Relief precursors with enhanced stability

Abstract

SOLUTION: There is provided a photosensitive composition (PC) for forming a photosensitive layer of a relief precursor (RP). The composition comprises: a radical initiator (R) such as a photoinitiator, a photoinitiator system or a thermal initiator; and optionally an ethylenically unsaturated compound (EC); a stabilizer (S1) for promoting extrusion stability, the stabilizer being a vitamin or a vitamin derivative; and a binder (B), the binder being a thermoplastic elastomer block copolymer having a first monomeric unit (Mu1) derived from a vinyl aromatic monomer and a second monomeric unit (Mu2), the second monomer unit being derived from an ene-monomer and / or a diene-monomer; or combinations thereof.EFFECT: By including the stabilizer and binder as described herein the stability of the melt of the photosensitive composition during production, e.g. production by extrusion, can be enhanced significantly.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to relief precursors with improved stability during extrusion without negatively affecting their photochemical properties. Improved extrusion stability can improve the development of the relief precursor and the final properties of the relief formed with the relief precursor. [Background technology]

[0002] A relief having a relief structure can be created using a relief precursor, such as a printing plate precursor (e.g. a printing blanket or sleeve). The relief (e.g. a cliché) can be used to press ink onto a substrate. Generally, the relief precursor is made of several layers. A backing layer, also called a carrier layer, is used for mechanical stability. A photosensitive layer is placed on top and selectively hardened (e.g. by exposure to light or heat) to create hardened areas in the photosensitive layer. The unhardened areas are then removed (e.g. by washing away), leaving behind the hardened areas to form the relief structure. This process is called development of the relief precursor.

[0003] However, some unintended premature curing may occur due to heating of the precursor before or during development, for example during production, during development and / or during long term storage. Unintended curing can have a significant impact on the precursor production process or on the performance of the final relief formed with the precursor. That is, the precursor is typically produced by an extrusion process in which a thermoplastic elastomer, such as a block copolymer, is melted and other solid or liquid components are added to the melt in an extrusion line. To homogenize the mixture, the extrusion line may contain kneading elements. However, the kneading by such kneading elements can result in mechanical and thermal stresses in the rubber mixture, which can result in unintended gel formation.

[0004] Therefore, to avoid or minimize such gel formation, stabilizers can be added to the mixture to prevent unintended premature curing, for example, thermal polymerization inhibitors can be added. However, conventional stabilizers may also affect the intended curing process during development of the relief precursor. As a result, conventional stabilizers may affect the performance characteristics of the relief structure, for example the creation of fine dots. Moreover, conventional stabilizers may not be efficient enough to prevent gel formation caused by mechanical and thermal stress.

[0005] To generate a relief that can be used as a printing plate, the relief precursor can be exposed to electromagnetic radiation through a mask carrying image information to form a relief structure. Due to the exposure to electromagnetic radiation, the exposed parts of the relief precursor harden and become insoluble or non-meltable. In a development step, the soluble or meltable parts of the relief precursor can be removed, resulting in the formation of the required relief. In the exposure step, the stabilizer should not interfere with the curing reaction. Also, compositions containing stabilizers should preferably provide good resolution with short exposure times and improved accuracy of the formed relief close to the target structure.

[0006] As a result, the inventors have recognized that there is a need for an improved binder-stabilizer system, in which the binder is sufficiently resistant to unintended polymerization and the formation of gel particles due to mechanical and thermal stress, and preferably does not affect the desired performance of the relief structure. Summary of the Invention

[0007] One object of several embodiments of the present invention is to provide relief precursors with improved ability to be developed into high performance relief structures, more particularly high quality relief structures, such as relief precursors for printing plates, and even more particularly flexographic printing plates.

[0008] Additionally, embodiments of the present invention provide a photosensitive composition (PC) for forming the photosensitive layer of the relief precursor (RP), the composition comprising: a radical initiator (R), such as a photoinitiator, a photoinitiator system or a thermal initiator, and optionally an ethylenically unsaturated compound (EC); a stabilizer (S1) that promotes extrusion stability, the stabilizer (S1) being a vitamin or a vitamin derivative; A binder (B), a first monomer unit (Mu1) derived from a vinyl aromatic monomer, and A second monomer unit (Mu2) derived from an ene monomer and / or a diene monomer and combinations thereof. A binder (B) which is a thermoplastic elastomeric block copolymer having the following structure: Includes.

[0009] Surprisingly, it has been found that combining a vitamin stabilizer or vitamin derivative with a thermoplastic elastomeric block copolymer binder results in a binder-stabilizer system with improved stability in the melt, which means, for example, better resistance to thermal and mechanical stresses during extrusion and production of the relief precursor.

[0010] It has been found that the inclusion of stabilizers and binders as described herein can significantly improve the stability of the melt of the photosensitive composition during production, e.g., production by extrusion. Surprisingly, such improved stability can be achieved without or with minimal undesirable effects on the printing performance and / or imaging properties resulting from the relief formed by developing the relief precursor.

[0011] Moreover, it has been found that the inclusion of vitamins or vitamin derivatives as stabilizers can improve both the production and the exposure and development performance of the photosensitive composition. That is, the functionality of the initiator and the thermoplastic elastomer block is better maintained without or with minimal effects of temperature rise resulting from thermal and / or mechanical stress during extrusion. Also, gel formation as a result of "unintended pre-cure" during production (before curing by exposure) can be avoided or minimized.

[0012] Unintended pre-curing can be understood as the occurrence of a curing reaction that is (already) initiated prior to exposure of the relief precursor (eg development by LED-exposure).

[0013] Unintended pre-cure can negatively impact final print properties, such as dot size, and final imaging properties, such as target value.

[0014] A further aspect relates to a relief, e.g., a printing plate, having a relief precursor (RP) comprising a photosensitive composition (PC) as described herein and a relief structure (RS) formed by exposing and developing the relief precursor (RP). By including a composition having a stabilizer-binder system as described herein, the relief precursor is less sensitive to UV-induced vulnerability. Furthermore, suitable development compatibility with high intensity LED exposure can be achieved. Furthermore, the presence of a properly formulated stabilizer can keep the exposure time consistent during exposure.

[0015] By including a vitamin or vitamin derivative in the photosensitive composition, a relief precursor, e.g., a printing plate precursor, can be obtained that has improved stability against oxidation. In this way, the printing plate can remain stable for long periods of time, e.g., during storage.

[0016] A further aspect relates to a method of developing a relief precursor to form a relief. It has been found that the vitamin or vitamin derivative stabilizer described herein can stabilize a photosensitive composition against unintended crosslinking without affecting the intended photopolymerization and curing. Thus, the quality of the relief structure formed from the relief precursor with the photosensitive composition in the photosensitive layer of the relief precursor is improved. A relief can be formed from the relief precursor having an improved relief structure thereon, e.g. smaller dots remain after development. Furthermore, the precision of the relief structure can be improved, since the dot size can be closer to the target value.

[0017] Additionally, the precursor may be further treated with UV-A and / or UV-C radiation after the development step to reduce the tackiness of the printing plate. A side effect may be increased vulnerability and susceptibility of the printing plate to mechanical defects. It has been found that the photosensitive compositions described herein can prevent UV-induced vulnerability.

[0018] In one embodiment, the vitamin or vitamin derivative stabilizer (S1) has a predicted log octanol-water coefficient calculated from Log Kow (WSKOW v 1.68 estimate) within EPI Suite v4.11, said predicted octanol-water coefficient (OWc) being higher than -4, preferably higher than -2, more preferably higher than 0, even more preferably higher than 5, preferably about 6. It has been found that by including fine selection in the predicted octanol-water coefficient of the vitamin or vitamin derivative stabilizer, its behavior within thermoplastic elastomer binder systems can be improved (e.g. improved phase stabilization within organic binder systems such as systems with SBS and / or SIS binders). According to one embodiment, the predicted log octanol-water coefficient is calculated from the Log Kow (WSKOW v 1.68 estimate) in EPI Suite v4.11 in the range of -4.0 to 12.0, more preferably in the range of -2.0 to 11.0, even more preferably in the range of 0.0 to 10.0, even more preferably in the range of 1.0 to 8.0, such as a coefficient in the range of 2.0 to 6.5, more particularly such as a coefficient in the range of 5.0 to 6.5. Careful selection of the Log Kow value (also referred to herein as the predicted log octanol-water coefficient) can improve compatibility with other components in the composition, benefiting improved behavior and thermal stabilization throughout the extrusion of the composition to make the relief precursor of the printing plate. Derivatives and materials not within the preferred range may cause phase separation in the relief precursor or migration to the surface. Moreover, the block copolymer binder system itself phase separates at a microscopic level. Adequate stabilization can only be achieved when the stabilizer is present in a phase that is particularly susceptible to unintended precure, and is highly dependent on the overall formulation, binder system, and monomer composition.

[0019] The photosensitive composition may have a further second stabilizer (S2) selected from one of the following classes: phenolic, phenolic and acrylates, thioethers, hindered amines, phenolic and amines, amines, thioether amines, polyfunctional amines and acrylates. Surprisingly, vitamins or vitamin derivatives, such as ascorbyl palmitate, may synergistically improve the stabilization of the second stabilizer.

[0020] In one embodiment, the vitamin or vitamin derivative stabilizer (S1) has a molecular weight in the range of 50-800 g / mol, preferably 50-600 g / mol, more preferably 100-490 g / mol, even more preferably 120-480 g / mol, and most preferably 200-430 g / mol.

[0021] In one embodiment, the vitamin or vitamin derivative stabilizer (S1) is selected from vitamins A, C, and E or derivatives thereof, preferably C and E, more preferably C, since its radical scavenging properties may improve extrusion stability.

[0022] In one embodiment, the vitamin or vitamin derivative stabilizer (S1) is a hydroxytetronic acid (HTAD) derivative. Hydroxytetronic acid can be included as a substructure in the stabilizer and can provide stabilization of sensitive ingredients by trapping (uncontrolled) free radicals, thereby avoiding or minimizing their effect on sensitive ingredients in the composition.

[0023] In one embodiment the vitamin or vitamin derivative stabilizer (S1) is a vitamin C derivative, preferably an ascorbic acid ester, even more preferably a fatty acid ester of ascorbic acid, more particularly ascorbyl palmitate (AP).

[0024] In one embodiment, the vitamin or vitamin derivative stabilizer (S1) is present in a concentration of 0.1-10 wt.%, preferably 0.1-8 wt.%, more preferably 0.2-6 wt.%, even more preferably 0.5-2%, based on the total weight of the photosensitive composition (PC). In this way, a balance can be achieved between the stabilization behavior, e.g. prevention of unintended hardening, and the crosslinking ability (intended hardening) of the photosensitive composition. Thus, gel formation during the production process, e.g. extrusion, can be avoided and / or minimized without having to compromise the final printing properties of the relief formed with the photosensitive composition.

[0025] In one embodiment, the binder has a total styrene content in the range of 3 to 50%, preferably 8 to 38%, more preferably 10 to 30%, and most preferably 15 to 30%.

[0026] In one embodiment, the binder (B) is selected from styrene-butadiene-styrene (SBS) triblock copolymers and / or styrene-isoprene-styrene (SIS) triblock copolymers.

[0027] In one embodiment, the binder (B) is selected from SBS triblock copolymers having a styrene content in the range of 8-48%, preferably 13-43%, more preferably 18-38%, for example approximately 28%.

[0028] In one embodiment, the binder (B) is a SIS triblock copolymer having a styrene content in the range of 3 to 27%, preferably 5 to 25%, for example approximately 15%.

