It may be a linear, branched or cyclic, aliphatic hydrocarbon radical as well as aromatic radicals. It is preferably a divalent, linear alkylene radical having 2 to 12 C-atoms, preferably 2 to 6 C-atoms.

Examples of suitable diesters include dimethyl butanedicarboxylate, dimethyl hexanedicarboxylate, dimethyl octanedioate, diethyl decadicarboxylate, propylene glycol diacetate or ethylene glycol diacetate.

It can of course also be a mixture of different diesters. Particularly preferred is a mixture of different diesters of the general formula H ₃ COOC-R ^{8 '} --COOCH ₃ , where R ^{8' is} a divalent linear hydrocarbon radical having 2 to 6 C atoms, in particular - (CH ₂ ) ₂ -, - (CH ₂ ) ₄ - and - (CH ₂ ) ₆ -. Such ester mixtures are also commercially available.

Optionally, the radicals R ⁷ or R ^{7 '} and R ^{8 may} also have further substituents, in particular those selected from the group of -F, -Cl, -Br, -OH or = O and / or may not be adjacent in the radicals C atoms are replaced by O atoms. The person skilled in the art will optionally make an appropriate choice as to the nature and number of such substituents depending on the desired properties of the detergent.

Component (A6) is ether alcohols of the general formula R ⁹ O - (- R ¹⁰ -O) _n H. n is a natural number of 2 to 5, preferably 2 or 3. R ^{9 is} H or one straight-chain or branched alkyl radical having 1 to 6 C atoms, such as, for example, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, t-butyl, 1-pentyl or 1- hexyl radicals. R ¹⁰ represents straight-chain or branched alkylene radicals having 2 to 4 C atoms, in particular 1,2-ethylene, 1,3-propylene, 1,2-propylene-1,2-butylene or 1,4-butylene radicals. The radicals R ¹⁰ in an ether alcohol may be the same or different. Of course, mixtures of different ether alcohols of the formula mentioned can also be used.

R ¹⁰ is preferably a propylene radical. In a particularly preferred embodiment, it is dipropylene glycol monomethyl ether. Dipropylene glycol monomethyl ether and isomer mixtures thereof are commercially available.

The person skilled in the art makes a suitable choice among the components A1 to A6 depending on the desired properties of the cleaning agent, with the proviso that the components (A1) to (A6) each have a boiling point in the range from 150 ° C. to 300 ° C. The preferred boiling range is 160 to 280 ° C, and more preferably 170 to 250 ° C.

The components (A1) to (A6) have in common that they have a certain degree of hydrophilicity due to the functional groups in the molecules, without being particularly hydrophilic. Due to these properties, the compounds do not swell hydrophobic relief layers to any significant extent. Remains of the cleaning agent can still be washed off with water from the surface after the post-cleaning process. Nevertheless, they are sufficiently hydrophobic to be able to wash off the decomposition products of the layer from the surface of the relief printing form.

The components (A1) to (A6) furthermore have no long, hydrophobic alkyl radicals with more than 12 C atoms. Such long alkyl radicals usually have a high plasticizing effect on relief layers and lead to undesirable loss of hardness. This is avoided by the inventive use of the components (A1) to (A6).

The desired degree of hydrophilicity can be set by those skilled in the art by selecting the type and amount of components (A1) to (A6). As a rule, the cleaning agent should not be substantially miscible with water, but on the other hand it should be so hydrophilic that it can be washed off with water from the surface of the flexographic printing plate.

According to the invention, the cleaning agent comprises at least 50% by weight of one or more components (A) selected from the group of (A1) to (A6), based on the amount of all components of the cleaning agent. The cleaning agent preferably comprises at least 70% by weight and particularly preferably at least 80% by weight of the components A1 to A6.

In a preferred embodiment of the invention, the cleaning agent consists of a mixture of at least two of the components A1 to A6.

