Relief precursors with enhanced stability

Abstract

The present invention relates to relief precursors with enhanced stability. The present invention relates to relief precursors with enhanced ability to be developed into high performance relief structures, more particularly high quality relief structures such as printed boards. In addition, the present invention provides a photosensitive composition (PC) for forming a photosensitive layer of a relief precursor (RP), the photosensitive composition (PC) comprising specific stabilizers and binders. By including a stabilizer and a binder as described herein, it was found that the stability of a melt of a photosensitive composition during production, e.g., by extrusion production, can be significantly enhanced. Surprisingly, such enhanced stability may be achieved without or with minimal undesirable impact on the resulting printing performance and / or imaging characteristics of the relief formed by developing the relief precursor.

Description

[0001] The present invention relates to relief precursors having enhanced stability during extrusion without negatively affecting the photochemical properties.By having enhanced extrusion stability, the development of the relief precursor and the final properties of the relief formed with the relief precursor can be improved. background

[0003] A relief precursor such as a printing plate precursor (e.g., a printing blanket or a printing sleeve) can be used to produce a relief having a relief structure. A relief (e.g., a cliché) can be used to press ink onto a substrate. Typically, a relief precursor is made of several layers. A backing layer, also referred to as a carrier layer, is used for mechanical stability. A photosensitive layer is placed on the backing layer and selectively cured (e.g., by exposure or heating) to produce cured portions within the photosensitive layer. The uncured portions are then removed (e.g., by washing them off) so that the cured portions remain and form a relief structure. This process is referred to as developing the relief precursor.

[0004] However, some unintentional pre-curing may occur prior to or during development of the precursor, for example due to heating of the precursor during production, upon development and / or during extended storage.

[0005] Unintentional solidification can greatly affect the production technology or performance of the final relief formed with the precursor. That is, the production of the precursor is usually carried out by extrusion process, wherein thermoplastic elastomer such as block copolymer is melted, and other solid components or liquid components are added to the melt in the extrusion line (extrusion line). In order to make the mixture homogenized, the extrusion line can include a kneading element (kneading element). However, kneading with such a kneading element can cause mechanical stress and thermal stress in the rubber mixture, which may cause unexpected gel formation.

[0006] Therefore, in order to avoid or minimize such gel formation, stabilizers may be added to the mixture to prevent unintentional pre-curing, for example, thermal polymerization inhibitors may be added. However, conventional stabilizers may also affect the intended curing process during the development of the relief precursor. Therefore, conventional stabilizers may affect the performance characteristics of the relief structure, such as the generation of fine dots. In addition, due to mechanical and thermal stresses, conventional stabilizers may not be effective enough in preventing gel formation.

[0007] In order to produce a relief that can be used as a printing plate, the relief structure can be formed by exposing a relief precursor to electromagnetic radiation through a mask carrying image information. Due to exposure to radiation, the exposed part of the relief precursor is cured and becomes insoluble or infusible. In the development step, the soluble part or the fusible part of the relief precursor can be removed so that the desired relief is formed. In the exposure step, the stabilizer should not interfere with the curing reaction. In addition, the composition with the stabilizer should preferably provide a short exposure time and good resolution, with the formed relief close to the target structure. Improved accuracy.

[0008] The present inventors have therefore recognised that there is a need for an improved binder-stabiliser system, wherein the binder is sufficiently resistant to undesired polymerisation and formation of gel particles due to mechanical and thermal stresses and preferably does not affect the desired properties of the relief structure. SUMMARY OF THE INVENTION

[0010] It is an object of embodiments of the present invention to provide relief precursors having an enhanced ability to be developed into high performance relief structures, more particularly high quality relief structures such as printing plates, even more particularly relief precursors for flexographic printing plates.

[0011] In addition, an embodiment of the present invention provides a photosensitive composition (PC) for forming a photosensitive layer of a relief precursor (RP). The composition comprises:

[0012] a free radical initiator (R) such as a photoinitiator, a photoinitiator system or a thermal initiator; and optionally an ethylenically unsaturated compound (EC);

[0013] a stabilizer (S1) for promoting extrusion stability, the stabilizer being a vitamin or a vitamin derivative; and

[0014] Adhesive (B), the adhesive is a thermoplastic elastomer block copolymer, the thermoplastic elastomer block copolymer having

[0015] a first monomer unit (Mu1), the first monomer unit being derived from a vinyl aromatic monomer, and

[0016] The second monomer unit (Mu2) is derived from an olefin monomer and / or a diene monomer; or a combination thereof.

[0017] Surprisingly, it has been found that when a vitamin or vitamin derivative stabilizer is combined with a thermoplastic elastomer block copolymer binder, a binder-stabilizer system with improved stability in the melt is achieved. This means better resistance to thermal and mechanical stresses, for example during extrusion and production of relief precursors.

[0018] By including stabilizers and binders as described herein, it was found that the stability of the melt of the photosensitive composition during production (e.g., by extrusion) can be significantly enhanced. Surprisingly, such enhanced stability can be achieved with no or minimal undesirable effects on the resulting printing performance and / or imaging characteristics of the relief formed by developing the relief precursor.

[0019] In addition, it was found that by including vitamins or vitamin derivatives as stabilizers, both the production and exposure and development properties of the photosensitive composition can be improved. That is, the functionality of the initiator and the thermoplastic elastomer block is better maintained and is not affected or minimally affected by the elevated temperature caused by thermal and / or mechanical stress during extrusion. In addition, gel formation due to "unintentional pre-curing" during production (before curing by exposure) can be avoided or minimized.

[0020] Unintentional pre-curing may be understood as the occurrence of a curing reaction which is (already) initiated before exposure of the relief precursor (eg development with LED exposure).

[0021] Unintentional pre-curing can have a negative impact on final print characteristics such as final imaging characteristics like dot size and target value.

[0022] Additional aspects relate to a relief precursor (RP) comprising a photosensitive composition (PC) as described herein and a relief, such as a printing plate, having 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 susceptible to UV-induced brittleness. In addition, suitable development compatibility with high-intensity LED exposure can be achieved. Moreover, due to the presence of a well-designed stabilizer, the exposure time during exposure can be kept consistent.

[0023] By including vitamins or vitamin derivatives in the photosensitive composition, relief precursors, such as printing plate precursors, having enhanced oxidative stability can be obtained. In this way, the plate can remain stable for extended periods of time, such as during storage.

[0024] Additional aspects relate to methods of developing a relief precursor to form a relief. It has been found that a vitamin or vitamin derivative stabilizer as described herein can stabilize a photosensitive composition against unintended crosslinking without affecting the intended photopolymerization and curing. Thus, the quality of a relief structure formed from a relief precursor having a photosensitive composition within a photosensitive layer of the relief precursor is improved. A relief can be formed from a relief precursor having an improved relief structure thereon, such as smaller dots remaining after development. Furthermore, the accuracy of the relief structure can be improved because the dot size can be closer to a target value.

[0025] Furthermore, in order to reduce the stickiness of the plate, after the development step, the precursor can be further treated with UV-A irradiation and / or UV-C irradiation. A side effect can be an increase in the brittleness of the printed plate and the sensitivity to mechanical defects. It was found that the photosensitive composition as described herein can prevent UV-induced brittleness.

[0026] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) has a predicted log octanol-water coefficient as calculated from Log Kow (WSKOW v 1.68 estimate) within EPI Suite v4.11, and wherein the predicted log octanol-water coefficient (OWc) is above -4, preferably above -2, more preferably above 0, even more preferably above 5, preferably about 6. By including careful selection of the predicted log octanol-water coefficient of the vitamin or vitamin derivative stabilizer, it was found that the behavior of the stabilizer in thermoplastic elastomer binder systems can be improved (e.g., improved phase stability in organic binder systems such as systems with SBS and / or SIS binders). According to an embodiment, the predicted log octanol-water coefficient is 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 the coefficient is in the range of 2.0 to 6.5, more particularly such as in the range of 5.0 to 6.5. By carefully selecting the Log Kow value (also described as the predicted log octanol-water coefficient in this article), the compatibility with other components in the composition can be improved, which is beneficial to the behavior and thermal stability of the overall improvement during the extrusion composition to prepare the relief precursor of the printing plate. For derivatives and substances that are not in the preferred range, phase separation in the relief precursor or migration to the surface may occur. In addition, the block copolymer adhesive system itself is phase separated at the microscopic level. Sufficient stabilization can only be achieved when the stabilizer is present in those phases that are particularly susceptible to unintentional precuring, which depends strongly on the overall formulation, adhesive system and monomer composition.

[0027] The photosensitive composition may have an additional second stabilizer (S2) selected from one of the following categories: phenols, phenols and acrylates, thioethers, hindered amines, phenols and amines, amines, thioetheramines, multifunctional amines and acrylates. Surprisingly, vitamins or vitamin derivatives, such as ascorbyl palmitate, can improve the stability of the second stabilizer in a synergistic manner.