[0029] In one embodiment, the binder (B) is a diblock copolymer or a triblock copolymer with a diblock fraction in the range of 5 to 50%, preferably 5 to 30%, more preferably 8 to 28%, even more preferably 10 to 24%, for example approximately 17% to 19%.

[0030] The binder (B) described above has been found to have good compatibility with vitamin or vitamin derivative stabilizers. A good binder-stabilizer system could be included in the composition to produce a relief precursor with great melt stability and without or with minimal undesirable effects on development performance such as exposure time and final printing performance such as resolution.

[0031] In one embodiment, the vitamin or vitamin derivative stabilizer (S1) is ascorbyl palmitate (AP) and the binder (B) is an SI diblock and / or SIS triblock copolymer, since such a combination may aid in exceptional processing behavior, especially during extrusion, with no or minimal impact on the final print performance.

[0032] In one embodiment, the composition further comprises a bio-based plasticizer (P), preferably a vegetable oil, a fatty acid and / or a fatty acid ester of mono- and polyfunctional alcohols. Preferably, the plasticizer is characterized by a UV transmittance at 365 nm of a 33 wt% solution of the plasticizer in n-hexane higher than 1%, preferably higher than 10%, more preferably higher than 50%, even more preferably higher than 60%. Preferably; the plasticizer has an iodine value according to ISO 3961:2018 of less than 200, preferably less than 150, so that a high quality can be achieved. In one embodiment, the plasticizer is characterized by a Gardner color of less than 7 according to ISO 4630:2015. The plasticizer can be used to maintain flexibility over a range of varying temperatures, which is convenient when carrying out mass production processes such as extrusion production. More preferably, the UV transmittance is higher than 15%, preferably higher than 25%, more preferably higher than 50%, even more preferably higher than 60%. The bio-based plasticizer is preferably present in the composition in an amount of at least 11 wt%, preferably at least 14 wt%, and even more preferably at least 16 wt%, based on the total weight of the components in the photosensitive composition. The bio-based plasticizer may achieve some additional benefits since it contributes to the flexibility, flow, thermal stability, and impact resistance of the relief precursor and / or printing plate. The bio-based plasticizer may be present in an amount of 11-60 wt%, preferably 12-55 wt%. By including the described plasticizers, development times may be reduced and energy savings may be achieved. Furthermore, it has been found that the use of bio-based plasticizers enhances the final printing performance. Preferably, the bio-based plasticizer is selected from rapeseed oil, sunflower oil, palm kernel oil, soybean oil, rapeseed oil (canola oil), sunflower oil, soybean oil, palm oil, palm kernel oil, coconut oil, medium chain triglycerides (MCT), linseed oil, safflower oil, corn oil and / or cottonseed oil, as long as the UV transmittance at 365 nm of a 33 wt % solution of the plasticizer in n-hexane is higher than 15%. More preferably, the bio-based plasticizer is preferably selected from sunflower oil or rapeseed oil (also called canola oil).

[0033] A further embodiment is a method for producing a relief precursor (RP), comprising the steps of: extruding a photosensitive composition (PC) as described herein to form an extruded photosensitive layer; applying the extruded layer to a dimensionally stable support (L1); The present invention relates to a method comprising the steps of:

[0034] It has been found that the relief precursor can be produced in large quantities by deploying an extrusion process. In particular, due to the incorporation of the stabilizer described herein, the extrusion stability of the photosensitive composition can be improved and gel formation during production can be avoided. Of course, the photosensitive composition in the relief precursor can have any of the characteristics described in connection with the photosensitive composition. Surprisingly good performance has been obtained by having the combination of stabilizer and binder described herein.

[0035] A further embodiment is a relief precursor (RP) that is developed into a relief (RS), a dimensionally stable support (L1), such as a support layer, such as a PET layer; a photosensitive layer (L2) comprising the photosensitive composition described herein; The present invention relates to a relief precursor (RP) comprising:

[0036] The dimensionally stable support may be referred to as a carrier layer and may be made from a material selected from the group consisting of aluminum, steel, polymers, and synthetic composites.

[0037] In one embodiment, the relief (RS) developed from the relief precursor (RP) serves as a printing sleeve or printing blanket.

[0038] A further aspect relates to the use of the invention, said use comprising: Use of a vitamin or vitamin derivative, preferably ascorbyl palmitate (AP), to improve the extrusion stability of a mixture, preferably a vitamin containing hydroxytetronic acid (HTAD) as a substructure. Use of a stabilizer (S1) which is a vitamin or vitamin derivative to improve the thermal stabilization of a second stabilizer (S2) which is a thermal stabilizer. Preferably, the second stabilizer (S2) is selected from one of the following classes: phenolic, phenolic and acrylates, thioethers, hindered amines, phenolic and amines, amines, thioether amines, polyfunctional amines and acrylates. The second stabilizer (S2) may be butylated hydroxytoluene (BHT).

[0039] According to one embodiment, there is provided a vitamin derivative for stabilizing heat and / or radiation sensitive components such as components in a photosensitive layer of a relief precursor for forming a relief such as a printing plate (also called a cliche), wherein the vitamin derivative is an ascorbic acid derivative (AAD) for stabilizing heat and / or radiation sensitive components, in particular said ascorbic acid derivative (AAD) is a carbamate derivative of formula I or a stereoisomer thereof, wherein formula I is [ka] [In the formula, m1 and m2 are independently one of 0 to 1; n1 and n2 are independently one of 0 to 1; however, m1 and n1 are not 0 at the same time, m2 and n2 are not 0 at the same time, L1 and L2 are each independently a sulfonyl group, or Linear or branched Cx-carbon chain (C), e.g. n-butyl wherein x is selected from 0 to 20, preferably 0 to 18; said carbon chain is optionally substituted; R1 and R2 are each independently Optionally substituted aromatic groups (Ar), such as phenyl; or optionally substituted cycloalkyl (CyC), such as cyclohexyl; or Groups containing a Si atom (Si), preferably silyl groups, such as mono-, (di-) or tri-alkylsilyl, for example trimethylsilyl or mono-, (di-) or tri-alkyloxysilyl, for example triethoxysilyl; or Acrylate groups (COOC), preferably alkyl acrylates, e.g. methacrylates represents] Represents.

[0040] The inventive insight of the present invention provides that carbamate derivatives function well as stabilizers (S1) within the photosensitive compositions described hereinabove. According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I: m is 1 and n is 1, L1 and L2 contain a sulfonyl group; R1 and R2 are each independently an Ar-group, preferably a C6-aromatic group, optionally substituted (e.g., with a methyl group). The sulfonyl group may provide thermal stabilization due to a combination of electronic, steric, bridging, oxidation resistance, and stability properties. The inclusion of aromatic groups can provide bulky components, providing steric hindrance, restricting molecular motion, and preventing thermally induced reactions from occurring. Thus, stabilization can be achieved.

[0041] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 0; n is 1; and R1 and R6 are C6-aromatic, such as phenyl.

[0042] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 0; L1 and L2 are each independently a Cx-chain, and x is 0 to 6. Preferably, L1 and L2 are butyl, preferably n-butyl.

[0043] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 1; L1 and L2 are each independently a Cx-chain; x is 0-6; preferably 3 (propyl); R1 and R2 are each independently a trialkyloxysilyl group, preferably a triethoxysilyl group.

[0044] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 0; L1 and L2 are each independently a Cx-chain; x is 0-6; preferably 4 (t-butyl).

[0045] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 1; L1 and L2 are each independently a Cx-chain; x is 0-6; preferably 2 (ethyl). R1 ​​and R2 are each independently an alkylacrylate, preferably a methacrylate.

[0046] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 0; n is 1; and R1 and R2 are each independently cycloalkyl, preferably cyclohexyl.

[0047] According to one embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 0; n is 1; and R1 and R2 are each independently a trialkyloxysilyl group, preferably a triethoxysilyl group.

[0048] These embodiments of the compound are based on the inventive insight that can provide improved stabilization of heat and / or radiation sensitive components. In particular, the inventive insight of the present invention provides improved stabilization of compositions that include binder systems, such as organic non-polar binder systems. More specifically, the ascorbic acid derivatives (AAD) represented by formula I are particularly useful for stabilizing binder systems that include units selected from styrene, butadiene, isoprene, such as SBS or SIS binders. The binders can be copolymers, such as duo- or triblock polymers. Examples of binders that can be stabilized are binders that include styrene-isoprene-styrene (SIS) units, styrene-ethylene-butylene-styrene (SEBS) or styrene-ethylene-propylene-styrene (SEPS) units, particularly those binders described herein above.

[0049] A further aspect relates to a method for obtaining the ascorbic acid derivatives (AAD) provided herein, the method comprising the steps of: a) providing ascorbic acid (AA), preferably either D-ascorbic acid or L-ascorbic acid; b) adding an isocyanate (IC) and reacting the isocyanate with ascorbic acid to obtain an ascorbic acid derivative (AAD); The isocyanate (IC) is represented by formula II: [ka] [In the formula, m and n are each a number between 0 and 1, provided that m and n are not both 0; L is a sulfonyl group (e.g., an -S atom bonded to two O atoms), or Linear or branched Cx-carbon chain (C), e.g. n-butyl Including, x is selected from 0 to 20, preferably 0 to 18; said carbon chain is optionally substituted; R is Optionally substituted aromatic groups (Ar), such as phenyl; or optionally substituted cycloalkyl (CyC), such as cyclohexyl; or Groups containing a Si atom (Si), preferably silyl groups, such as mono-, (di-) or tri-alkylsilyl, for example trimethylsilyl or mono-, (di-) or tri-alkyloxysilyl, for example triethoxysilyl; or Acrylate groups (COOC), preferably alkyl acrylates, e.g. methacrylates represents] The steps are represented by Includes.

[0050] Preferably, in the method, the isocyanate (IC) is Alkoxysilylalkyl isocyanates, such as (triethoxysilyl)-propyl isocyanate; Alkylsilylisocyanates, such as trimethylsilylisocyanate, Alkyl-aryl isocyanates, such as α,α-dimethyl-3-isopropenyl-benzyl isocyanate, 4-isopropylphenyl isocyanate, m-tolyl isocyanate, p-tolyl isocyanate, or 2-phenylethyl isocyanate; Aryl isocyanates, such as phenyl isocyanate or 1-naphthyl isocyanate, Cycloalkyl isocyanates, such as cyclohexyl isocyanate; Alkyl methacrylates, such as 2-isocyanatoethyl methacrylate, Alkyl isocyanates, such as tert.-butyl isocyanate, n-butyl isocyanate, octadecyl isocyanate or dodecyl isocyanate, Sulfonyl isocyanates, such as p-toluenesulfonyl isocyanate is selected from one of the following:

[0051] Preferably, in the method, the reaction is carried out at a temperature between 10 and 40° C., for example at room temperature, without a catalyst (K). More preferably, the reaction is carried out at a temperature higher than 40° C., using a catalyst (K) or a mixture of catalysts selected from non-nucleophilic amine bases and Lewis acids and combinations thereof, such as titanium(IV)(triethanolaminato)isopropoxide, zinc methacrylate, zinc acetate, dibutyltin dichloride, dibutyltin diacetate, DABCO (1,4-diazabicyclo[2.2.2]octane), TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), 2,2-dimorpholinodiethyl ether (DMDEE), bismuth 2-ethylhexanoate, preferably di-n-butyltin dilaurate. When several catalysts are used in combination, particularly the combination of a non-nucleophilic amine and a Lewis acid, such as DABCO and di-n-butyltin dilaurate, is preferred.