In particular, a mixture of 50 to 99% by weight of one or more components selected from the group consisting of A1, A2, A3, A4 and A5 and 1 to 50% by weight of at least one compound A6 has proved suitable.

In such a mixture, the amount of components A1 to A5 is preferably from 55 to 95% by weight and very particularly preferably from 60 to
90% by weight. The amount of component A6 is preferably from 5 to 45% by weight and very particularly preferably from 10 to 40% by weight.

Particularly preferred is a mixture of one or more compounds of components A5 and A6.

In addition to the components A1 to A6, the cleaning agent may optionally also comprise one or more auxiliaries (B).
The auxiliaries may be, for example, surfactants, emulsifiers, antistatic agents, defoamers, dyes or compatibilizers. The cleaning agent preferably comprises at least one surfactant. Examples of suitable surfactants include fatty alcohol polyglycol ethers, salts of fatty alcohol polyglycol ether sulfonic acids, fatty alcohol polyglycol ether carboxylic acids, and ethoxy group-containing esters of mono- and dicarboxylic acids.

The type and amount of auxiliaries (B) is determined by the person skilled in the art according to the desired properties of the cleaning agent. The amount should, however, as a rule not exceed 15% by weight, preferably 10% and more preferably 5% by weight, relative to the amount of all components of the cleaning agent.

Furthermore, the cleaning agent according to the invention may also comprise further solvents (C) other than components A1 to A6. These can be used in particular for fine adjustment of the properties of the cleaning agent. Preferably, such additional solvents should have a boiling range of 150 to 300 ° C, preferably 160 ° C to 280 ° C. Examples include high-boiling alcohols or glycols such as cyclohexanol, methylcyclohexanol, trimethylcyclohexanol, benzyl alcohol, C7-C12 alcohols, terpene alcohols, propylene glycol, dipropylene glycol or propylheptanol, high-boiling hydrocarbons such as dearomatized petroleum fractions with a boiling range between 150 ° C and 300 ° C, hydrogenated aromatic Hydrocarbons, diisopropylbenzene or terpenes and N-methylpyrrolidone.

The type and amount of additional solvent (C) is determined by the skilled person depending on the desired properties of the cleaning agent. The amount should, however, as a rule not exceed 5% by weight, preferably 15% and particularly preferably 10% by weight, relative to the amount of all components of the cleaning agent.

The preparation of the cleaning agent can be done by simply mixing the components.

The production can be carried out for example by an end user such as printers or stereotypes even on site. The production can also be made by a third party.

The post-cleaning of the printing plate in process step (2) can be done, for example, by simply dipping or spraying the relief printing plate with the detergent.

However, it can preferably also be supported by mechanical means, such as brushes and / or plushes. Particularly preferably, brush washers, which are customary for the development of photopolymerizable flexographic printing elements, can be used for the post-cleaning step.

For example, flexographic printing plates can be a continuous system which has rotating round brushes, movable flat brushes or plushes.

In the case of seamless sleeves or plates already mounted on cylindrical carriers, it has proven useful to have washing devices which have at least one receiving device for the round printing form and at least one rotating brush whose distance from the round printing form is preferably adjustable. The devices may also have additional components for drying, such as a rotating brush, an air knife, a nip roll or the like. The recording for the round printing form can also consist of brushes, in the gap, the round printing form is placed and is driven by different Rotationsgeschwindgkeiten / -richtungen. The edition of the round printing form can be done by its own weight or an additional roller.

The cleaning process can also be assisted by spraying the cleaning agent onto the surface of the engraved flexographic printing plate under elevated pressure using so-called spray washers.

The contact time with the cleaning agent should not exceed 15 minutes, preferably 10 minutes, and is more preferably 2 to 8 minutes.

Before use, it is generally advisable to remove any residues of the cleaning agent from the surface of the post-cleaned flexographic printing plate. Due to the low swelling tendency, however, time-consuming drying processes are superfluous. The drying process usually lasts no more than 30 minutes, preferably not more than 20 minutes and particularly preferably not more than 10 minutes.