[0028] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) has a molecular weight in the range of 50 g / mol-800 g / mol, preferably 50 g / mol-600 g / mol, more preferably 100 g / mol-490 g / mol, even more preferably 120 g / mol-480 g / mol, most preferably 200 g / mol-430 g / mol.

[0029] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) is selected from vitamin A, vitamin C and vitamin E or derivatives thereof, preferably vitamin C and vitamin E, more preferably vitamin C, because their free radical scavenging properties can improve extrusion stability.

[0030] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) is a hydroxytetronic acid (HTAD) derivative. Hydroxytetronic acid can be included in the stabilizer as a substructure and can provide stability to sensitive components by capturing (uncontrolled) free radicals, thereby avoiding or minimizing its effect on sensitive components in the composition.

[0031] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) is a vitamin C derivative, preferably an ascorbyl ester, even more preferably a fatty acid ester of ascorbic acid, more particularly ascorbyl palmitate (AP).

[0032] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) is present in a concentration of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 8 wt%, more preferably 0.2 wt% to 6 wt%, even more preferably 0.5 wt% to 2 wt%, based on the total weight of the photosensitive composition (PC). In this way, a balance between the stabilizing behavior of the photosensitive composition, such as prevention of unintended curing and the crosslinking ability (intended curing), can be achieved. Thus, gel formation during the production process, such as extrusion, can be avoided and / or minimized without having to compromise the final printing properties of the relief formed with the photosensitive composition.

[0033] In an embodiment, the adhesive has a total styrene content in the range of 3%-50%, preferably 8%-38%, more preferably 10%-30%, most preferably 15%-30%.

[0034] In an embodiment, the binder (B) is selected from styrene-butadiene-styrene (SBS) triblock copolymers and / or styrene-isoprene-styrene (SIS) triblock copolymers.

[0035] In an embodiment, 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 about 28%.

[0036] In an embodiment, binder (B) is a SIS triblock copolymer having a styrene content in the range of 3%-27%, preferably 5%-25%, for example about 15%.

[0037] In an embodiment, binder (B) is a diblock copolymer or a triblock copolymer having a diblock fraction in the range of 5%-50%, preferably 5%-30%, more preferably 8%-28%, even more preferably 10%-24%, for example about 17%-19%.

[0038] Binder (B) as described above was found to have good compatibility with vitamins or vitamin derivative stabilizers. A good binder-stabilizer system can be included in the composition so that relief precursors can be produced while maintaining great melt stability and with no or minimal undesirable effects on development properties such as exposure time and final printing properties such as resolution.

[0039] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) is ascorbyl palmitate (AP) and the binder (B) is a SB diblock copolymer and / or a SBS triblock copolymer, as such a combination can contribute to excellent processing behavior, especially during extrusion, with no or minimal impact on the final printing properties.

[0040] In an embodiment, the vitamin or vitamin derivative stabilizer (S1) is ascorbyl palmitate (AP) and the binder (B) is a SI diblock copolymer and / or a SIS triblock copolymer, as such a combination can contribute to excellent processing behavior, especially during extrusion, with no or minimal impact on the final printing properties.

[0041] In an embodiment, the composition further comprises a bio-based plasticizer (P), preferably a fatty acid ester of a vegetable oil, a fatty acid, and / or a monofunctional alcohol and a polyfunctional alcohol. Preferably, the plasticizer is characterized by a UV transmittance of a solution of 33 wt % plasticizer in n-hexane at 365 nm higher than 1%, preferably higher than 10%, more preferably higher than 50%, and even more preferably higher than 60%. Preferably, the plasticizer has an iodine value lower than 200, preferably lower than 150 according to ISO 3961:2018, so that high quality can be achieved. In an embodiment, the plasticizer is characterized by a Gardner color lower than 7 according to ISO 4630:2015. The plasticizer can be used to maintain flexibility in different temperature ranges, which is beneficial 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%, and 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. Bio-based plasticizers can also achieve several benefits because they contribute to the flexibility, fluidity, thermal stability, and impact resistance of the relief precursor and / or printing plate. The bio-based plasticizer can be present in an amount between 11 wt%-60 wt%, preferably between 12 wt%-55 wt%. By including a plasticizer as described, the development time can be shortened and energy saving can be achieved. In addition, it is found that the use of a bio-based plasticizer promotes the final printing performance. Preferably, the bio-based plasticizer is selected from rapeseed 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 of a solution of 33 wt% plasticizer in n-hexane at 365 nm is higher than 15%. More preferably, the bio-based plasticizer is preferably selected from sunflower oil or rapeseed oil (also known as canola oil).

[0042] A further aspect relates to a method of producing a relief precursor (RP), the method comprising the steps of:

[0043] extruding a photosensitive composition (PC) as described herein to form an extruded photosensitive layer;

[0044] The extruded layer is applied to a dimensionally stable support (L1).

[0045] It has been found that relief precursors can be mass produced by utilizing an extrusion process. In particular, due to the incorporation of stabilizers as described herein, the extrusion stability of the photosensitive composition can be improved and gel formation during production can be avoided. Understandably, the photosensitive composition within the relief precursor can have any of the features as described for the photosensitive composition. By having a combination of stabilizers and binders as described herein, surprisingly good performance is achieved.

[0046] A further aspect relates to a relief precursor (RP) for being developed into a relief (RS), the relief precursor (RP) comprising:

[0047] a dimensionally stable support (L1), such as a support layer, for example a PET layer,

[0048] A photosensitive layer (L2) comprising a photosensitive composition as described herein.

[0049] The dimensionally stable support body may also be referred to as carrier layer and may be made of a material selected from the group consisting of aluminum, steel, polymers and synthetic composites.

[0050] In an embodiment, the relief (RS) developed from the relief precursor (RP) is used as a printing sleeve or printing blanket.

[0051] A further aspect relates to the use of the present invention comprising:

[0052] Use of a vitamin or a vitamin derivative, preferably ascorbyl palmitate (AP), for improving the extrusion stability of the mixture. Preferably, the vitamin comprises hydroxytetraonic acid (HTAD) as a substructure.

[0053] Use of a stabilizer (S1) as a vitamin or vitamin derivative for enhancing the thermal stability of a second stabilizer (S2) as a thermal stabilizer. Preferably, the second stabilizer (S2) is selected from one of the following categories: phenols, phenols and acrylates, thioethers, hindered amines, phenols and amines, amines, thioetheramines, multifunctional amines and acrylates. The second stabilizer (S2) may be butylated hydroxytoluene (BHT).

[0054] According to aspects, a vitamin derivative is provided for stabilizing a heat-sensitive component and / or a radiation-sensitive component, such as a component in a photosensitive layer of a relief precursor for forming a relief such as a printing plate (also known as a cliché). In addition, the vitamin derivative is an ascorbic acid derivative (AAD) for stabilizing the heat-sensitive component and / or the radiation-sensitive component, in particular, the ascorbic acid derivative (AAD) is a carbamate derivative represented by formula I or a stereoisomeric form thereof, wherein formula I represents:

[0055]

[0056] Where m1 and m2 are independently one of 0-1;

[0057] Where n1 and n2 are independently one of 0-1;

[0058] The condition is

[0059] m1 and n1 are not 0 at the same time, and

[0060] m2 and n2 are not 0 at the same time;

[0061] Wherein L1 and L2 include one or more, each independently selected from:

[0062] Sulfonyl group;

[0063] or a linear or branched Cx carbon chain (C), such as n-butyl,

[0064] wherein x is selected from 0-20, preferably 0-18,

[0065] The carbon chain is optionally substituted;

[0066] Wherein R1 and R2 each independently represent:

[0067] an optionally substituted aromatic group (Ar), such as phenyl;

[0068] or

[0069] Optionally substituted cycloalkyl (CyC), such as cyclohexyl;

[0070] or

[0071] A group having a Si atom (Si), preferably a silyl group, such as a monoalkylsilyl group, a dialkylsilyl group or a trialkylsilyl group, such as a trimethylsilyl group; or a monoalkoxysilyl group, a dialkoxysilyl group or a trialkoxysilyl group, such as a triethoxysilyl group;

[0072] or

[0073] Acrylate groups (COOC), preferably alkyl acrylates, such as methacrylate.

[0074] The insights of the present invention have provided that carbamate derivatives function well as stabilizers (S1) in photosensitive compositions as described herein before. According to an embodiment of the ascorbic acid derivative (AAD) represented by formula I,

[0075] m is 1; n is 1; and

[0076] L1 and L2 include a sulfonyl group;

[0077] R1 and R2 are each independently an optionally substituted (e.g., methyl) Ar group, preferably a C6 aromatic group. Due to the combination of electronic properties, spatial properties, cross-linking properties, antioxidant properties, and stability properties, the sulfonyl group can provide thermal stability. By including an aromatic group, a bulky component can be obtained, thereby providing steric hindrance, limiting molecular motion, and preventing the occurrence of thermally induced reactions. In this way, stability can be achieved.

[0078] According to an embodiment of the ascorbic acid derivative (AAD) represented by Formula I, m is 0; n is 1; and R1 and R2 are C6 aromatic groups, such as phenyl.