[0052] In the case of liquid or fusible isocyanates, the reaction may be carried out without a solvent.Preferably, in said process, the reaction is carried out in a solvent (S) or mixture of solvents, preferably dichloromethane (DCM), trichloromethane (TCM), 1,4-dioxane, dimethylsulfoxide (DMSO), dimethylcarbonate (DMC), more preferably 2-methyltetrahydrofuran (2-MeTHF), even more preferably tetrahydrofuran (THF).

[0053] A further embodiment relates to a photosensitive composition (PC') comprising an ethylenically unsaturated component (a), a thermal initiator and / or a photoinitiator (b) and a stabilizer (c), wherein said stabilizer is a derivative (AAD) as described above in relation to formula I or a derivative obtainable according to the process as described above in relation to formula II.

[0054] Preferably, the photosensitive composition (PC') further comprises a binder (d), said binder being a SIS or SBS block copolymer and / or a binder as previously described above.

[0055] A further embodiment relates to the use of ascorbic acid derivatives having a carbamate functional group (CF), preferably at least two carbamate functional groups, to stabilize heat or radiation sensitive components in a photosensitive composition (PC). Generally, the carbamate functional group has the following structure: [ka] It can be recognized by:

[0056] Preferably, the photosensitive composition (PC) is comprised in a relief precursor, preferably a relief precursor that is developed into a relief structure such as a printing plate or a sleeve. Another embodiment also relates to the use of an ascorbic acid derivative as described above in relation to formula I or obtained according to the method described above in relation to formula II for stabilizing heat or radiation sensitive components in a photosensitive composition, such as a composition used in the photosensitive layer of a relief precursor for producing a printing plate.

[0057] Preferably, the relief precursor is a printing plate or pad, in particular a precursor of the type for non-lithographic printing, said types including precursors for flexographic, gravure or pad printing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Photosensitive composition (PC) A photosensitive composition is understood to be a composition that can be cured by heat and / or electromagnetic radiation (i.e. UV radiation). Curing can be understood as strengthening or hardening of the blend by crosslinking of the polymer chains in the blend. The photosensitive compositions described herein can be used in printing plates, flexographic printing plates, letterpress printing plates, intaglio printing plates, microfluidic devices, microreactors, electrophoretic cells, photonic crystals or optical devices. Partial exposure can be provided.

[0059] Radical initiator (R) A "radical initiator" is typically a species that initiates crosslinking in the photosensitive layer by generating free radicals as a result of, for example, exposure to heat or UV radiation. The term radical initiator can be understood as a compound or substance that can generate radical species under mild conditions, for example, UV exposure and / or heating. In this way, the radical initiator can promote a radical reaction. Suitable radical initiators typically have weak bonds and can be selected on the basis of having small bond dissociation energy. Preferred radical initiators are preferably selected from photoinitiators or photoinitiator systems or thermal initiators.Such initiators are known to those skilled in the art and are described, for example, in Bruce M. Monroe et al., Chemical Review, 93, 435 (1993), RS Davidson, Journal of Photochemistry and Biology A: Chemistry, 73, 81 (1993), M. Tsunooka et al., 25 Prog. Polym. Sci., 21, 1 (1996), FD Saeva, Topics in Current Chemistry, 1 56, 59 (1990), GG Maslak, Topics in Current Chemistry, 168, 1 (1993), HB Shuster et al., JACS, 112, 6329 (1990) and IDFEaton et al., JACS, 102, 3298 (1980), P. Fouassier and JF Rabek, Radiation Curing in Polymer Science and Technology, pages 77 to 117 (1993) or K.K. Dietliker, Photoinitiators for free Radical and Cationic Polymerisation, Chemistry & Technology of UV & EB Formulation for Coatings, Inks and Paints, Volume, 3, Sita Technology LTD, London 1991; or R.S. Davidson, Exploring the Science, technology and Applications of UV and EB Curing, Sita Technology LTD, London 1999.Further initiators are described in JP-A-45-37377, JP-A-44-86516, U.S. Pat. No. 3,567,453, U.S. Pat. No. 4,343,891, EP-P-109772, EP-P-109773, JP63138345, JP63142345, JP63142346, JP63143537, JP4642363, JP59152396, JP61151197, JP6341484, JP2249, and JP24705, JP626223, JP-A-6314340, JP1559174831, JP1304453, and JP1152109. One example of a suitable photoinitiator is benzyl dimethyl ketal (BDMK).

[0060] Ethylenically unsaturated compounds (EC) Preferably, the photopolymer layer (also called photosensitive layer) further comprises at least one component having at least one unsaturated group. Preferably, these components are reactive compounds or monomers suitable for the preparation of a mixture that is polymerizable and compatible with the binder. Useful monomers of this type generally have a boiling point above 100° C. They usually have a molecular weight of less than 3000 g / mol, preferably less than 2000 g / mol. More preferably, ethylenically unsaturated monomers are used that should be compatible with the binder, and that have at least one polymerizable ethylenically unsaturated group. As monomers it is possible to use in particular esters or amides and hydroxyesters of acrylic or methacrylic acid with mono- or polyfunctional alcohols, amines, aminoalcohols or hydroxyethers, esters of fumaric or maleic acid, and allyl compounds. Even more preferred are esters of acrylic or methacrylic acid. Preference is given to 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol diacrylate or trimethylolpropane tri(meth)acrylate. Mixtures of different monomers can of course be used. The combined total amount of all monomers used in the relief-forming layer is generally in each case 1 to 20 wt.-%, preferably 5 to 20 wt.-%, based on the sum of all constituents of the relief-forming layer. The amount of monomers having two ethylenically unsaturated groups is preferably 5 to 20 wt.-%, more preferably 8 to 18 wt.-%, based on the sum of all constituents of the relief-forming layer.

[0061] Binder (B) The preferred binder (B) is a thermoplastic elastomeric block copolymer, such as a diblock or triblock copolymer. Thermoplastics are a class of polymers that can be processed after softening by heating. This behavior is advantageous and creates the possibility of producing the relief precursor in larger quantities, for example by extrusion. Also, when using a thermoplastic elastomeric block copolymer binder, processes such as injection molding, thermoforming and blow molding can be used. The choice of a thermoplastic binder is advantageous over, for example, SBR rubber (which belongs to the thermosetting elastomers), which does not work well in mass extrusion production processes.

[0062] The binder (B) has a first monomer unit which is a vinyl aromatic monomer and a second monomer unit, the second monomer unit being an ene monomer and / or a diene monomer. An ene monomer means a monomer that contains a carbon-carbon double bond (C=C) in its molecular structure. A diene monomer means a monomer that contains two carbon-carbon double bonds (C=C=C) in its molecular structure.

[0063] The vinyl aromatic may be, for example, styrene, alpha-methylstyrene, or vinyltoluene. Styrene is preferred. The diene is preferably butadiene and / or isoprene. These block copolymers may be linear, branched, or radial block copolymers. Generally speaking, they are ABA type triblock copolymers, but may also be AB type diblock polymers, or may have multiple alternating elastomeric and thermoplastic blocks, e.g., ABABA.

[0064] Additionally, star copolymers and / or branched copolymers or combinations thereof may be used.

[0065] Mixtures of two or more different block copolymers may also be used. Commercially available triblock copolymers often contain a certain proportion of diblock copolymers. The diene units may be 1,2- or 1,4-linked. The double bonds in the binder backbone provide the ability for crosslinking between the binders, particularly in the photosensitive layer, to cause hardening upon exposure of the relief precursor. Thermoplastic elastomeric block copolymers with styrene and block and random styrene-butadiene central blocks may also be used. Of course, mixtures of two or more thermoplastic-elastomeric binders may also be used, provided that there is no negative effect on the properties of the relief-forming layer as a result. As well as the thermoplastic-elastomeric block copolymers mentioned above, the photopolymerizable layer may also contain further elastomeric binders other than the block copolymers. This type of additional binder, also called secondary binders, allows the properties of the photopolymerizable layer to be modified. An example of a secondary binder is vinyltoluene-a-methylstyrene copolymer.

[0066] These polymeric binders generally comprise 20-98%, preferably 50-90% by weight of the total composition. Copolymers such as styrene-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) diblock or triblock copolymers show advantages over random copolymers such as styrene-butadiene rubber SBR.

[0067] Random copolymers such as SBR should not be confused with styrene-butadiene block copolymers, although they can be derived from the same monomers. Random SBR is often used in elastomeric products such as tires, shoe soles, or seals. Due to its irregular molecular structure, SBR does not have a sufficiently pronounced microphase separation. As a result, uncured SBR polymer without fillers will not keep its shape during storage. Therefore, the addition of fillers as well as the simultaneous curing of SBR is required to preserve the shape and improve its physical properties. Nevertheless, any fillers added to the printing plate precursor formulation will scatter UV light and disrupt the crosslinking process during the intended UV light curing.

[0068] Curing of SBR, typically accomplished by reaction with sulfur, makes the filled SBR polymer elastomeric. Because the structure is held together by chemical bonds, the cured SBR decomposes rather than melts under heat and is therefore not thermoplastic.

[0069] In contrast to (thermosetting) SBR random polymers, styrene-butadiene block copolymers are thermoplastic elastomers. They can be melted, mixed and molded under heat without the need for solvents. The block copolymer structure, e.g. SBS or SIS, results in microphase separation of polystyrene and polybutadiene or polyisoprene domains. The elastomeric behavior is rooted in this network of physical crosslinks of elastic blocks (polybutadiene) and restraining blocks (polystyrene). Also, printing plate precursors based on styrene-butadiene block copolymers mostly retain their shape for a longer storage time, typically 1-2 years after production. Long storage times are essential for printing plate precursors, since their curing is not done on-site but in the repro house or printing facility. In conclusion, in contrast to block copolymers, SBR as a random copolymer is not a suitable binder for printing plate precursors. Examples of binders are shown below.

[0070] [ka]

[0071] The binder preferably has a total styrene content in the range of 3-50%, preferably 8-38%, more preferably 10-35%, and most preferably 14-32%. These ranges improve the Newtonian behavior of the binder and allow setting both the kinematic and dynamic viscosity of the binder suitable for extrusion production.

[0072] Preferably, the binder is selected from binders (B) selected from styrene-butadiene-styrene (SBS) triblock copolymers and / or styrene-isoprene-styrene (SIS) triblock copolymers.

[0073] In one embodiment, the binder is selected from SBS triblock copolymers having a styrene content in the range of 8 to 48%, preferably 13 to 43%, more preferably 18 to 38%, for example approximately 28%.

[0074] In one embodiment, the binder is selected from SIS triblock copolymers having a styrene content in the range of 3 to 27%, preferably 5 to 25%, for example approximately 15%.

[0075] In one embodiment, the binder is a diblock copolymer or comprises a triblock copolymer with a diblock proportion in the range of 5-30%, preferably 8-28%, more preferably 10-24%, for example around 17% or 19%, which proportions have been found to be suitable for extrusion processes.

[0076] Stabilizer (S1) The term "stabilizer" is understood to mean a member that preferably has a stabilizing effect, but is not limited thereto functionally. Stabilizer S1 is a vitamin or vitamin derivative, as further described below.

[0077] Vitamins or vitamin derivatives The term vitamin is well known and includes several chemical structures. Traditionally, vitamins are divided into two groups: water-soluble and fat-soluble vitamins. The water-soluble vitamins are thiamine, riboflavin, niacin, vitamin B6, folic acid, vitamin B12, pantothenic acid, biotin, and vitamin C. The fat-soluble vitamins are vitamin A, vitamin E, vitamin D, and vitamin K.