The removal can be done, for example, by simply blotting with an absorbent material such as fabric or paper, or by simply drying in air at room temperature or elevated temperatures to about 65 ° C with or without air exchange. The remainders of the cleaning agent can also be removed by rapid rotation in the case of a round printing form, with the remainder of the detergent being thrown off. Furthermore, brushes, air squeegee and / or squeeze rollers can be used.

The method according to the invention may of course also comprise further method steps.

In particular, the method may comprise further post-purification steps. For example, residues of dust or the like can be removed immediately after the engraving by blowing off with compressed air or brushing.

It is particularly advantageous to use water or an aqueous cleaning agent in a further post-purification step. The step may be before step (2) and preferably after step (2). By a (2) subsequent post-washing step, the residues of the liquid cleaning agent used according to the invention are particularly advantageously removed.

Aqueous cleaning agents for a further post-purification step (3) consist essentially of water and optionally small amounts of alcohols and / or auxiliaries, such as, for example, surfactants, emulsifiers, dispersing aids or bases. Preferably, only water is used. The residues of water or of the aqueous cleaning agent can then be removed, for example, by simply blowing off the surface with compressed air.

The cleaning agent of carboxylic acid esters and ether alcohols used according to the invention is only slightly swelling active, so that no lengthy drying of the printing plate is required. On the one hand, it has a very good cleaning action with respect to organic impurities on the surface, but it can still be washed off with water from the surface of the printing plate. Additional layer thickness tolerances as used conventional detergents due to swelling and drying, can be effectively avoided. This leads to a more uniform color transfer and thus to a higher-quality print result.

The inventive method for laser direct engraving using detergents immediately after the post-cleaning a ready-to-use flexographic printing plate is obtained. The processing time is thus significantly shorter compared to the use of conventional detergents.

The following examples are intended to explain the invention in more detail.

GENERAL RULES Production of unreinforced flexographic printing elements

The production of the flexographic printing elements used for the process according to the invention is carried out by the usual method. In the following examples, the photopolymerizable composition was extruded, discharged through a slot die and calendered between a support layer and a cover element. This procedure is in EP-B 084 851 described in detail.
In the examples below, the cover element consisted of a silicone-coated 125 μm thick PET cover film.

The extrusion equipment used was a twin-screw extruder (ZSK 53, Werner & Pfleiderer) at a throughput of 30 kg / h. The calendering was carried out between two calender rolls heated to 90 ° C., wherein the backing film was passed over the upper calender roll and the cover element over the lower calender roll.

The resulting sandwich composite was transported via a suction belt, cooled and assembled.

Details of the composition of the photopolymerizable composition, preparation parameters and the carrier and cover elements used are described in the respective examples.

Photochemical reinforcement of the flexographic printing elements

The photochemical reinforcement of the flexographic printing elements takes place by irradiation of the unreinforced flexographic printing element by means of long-wave UV light (UVA) through the cover element. The applied UV dose is approximately 12 J / cm ² for a flexographic printing element of 1.14 mm thickness. After removal of the cover element, the relief layer is detackified by means of short-wave UV light (UVC).

Laser engraving of reinforced flexographic printing elements

The reinforced flexographic printing elements were laser-engraved with the aid of a 3-beam CO ₂ laser (BDE 4131, Stork Prints Austria) with a test motif at a resolution of 1270 dpi. The parameters used were: Oberflächengeschwindgkeit: 10 m / s Relief Depth: 550 μm Flank angle: 59 ° First Step: 60 μm

The test motif contains flexographic relevant test elements such as fine positive and negative lines (line width 60 μm to 1 mm) and dots (diameter 60 μm to 1 mm), raster (1-99% at 100 and 133 Ipi), fine fonts Grid (line width 60 μm) and a checkerboard pattern with an edge length of 500 μm.