[0079] According to an embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 0; and L1 and L2 are each independently a Cx chain, wherein x is 0 to 6. Preferably, wherein L1 and L2 are butyl, preferably n-butyl.

[0080] According to an embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 1; and L1 and L2 are each independently a Cx chain, wherein x is 0-6, preferably 3 (propyl); R1 and R2 are each independently a trialkoxysilyl group, preferably a triethoxysilyl group.

[0081] According to an embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 0; and L1 and L2 are each independently a Cx chain, wherein x is 0-6, preferably 4 (tert-butyl).

[0082] According to an embodiment of the ascorbic acid derivative (AAD) represented by formula I, m is 1; n is 1; and L1 and L2 are each independently a Cx chain, wherein x is 0-6, preferably 2 (ethyl). R1 ​​and R2 are each independently an alkyl acrylate, preferably a methacrylate.

[0083] According to an 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.

[0084] According to an 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 trialkoxysilyl group, preferably a triethoxysilyl group.

[0085] These aspects of the compound are based on the insights of the present invention, that is, the enhanced stability of heat-sensitive components and / or radiation-sensitive components can be provided. In particular, the insights of the present invention provide the enhanced stability of the composition comprising an adhesive system such as an organic non-polar adhesive system. More particularly, the ascorbic acid derivative (AAD) represented by Formula I is particularly useful for stabilizing an adhesive system such as an SBS adhesive or a SIS adhesive comprising a unit selected from styrene, butadiene, and isoprene. The adhesive can be a copolymer, such as a diblock polymer or a triblock polymer. The example of an adhesive that can be stabilized is an adhesive comprising styrene-isoprene-styrene (SIS) units, styrene-ethylene-butylene-styrene (SEBS) units or styrene-ethylene-propylene-styrene (SEPS) units, and particularly an adhesive as described herein above.

[0086] Another aspect relates to a method for obtaining an ascorbic acid derivative (AAD) as provided herein. The method comprises:

[0087] a) providing ascorbic acid (AA), preferably any one of D ascorbic acid or L ascorbic acid;

[0088] b) adding isocyanate (IC); and allowing the isocyanate to react with ascorbic acid to obtain an ascorbic acid derivative (AAD);

[0089] Wherein isocyanate (IC) is represented by formula II:

[0090]

[0091] in

[0092] m and n are one of 0-1, provided that m and n are not 0 at the same time;

[0093] Where L includes:

[0094] a sulfonyl group (e.g. a -S atom coupled to two O atoms);

[0095] or a linear or branched Cx carbon chain (C), such as n-butyl,

[0096] wherein x is selected from 0-20, preferably 0-18,

[0097] The carbon chain is optionally substituted;

[0098] Where R represents:

[0099] an optionally substituted aromatic group (Ar), such as phenyl;

[0100] or

[0101] Optionally substituted cycloalkyl (CyC), such as cyclohexyl;

[0102] or

[0103] A group having a Si atom (Si), preferably a silyl group, such as a monoalkylsilyl group, a dialkylsilyl group or a trialkylsilyl group, such as a trimethylsilyl group; or a monoalkoxysilyl group, a dialkoxysilyl group or a trialkoxysilyl group, such as a triethoxysilyl group;

[0104] or

[0105] Acrylate groups (COOC), preferably alkyl acrylates, such as methacrylate.

[0106] Preferably, in the method, the isocyanate (IC) is selected from one of the following:

[0107] Alkoxysilylalkyl isocyanates, such as (triethoxysilyl)-propyl isocyanate;

[0108] Alkylsilyl isocyanates, such as trimethylsilyl isocyanate;

[0109] 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;

[0110] Aryl isocyanates, such as phenyl isocyanate or 1-naphthyl isocyanate;

[0111] Cycloalkyl isocyanates, such as cyclohexyl isocyanate;

[0112] Alkyl methacrylates, such as 2-isocyanatoethyl methacrylate;

[0113] Alkyl isocyanates, such as tert-butyl isocyanate, n-butyl isocyanate, octadecyl isocyanate or dodecyl isocyanate;

[0114] Sulfonyl isocyanates, such as p-toluenesulfonyl isocyanate.

[0115] Preferably, in the process, the reaction is carried out at a temperature between 10° C. and 40° C., such as room temperature, and in the absence of a catalyst (K). More preferably, the reaction is carried out at a temperature above 40° C. and in the presence of a catalyst (K) or a mixture of catalysts selected from non-nucleophilic amine bases and Lewis acids and combinations thereof, such as (triethanolaminato)isopropoxide, zinc methacrylate, zinc acetate, dibutyltin dichloride, dibutyltin di(acetate), 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-dimorpholinodiethylether (DMDEE), bismuth 2-ethylhexanoate, preferably di-n-butyltin dilaurate. When several catalysts are used in combination, in particular a combination of a non-nucleophilic amine and a Lewis acid is preferred, such as DABCO and di-n-butyltin dilaurate.

[0116] For liquid or meltable isocyanates, the reaction can be carried out without a solvent. Preferably, in the process, the reaction is carried out in a solvent (S) or a solvent mixture, preferably dichloromethane (DCM), trichloromethane (TCM), 1,4-dioxane, dimethyl sulfoxide (DMSO), dimethyl carbonate (DMC), more preferably 2-methyltetrahydrofuran (2-MeTHF), even more preferably tetrahydrofuran (THF).

[0117] Another aspect relates to a photosensitive composition (PC') comprising an ethylenically unsaturated component (a); a thermal initiator and / or a photoinitiator (b); a stabilizer (c), wherein the stabilizer is an ascorbic acid derivative (AAD) as described above in conjunction with formula I or a derivative obtained according to the method as described above in conjunction with formula II.

[0118] Preferably, the photosensitive composition (PC') further comprises a binder (d), which is a SIS block copolymer or a SBS block copolymer and / or a binder as previously described above.

[0119] A further aspect relates to the use of ascorbic acid derivatives having carbamate functional groups (CF), preferably at least two carbamate functional groups, for stabilizing heat-sensitive components or radiation-sensitive components in photosensitive compositions (PC). In general, the carbamate functional groups can be identified by the following structure:

[0120]

[0121] Preferably, wherein the photosensitive composition (PC) is contained in a relief precursor, preferably a relief precursor to be developed into a relief structure such as a printing plate or sleeve. Furthermore, another aspect relates to the use of an ascorbic acid derivative as described above in connection with formula I or obtained according to a process as described above in connection with formula II for stabilizing heat-sensitive components or radiation-sensitive components in a photosensitive composition, such as a composition for use in a photosensitive layer of a relief precursor, for example for the manufacture of a printing plate.

[0122] Preferably, the relief precursor is a precursor for a printing plate or pad, in particular a precursor of the type used for non-lithographic printing, including precursors for flexographic printing, gravure printing or pad printing.

[0123] Details

[0124] Photosensitive composition (PC)

[0125] Photosensitive compositions are understood to be compositions that can be cured by thermal radiation and / or electromagnetic radiation (i.e., UV radiation). Curing can be understood to be toughening or hardening the blend by crosslinking the polymer chains therein. The photosensitive compositions described herein can be used for printing plates, flexographic printing plates, letter press plates, intaglio printing plates, microfluidic devices, microreactors, electrochemical cells, photonic crystals, or optical devices. Partial exposure can be provided.

[0126] Free Radical Initiator(R)

[0127] "Free radical initiators" are generally substances that initiate crosslinking in the photosensitive layer by generating free radicals, for example due to exposure to heat or UV radiation. The term free radical initiator can be understood as a compound or substance that can generate free radical species under mild conditions, such as UV exposure and / or heating. In this way, free radical initiators can promote free radical reactions. Suitable free radical initiators generally have weak bonds and can be selected based on having a small bond dissociation energy. Preferred free radical initiators are preferably selected from photoinitiators or photoinitiator systems or thermal initiators. Such initiators are known to the person 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 ID F Eaton et al., JACS, 102, 3298 (1980), P. Fouassier and JF Rabek, Radiation Curing in Polymer Science andTechnology, pages 77 to 117 (1993) or KK 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 RS Davidson, Exploring the Science, technology and Applications of UV and E.B. Curing, Sita Technology LTD, London 1999.Further initiators are described in JP45-37377, JP44-86516, US3567453, US4343891, EP109772, EP109773, JP63138345, JP63142345, JP63142346, JP63143537, JP4642363, JP59152396, JP61151197, JP6341484, JP2249 and JP24705, JP626223, JPB6314340, JP1559174831, JP1304453 and JP1152109. An example of a suitable photoinitiator is benzyl dimethyl ketal (BDMK).