[0078] Surprisingly, it has now been found that vitamins and their derivatives have a stabilizing effect against the thermal and mechanical stresses to which the melt of the thermoplastic elastomeric binder system is exposed during the production of the relief precursor. Furthermore, vitamins can be used in the relief precursor to improve storage stabilization. Also, the development properties of the precursor can be improved so that the relief formed therefrom can achieve improved imaging properties. These imaging properties include in particular a smaller dot size after development, and the resulting dot size can be closer to the target value. Representative types of vitamins are shown in the table below.

[0079] [Table 1] [Table 2]

[0080] In one embodiment, the stabilizer (S1) is selected from one or more of folic acid (vitamin B9), ascorbyl palmitate (vitamin C derivative), and pyridoxine hydrochloride (vitamin B6).

[0081] These stabilizers have been found to achieve high thermal stabilization, such that the relief precursor can be stored for extended periods of time without affecting the quality of the relief structure formed thereon.

[0082] In a preferred embodiment, the structure of the vitamin or vitamin derivative comprises a first group (G1) selected from an aromatic or cyclic unsaturated group to which at least one -OH group is attached, and preferably a second group (G2), e.g. an apolar moiety, said second group being a linear or branched carbon chain lacking a permanent electric dipole moment or with a minimal dipole moment. The cyclic unsaturated group preferably comprises a furan group containing a 5-membered aromatic ring of 4 carbon atoms and one oxygen atom. The number of carbon atoms in the backbone of the second group is preferably selected from 2 to 25, 3 to 20, 3 to 17, 3 to 16 carbon atoms. The chain may be substituted, so long as the symmetry of the charge density distribution in the chain is kept equally distributed, so that the dipole moment in the chain is lacking or minimal. The second group may improve compatibility with the organic binder system in the photosensitive composition (PC), while the first group may avoid the initiation of unintended curing reactions, e.g. by trapping free radicals. Preferably the first group (G1) comprises at least two -OH groups, each of which is attached to a doubly bonded C-atom.

[0083] In one embodiment, the stabilizer (S1) comprises a substructure selected from hydroxytetronic acid (HTAD) or modifications thereof. The modifications may improve compatibility with binder systems.

[0084] A preferred stabilizer (S1) for stabilizing heat and / or radiation sensitive components contains hydroxytetronic acid as a substructure. [ka]

[0085] Derivatives of hydroxytetronic acid (HTAD) are believed to produce a stabilizing effect and therefore may be beneficially included in photosensitive compositions. Hydroxytetronic acid derivatives, also referred to herein as HTAD, are preferably reductones, RC(OH)=C(OH)C(=O)R, containing an enediol structure stabilized by conjugation and hydrogen bonding with adjacent carbonyl groups. Reductones are efficient reducing agents and antioxidants capable of reacting with oxygen and hydroxyl radicals.

[0086] Particular efficiency has been found when the HTAD derivative further contains one or more solubilizing moieties, which contribute to the uniform distribution of the respective binder and its various phases. For example, SBS and SIS rubbers contain styrene and butadiene or isoprene phases that need to be properly stabilized.

[0087] Depending on the overall formulation, for example, monomers may accumulate in one or both of the phases depending on the particular monomer structure. By utilizing the appropriate combination of HTAD derivatives, binders and monomers, exceptional stabilization under the influence of air and heat is achieved.

[0088] In one embodiment, the stabilizer (S1) is an ascorbic acid derivative, such as ascorbyl palmitate, L-ascorbic acid, D-isoascorbic acid, L-ascorbyl monostearate, sodium L-ascorbate, and sodium D-isoascorbate. Representative structures are shown below.

[0089] [ka]

[0090] In one embodiment, the vitamin or vitamin derivative is selected from sodium D-isoascorbate (SDI) or ascorbyl palmitate (AP).

[0091] In one embodiment, the stabilizer (S1) is selected from ascorbic acid or vitamin derivatives, with the proviso that the stabilizer is not selected from ascorbic acid (176 g / mol), L-ascorbyl monostearate (AMS) (442 g / mol), sodium L-ascorbate (198 g / mol) and sodium D-isoascorbate (198 g / mol).

[0092] The preferred stabilizer is ascorbyl palmitate (AP) (414 g / mol) because it has improved free radical scavenging properties.

[0093] The stabilizer (S1) is preferably present in a concentration of 0.1 to 10 wt.%, preferably 0.1 to 8 wt.%, more preferably 0.2 to 6 wt.%, based on the total weight of the composition. In this way, it has been found that the extrusion stability can be improved without or with a minimal effect on the curability of the photosensitive composition. By reducing the (undesirable) effect on the (final) curability, e.g. the curing during development of the relief precursor, final printing properties can be achieved.

[0094] In a preferred embodiment, the stabilizer (S1) can be an ascorbic acid derivative (AAD) represented by Formula I described herein or a stereoisomer thereof.

[0095] In a preferred embodiment, the ascorbic acid derivative (AAD) is a) providing ascorbic acid (AA), preferably either D-ascorbic acid or L-ascorbic acid; b) adding an isocyanate (IC) and reacting the isocyanate with ascorbic acid to obtain an ascorbic acid derivative (AAD), wherein the isocyanate (IC) is represented by formula II as described herein; is obtained by To obtain different degrees of functionalization and / or preferred properties, the isocyanate component can be varied from 0.1 to 10 equivalents relative to ascorbic acid (=1 molar equivalent), preferably from 0.1 to 5 equivalents, more preferably from 0.5 to 3 equivalents, even more preferably from 1 to 2 equivalents, and most preferably 2 equivalents.

[0096] The reaction temperature can vary from 0 to 80°C, more preferably from 20 to 80°C, and even more preferably from 60 to 80°C. Various catalysts can be selected from non-nucleophilic amine bases and Lewis acids and their combinations (e.g. titanium(IV)(triethanolaminato)isopropoxide, zinc methacrylate, zinc acetate, dibutyltin dichloride, dibutyltin diacetate, (1,4-diazabicyclo[2.2.2]octane (DABCO), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), DBU (1,8-diazabicyclo(5.4.0)undec-7-ene), DMDEE (2,2-dimorpholinodiethyl ether), bismuth 2-ethylhexanoate). The catalyst concentration can vary from 0.01 to 1 equivalent relative to ascorbic acid (=1 molar equivalent), more preferably 0.02 to 0.5 equivalent, even more preferably 0.03 to 0.2 equivalent, most preferably 0.05 to 0.1 equivalent).

[0097] A variety of solvents can be used, such as dichloromethane (DCM), trichloromethane (TCM), 1,4-dioxane, dimethylsulfoxide (DMSO), dimethylcarbonate (DMC), more preferably 2-methyltetrahydrofuran (2-MeTHF), and even more preferably tetrahydrofuran (THF).

[0098] Solvents can be tested and concentrations varied from 5-99 w% solvent, preferably 30-90 w% solvent, more preferably 50-90 w% solvent, even more preferably 50-70 w% solvent, and most preferably 60-70 w% solvent. In the case of liquid isocyanates, it is possible to carry out the reaction without additional solvent.

[0099] Second stabilizer (S2) It has been found that when a vitamin or vitamin derivative, particularly an ascorbic acid derivative, is combined with a second stabilizer typically used in relief precursor compositions, such combination synergistically enhances the thermal stability of the composition.

[0100] The second stabilizer S2 is preferably selected from one of the following classes: phenolic, phenolic and acrylate, thioether, hindered amine, phenolic and amine, amine, thioether amine, polyfunctional amine and acrylate. Surprisingly, vitamin derivatives, preferably ascorbic acid derivatives, can synergistically improve the thermal stability of the second stabilizer.

[0101] In one embodiment, the second stabilizer (S2) is 2,6-di-tert-butyl-4-methylphenol (BHT), 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), tris(2,4-di-tert-butylphenyl)phosphite, didodecyl 3,3′-thiodipropionate, 1,5,8,12-tetrakis[4,6-bis(N-butyl-N-1,2,2,6,6-pentamethyl-4-piperidylamino)-1,3,5-triazin-2-yl]- ... and selected from one or more of azododecane, 2',3-bis[[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide, bis[4-(2-phenyl-2-propyl)phenyl]amine, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, tertiary amines and acrylates, preferably 1H-azepine-1-propanoic acid, hexahydro-,2,2-bis[[(1-oxo-2-propen-1-yl)oxy]methyl]butyl ester or 2,2-bis[[(1-oxo-2-propen-1-yl)oxy]methyl]butyl hexahydro-1H-azepine-1-propanoate.

[0102] Additives The photopolymer layer may include additional components selected from the group consisting of additional polymers, fillers, plasticizers, antiblocking agents, monomers, additives (e.g., stabilizers, dyes), crosslinkers, binders, color forming compounds, dyes, pigments, antioxidants, and combinations thereof.

[0103] Plasticizer The photosensitive composition (PC) may further comprise a plasticizer. Suitable plasticizers include modified and unmodified natural oils and resins, such as high-boiling paraffinic, naphthenic or aromatic mineral oils, synthetic oligomers or resins, such as oligostyrenes, high-boiling esters, oligomeric styrene-butadiene copolymers, oligomeric alpha-methylstyrene / p-methylstyrene copolymers, liquid oligobutadienes, especially those with a molecular weight of 500 to 5000 g / mol, or liquid oligomeric acrylonitrile-butadiene copolymers or oligomeric ethylene-propyl-ene-diene copolymers. Preference is given to polybutadiene oils (liquid oligobutadienes), especially those with a molecular weight of 500 to 5000 g / mol, high-boiling aliphatic esters, such as alkyl esters, especially of mono- and dicarboxylic acids, for example stearic acid esters or adipic acid esters, and mineral oils. Particular preference is given to high-boiling, substantially paraffinic and / or naphthenic mineral oils. For example, it is possible to use what are called paraffin-based solvates and specialty oils. With regard to mineral oils, the skilled artisan distinguishes between industrial white oils, which may also contain very low aromatic content, and medical white oils, which are substantially free of aromatic compounds. They are commercially available and are equally well suited. Particularly popular as plasticizers are white oils or oligomeric plasticizers, such as, in particular, polybutadiene oils, carboxylic acid esters, phthalates. For this, reference may be made, for example, to EP 992849 and EP 2279454. In some embodiments, bio-based plasticizers can be used to enhance the processing behavior, for example during extrusion processes. Bio-based plasticizers are typically derived in part from renewable biological sources, such as plants (e.g., agricultural crops or wood), microorganisms (e.g., algae or yeast), or animals, as described in International Application: PCT / EP2022 / 062430, which is incorporated herein by reference.