Cleaning the laser-engraved flexographic printing elements

The laser-engraved flexographic printing elements were cleaned with the aid of a commercial brush flat washer (W 32 × 40, BASF Drucksysteme GmbH) for the specified cleaning time with the respective cleaning agent.

Used feedstocks

KRATON ^® D-1102: SBS block copolymer (Kraton Polymers) M _W = 125,000 g / mol, 17% SB diblock fraction 30% styrene, 63% 1,4-butadiene, 7% 1,2-butadiene units Nisso ^® PB B-1000: Oligomeric polybutadiene oil (Nippon soda) Ondina ^® 934: Medicinal white oil (Shell Chemicals) Laromer® ^® HDDA: 1,6-hexanediol diacrylate (BASF) Irgacure ^® 651: Benzil dimethyl ketal (Ciba Specialty Chemicals) Kerobit ^® TBK: 2,6-di-tert-butyl-p-cresol (Raschig) Buyrolacton: Butyrolactone (BASF) Starsol ^® : commercial mixture of dimethyl succinate, dimethyl glutarate and dimethyl adipate (dibasic ester mixture) Solvenon ^® DPM: Dipropylene glycol monomethyl ether, mixture of isomers (BASF)

example 1

After the extrusion process described above, initially an unreinforced flexographic printing element was used in analogy to WO 03/106172 manufactured in a total thickness of 1.29 mm including cover element. The relief layer had the following composition: components feedstocks wt% binder KRATON ^® D-1102 56.96 softener NISSO ^® PB B-1000 15.00 Ondina ^® G 34 15.00 monomers Laromer ^® HDDA 10.00 photoinitiator Irgacurc ^® 651 2.00 additives Kerobit ^® TBK 1.00 dye 0.04

The unprimed flexographic printing element produced in this way was photochemically reinforced as described above and laser-engraved with the test motif.

As in illustration 1 To recognize the flexographic printing on strong deposits on both the surface and on the flanks. On the flanks, the sticky deposits built up increasingly, which would lead to an unclean print image in print.

Example 2

An inventive cleaning agent consisting of 80 parts by weight and 20 parts by weight Butyrolcaton Solvenon ^® DPM was prepared by intensive mixing.
An unpurified laser-engraved flexographic printing element analogous to Example 1 was cleaned for 1 minute in a scrubber with this cleaning mixture and blown dry with the aid of compressed air.

The layer thickness increase was only 3 μm.

As based on Figure 2 To recognize the impurities were already almost completely removed both on the surface and on the flanks. The cleaned printing form can be used for flexographic printing without causing an unclean printed image.

Example 3

An unpurified laser-engraved flexographic printing element analogous to Example 1 was cleaned for 5 minutes in a friction washer with the cleaning mixture from Example 2 according to the invention and blown dry with the aid of compressed air.

The layer thickness increase was only 4 μm.

As based on Figure 3 To recognize the impurities were completely removed both on the surface and on the flanks. The cleaned printing form can be used for flexographic printing without causing an unclean printed image.

Example 4

An inventive cleaning agent consisting of 80 parts by weight Starsol ^® and 20 parts by weight Solvenon DPM was prepared by intensive mixing.
An unpurified laser-engraved flexographic printing element analogous to Example 1 was cleaned for 5 minutes in a scrubber with this cleaning mixture, then rinsed for 2 minutes with water and blown dry with the aid of compressed air. The detergent was easily removed from the surface of the flexographic printing element by rinsing with water.

The layer thickness increase was only 17 μm.

As based on Figure 4 To recognize the impurities were removed on both the surface and on the flanks for the most part. The cleaned printing form can be used for flexographic printing without causing an unclean printed image.

Example 5 (comparative example)

For comparison, a microemulsion cleaner according to WO 99/62723 Made from the following components: Rapeseed oil methyl ester, water, emulsifiers and auxiliaries An unpurified laser-engraved flexographic printing element analogous to Example 1 was cleaned with the microemulsion cleaner for 5 minutes in a reaming machine, then rinsed with water for 2 minutes and blown dry with the aid of compressed air. The detergent was well by the rinsing with water of the
Remove the surface of the flexographic printing element.