[0128] Ethylenically Unsaturated Compounds (EC)

[0129] Preferably, the photopolymer layer (also referred to as photosensitive layer) also comprises at least one component having at least one unsaturated group. Preferably, these components are reactive compounds or monomers, and those that are suitable for the preparation of the mixture are polymerizable and compatible with the adhesive. Useful monomers of this type generally have a boiling point above 100° C. They generally 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 adhesive and that have at least one polymerizable ethylenically unsaturated group. As monomers, in particular esters or amides of acrylic acid or methacrylic acid with monofunctional or polyfunctional alcohols, amines, amino alcohols or hydroxy ethers and hydroxy esters, esters of fumaric acid or maleic acid and allyl compounds can be used. Esters of acrylic acid or methacrylic acid are even more preferred. 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 total amount of all monomers used in the relief-forming layer together is typically 1 wt % to 20 wt %, preferably 5 wt % to 20 wt %, based on the sum of all ingredients of the relief-forming layer in each case. The amount of monomers having two ethylenically unsaturated groups is preferably 5 wt % to 20 wt %, more preferably 8 wt % to 18 wt %, based on the sum of all ingredients of the relief-forming layer.

[0130] Adhesive (B)

[0131] Preferred adhesive (B) is a thermoplastic elastomer block copolymer, such as a diblock copolymer or a triblock copolymer. Thermoplastic plastics are a class of polymers that can be softened by heating and then processed. This behavior is advantageous, and causes the possibility of producing relief precursors with a larger volume, for example, by extrusion. In addition, when using a thermoplastic elastomer block copolymer adhesive, a process such as injection molding, thermoforming and blow molding can be used. The selection of thermoplastic adhesives is advantageous relative to, for example, SBR rubber (belonging to thermosetting elastomers), which performs poorly in large-scale extrusion production processes.

[0132] The binder (B) comprises a first monomer unit and a second monomer unit, wherein the first monomer unit is a vinyl aromatic monomer, and the second monomer unit is an olefin monomer and / or a diene monomer. An olefin monomer refers to a monomer containing a carbon-carbon double bond (C=C) in its molecular structure. A diene monomer refers to a monomer containing two carbon-carbon double bonds (C=C=C) in its molecular structure.

[0133] Vinyl aromatics 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 copolymers, branched copolymers or radial block copolymers. In general, they are triblock copolymers of the ABA type, but they may also be diblock polymers of the AB type, or may be polymers having more than one alternating elastomeric block and thermoplastic block, for example ABABA.

[0134] Furthermore, star copolymers and / or branched copolymers or combinations thereof may be used.

[0135] Mixtures of two or more different block copolymers can also be used. Commercial triblock copolymers typically include some portion of a diblock copolymer. The diene units can be 1,2-linked or 1,4-linked. The double bonds in the adhesive backbone provide crosslinking capabilities, especially between the adhesives in the photosensitive layer, thereby causing curing when the relief precursor is exposed. In addition, thermoplastic elastomer block copolymers with styrene and blocks and random styrene-butadiene midblocks can also be used. Of course, mixtures of two or more thermoplastic-elastomeric adhesives can also be used, provided that the properties of the relief-forming layer are not negatively affected thereby. In addition to the stated thermoplastic-elastomeric block copolymers, the photopolymerizable layer can also contain additional elastomeric adhesives in addition to the block copolymers. The use of additional adhesives of this type, also referred to as secondary adhesives, can change the properties of the photopolymerizable layer. An example of a secondary adhesive is a vinyltoluene-α-methylstyrene copolymer.

[0136] These polymer binders typically comprise from 20% by weight to 98% by weight, preferably from 50% by weight to 90% by weight of the total composition. Copolymers, such as styrene-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) diblock copolymers or triblock copolymers, exhibit benefits relative to random copolymers such as styrene-butadiene rubber SBR.

[0137] Random copolymers such as SBR should not be confused with styrene-butadiene block copolymers, although they can be derived from the same monomer. Random SBR is commonly used in elastomeric products such as tires, soles or seals. Due to its irregular molecular structure, SBR does not have very obvious microphase separation. As a result, the uncured SBR polymer without filler will not maintain its shape during storage. Therefore, it is necessary to add filling materials and simultaneously cure SBR to maintain shape and enhance its physical properties. However, any filling material added to the printing plate precursor preparation will scatter UV light and interfere with the crosslinking process during the intentional curing by UV light.

[0138] By curing of SBR (which is usually achieved by reaction with sulfur), filler-reinforced SBR polymers become elastomeric. Since the structure is maintained by chemical bonds, cured SBR decomposes rather than melts under heating and is therefore not thermoplastic.

[0139] In contrast to (thermosetting) SBR random polymers, styrene-butadiene block copolymers are thermoplastic elastomers. They can be melted, mixed and molded under heating without the need for solvents. For example, the block copolymer configuration of SBS or SIS causes microphase separation of polystyrene and polybutadiene or polyisoprene domains. Elastomer behavior is rooted in the physical crosslinking network with elastic blocks (polybutadiene) and constraint blocks (polystyrene). The printing plate precursor based on styrene-butadiene block copolymers also mostly maintains its shape during a long storage time, usually one to two years after production. Long storage time is necessary for printing plate precursors, because the curing of printing plate precursors does not occur at the production site, but occurs at the duplication room or printing facility. In short, in contrast to block copolymers, SBR as a random copolymer is not a suitable adhesive for printing plate precursors. Examples of adhesives are shown below.

[0140]

[0141] SBR random polymer block copolymer SBS and SIS

[0142] Preferably, the adhesive has a total styrene content in the range of 3%-50%, preferably 8%-38%, more preferably 10%-35%, most preferably 14%-32%. These ranges improve the Newtonian behavior of the adhesive and can set both the kinematic viscosity and the dynamic viscosity of the adhesive suitable for extrusion production.

[0143] Preferably, the binder is selected from a binder (B) selected from a styrene-butadiene-styrene (SBS) triblock copolymer and / or a styrene-isoprene-styrene (SIS) triblock copolymer.

[0144] In an embodiment, the binder 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 about 28%.

[0145] In an embodiment, the binder is selected from SIS triblock copolymers having a styrene content in the range of 3%-27%, preferably 5%-25%, for example about 15%.

[0146] In an embodiment, the adhesive is a diblock copolymer or a triblock copolymer with a diblock fraction in the range of 5%-30%, preferably 8%-28%, more preferably 10%-24%, for example about 17% or 19%. Such fractions have been found to be suitable for extrusion processing.

[0147] Stabilizer (S1)

[0148] The term "stabilizer" is understood to mean preferably, but not functionally limited, a component having a stabilizing effect. Stabilizer S1 is a vitamin or a vitamin derivative and will be discussed further below.

[0149] Vitamins or vitamin derivatives

[0150] The term vitamin is known and includes several chemical structures. Traditionally, vitamins are divided into two groups, water-soluble vitamins and fat-soluble vitamins. Water-soluble vitamins are thiamine, riboflavin, niacin, vitamin B6, folic acid, vitamin B12, pantothenic acid, biotin and vitamin C. Fat-soluble vitamins are vitamin A, vitamin E, vitamin D and vitamin K.

[0151] Surprisingly, it has now been found that vitamins and their derivatives have a stabilizing effect on the thermal and mechanical stresses to which the melt of the thermoplastic elastomer binder system is exposed during the production of the relief precursor. In addition, vitamins can be used in relief precursors to improve storage stability. In addition, the development characteristics of the precursor can be improved so that the relief formed therefrom can achieve improved imaging characteristics. These imaging characteristics especially include smaller dot sizes after development, and the achieved dot sizes can be closer to the target value. Exemplary vitamin types are shown in the table below.

[0152]

[0153]

[0154] In an embodiment, the stabilizer (S1) is selected from one or more of the following: folic acid (vitamin B9), ascorbyl palmitate (vitamin C derivative) and pyridoxine hydrochloride (vitamin B6).

[0155] These stabilizers have been found to achieve high thermal stability, so that the relief precursor can be stored for extended periods of time without affecting the quality of the subsequently formed relief structure.

[0156] In a preferred embodiment, the structure of the vitamin or vitamin derivative comprises a first group (G1) and preferably a second group (G2), such as a non-polar part, wherein the first group is selected from an aromatic group or a cyclic unsaturated group to which at least one -OH group is coupled, and the second group is a linear or branched carbon chain lacking a permanent electric dipole moment or having a minimum dipole moment. The cyclic unsaturated group preferably comprises a furan group comprising a five-membered aromatic ring having four carbon atoms and one oxygen atom. The number of carbon atoms in the main chain of the second group is preferably selected from any one of 2 to 25, 3 to 20, 3 to 17, and 3 to 16 carbon atoms. The chain may be substituted as long as the symmetry of the charge density distribution in the chain remains uniformly distributed so that there is no dipole moment or a minimum dipole moment in the chain. The second group can improve the compatibility with the organic binder system in the photosensitive composition (PC), while the first group can, for example, avoid the start of an unexpected curing reaction by capturing free radicals. Preferably, the first group (G1) comprises at least two -OH groups, each of which is coupled to a double-bonded C atom.

[0157] In an embodiment, the stabilizer (S1) comprises a substructure selected from hydroxytetraonic acid (HTAD) or a modified form thereof. The modification may improve compatibility with the adhesive system.