[0104] Bio-based plasticizers are derived at least partially from renewable biological sources such as plants (e.g., agricultural crops or wood), microorganisms (e.g., algae or yeast), or animals. Bio-based plasticizers are environmentally friendly and often, but not necessarily, biodegradable. Bio-based materials may be chemically altered or modified with synthetic compounds, for example to change their physical and / or chemical properties. In that case, they still remain bio-based materials. These plasticizers are generally used to maintain softness and flexibility over a range of temperatures. These plasticizers can be at least partially replaced by other plasticizers, such as synthetic plasticizers. Many of the non-bio-based plasticizers, especially the so-called phthalates, are harmful to human health and can affect hormone balance. Others are based on mineral oil or polybutadiene and are not readily biodegradable. It is therefore advantageous to replace them at least partially by bio-based plasticizers. The inventors have also found that when bio-based plasticizers are used for thermal development, higher relief depths can be achieved at all concentrations examined. Furthermore, the inventors have found that using, for example, rapeseed oil instead of mineral oil allows for faster flow rates, resulting in shorter process times. More preferably, the bio-based plasticizer is a vegetable oil, a fatty acid and / or a fatty acid ester with mono- and polyfunctional alcohols having no more than one free hydroxyl group. More preferably, the bio-based plasticizer is one or more of rapeseed oil, sunflower oil, soybean oil, palm oil, palm kernel oil, coconut oil, medium chain triglyceride (MCT) oil and / or linseed oil.Further examples are acai oil, wool fat, ahiflower oil, algea oil, aloe vera, amaranth oil, apricot kernel oil, argan oil, avocado oil, babassu oil, baobab oil, beeswax, black cumin oil, black cumin seed oil, black currant oil, borage oil, Brazil nut oil, broccoli seed oil, calendula oil, camelina oil, candelilla wax, carnauba wax, castor oil, cocoa butter, chia oil, hazelnut oil, cocoa butter, corn oil, cottonseed oil, cupuaçu butter, evening primrose oil, fish oil, and the like. Oil, glycerol, grapeseed oil, peanut oil, hazelnut oil, hemp oil, high oleic canola oil, high oleic soybean oil, high oleic sunflower oil, illipe butter, jasmine oil, jojoba oil, kukui nut oil, lanolin, bay leaf oil, macadamia nut oil, marula oil, mango butter, manketti oil, marula oil, meadowfoam seed oil, milk thistle oil, moringa oil, murumuru butter, mustard seed oil, olive oil, vegetable oil (olus oil), omega-3-6-9-oil, palm olein, palm stearin, paradise nut oil, passion fruit seed oil, peach kernel oil, peanut oil, pecan nut oil, perilla oil, pistachio nut oil, plum kernel oil, pomegranate oil, poppy seed oil, pumpkin seed oil, hydrogenated rapeseed oil, raw wool fat, rice bran oil, rosehip oil, sacha inchi oil, safflower oil, monkey fat, sea buckthorn oil, sesame oil, shea butter, hydrogenated soybean oil, partially hydrogenated soybean oil, squalane, hydrogenated sunflower oil, sunflower wax, Japan wax, tallow, tamanu oil, walnut oil, wheat germ oil, wool fat, wool alcohol. Different types of plasticizers may be combined to fine-tune the properties of the layer. For example, bio-based plasticizers may be used as a replacement or in addition to the plasticizers listed above. The amount of plasticizer optionally present can be determined according to the desired properties of the layer.

[0105] The bio-based plasticizer may have one or more of the following characteristics: The plasticizer is a bio-based plasticizer, preferably vegetable oils, fatty acids and / or fatty acid esters of mono- and polyfunctional alcohols. The plasticizer is characterized by a UV transmittance at 365 nm of a 33 wt % solution of the plasticizer in n-hexane of greater than 1%, preferably greater than 10%, more preferably greater than 50%, and even more preferably greater than 60%. The plasticizer is characterized by a Gardner color lower than 7 according to ISO 4630:2015. The plasticizers are characterized by a hydroxyl value of less than 430, preferably less than 250, and even more preferably less than 168 according to ASTM D1957-86. The plasticizer has an iodine value according to ISO 3961:2018 of less than 200, preferably less than 150. The plasticizer has a Hansen solubility parameter δt in the range of 16.0 to 20.5, preferably in the range of 16.0 to 17.5.

[0106] Determination of UV transmittance: UV transmittance at 365 nm was measured in a macrocuvette 110-QS, 10 mm, at a plasticizer concentration of 5 parts by weight in n-hexane. UV / Vis spectra were recorded on a Varian Cary 50, Scan Software version: 02.00, Beam mode: Dual Beam. Baseline correction was performed using a blank sample of pure n-hexane and applied using the instrument's built-in software.

[0107] Determination of light transmittance: Pure oil was filled into a macrocuvette 110-QS, 10 mm, the cuvette was placed in a density meter Gretag Macbeth D 200 II (measuring tube: V(λ), measuring aperture: 3 mm diameter) and the light transmittance was measured by pressing the probe head into the macrocuvette. The measurement of a transparent MCT-oil, which is resistant to oxidation due to the lack of double bonds, was set as the standard for 100% transmittance. The average value of three measurements was determined. For further details on biobased plasticizers, reference is made to international application PCT / EP2022 / 062430, which is incorporated herein by reference.

[0108] The concentration of the plasticizer in the photopolymer layer (also referred to herein as the photosensitive layer) is preferably in the range of 3 to 70 wt %, preferably in the range of 5 to 65%, more preferably in the range of 10 to 65 wt %, and even more preferably in the range of 20 to 60 wt %, based on the total weight of the photopolymer layer.

[0109] Relief Precursor (RP) The relief precursor (RP) comprises the above-mentioned photopolymer layer (also called photosensitive layer L2) applied to a dimensionally stable support (L1), also called dimensionally stable carrier layer (L1). Such a support layer can be a PET sheet. Preferably, the carrier layer L1 comprises a metal sheet, steel, an alloy, a natural or artificial polymer, a polymer blend, a polymer film, or any combination thereof. Examples of suitable dimensionally stable carriers are plates, foils and cylindrical tubes, known as cones and sleeves, made of metals, such as steel, aluminum, copper or nickel, or plastics, such as polyethylene terephthalate, polybutylene terephthalate, polyamide or polycarbonate, woven or non-woven fabrics, such as woven glass fiber fabrics, or composite materials made of glass fiber and plastic. Particularly suitable as dimensionally stable carriers are dimensionally stable carrier foils or metal sheets, examples being polyethylene or polyester foils or steel or aluminum sheets. The carrier foils or metal sheets generally have a thickness of 50 to 1500 μm, preferably 75 to 400 μm, for example approximately 250 μm. If steel is used as the carrier material, steel sheets having a thickness of 0.05 to 0.3 mm are preferred. For protection against corrosion, preference is given to the use of tin-plated steel sheets. These carrier foils or carrier sheets may be coated with a thin adhesion-promoting layer, for example a layer having a thickness of 0.1 μm to 2 μm, on the side of the carrier foil facing the radiation-curable relief-forming layer. In a preferred embodiment, the carrier layer is a PET carrier layer made of polyethylene terephthalate.

[0110] Typically, at least the photosensitive layer L2 comprises a photosensitive composition as described herein. Preferably, the photosensitive layer L2 has a thickness in the range of 25 μm to 7000 μm, preferably 0.01 to 4 mm, more preferably 0.02 to 3 mm, and most preferably 0.03 mm to 3 mm.

[0111] The relief also comprises a mask layer L3, which comprises at least a compound capable of absorbing electromagnetic radiation and a component that can be removed by ablation (also called digital plate precursor).

[0112] The reference of layers L1, L2 and L3 cannot and is not intended to limit them to a particular order. The relief precursor may include further layers, if necessary, such as an oxygen barrier layer, an adhesive layer, a release layer or disbonding layer, a UV / VIS light and / or IR light absorbing layer, a monomer diffusion control layer, a surface adjusting layer, a protective layer, a cover foil, a cover film or a combination thereof. In one embodiment, there may be an adhesive coating layer with an optional top coating layer thereon. Such an adhesive coating layer may be, for example, a layer of polyurethane adhesive coating material, for example as described in DE3045516.

[0113] Preferably the mask layer is an integral layer of the relief precursor and is in direct contact with the photosensitive layer or with a functional layer arranged between the photosensitive layer and the mask layer. This functional layer is preferably a barrier layer and blocks oxygen. The mask layer can be imageable by ablation and removable by solvent or by thermal development. The mask layer is heated and removed by irradiation with high energy electromagnetic radiation, thereby forming an imagewise structured mask, which is used to transfer the structure to the relief precursor. To do so the mask layer is not transparent in the UV region and may absorb radiation in the VIS-IR region of the electromagnetic spectrum. The layer can then be heated and ablated using VIS-IR radiation. The optical density of the mask layer in the UV region of 330-420 nm is in the range of 1-5, preferably in the range of 1.5-4, more preferably in the range of 2-4.

[0114] The layer thickness of the ablative mask layer may be in the range of 0.1 to 5 μm, preferably 0.3 to 4 μm, and more preferably 1 to 3 μm. 2 The laser sensitivity of the mask layer (measured as the energy required to ablate the 2 in the range of 0.3 to 5 J / cm 2 in the range of 0.5 to 5 J / cm 2 The range may be:

[0115] Development of the relief precursor (RP) and production of a relief (RS) with a relief structure The relief precursor can be imaged by ablation of a mask layer, by exposure through a mask, or by direct imaging. In this way, the precursor can be developed into a relief (e.g., a cliché) with a relief structure. The mask layer can be a separate layer and is applied to the relief precursor after removal of a possibly present protective layer or an essential layer of the precursor that is in contact with the relief layer or one of the optional layers above the relief layer and is covered by a possibly present protective layer.

[0116] The mask layer may also be a commercially available negative that can be produced by a photographic process based on silver halide chemistry. The mask layer may be a composite layer material in which a transparent layer is produced in an otherwise non-transparent layer by imagewise exposure, as described for example in EP-A-3 139 210, EP-A-1 735 664, EP-A-2 987 030, EP-A-2 313 270. This may be done by ablation of a non-transparent layer on a transparent carrier layer, as described for example in US Pat. No. 6,916,596, EP-A-816 920, or by selective application of a non-transparent layer to a transparent carrier layer, as described for example in EP-A-992 846, or may be written directly onto the relief-forming layer, for example by printing with a non-transparent ink by inkjet, as described for example in EP-A-1 195 645.

[0117] The image-wise removal of the mask layer is preferably carried out using an ablation technique. Typically, the electromagnetic radiation for ablating the mask is radiation having a wavelength generally in the range of 300 nm to 20000 nm, preferably in the range of 500 nm to 20000 nm, particularly preferably in the range of 800 nm to 15000 nm, very particularly preferably in the range of 800 nm to 11000 nm. In addition to solid-state lasers, gas lasers or fiber lasers can also be used. Preferably, in laser ablation, Nd:YAG lasers (1064 nm) or CO2-lasers (9400 nm and 10600 nm) are used. For selective removal of the mask layer, one or more laser beams are controlled so that the desired print image is generated.

[0118] Direct image exposure can be achieved in that the areas to be crosslinked are selectively exposed. This can be achieved, for example, with one or more appropriately controlled laser beams, by using a monitor where specific image points are activated to emit radiation, by using movable LED strips, by LED arrays where individual LEDs are specifically switched on and off, by using an electronically controllable mask that switches the image points transparent to allow radiation from the radiation source to pass through, by using a projection system where the image points are exposed to radiation from the radiation source by appropriate orientation of mirrors, or by a combination of these. Preferably, direct exposure is performed by a controlled laser beam or a projection system with mirrors. The absorption spectrum of the initiator or initiator system and the emission spectrum of the radiation source must at least partially overlap.

[0119] The wavelength of the electromagnetic radiation is in the range of 200 nm to 20000 nm, preferably in the range of 250 nm to 1100 nm, particularly preferably in the UV range, very particularly preferably in the range of 300 nm to 450 nm. In addition to broadband irradiation with electromagnetic radiation, it may be advantageous to use narrowband or monochromatic wavelength ranges, which can be generated, for example, by using suitable filters, lasers or light-emitting diodes (LEDs). In these cases, the wavelengths 350 nm, 365 nm, 385 nm, 395 nm, 400 nm, 405 nm, 532 nm, 830 nm, 1064 nm (and about 5 nm to 10 nm below and / or above this) themselves or combinations thereof are preferred.