The layer thickness increase was 28 μm.

As based on Figure 5 To recognize the impurities on the surface were indeed mostly removed, on the flanks, however, they are still clearly present. When used in flexographic printing, it will lead to an unclean printed image, since the contusion of the printing form mitdrucken impurities on the edges.

Example 6 (comparative example)

For comparison, an unpurified laser-engraved flexographic printing element was cleaned analogously to Example 1 for 5 min in a scrubber with tap water and blown dry with the aid of compressed air.

A layer thickness increase could not be determined.

As based on Figure 6 To recognize only a part of the particulate impurities was removed purely mechanically on the surface. The sticky deposits on the flanks are still completely present. The thus-cleaned flexographic printing plate is unsuitable for flexographic printing.

Example 7 (comparative example)

For comparison, a conventional washout agent for flexographic printing plates (nylosolv A, BASF Drucksysteme GmbH) was used.
An unpurified laser-engraved flexographic printing element analogous to Example 1 was cleaned for 3 minutes in a scrubber with nylosolv A and blown dry with the aid of compressed air.

The layer thickness increase was 46 μm.

Due to the high layer thickness increase, the cleaned flexographic printing element would have to be dried time-consuming before use in flexographic printing.

Abbildung 1:

Lasergraviertes Flexodruckelement gemäß Beispiel 1 (ungereinigt)

Abbildung 2:

Lasergraviertes Flexodruckelement gemäß Beispiel 2, gereinigt 1 min BL/DPM 8:2

Abbildung 3:

Lasergraviertes Flexodruckelement laut Beispiel 3, gereinigt 5 min BL/DPM 8:2

Abbildung 4:

Lasergraviertes Flexodruckelement laut Beispiel 4, gereinigt 5 min Starsolv/DPM 8:2

Abbildung 5:

Lasergraviertes Flexodruckelement laut Beispiel 5, gereinigt 5 min Printclean classic

Abbildung 6:

Lasergraviertes Flexodruckelement laut Beispiel 6, gereinigt 5 min Wasser

List of pictures:

Illustration 1:

Laser-engraved flexographic printing element according to Example 1 (unpurified)

Figure 2:

Laser-engraved flexographic printing element according to Example 2, cleaned 1 min BL / DPM 8: 2

Figure 3:

Laser engraved flexographic printing element according to Example 3, cleaned 5 min BL / DPM 8: 2

Figure 4:

Laser engraved flexographic printing element according to Example 4, cleaned 5 min Starsolv / DPM 8: 2

Figure 5:

Laser engraved flexographic printing element according to example 5, cleaned 5 minutes Printclean classic

Figure 6:

Laser-engraved flexographic printing element according to Example 6, cleaned for 5 min water

Claims (15)

1. A process for the production of flexographic printing plates by means of direct laser engraving, in which the starting material used is a laser- engravable flexographic printing element, at least comprising a dimensionally stable substrate and an elastomeric, relief-forming layer having a thickness of at least 0.2 mm, and for which the process comprises at least the following steps:

   (1) engraving of a printing relief in the relief-forming layer with the aid of a laser, the depth of the relief elements to be engraved by means of the laser being at least 0.03 mm, and

   (2) cleaning of the resulting printing plate by means of a liquid cleaning agent,

   wherein the cleaning agent comprises at least 50% by weight, based on the amount of all components of the cleaning agent, of one or more components (A) selected from the group consisting of

   (A1) lactones having 5, 6 or 7-membered rings,

   (A2) hydroxymonocarboxylic esters of the general formula R¹-COO-R², where R¹ and R², independently of one another, are a linear or branched alkyl, aralkyl, aryl or alkylaryl radical having 1 to 12 carbon atoms and at least one of the radicals R¹ or R² is substituted by at least one OH group, with the proviso that the esters have 5 to 20 carbon atoms,