[0158] Preferred stabilizers (S1) for stabilizing the heat-sensitive component and / or the radiation-sensitive component include hydroxytetrahydrofuran acid as a substructure

[0159] Derivatives of hydroxytetraonic acid (HTAD) are believed to cause a stabilizing effect and therefore may be beneficial to include in photosensitive compositions. Hydroxytetraonic acid derivatives, also referred to herein as HTAD, are preferably reductones, containing an enediol structure RC(OH)=C(OH)C(=O)R stabilized by conjugation and hydrogen bonding with adjacent carbonyl groups. Reductones are effective reducing agents and antioxidants capable of reacting with oxygen and hydroxyl radicals.

[0160] Particular efficiency is found when the HTAD derivatives also contain one or more solubilizing moieties. These solubilizing moieties contribute to a uniform distribution in the respective adhesive and its different phases. For example, SBS rubber and SIS rubber contain styrene and butadiene or isoprene phases, which need to be appropriately stabilized.

[0161] Depending on the overall formulation, for example the monomers may accumulate in one phase or in two phases, depending on the specific monomer structure.By utilizing appropriate HTAD derivatives, binders and monomer combinations, excellent stability under the influence of air and heat is achieved.

[0162] In an embodiment, the stabilizer (S1) is an ascorbic acid derivative, such as ascorbyl palmitate, L-ascorbic acid, D-isoascorbic acid, L-ascorbic acid monostearate, sodium L-ascorbate, and sodium D-isoascorbate. Exemplary structures are shown below.

[0163]

[0164]

[0165] In an embodiment, the vitamin or vitamin derivative is selected from sodium D-isoascorbate (SDI) or ascorbyl palmitate (AP).

[0166] In an embodiment, the stabilizer (S1) is selected from ascorbic acid derivatives or vitamin derivatives, with the proviso that the stabilizer is not selected from ascorbic acid (176 g / mol), L-ascorbic acid monostearate (AMS) (442 g / mol), sodium L-ascorbate (198 g / mol) and sodium D-isoascorbate (198 g / mol).

[0167] A preferred stabilizer is ascorbyl palmitate (AP) (414 g / mol) due to its improved free radical scavenging properties.

[0168] The stabilizer (S1) is preferably present in a concentration of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 8 wt%, more preferably 0.2 wt% to 6 wt%, based on the total weight of the composition. It has been found that in this way, the extrusion stability can be improved without or with minimal effect on the curing ability of the photosensitive composition. The final printing properties can be achieved by reducing the (undesirable) effect on the (final) curing ability (e.g. curing during development of the relief precursor).

[0169] In a preferred embodiment, the stabilizer (S1) may be an ascorbic acid derivative (AAD) represented by Formula I as described herein, or a stereoisomeric form thereof.

[0170] In a preferred embodiment, the ascorbic acid derivative (AAD) is obtained by:

[0171] a) providing ascorbic acid (AA), preferably any one of D ascorbic acid or L ascorbic acid;

[0172] b) adding isocyanate (IC) and allowing the isocyanate to react with ascorbic acid, thereby obtaining an ascorbic acid derivative (AAD); wherein the isocyanate (IC) is represented by Formula II as described herein.

[0173] In order to obtain different degrees of functionalization and / or preferred properties, the isocyanate component can be varied between 0.1 equivalents and 10 equivalents, preferably between 0.1 equivalents and 5 equivalents, more preferably between 0.5 equivalents and 3 equivalents, even more preferably between 1 equivalent and 2 equivalents, most preferably 2 equivalents, relative to ascorbic acid (=1 molar equivalent).

[0174] The reaction temperature can vary from 0° C. to 80° C., more preferably 20° C.-80° C., even more preferably 60° C.-80° C. The different catalysts can be selected from non-nucleophilic amine bases and Lewis acids and combinations thereof (e.g., titanium (IV) (triethanolamine) isopropoxide, zinc methacrylate, zinc acetate, dibutyltin dichloride, dibutyltin di(acetate), 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 may vary between 0.01 equivalents and 1 equivalents, more preferably between 0.02 equivalents and 0.5 equivalents, even more preferably between 0.03 equivalents and 0.2 equivalents, most preferably between 0.05 equivalents and 0.1 equivalents relative to ascorbic acid (=1 molar equivalent).

[0175] Different solvents may be used, such as dichloromethane (DCM), trichloromethane (TCM), 1,4-dioxane, dimethyl sulfoxide (DMSO), dimethyl carbonate (DMC), more preferably 2-methyltetrahydrofuran (2-MeTHF), even more preferably tetrahydrofuran (THF).

[0176] The solvent may be tested and the concentration varied from 5-99w% solvent, preferably 30-90w% solvent, more preferably 50-90w% solvent, even more preferably 50-70w% solvent, most preferably 60-70w% solvent. For liquid isocyanates, the reaction may be carried out without additional solvent.

[0177] Second stabilizer (S2)

[0178] It has been discovered that when vitamins or vitamin derivatives, particularly ascorbic acid derivatives, are combined with a secondary stabilizer typically used in relief precursor compositions, such a combination enhances the thermal stability of the composition in a synergistic manner.

[0179] The second stabilizer S2 is preferably selected from one of the following categories: phenols, phenols and acrylates, thioethers, hindered amines, phenols and amines, amines, thioetheramines, multifunctional amines and acrylates. Surprisingly, vitamin derivatives, preferably ascorbic acid derivatives, can enhance the thermal stability of the second stabilizer in a synergistic manner.

[0180] In an embodiment, the second stabilizer (S2) is selected from one or more of the following: 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, 3,3'-dithiodipropionate, 1,5,8,12-tetrakis[4,6-bis(N -butyl-N-1,2,2,6,6-pentamethyl-4-piperidinylamino)-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-aza 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-propionate.

[0181] additive

[0182] The photopolymer layer may contain additional components. The additional components are selected from the group consisting of additional polymers, fillers, plasticizers, anti-blocking agents, monomers, additives (e.g., stabilizers, dyes), crosslinkers, binders, color forming compounds, dyes, pigments, antioxidants, and combinations thereof.

[0183] Plasticizers

[0184] Photosensitive composition (PC) can also comprise plasticizer.Suitable plasticizer comprises modified and unmodified natural oil and natural resin, such as high boiling point paraffin, naphthenic mineral oil or aromatic mineral oil, synthetic oligomer or resin such as oligostyrene, high boiling point ester, oligostyrene-butadiene copolymer, oligomeric alpha-methylstyrene / p-methylstyrene copolymer, liquid oligomeric butadiene, especially those with molecular weight of 500g / mol to 5000g / mol, or liquid oligomeric polyacrylonitrile-butadiene copolymer or oligomeric polyethylene-propylene-diene copolymer.Preferred polybutadiene oil (liquid oligomeric butadiene), especially polybutadiene oil with molecular weight of 500g / mol to 5000g / mol, high boiling point aliphatic ester, such as, especially alkyl ester of monocarboxylic acid and dicarboxylic acid, example is stearate or adipic acid ester and mineral oil.Particularly preferred is high boiling point substantially paraffin and / or naphthenic mineral oil.For example, so-called paraffin-based solvates and special oils can be used. In the case of mineral oils, the skilled person distinguishes between industrial white oils, which may also contain a very small aromatic content, and medicinal white oils, which are substantially free of aromatic compounds. They are commercially available and are also very suitable. As plasticizers, particularly widely used are white oils or oligomeric plasticizers, such as, in particular, polybutadiene oils, carboxylates, phthalates. In this respect, reference may be made to EP 992 849 and EP 2 279 454 by way of example.

[0185] In some embodiments, bio-based plasticizers can be used to facilitate processing behavior during, for example, an extrusion process. Bio-based plasticizers are typically derived in part from renewable biological resources, such as plants (e.g., crops or wood), microorganisms (e.g., algae or yeast), or animals, as described in International Application PCT / EP2022 / 062430, which is included herein by reference.