[0120] The relief is produced by exposure to electromagnetic radiation through a mask film. Upon exposure, the exposed areas are crosslinked, whereas the unexposed areas of the precursor remain soluble or liquefiable and are removed by a suitable method. If an imaged mask is present, the irradiation can be widespread, or, when working without a mask layer, the irradiation can occur in an image-wise manner in small areas (practically dot-like) by a guided laser beam or by a spatially divided projection of electromagnetic radiation. In this case, the wavelength of the irradiated electromagnetic radiation is in the range of 200-2000 nm, preferably in the range of 200-450 nm, more preferably in the range of 250 nm-405 nm. The irradiation can occur continuously, or in the form of pulses, or in several short periods of continuous radiation. In addition to broadband radiation of electromagnetic radiation, it can be advantageous to use narrowband or monochromatic wavelength ranges, as can be produced by means of suitable filters, lasers or light-emitting diodes (LEDs).

[0121] In these cases, wavelengths in the range of 350, 365, 385, 395, 400, 405, 532, 830, 1064 nm individually (and about 5-10 nm above and / or below) or combinations are preferred. The intensity of the radiation here can be varied over a wide range, ensuring that a sufficient dose is used to cure the radiation-curable layer sufficiently for the subsequent development procedure. The radiation-induced reaction, possibly after further thermal treatment, must proceed sufficiently until the exposed areas of the radiation-sensitive layer become at least partially insoluble and therefore cannot be removed in the development step.

[0122] The intensity and dose of radiation depend on the reactivity of the formulation and the duration and efficiency of development.

[0123] The radiation intensity is 1 to 15,000 mW / cm 2 in the range of 5 to 5000 mW / cm 2 in the range of 10 to 1000 mW / cm 2 The radiation dose ranges from 0.3 to 6000 J / cm 2 in the range of 3 to 100 J / cm 2 in the range of 6 to 20 J / cm 2 The exposure to the energy source can also be carried out in an inert atmosphere such as noble gases, CO2 and / or nitrogen, or under a liquid that does not damage the relief precursor. The exposure through the mask can be carried out, for example, by using optical elements for beam expansion, by a two-dimensional arrangement of multiple point or line sources (e.g. light guides, emitters) such as fluorescent strip lamps arranged next to each other, by moving a line source or an elongated arrangement of LEDs (array) relative to the relief precursor, for example by a constant movement of the LEDs or a combination thereof. Preferably, a relative movement of a fluorescent strip lamp or one or more LED strips and the relief precursor arranged next to each other is used.

[0124] Irradiation can be done continuously with continuous radiation, in pulses, or in multiple short bursts.

[0125] The removal of the non-hardened areas of the precursor is preferably performed by treatment with heat and a developing material configured to adsorb the non-hardened material. More preferably, in step d) the precursor is heated to a temperature in the range of 70-200°C, preferably in the range of 80-180°C, more preferably in the range of 90-165°C. Heating of the exposed relief precursor can be performed by all techniques known to those skilled in the art, such as, for example, irradiation with IR light, the action of hot gas (e.g. air), the use of hot rollers, or any desired combination of these. To remove the (viscous) liquid areas, it is possible to use all techniques and processes familiar to those skilled in the art, such as, for example, spraying, suction, dabbing, blasting (by particles and / or droplets), stripping, wiping, transfer to a developing medium, and any desired combination of these. Preferably the liquid material is taken up (absorbed and / or adsorbed) by the developing medium which is in successive contact with the heated surface of the relief precursor. The procedure is repeated until the desired relief height is reached. The development media that can be utilized are papers, woven and nonwoven fabrics, and films capable of incorporating liquefied materials and can be composed of natural and / or polymeric fibers. Preference is given to the use of nonwoven fabrics or nonwoven fibrous webs of polymers such as cellulose, cotton, polyester, polyamide, polyurethane, and any desired combinations thereof that are stable at the temperatures used in development.

[0126] Alternatively, the precursor is treated with a developer to dissolve the non-cured material. The techniques used in this development step may be any that are familiar to those skilled in the art. The solvent or mixtures thereof, the aqueous solutions and the aqueous-organic solvent mixtures may contain auxiliaries that stabilize the formulation and / or increase the solubility of the components of the non-crosslinked regions. Examples of such auxiliaries are emulsifiers, surfactants, salts, acids, bases, stabilizers, corrosion inhibitors and suitable combinations thereof. For development with these solutions, it is possible to use all the techniques known to those skilled in the art, such as, for example, immersion, washing or spraying with the development medium, brushing in the presence of the development medium and suitable combinations thereof. Preference is given to development with neutral aqueous solutions or water and removal assisted by a rotating brush or brush web. Another way of influencing the development is to control the temperature of the development medium and to speed it up, for example by increasing the temperature. In this step, it is also possible to remove further layers still present on top of the radiation-sensitive layer, provided that they are separated during development and can be sufficiently dissolved and / or dispersed in the development medium.

[0127] Optionally, one or more steps of post-treatment, post-exposure and / or detackification are carried out. These include, for example, heat treatment, drying, treatment with electromagnetic waves, plasma, gas or liquid, attachment of identification features, cutting into a format, coating and any desired combination of these. Heat treatment can be used, for example, to initiate and / or complete reactions, to increase the mechanical and / or thermal stability of the relief structure and to remove volatile constituents. For heat treatment, known techniques can be used, for example heating using heated gas or liquid, IR radiation and any desired combination of these. In these cases, ovens, blowers, lamps and any desired combination of these can be used. In addition to disbanding, surface modification can also be achieved with treatment with gas, plasma and / or liquid, especially if more reactive substances are also used. Treatment with electromagnetic radiation can be used, for example, for the purpose of detackifying the surface of the relief structure and initiating and / or completing polymerization and / or crosslinking reactions. In this case, the wavelength of the irradiated electromagnetic waves is in the range of 200 to 2000 nm. EXAMPLES

[0128] Preparation of Test Compositions and Relief Precursors Plates were made with the following test compositions: 10 parts by weight of hexanediol diacrylate (HDDA) as an ethylenically unsaturated compound; 2.0 parts by weight of benzyl dimethyl ketal (BDK) as a photoinitiator; 21 parts by weight of liquid polybutadiene polymer (PBP) as a plasticizer; 1.1 parts by weight of further components, such as additives and dyes (A), 59 to 66 parts by weight of a binder (B), an SBS triblock copolymer having a styrene content of about 28.5% and a diblock proportion of approximately 17% (hence SBS-rubber based), and 0 to 6.5 parts by weight of a stabilizer (S).

[0129] In the given examples, the amount of stabilizer was varied from 0 to 6.5 parts by weight, with the excess being balanced by the amount of binder, respectively.

[0130] The components were dissolved in the solvent toluene (also known as methylbenzene) and heated under reflux to obtain a homogeneous solution (concentration in toluene: 45 wt.%).

[0131] The solution was then cast onto a carrier sheet, the plate thickness was controlled using a doctor blade with a gap of 3 mm to the carrier sheet (175 μm thick PET film).

[0132] The solvent was allowed to evaporate for 16 hours at room temperature, followed by heating at 65°C for 4 hours. To allow digital imaging, a mask layer (ML) coated on a cover sheet (CL) was laminated onto the relief precursor using an Excelam-Q laminator (GMP Deutschland GmbH, Germany). Lamination was performed at a heated roll temperature of 110°C, a speed of 8.8 mm / s, and a gap of 1.5 mm. To finish the lamination, the cast plate was sandwiched between two aluminum plates and kept at 65°C for 3 hours.

[0133] Sample evaluation Thermal Melt Stability Thermal melt stability was assessed by recording the melt viscosity during heating. Crosslinking of the samples was recorded as an increase in viscosity. Oscillatory rheological measurements were performed under isothermal (T = 160 °C) conditions using a Kinexus lab+ rheometer (Malvern Instruments Ltd., UK). Data were recorded using the corresponding software rSPACE version 1.76 (Malvern Instruments Ltd., UK). As measurement geometry a parallel plate with an upper plate of 2.5 cm diameter was chosen. As samples a disk of relief precursor with a diameter of 2.5 cm was used. Prior to the measurements any foils (e.g. cover sheets) and mask layers were removed from the relief precursor. Measurements were performed in oscillatory single frequency mode. The frequency was set at 1 Hz. The gap between the parallel plates was kept constant for each sample thickness. Data points were recorded every 15 seconds. Complex shear viscosity η * was monitored over time t. The "start time of crosslinking" was defined as "Δt = 15 s with a differential coefficient Δη * The onset time was specified as the time when the thermal stability and mechanical stress stability are increased.

[0134] Print version evaluation To obtain the clichés, a laser ablative mask was imaged on the front side with a TfxX20 laser (Flint Group Germany GmbH, Germany, rotation speed: 10-11 times / s, power: 35 W (100% intensity)). The relief precursor was exposed to UV light from the backside through the carrier foil for 20-40 s and from the frontside through the mask layer for 15 min. There was no active heating during exposure at room temperature (approximately 18-25 °C). As a result of the crosslinking reaction resulting from the exposure, the temperature of the plate rose to approximately 40 °C (machine type: Combi FIII (Flint Group Germany GmbH, Germany), UVA intensity mW / cm). 2, UVA tube type: Philips TL 80W / 10-R). Non-polymerized material and residual black mask layer were removed using a nyloflex® Digital Washer FIII (Flint Group Germany GmbH, Germany) and nylosolv® A (Flint Group Germany GmbH, Germany) as effluent solvent at a solvent temperature of 35°C, effluent speed of 230-240 mm / min, and brush height of 0 mm. After effluent, the plate was dried at 60°C for 2 h (Combi FIII (Flint Group Germany GmbH, Germany)). Post-curing was performed from the front side with UVA and UVC (machine type: Combi FIII (Flint Group Germany GmbH, Germany)), UVA exposure time: 10 min, UVA intensity: 11 mW / cm 2 , UVA tube type: Philips TL 60W / 10-R, UVC exposure time: 5 minutes, UVC intensity: 13mW / cm 2 , UVC tube type Philips TUV 75W HO G75 T8, UVA and UVC post-exposure started simultaneously).

[0135] Example 1 The test compositions described above were used. In this example, each sample had a particular type and / or concentration of stabilizer. Butylhydroxytoluene (BHT), also known as 2,6-di-tert-butyl-4-methylphenol, was used as the reference stabilizer. A representative structure is shown below. [ka]

[0136] As a stabilizer in the present invention, the vitamin derivative ascorbyl palmitate (AP) was used, which can be understood as a fatty acid ester of ascorbic acid and palmitic acid, and the representative structure is shown below. [ka]

[0137] -(CH2) 14 The carbon chain being a CH3 chain is believed to improve the compatibility of the vitamin derivative in the SBS rubber. Furthermore, the surfactant-like structure of the vitamin derivative may result in improved stabilization against oxygen at the interface.

[0138] Table 1 shows the type of each stabilizer, its concentration (wt.% and molar equivalent) and the onsite time of crosslinking obtained. For the onset time of crosslinking t, the average value of two measurements was used.

[0139] [Table 3]

[0140] The stabilizer ascorbyl palmitate (AP) was found to have a longer initiation time for crosslinking than an equimolar amount of tert-butyl hydroxytoluene (also known as BHT) (Table 1), indicating better stabilization since it took longer before the viscosity increased due to the addition and crosslinking reaction. The reference ascorbic acid was not compatible with the formulation under test and therefore could not be tested.