   (A3) alkoxymonocarboxylic esters of the general formula R ^3_COO-R⁴ where R³ and R⁴, independently of one another, are a linear or branched alkyl, aralkyl or alkylaryl radical having 1 to 12 carbon atoms, and in which one or more, nonneighboring, nonterminal aliphatic carbon atoms in at least one of the radicals are replaced by an oxygen atom and the remainder can also have a terminal OH group, with the proviso that the esters have 5 to 20 carbon atoms,

   (A4) ketomonocarboxylic esters of the general formula R⁵-COO-R⁶, where R⁵ and R⁶, independently of one another, are a linear or branched alkyl, aralkyl or alkylaryl radical having 1 to 12 carbon atoms, and in which one or more, nonneighboring, nonterminal aliphatic carbon atoms in at least one of the radicals are replaced by a keto group > C = O, with the proviso that the esters have 5 to 20 carbon atoms,

   (A5) esters of the general formula R⁷OOC-R⁸-COOR^7' and/or R⁷COO-R⁸ OOCR^7' where R⁷ and R^7', independently of one another, are linear or branched alkyl radicals having 1 to 4 carbon atoms and R⁸ is a divalent hydrocarbon radical having 2 to 12 carbon atoms, with the proviso that the esters have 6 to 20 carbon atoms, and where the radicals R⁷ or R^7' and R⁸ can, if appropriate, also have further substituents selected from the group consisting of F, Cl, Br, OH or = O and/or nonneighboring carbon atoms in the radicals may optionally be replaced by oxygen atoms,

   (A6) ether alcohols of the general formula R⁹O-(-R¹⁰-O)_nH, where n is a natural number from 2 to 5, R⁹ is H or a straight-chain or branched alkyl radical having 1 to 6 carbon atoms and R¹⁰ are identical or different alkylene radicals having 2 to 4 carbon atoms,
   with the proviso that the components (A1) to (A6) each have a boiling point in the range from 150°C to 300°C.
2. The process according to claim 1, wherein the cleaning agent comprises at least one assistant (B).
3. The process according to claim 2, wherein at least one of the assistants (B) is a surfactant.
4. The process according to any of claims 1 to 3, wherein the cleaning agent comprises at least one further solvent (C) which differs from the components A1 to A6 and has a boiling point in the range from 150°C to 300°C.
5. The process according to claim 4, wherein not more than 25% by weight, based on the amount of all components, of the additional solvent (C) are present.
6. The process according to any of claims 1 to 5, wherein the cleaning agent comprises from 50 to 99% by weight of one or more components selected from the group consisting of A1, A2, A3, A4 and A5 and from 1 to 50% by weight of at least one compound A6.
7. The process according to claim 6, wherein it is a mixture of component A5 and component A6.
8. The process according to any of claims 1 to 7, wherein R¹ and R², independently of one another, are linear or branched alkyl radicals having 1 to 6 carbon atoms.
9. The process according to any of claims 1 to 7, wherein R⁸ is a divalent linear alkylene radical having 2 to 6 carbon atoms.
10. The process according to any of claims 1 to 7, wherein component (A5) is a mixture of different diesters of the general formula H₃COOC-R⁸-COOCH₃, where R⁸ is a divalent linear hydrocarbon radical having 2 to 6 carbon atoms.
11. The process according to any of claims 1 to 7, wherein R¹⁰ is a propylene radical.
12. The process according to any of claims 1 to 7, wherein the component (A6) is dipropylene glycol monomethyl ether.
13. The process according to any of claims 1 to 12, wherein the cleaning is carried out using a brush washer.
14. The process according to any of claims 1 to 12, wherein the cleaning is carried out by spraying the cleaning agent onto the printing plate surface under high pressure.
15. The process according to any of claims 1 to 14, wherein the residues of the liquid cleaning agent are removed in a subsequent process step with water or with an aqueous cleaning agent.

Images