[0186] Bio-based plasticizers are derived at least in part from renewable biological resources, such as plants (e.g., crops or wood), microorganisms (e.g., algae or yeast), or animals. Bio-based plasticizers are environmentally friendly, usually but not necessarily biodegradable. Bio-based materials can be chemically altered, or modified with synthetic compounds, to change, for example, physical and / or chemical properties. They are then still bio-based materials. These plasticizers are generally used to maintain softness and flexibility over a variable temperature range. These plasticizers can at least partially replace other plasticizers, such as synthetic plasticizers. Many non-bio-based plasticizers, especially so-called phthalates, are harmful to human health and may affect hormone balance. Others are based on mineral oil or polybutadiene and are not easily biodegradable. Therefore, it is advantageous to replace them at least in part with bio-based plasticizers. We have also found that when bio-based plasticizers are used for thermal development, for all concentrations studied, a higher relief depth can be achieved. In addition, we have found that using, for example, rapeseed oil to replace mineral oil allows for higher rinsing speeds and results in shorter processing times. More preferably, the bio-based plasticizer is a vegetable oil, a fatty acid, and / or a fatty acid ester of a monofunctional alcohol and a polyfunctional alcohol having one or less free hydroxyl groups. 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. Another example is acai oil ( oil), lanolin (adeps lanae), ahiflower oil, algae oil, aloe vera juice, amaranth oil, almond oil, argan oil, avocado oil, babassu oil, baobab oil, beeswax, nigella 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, chile hazelnut oil, corn oil, cottonseed oil, asafoetida oil ( butter, evening primrose oil, fish oil, glycerin, grapeseed oil, peanut oil, hazelnut oil, high oleic canola oil, high oleic soybean oil, high oleic sunflower oil, illipe butter, jatropha curcas oil, jojoba oil, kukuinut oil, lanolin, laurel oil, macadamia oil, marula oil, mango butter, manketti oil, meadowfoam seed oil, milk thistle oil, moringa oil, murumuru butter, mustard seed oil, olive oil, olus oil, omega-3-6-9-oil, palmolein, palm stearin, paradise nut oil, passionflower seed oil, peach kernel oil, peanut oil, pecan oil, perilla oil, pistachio oil, prune kernel oil, pomegranate oil, pumpkin seed oil, hydrogenated rapeseed oil, raw wool The invention relates to a plasticizer comprising a plurality of plasticizers, e.g., grease, rice bran oil, rosehip kernel oil, sacha inchi oil, safflower oil, salfat, sea buckthorn oil, sesame oil, shea butter, hydrogenated soybean oil, partially hydrogenated soybean oil, squalane, hydrogenated sunflower oil, sunflower wax, sumac wax, animal fat, tamanu oil, walnut oil, wheat germ oil, woolfat, lanolin alcohol. Different types of plasticizers can be combined to fine-tune the properties of the layer. For example, as an alternative to the plasticizers described above or in addition to the plasticizers described above, a bio-based plasticizer can be used. The amount of plasticizer optionally present can be determined according to the desired properties of the layer.

[0187] Bio-based plasticizers may have one or more of the following characteristics:

[0188] Wherein the plasticizer is a bio-based plasticizer, preferably a vegetable oil, a fatty acid, and / or a fatty acid ester of a monofunctional alcohol and a polyfunctional alcohol.

[0189] The plasticizer is characterized by a UV transmittance of a 33 wt% solution of the plasticizer in n-hexane at 365 nm higher than 1%, preferably higher than 10%, more preferably higher than 50%, even more preferably higher than 60%.

[0190] Therein the plasticizer is characterized by a Gardner color of less than 7 according to ISO 4630:2015.

[0191] Therein the plasticizer is characterized by a hydroxyl value below 430, preferably below 250, even more preferably below 168 according to ASTM D1957-86.

[0192] Wherein the plasticizer has an iodine value below 200, preferably below 150 according to ISO 3961:2018.

[0193] Therein the plasticizer has a Hansen solubility parameter δt in the range of 16.0 to 20.5, preferably in the range of from 16.0 up to 17.5.

[0194] Determination of UV transmittance: UV transmittance at 365 nm was measured in n-hexane with a plasticizer concentration of 5 parts by weight in a 10 mm cuvette 110-QS. UV / Vis spectra were recorded on a Varian Cary 50, scanning 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 integrated software.

[0195] Determination of transmittance: The pure oil was filled in a 10 mm large cuvette 110-QS, and the transmittance was measured by placing the cuvette in a densitometer Gretag Macbeth D 200II (measuring tube: V (λ), measuring aperture: 3 mm diameter) and pressing the probe head onto the large cuvette. The measurement of the transparent MCT-oil, which is resistant to oxidation due to the lack of double bonds, was set as a standard with a transmittance of 100%. The average value of 3 measurements was determined. For more details about bio-based plasticizers, reference is made to PCT / EP2022 / 062430, which is incorporated herein by reference.

[0196] The concentration of the plasticizer in the photopolymer layer (also referred to herein as the photosensitive layer) is preferably in the range of from 3 wt % to 70 wt %, preferably in the range of from 5 wt % to 65 wt %, more preferably in the range of from 10 wt % to 65 wt %, even more preferably in the range of from 20 wt % to 60 wt %, based on the total weight of the photopolymer layer.

[0197] Relief Precursor (RP)

[0198] The relief precursor (RP) comprises a photopolymer layer (also referred to as photosensitive layer L2) as described above, which is applied on a dimensionally stable support (L1) (also referred to as 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 supports are plates, foils and also conical and cylindrical tubes known as sleeves, which are made of metals such as steel, aluminum, copper or nickel, or of plastics such as polyethylene terephthalate, polybutylene terephthalate, polyamide or polycarbonate, of woven or non-woven fabrics such as woven glass fiber fabrics, or of composite materials comprising glass fibers and plastics. Particularly suitable as a dimensionally stable support are dimensionally stable carrier foils or metal sheets, examples being foils of polyethylene or polyester or steel or aluminum sheets. In general, the carrier foil or metal sheet has a thickness of 50 μm to 1500 μm, preferably 75 μm to 400 μm, for example about 250 μm. If steel is used as carrier material, steel sheets with a thickness of 0.05 mm to 0.3 mm are preferred. In order to prevent corrosion, it is preferred to use tinned steel sheets. These carrier foils or carrier sheets can be coated with a thin adhesion-promoting layer, for example a 0.1 μm to 2 μm thick layer, 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.

[0199] 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 to 7000 μm, preferably 0.01 to 4 mm, more preferably 0.02 to 3 mm and very preferably 0.03 to 3 mm.

[0200] The relief also comprises a masking layer L3 comprising at least a compound capable of absorbing electromagnetic radiation and a component removable by ablation (also called digital plate precursor).

[0201] The reference mark L1, L2 and L3 of layer can but in no way be intended to be limited to specific sequence. If necessary, relief precursor can include other layer, for example oxygen blocking barrier layer (oxygen blocking barrier layer), adhesion layer (adhesion layer), demoulding layer or stripping layer (disbonding layer), UV / VIS light and / or IR light absorption layer, monomer diffusion control layer, surface control layer, protective layer, cover foil, cover film or its combination. In embodiments, there can be an adhesion coating with optional top coating thereon. Such adhesion coating can be the layer of polyurethane adhesion coating material, for example as described in DE3045516.

[0202] Preferably, the mask layer is an integral layer of the relief precursor and is in direct contact with the photosensitive layer or a functional layer disposed between the photosensitive layer and the mask layer. The functional layer is preferably a barrier layer and blocks oxygen. The mask layer can be imageable by ablation and removable by a solvent or by thermal development. The mask layer is heated and removed by irradiation with high-energy electromagnetic radiation, thereby forming an image-level structured mask that is used to transfer the structure to the relief precursor. To do this, the mask layer can be opaque in the UV region and absorb radiation in the VIS-IR region of the electromagnetic spectrum. The VIS-IR radiation can then be used to heat and ablate the layer. The optical density of the mask layer in the UV region between 330nm and 420nm is in the range of 1 to 5, preferably in the range of 1.5 to 4, and more preferably in the range of 2 to 4.

[0203] The layer thickness of the ablatable mask layer can be in the range of 0.1 μm to 5 μm, preferably in the range of 0.3 μm to 4 μm, more preferably in the range of 1 μm to 3 μm. The laser sensitivity of the mask layer (measured as ablation of 1 cm 2 The energy required can be 0.1 J / cm 2 Up to 10J / cm 2 In the range of 0.3 J / cm 2 Up to 5J / cm 2 In the range of 0.5 J / cm 2 Up to 5J / cm 2 within the range.

[0204] Developing a relief precursor (RP) and producing a relief with a relief structure (RS)

[0205] The relief precursor can be imaged by ablating a mask layer, by exposure through a mask or by direct imaging. In this way, the precursor can be developed into a relief with a relief structure (e.g. a cliché). The mask layer can be a separate layer, which is applied to the relief precursor after removing a possible protective layer, or an integral layer of the precursor, which is in contact with the relief layer or one of the optional layers above the relief layer and is covered by a possible protective layer.

[0206] The mask layer can also be a commercially available negative film, which can be produced, for example, by a photographic method based on silver halide chemistry. The mask layer can be a composite layer material, in which a transparent layer is produced in an otherwise opaque layer by image-based exposure, as described, for example, in EP 3 139 210 A1, EP 1 735 664 B1, EP 2 987 030 A1, EP 2 313 270 B1. This can be achieved by ablating an opaque layer on a transparent carrier layer, as described, for example, in US 6,916,596, EP 816 920 B1, or selectively applying an opaque layer to a transparent carrier layer, as described in EP 992 846 B1, or writing directly on a relief-forming layer, such as, for example, by printing with an opaque ink by means of an inkjet, as described, for example, in EP 1 195 645 A1.

[0207] The image-level removal of the mask layer is preferably carried out using ablation techniques. Typically, the electromagnetic radiation used to ablate the mask will typically be radiation with a wavelength in the range from 300 nm to 20,000 nm, preferably in the range from 500 nm to 20,000 nm, particularly preferably in the range from 800 nm to 15,000 nm, very particularly preferably in the range from 800 nm to 11,000 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. In order to selectively remove the mask layer, one or more laser beams are controlled so that the desired printed image is produced.