[0141] Example 2 The test compositions described above were used. In this example, ascorbyl palmitate was tested as a stabilizer at various concentrations and compared to plates containing no additional stabilizer.

[0142] [Table 4]

[0143] The time to onset of crosslinking increases with increasing amount of stabilizer, indicating higher thermal stability (Table 2). Preferably, the stabilizer concentration is 0.1 wt.% or more, more preferably 0.3 wt.% or more, even more preferably 0.8 wt.% or more, and even more preferably 1 wt.% or more.

[0144] Example 3A The test compositions described above were used. In this example, different stabilizer types and / or stabilizer concentrations and / or different combinations of stabilizers were tested.

[0145] [Table 5]

[0146] In combination with other stabilizer classes, synergistic effects were observed between ascorbyl palmitate and the stabilizers tested. The onset times of crosslinking obtained for the stabilizer combination exceeded those obtained for equimolar amounts of a single stabilizer alone. See for example sample 3.6, which achieves improved thermal stabilization (79 min) over samples 3.3 (67 min) and 3.5 (39 min) (Table 3A).

[0147] Example 3B The test compositions described above were used. In this example, additional samples were tested that further contained other stabilizer classes (e.g., phenolic acrylate types, tertiary amine acrylates, etc.) in formulations with or without AP stabilizers. Synergistic effects were seen when vitamin derivatives (S1) were combined with other stabilizers (S2). Thus, in some embodiments, it is preferred to have a first stabilizer that is a vitamin or vitamin derivative, and a second (additional) stabilizer. Representative second stabilizers are shown in Table 3Ba.

[0148] [Table 6] [Table 7]

[0149] The onset times of crosslinking for combinations containing both a first stabilizer (S1) and a second stabilizer (S2) are listed in Table 3Bb.

[0150] [Table 8] [Table 9]

[0151] Example 4 In this example, the effect of stabilizers on the tone value of the obtained printing plate was evaluated, since conventional stabilizers may interfere with curing and thus affect the tone value. The above-mentioned test composition was used for the sample containing BHT and AP as stabilizers. The example shows that AP stabilizer has a much lesser effect on the tone value. The effect of stabilizers on the tone value was calculated as the difference between the tone value of 5% halftone at 146 lpi of the plate without additional stabilizer compared to the respective tone value of the plate containing stabilizer.

[0152] [Table 10]

[0153] BHT prevented crosslinking during UV exposure. As a result, halftone dots smaller than 5% tone value were not fixed in the relief. BHT also reduced the resulting dot size. A 5% halftone produced a tone value of 0.7% with only clichés.

[0154] Without additional stabilizers, significantly smaller dots can be reproduced in the cliché than with BHT, resulting in a gradation value of 3.7% in the cliché, starting from a halftone of 1.2%. Nevertheless, without additional stabilizers, the melt (already) undergoes crosslinking upon heating, for example during the production of the relief precursor. The reference ascorbic acid was not compatible with the formulation under test and therefore could not be tested.

[0155] The stabilizer ascorbyl palmitate of the present invention resulted in improved thermal stability of the melt (see Table 1). At the same time, the copy properties were only slightly affected (only 0.8%) (Table 4). The addition of 1 wt.% ascorbyl palmitate to the plate formulation resulted in a slight increase in the first stable halftone at 146 lpi from 1.2% to 1.8% and a slight decrease in dot size (tone value decreased from 3.7% to 2.9%). The effect of ascorbyl palmitate on copy properties was significantly less than that of the equimolar reference BHT (Table 4).

[0156] It is thus shown that the performance of the AP replaces that of the BHT stabilizer, and due to the improved thermal stability brought about by the ascorbyl palmitate stabilizer, unintended gel formation caused by mechanical and thermal stresses, for example due to kneading during the extrusion of the rubber-like mixture to form the relief precursor, can be avoided.

[0157] Example 5 In this example, another test formulation based on SIS triblock copolymer was used. A plate-shaped material was prepared according to the method described above with the following composition: 10 parts by weight of hexanediol diacrylate (HDDA), 2.0 parts by weight of benzyl dimethyl ketal as a photoinitiator (BDK); 5 parts by weight of a hydrocarbon resin (CAS9017-27-0), 1.1 parts by weight of further components, such as additives and dyes (A), 81 to 82 parts by weight of a binder (B), i.e., a SIS triblock copolymer having a styrene content of approximately 15% and a diblock proportion of approximately 19%, and 0 to 1 parts by weight of a stabilizer (S).

[0158] In the given examples, the amount of stabilizer was varied from 0 to 1 part by weight, with the excess being balanced by the amount of binder, respectively.

[0159] [Table 11]

[0160] Without additional stabilizer, crosslinking was observed after a measured time of 5 minutes. The reference ascorbic acid was not compatible with the formulation under test and therefore could not be tested. With BHT, the onset time of crosslinking increased from 5 to 16 minutes. The effect of ascorbyl palmitate (AP) on the onset time of crosslinking was more than 5 times that of an equimolar amount of BHT, indicating higher thermal stability and better manufacturability during the extrusion process (Table 5).

[0161] Example 6 In this example, the type of plasticizer and the type and concentration of stabilizer were varied. Plate-shaped materials were made according to the method described above with the following test compositions: 10 parts by weight of hexanediol diacrylate (HDDA) as an ethylenically unsaturated compound; 2 parts by weight of benzyl dimethyl ketal (BDK) as a photoinitiator; 21 parts by weight of a liquid plasticizer, i.e. polybutadiene or bio-based plasticizer, 1 part by weight of further components, such as additives and dyes (A), 64 to 66 parts by weight of a binder (B), an SBS triblock copolymer having a styrene content of about 25% and a diblock proportion of approximately 10% (hence SBS-rubber based), and 0 to 1.5 parts by weight of a stabilizer (S).

[0162] In the given examples, the amount of stabilizer was varied from 0 to 1.5 parts by weight, with the excess being balanced by the amount of binder, respectively. The type of stabilizer and the type of plasticizer were varied. The rheological measurement time was 30 minutes, respectively.

[0163] [Table 12]

[0164] The reference ascorbic acid was not compatible with the formulation under test and therefore could not be tested.Compared to sample 6.1 without additional stabilizer, the onset time of crosslinking was found to increase for the stabilizers ascorbyl palmitate and tocopherol of the invention and in the presence of various types of liquid plasticizers, such as polybutadiene or bio-based plasticizers (Table 6).

[0165] Example 7 The kneading tests were carried out using a ThermoFisher Scientific Haake kneader equipped with a Haake PolyLab OS RheoDrive 7 control unit, a Haake Rheomix 600 OS heating and kneading chamber, and Roller Rotors R600. Torque and sample temperature were recorded using the software PolySoft, version 2.1.0.1. A temperature of 180°C was applied for the measurements. Each measurement was carried out for 60 minutes. The components were added to the kneader as solids and mixed in the kneader.

[0166] As samples, 50 g of the following composition was used: 99-100 parts by weight of a binder (B), an SBS triblock copolymer having a styrene content of about 25% and a diblock proportion of approximately 10% (hence SBS-rubber based), and 0 to 1.0 parts by weight of a stabilizer (S).

[0167] For a given sample, the amount of stabilizer was varied from 0 to 1.0 parts by weight, with the excess being balanced by the amount of binder, respectively.

[0168] [Table 13]

[0169] The increase in torque indicated the onset of crosslinking of the SBS-rubber due to insufficient stabilization. Without additional stabilizer, the increase in torque was observed within the first 10 minutes of the measurement time. With BHT as stabilizer, the increase in torque was detected after 28 minutes of heating at 180°C. The best results were obtained with ascorbyl palmitate, where crosslinking was observed after 50 minutes. The reference ascorbic acid was not compatible with the formulation under test and therefore could not be tested.

[0170] Example 8 The test composition described in Example 1 was used. The printing plate precursor was developed according to the procedure described in the printing plate evaluation section. The developed printing plate was then further irradiated (machine type: Combi FIII (Flint Group Germany GmbH, Germany), UVA exposure time: 40 min, UVA intensity: 11 mW / cm) to evaluate its resistance to UV light and cracking. 2 , UVA tube type: Philips TL 60W / 10-R, UVC exposure time: 40 minutes, UVC intensity: 13mW / cm 2 (UVC tube type Philips TUV 75W HO G75 T8, UVA and UVC post-exposure started simultaneously). On a 5x8 cm piece of the solid printed area, the central edge of the long side was cut with a knife (0.2 mm). The plate piece was bent at an angle of 180° so that the cut could run along the relief layer (carrier foil on carrier foil). After 5 minutes, the total length of the relief layer that had torn along the bend was measured and the initial cut length was subtracted. Cracks that did not follow the original cut (e.g. starting in the middle of the bend due to weakness) were also taken into account.

[0171] [Table 14]

[0172] Longer cracks indicate less stability after prolonged UV exposure. Best results were obtained with ascorbyl palmitate without any avoidance. Cracks were more pronounced with an equimolar mount of BHT. The longest cracks were observed without any additional stabilizer.

[0173] Example 9 Several carbamate derivatives derived from ascorbic acid (AAD) were synthesized and used in similar test compositions as described above in Example 1. The reaction mixture was used completely without purification and simply added to the plate formulation during homogenization in toluene solution. The stoichiometric amounts of reactants were calculated to obtain a concentration of 1 wt% carbamate derivative in the plate formulation assuming complete conversion of the reactants. For the synthesis of each of the entries in Table 9 below, 1.0 molar equivalent (equivalent) of ascorbic acid (AA), 2.0 molar equivalents of isocyanate (IC) and 0.05 molar equivalents of catalyst (di-n-butyltin dilaurate) were suspended in THF (concentration: 35 wt% reactants, 65% wt% solvent) and heated to 60°C for 5 hours. The reaction was quenched with excess ethanol (same volume as the reaction mixture) and added to the plate formulation in toluene solution. The procedure for the preparation of the plate precursor was followed as described above. The solution was cast onto a carrier sheet and traces of THF / ethanol were evaporated together with toluene during the drying step of the plate precursor.

[0174] For the references in Table 9 below (Ref.), the same procedure was followed but without the addition of AAD.

[0175] Detailed steps for the entry 1 example:1.84 g of n-butyl isocyanate (0.0186 mol, 2 eq.), 1.61 g of L-ascorbic acid (0.0093 mol, 1 eq.) and 0.294 g of di-n-butyltin dilaurate (0.000465 mol, 0.05 eq.) were suspended in 7 g of THF and stirred for 5 h at 60° C. The progress of the reaction was monitored by thin layer chromatography (silica gel 60 F254, Aldrich, solvent: dichloromethane:ethanol 3:1, Rf (retention factor, ascorbic acid) = 0.02), Rf (product) = 0.70). The compounds were visualized on the TLC plate by staining with Seebach-solution (mixture of phosphomolybdic acid hydrate, cerium(IV) sulfate, sulfuric acid and water). To quench the reaction, 10 mL of ethanol was added to the mixture.