[0208] Direct image exposure can be achieved in that the areas to be crosslinked are selectively exposed. This can be achieved, for example, by using one or more appropriately controlled laser beams, by using a monitor in which specific image points emitting radiation are activated, by using a movable LED strip, by means of an LED array in which individual LEDs are specifically switched on and off, by using an electronically controllable mask in which image points that allow the radiation from the radiation source to pass are switched to transparent, by using a projection system in which by means of appropriate orientation of mirrors, the image points are exposed to the radiation from the radiation source, or a combination thereof. Preferably, direct exposure is performed by means of 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.

[0209] The wavelength of the electromagnetic radiation is in the range of from 200 nm to 20000 nm, preferably in the range of from 250 nm to 1100 nm, particularly preferably in the UV range, very particularly preferably in the range of from 300 nm to 450 nm. In addition to broadband irradiation with electromagnetic radiation, it may be advantageous to use narrowband or monochromatic wavelength ranges, such as can be generated by using appropriate filters, lasers or light emitting diodes (LEDs). In these cases, wavelengths of 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) are preferred, either alone or in combination.

[0210] The relief is produced by exposure to electromagnetic radiation through a mask film. When exposed, the exposed area undergoes crosslinking, while the unexposed area of ​​the precursor remains soluble or liquefiable and is removed by an appropriate method. In the presence of an imaged mask, the irradiation can occur extensively, or if operated without a mask layer, the irradiation can occur in a small area (vertical spot) in an imaged manner by means of a guided laser beam or a localized analytical projection of electromagnetic radiation. In this case, the wavelength of the irradiated electromagnetic wave is in the range of from 200nm to 2000nm, preferably in the range of from 200nm to 450nm, more preferably in the range of from 250nm to 405nm. The irradiation can occur continuously or in pulsed form or in the case of continuous radiation with more than one short period. In addition to the broadband radiation of electromagnetic waves, it may be advantageous to use a narrowband or monochromatic wavelength range, which can be produced using an appropriate filter, laser or light emitting diode (LED).

[0211] In these cases, wavelengths in the range of 350 nm, 365 nm, 385 nm, 395 nm, 400 nm, 405 nm, 532 nm, 830 nm, 1064 nm are preferred, either individually (and about 5 nm-10 nm higher and / or lower) or as a combination. The intensity of the radiation here can be varied within a wide range, ensuring that a dose is used which is sufficient to cure the radiation-curable layer sufficiently for a later development procedure. The radiation-induced reaction, possibly after an additional heat treatment, must proceed sufficiently that the exposed areas of the radiation-sensitive layer become at least partially insoluble and therefore cannot be removed in the development step.

[0212] The intensity and dose of radiation depends on the reactivity of the preparation and the duration and efficiency of development.

[0213] The intensity of the radiation ranges from 1mW / cm 2 Up to 15000mW / cm 2 In the range of 5mW / cm 2 Up to 5000mW / cm 2 In the range of 10 mW / cm 2 Up to 1000mW / cm 2 The radiation dose is from 0.3J / cm 2 Up to 6000J / cm 2 In the range of 3 J / cm 2 Up to 100J / cm 2 In the range of 6 J / cm 2 Up to 20J / cm 2 within a range of. The exposure to the energy source can also be carried out in an inert atmosphere, such as in a rare gas, CO2 and / or nitrogen or in a liquid that does not damage the relief precursor. The exposure through the mask can be accomplished by using optical means, for example for beam widening, by a two-dimensional arrangement of a plurality of point or linear sources (e.g. light guides, emitters), such as fluorescent strips arranged side by side with each other, by moving a linear source or an elongated arrangement of LEDs (arrays) relative to the relief precursor, for example by uniform movement of the LEDs, or a combination thereof. Preferably, fluorescent strips arranged side by side with each other or a relative movement between one or more LED strips and the relief precursor are used.

[0214] Irradiation can be performed continuously, in pulses, or in a plurality of short cycles in the case of continuous irradiation.

[0215] The removal of the uncured areas of the precursor is preferably carried out by treatment with heat and a developer material configured to adsorb the uncured material. More preferably, in step d), the precursor is heated to a temperature in the range of 70°C to 200°C, preferably in the range of 80°C to 180°C, more preferably in the range of 90°C to 165°C. The heating of the exposed relief precursor can be carried out by all techniques known to the skilled person, such as, for example, by irradiation with IR light, the action of hot gases (e.g., air), the use of hot rollers or any desired combination thereof. For removing the (viscous) liquid areas, all techniques and processes familiar to the skilled person can be used, such as, for example, blowing, suction, tapping, sandblasting (with particles and / or droplets), peeling, wiping, transfer to a developer medium, and any desired combination thereof. Preferably, the liquid material is sucked (absorbed and / or adsorbed) by the developer medium, which is in continuous contact with the heated surface of the relief precursor. The procedure is repeated until the desired relief height is reached. The developing media that can be used are paper, woven and nonwoven fabrics and films, which are capable of absorbing the liquefied material and can be composed of natural fibers and / or polymer fibers. It is preferred to use polymers such as cellulose, cotton, polyester, polyamide, polyurethane nonwovens or nonwoven fiber webs, and any desired combination thereof, which are stable at the temperature used during development.

[0216] Alternatively, the precursor is treated with a developer to dissolve the uncured material. The techniques applied in this development step may be all techniques familiar to the technician. The solvent or its mixture, the aqueous solution and the aqueous organic solvent mixture may contain an auxiliary agent, which stabilizes the formulation and / or increases the solubility of the components of the non-crosslinked region. Examples of such auxiliary agents are emulsifiers, surfactants, salts, acids, bases, stabilizers, corrosion inhibitors and suitable combinations thereof. For development with these solutions, all techniques known to the technician can be used, such as, for example, immersion, washing or spraying with a developer medium, brushing in the presence of a developer medium, and suitable combinations thereof. It is preferred to develop with a neutral aqueous solution or water, with the aid of a rotating brush or a plush net to assist removal. Another way to influence development is to control the temperature of the developer medium, and to accelerate development, for example, by increasing the temperature. In this step, it is also possible to remove additional layers still present on the radiation-sensitive layer, if these layers can be detached during development and fully dissolved and / or dispersed in the developer medium.

[0217] Optionally, one or more steps in post-treatment, post-exposure and / or debonding are carried out. These include, for example, heat treatment, drying, with electromagnetic rays, with plasma, with gas or with liquid treatment, the attachment of identification features, cutting into formats, coating and any desired combination thereof. Heat treatment can, for example, be used to initiate and / or complete reaction, to increase the mechanical stability and / or thermal stability of relief structure and to remove volatile components. For heat treatment, known techniques can be used, such as, for example, using heated gas or liquid heating, IR radiation and any desired combination thereof. In these cases, baking ovens, blowers, lamps and any desired combination thereof can be used. In addition to decomposition, surface modification can also be completed by treating with gas, plasma and / or liquid, particularly if there is also a reactive substance used in addition. For example, the processing utilizing electromagnetic radiation can be used to debond the surface of relief structure, and trigger and / or complete the purpose of polymerization and / or cross-linking reaction. In this case, the wavelength of the electromagnetic wave irradiated is in the range of from 200nm to 2000nm. Example

[0218] Experimental Composition and Preparation of Relief Precursors

[0219] Panels were produced using the following test compositions:

[0220] 10 parts by weight of hexanediol diacrylate (HDDA) as an ethylenically unsaturated compound;

[0221] 2.0 parts by weight of benzil dimethyl ketal (BDK) as a photoinitiator;

[0222] 21 parts by weight of a liquid polybutadiene polymer (PBP) as a plasticizer;

[0223] 1.1 parts by weight of additional ingredients such as additives and dyes (A);

[0224] 59 to 66 parts by weight of a binder (B) having a styrene content of about 28.5% and

[0225] An SBS triblock copolymer (thus based on SBS rubber) with a diblock fraction of approximately 17%; and

[0226] 0 to 6.5 parts by weight of a stabilizer (S).

[0227] In the given examples, the amount of stabilizer varies within the range of 0 to 6.5 parts by weight, and the excess is correspondingly offset by the amount of binder.

[0228] The components were dissolved in a solvent, toluene (also called methylbenzene), and heated under reflux to obtain a homogeneous solution (concentration in toluene: 45 wt %).

[0229] The solution was then cast on a support sheet. The plate thickness was adjusted using a doctor blade at a distance of 3 mm from the support sheet (PET film having a thickness of 175 μm).

[0230] The solvent was allowed to evaporate at room temperature for 16 hours, followed by heating at 65°C for 4 hours. To allow digital imaging, the mask layer (ML) coated on the cover sheet (CL) was laminated on top of the relief precursor using an Excelam-Q laminator (GMP Deutschland GmbH, Germany). Lamination was performed at a heating roller temperature of 110°C, a speed of 8.8mm / s and a gap of 1.5mm. To complete the lamination, the cast plate was sandwiched between two aluminum plates and kept at 65°C for 3h.