[0176] [Table 15] [Table 16]

[0177] Representative IR spectroscopy measurements of the dried crude product: L-Ascorbic Acid (reference) IR(ATR):3524.1, 3406.3, 3308.8, 3001.5, 2915.8, 2713.2, 1752.3, 1652.5, 1497.2, 1456.3, 1387.6, 1363.0, 1312 .8, 1271.3, 1246.8, 1220.9, 1197.0, 1111.1, 1075.3, 1043.7, 1022.6, 987.9, 869.3, 819.7, 753.7, 720.0, 679.7cm -1 . Entry 1- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diyl bis(butylcarbamate) IR(ATR):nd. Entry 2- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(tosylcarbamate) IR(ATR):nd. Entry 3- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(phenylcarbamate) IR(ATR):3305.8, 3138.7, 3062.4, 2979.8, 1703.5, 1598.6, 1537.6, 1500.3, 1444.3, 1 408.8, 1312.9, 1212.8, 1119.1, 1082.8, 1061.0, 1029.4, 897.6, 826.7, 751.3, 690.3cm -1 . Entry 4 - 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((3-(triethoxysilyl)propyl)carbamate) IR(ATR):nd. Entry 5- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diyl bis(tert-butylcarbamate) IR(ATR):nd. Entry 6- 6-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)-4,9-dioxo-5,8-dioxa-3,10-diazadodecane-1,12-diylbis(2-methylacrylate) IR(ATR):3352.2, 2958.5, 2359.1, 1704.1, 1634.9, 1538.3, 1452.4, 1404.0, 1319.7, 1296.1, 1252.8, 1154.3, 1039.2, 943.3, 814.1, 763.8cm -1 . Entry 7- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((2-(4-vinylphenyl)propan-2-yl)carbamate) IR(ATR):nd. Entry 8- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(cyclohexylcarbamate) IR(ATR):3320.8, 2930.2, 2853.8, 1771.1, 1530.2, 1449.2, 1313.1, 1277.0, 1250 .4, 1230.6, 1141.7, 1081.1, 1044.6, 967.8, 891.2, 844.7, 827.1, 775.6, 759.0cm -1 . Entry 9 - 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((trimethylsilyl)carbamate) IR(ATR):nd. Entry 10 - 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(octadecylcarbamate) IR(ATR):3445.4, 3303.0, 2954.6, 2916.2, 2848.6, 1741.1, 1717.4, 1682.8, 1552.7, 1463.9, 1356.1, 1287.2, 1270.7, 1261. 9, 1244.8, 1214.9, 1184.7, 1099.4, 1080.9, 1050.0, 968.5, 944.6, 915.9, 886.8, 854.9, 825.5, 774.7, 757.9, 719.4, 668.0cm -1 . Entry 11- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((4-isopropylphenyl)carbamate) IR(ATR):3306.5, 2957.6, 2869.0, 1682.8, 1598.1, 1537.6, 1515.2, 1460.0, 1415.9, 1382.7, 1361.7, 1338.1, 1309.8, 1284.6, 1217.4, 1115.6, 1053.9, 1017.5, 890.4, 830.5, 787.7, 754.3, 722.5, 660.7cm -1 . Entry 12- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(m-tolylcarbamate) IR(ATR):3295.4, 2916.5, 1738.1, 1634.1, 1610.8, 1597.3, 1548.8, 1488.9, 1454.2, 1405.5, 129 2.8, 1263.6, 1215.9, 1167.4, 1119.9, 1043.8, 947.5, 920.7, 878.1, 778.2, 748.1, 720.7, 688.5cm -1 . Entry 13- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(phenethylcarbamate) IR(ATR):3323.5, 3062.1, 3027.2, 2934.9, 1682.9, 1602.7, 1525.0, 1496.9 , 1454.2, 1414.8, 1333.2, 1242.0, 1201.5, 1142.9, 1030.5, 748.1, 698.0cm -1 . Entry 14 - 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(dodec-11-en-1-ylcarbamate) IR(ATR):nd. Entry 15- 1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(naphthalen-1-ylcarbamate) IR(ATR):3278.0, 3052.6, 2971.2, 2359.1, 1744.4, 1621.6, 1598.1, 1578.4, 1540.7, 1500.6, 1466.1, 1403.2, 1345.2, 1256.8, 1214.5, 1176.1, 1109.3, 1039.7, 1013.3, 935.7, 877.6, 791.8, 769.2, 737.3, 705.5, 677.0cm -1 . Entry 16- 9-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)-7,12-dioxo-3,8,11,16-tetraoxa-6,13-diazaoctadecane-1,18-diylbis(2-methylacrylate) IR(ATR):nd. Entry 17- 2-((8-((acryloyloxy)methyl)-3-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)-8-methyl-6,11-dioxo-2,5,10-trioxa-7-azatrides-12-en-1-oyl)amino)-2-methylpropane-1,3-diyl diacrylate IR(ATR):nd.

Claims

1. A photosensitive composition (PC) for forming a photosensitive layer of a relief precursor (RP), a radical initiator (R), such as a photoinitiator, a photoinitiator system or a thermal initiator, and optionally an ethylenically unsaturated compound (EC); a stabilizer (S1) for promoting extrusion stability, the stabilizer (S1) being a vitamin or a vitamin derivative; A binder (S1), a first monomer unit (Mu1) derived from a vinyl aromatic monomer; and A second monomer unit (Mu2) derived from an ene monomer and / or a diene monomer or a combination thereof. A binder (B) which is a thermoplastic elastomeric block copolymer having the formula: wherein the stabilizer (S1) is a hydroxytetronic acid (HTAD) derivative.

2. 2. The composition of claim 1, wherein the stabilizer (S1) has a predicted log octanol-water coefficient calculated from Log Kow (WSKOW v 1.68 estimate) within EPI Suite v4.11, said predicted octanol-water coefficient (OWc) being higher than -4, preferably higher than -2, more preferably higher than 0, even more preferably higher than 5.

3. 3. The composition according to claim 1 or 2, wherein the stabilizer (S1) has a predicted log octanol-water coefficient calculated from Log Kow (WSKOW v 1.68 estimate) within EPI Suite v4.11, said predicted octanol-water coefficient (OWc) being in the range of -4.0 to 12.0, more preferably in the range of -2.0 to 11.0, even more preferably in the range of 0 to 10.0, even more preferably in the range of 1.0 to 8.0, even more preferably in the range of 2.0 to 6.

50.

4. The composition further comprises a second stabilizer (S2), said second stabilizer being selected from one of the following classes: phenolic, phenolic and acrylate, thioether, hindered amine, phenolic and amine, amine, thioether amine, multifunctional amine and acrylate, more preferably said second stabilizer (S2) is 2,6-di-tert-butyl-4-methylphenol (BHT), 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Tris(2,4-di-tert-butylphenyl)phosphite, Didodecyl 3,3'-thiodipropionate, 1,5,8,12-tetrakis[4,6-bis(N-butyl-N-1,2,2,6,6-pentamethyl-4-piperidylamino)-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane, 2',3-bis[[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide, bis[4-(2-phenyl-2-propyl)phenyl]amine, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, Tertiary amines and acrylates, preferably 1H-azepine-1-propanoic acid, hexahydro-, 2,2-bis[[(1-oxo-2-propen-1-yl)oxy]methyl]butyl ester or 2,2-bis[[(1-oxo-2-propen-1-yl)oxy]methyl]butyl hexahydro-1H-azepine-1-propanoate. The composition according to any one of claims 1 to 3,

5. The composition according to any one of claims 1 to 4, wherein the stabilizer (S1) has a molecular weight in the range of 50 to 800 g / mol, preferably 50 to 600 g / mol, more preferably 100 to 490 g / mol, even more preferably 120 to 480 g / mol and most preferably 200 to 430 g / mol.

6. The composition according to any one of claims 1 to 5, wherein the stabilizer (S1) is selected from vitamin C, vitamin E or derivatives thereof.

7. The composition according to any one of claims 1 to 6, wherein the stabilizer (S1) is a vitamin C derivative, preferably an ascorbic acid ester, even more preferably a fatty acid ester of ascorbic acid.

8. The composition according to any one of claims 1 to 7, wherein the stabilizer (S1) is ascorbyl palmitate (AP).

9. The composition according to any one of claims 1 to 8, wherein the stabilizer (S1) is present in a concentration of 0.1 to 10 wt.%, preferably 0.1 to 8 wt.%, more preferably 0.2 to 6 wt.%, even more preferably 0.5 to 2% based on the total weight of the composition.

10. 10. The composition according to any one of claims 1 to 9, wherein the binder (B) has a total styrene content in the range of 3 to 50%, preferably 8 to 38%, more preferably 10 to 30%, and most preferably 15 to 30%.

11. The composition according to any one of the preceding claims, wherein the binder (B) is selected from styrene-butadiene-styrene (SBS) triblock copolymers and / or styrene-isoprene-styrene (SIS) triblock copolymers.

12. 12. The composition according to any one of claims 1 to 11, wherein the binder (B) is a styrene-butadiene-styrene (SBS) triblock copolymer having a styrene content in the range of 8 to 48%, preferably 13 to 43%, more preferably 18 to 38%, or the binder (B) is a styrene-isoprene-styrene (SIS) triblock copolymer having a styrene content in the range of 3 to 27%, preferably 5 to 25%.

13. 13. The composition according to any one of claims 1 to 12, wherein the binder (B) is a diblock copolymer or a triblock copolymer with a diblock percentage in the range of 5 to 50%, preferably 5 to 30%, more preferably 8 to 28%, even more preferably 10 to 24%.

14. 2. The composition of claim 1, wherein the stabilizer (S1) is ascorbyl palmitate (AP) and the binder (B) is a styrene-butadiene (SB) diblock and / or a styrene-butadiene-styrene (SBS) triblock copolymer, or the stabilizer (S1) is ascorbyl palmitate (AP) and the binder (B) is a styrene-isoprene (SI) diblock and / or a styrene-isoprene-styrene (SIS) triblock copolymer.

15. The composition further comprises a plasticizer (P), said plasticizer being a bio-based plasticizer, preferably a vegetable oil, a fatty acid and / or a fatty acid ester of a mono- and polyfunctional alcohol; said bio-based plasticizer is preferably present in the composition in an amount of at least 11 wt%, preferably at least 14 wt%, even more preferably at least 16 wt%; preferably said bio-based plasticizer is present in an amount of more than 15%, preferably more than 25%, more preferably more than 50%, and 15. The composition according to any one of claims 1 to 14, characterized by a UV transmittance at 365 nm of a 33 wt % solution of the plasticizer in n-hexane, more preferably higher than 60%; and / or the bio-based plasticizer is selected from rapeseed oil, sunflower oil, palm kernel oil, soybean oil, rapeseed oil, sunflower oil, soybean oil, palm oil, palm kernel oil, coconut oil, medium chain triglycerides (MCT), linseed oil, safflower oil, corn oil and / or cottonseed oil, preferably rapeseed oil or sunflower oil.

16. The composition according to any one of claims 1 to 15, wherein the stabilizer is an ascorbic acid derivative (AAD).

17. A method for producing a relief precursor (RP), comprising the steps of: extruding the photosensitive composition of any one of claims 1 to 16 to form an extruded photosensitive layer; applying the extruded layer to a dimensionally stable support (L1); A method comprising:

18. a relief precursor (RP) that is developed into a relief (RS), A dimensionally stable support (L1), A photosensitive layer (L2) comprising the photosensitive composition according to any one of claims 1 to 17; A relief precursor (RP) comprising:

19. A relief (RS) developed from a relief precursor according to claim 18, preferably serving as a printing sleeve or a printing blanket.

20. Use of a stabilizer (S1), which is a vitamin or vitamin derivative, preferably ascorbyl palmitate (AP), to improve the extrusion stability of a mixture and / or to increase the thermal stabilization of a second stabilizer (S2), which is a thermal stabilizer, preferably said second stabilizer (S2) being selected from one of the following classes: phenolic, phenolic and acrylates, thioethers, hindered amines, phenolic and amines, amines, thioether amines, polyfunctional amines and acrylates, more preferably the second stabilizer (S2) is butylated hydroxytoluene (BHT).

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