[0231] Evaluation samples

[0232] Hot melt stability

[0233] Hot melt stability was evaluated by recording the melt viscosity during heating.

[0234] The crosslinking of the sample is 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 a measurement geometry, a parallel plate with an upper plate having a diameter of 2.5 cm was selected. As a sample, a disc of a relief precursor having a diameter of 2.5 cm was used. Before measurement, any foil (e.g., cover sheet) and mask layer were removed from the relief precursor. The measurements were performed in an oscillating single-frequency mode. The frequency was set to 1 Hz. The gap between the parallel plates was set to be constant relative to the corresponding sample thickness. Data points were recorded every 15 s. The complex shear viscosity η* was monitored over time t. "Onset time of crosslinking" was determined as "the time when the difference quotient Δη* / Δt≥1Pa, where Δt=15s". A higher onset time indicates a higher thermal stability and stability to mechanical stress.

[0235] Printing board evaluation

[0236] To obtain the cliché, the laser ablatable mask on the front side was imaged using a TfxX 20 laser (Flint Group Germany GmbH, Germany, rotation speed: 10 rpm to 11 rpm, power: 35 W (100% intensity)). The relief precursor was exposed to UV light from the back side through the carrier foil for 20 s to 40 s and from the front side through the mask layer for 15 min. During the exposure at room temperature (about 18° C.-25° C.), there was no active heating. As a result of the cross-linking reaction caused by the exposure, the temperature of the plate rose to about 40° C. (machine type: Combi FIII (Flint Group Germany GmbH, Germany), UVA intensity mW / cm 2 , UVA tube type: Philips TL 80W / 10-R). Use Digital WasherFIII (Flint Group Germany GmbH, Germany) and A (Flint Group Germany GmbH, Germany) was used as the rinse solvent to remove the unpolymerized material and the residual black mask layer at a solvent temperature of 35°C, a rinse speed of 230 mm / min to 240 mm / min and a brush height of 0 mm. After rinsing, the board was dried at 60°C for 2 h (Combi FIII (Flint Group Germany GmbH, Germany)). Post-curing was performed from the front using UVA and UVC (machine type: CombiFIII (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: 5min, UVC intensity: 13mW / cm 2 , UVC tube type: PhilipsTUV 75W HO G75 T8, start UVA and UVC post exposure at the same time).

[0237] Example 1

[0238] The test compositions as mentioned above were used. In this example, each sample had a stabilizer of a certain type and / or concentration. As a reference stabilizer, butylated hydroxytoluene (BHT), also known as 2,6-di-tert-butyl-4-methylphenol, was used. Its exemplary structure is shown below.

[0239]

[0240] As a stabilizer of the present invention, vitamin derivative ascorbyl palmitate (AP) is used. This vitamin derivative can be considered as a fatty acid ester of ascorbic acid and palmitic acid, and an exemplary structure is shown below.

[0241]

[0242] It is believed that the carbon chain is -(CH2) 14 The CH3 chains improve the compatibility of the vitamin derivatives in SBS rubber. In addition, the surfactant-like structure of the vitamin derivatives may lead to improved stability to oxygen at the interface.

[0243] Table 1 shows the respective types of stabilizers, the concentrations in wt.% and molar equivalents and the resulting cross-linking start times. For the cross-linking start time t, the average of two measurements was used.

[0244]

[0245] Table 1: Different stabilizers in SBS rubber based formulations and their effect on the onset of crosslinking.

[0246] The stabilizer ascorbyl palmitate (AP) was found to have a higher crosslinking onset time than an equimolar amount of tert-butylhydroxytoluene (also known as BHT) (Table 1), which indicates better stability because a longer time is required before viscosity increases due to addition and crosslinking reactions. The reference ascorbic acid was incompatible with the test formulation and therefore could not be tested.

[0247] Example 2

[0248] The test compositions as mentioned above were used. In this example, ascorbyl palmitate was tested as a stabilizer at different concentrations and compared to plates containing no additional stabilizer.

[0249]

[0250] Table 2: Different concentrations of ascorbyl palmitate as stabilizer in SBS rubber based formulations and its effect on the crosslinking onset time.

[0251] As the amount of stabilizer increases, the crosslinking start time increases, 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 still even more preferably 1 wt% or more.

[0252] Example 3A

[0253] The test compositions as mentioned above were used. In this example, different stabilizer types and / or stabilizer concentrations and / or different combinations of stabilizers were tested.

[0254]

[0255] Table 3A: Formulations based on SBS rubber tested with or without 1 wt.% ascorbyl palmitate (AP) stabilizer in combination with other types of stabilizers. The crosslinking start time is taken as the average of two separate measurements.

[0256] In combination with other stabilizer classes, synergy between ascorbyl palmitate and the stabilizers tested was observed. The crosslinking start time obtained for the stabilizer combination exceeded the crosslinking start time obtained for the equimolar amount of the single stabilizer alone. See, for example, sample 3.6, which achieved improved thermal stability (79 min) compared to samples 3.3 (67 min) and 3.5 (39 min) (Table 3A).

[0257] Example 3B

[0258] The test composition as mentioned above was used. In this example, additional samples with additional other stabilizer classes (e.g., phenolic acrylate types, tertiary amine acrylates, etc.) in formulations with or without AP stabilizers were tested. When the vitamin derivative (S1) was combined with the other stabilizer (S2), a synergistic effect was found. Therefore, in some embodiments, it is preferred to have a first stabilizer that is a vitamin or vitamin derivative and a second (additional) stabilizer. Exemplary second stabilizers are shown in Table 3Ba.

[0259]

[0260]

[0261] Table 3Ba: Additional stabilizers (besides vitamins and vitamin derivatives).

[0262] The cross-linking start time for the combination comprising both the first stabilizer (S1) and the second stabilizer (S2) is listed in Table 3Bb.

[0263]

[0264]

[0265] Table 3Bb: Formulations with other types of stabilizers combined or not with 1 wt.% ascorbyl palmitate (AP) as stabilizer were tested. *Polymerization during sample preparation, **Time slightly increased (6%). In combination with AP, no increase. Regarding other types of stabilizers, a synergistic effect was observed when combined with AP stabilizer (Table 3Bb). The combined crosslinking onset time was found to be much higher than the plates stabilized with only one type of stabilizer.

[0266] Example 4

[0267] In this example, the effect of the stabilizer on the tone value of the resulting printed plate was evaluated, since conventional stabilizers can affect the tone value due to their potential hindrance to curing. For samples with BHT and AP as stabilizers, the test composition as mentioned above was used. This example shows that the AP stabilizer has a much smaller effect on the tone value. The effect of the stabilizer on the tone value is calculated as the difference in the tone value of the 5% halftone at 146 lpi of the plate without any additional stabilizer compared to the corresponding tone value of the plate containing the stabilizer.

[0268]

[0269] Table 4: Minimum halftone at 146 lines per inch (lpi) for SBS rubber based sample formulations with no stabilizer, with BHT stabilizer as a reference, and with AP stabilizer of the present invention.

[0270] BHT hinders crosslinking during UV exposure. Therefore, no halftone dots less than 5% tone value are anchored on the relief. BHT also reduces the resulting dot size. A 5% halftone produces only a 0.7% tone value on the cliché.

[0271] Without additional stabilizer, starting from a halftone of 1.2%, much smaller dots can be reproduced on the cliché than with BHT, resulting in a tint value of 3.7% on the cliché. However, without additional stabilizer, the melt (already) undergoes crosslinking when heated, for example during the production of relief precursors. The reference ascorbic acid is incompatible with the test formulation and could therefore not be tested.

[0272] Using the stabilizer ascorbyl palmitate according to the invention, an improved thermal stability of the melt is achieved (see Table 1). At the same time, the copy properties are only affected to a slight extent (only 0.8%) (Table 4). The addition of 1 wt.% ascorbyl palmitate to the plate formulation leads to a slight increase in the first stable halftone at 146 lpi from 1.2% to 1.8% and to a slight reduction in the resulting dot size (tone value from 3.7% to 2.9%). The effect of ascorbyl palmitate on the copy properties is much lower than that of an equimolar amount of the reference BHT (Table 4).

[0273] Thus, it is shown that the AP properties supersede the properties of the BHT stabilizer. Furthermore, due to the improved thermal stability caused by the ascorbyl palmitate stabilizer, unintended gel formation caused by mechanical and thermal stresses, for example due to kneading during extrusion of the rubbery mixture to form the relief precursor, can be avoided.

[0274] Example 5

[0275] In this example, another test formulation based on SIS triblock copolymer was used. The material in plate form was produced according to the method mentioned above with the following composition:

[0276] 10 parts by weight of hexanediol diacrylate (HDDA),

[0277] 2.0 parts by weight of benzil dimethyl ketal (BDK) as a photoinitiator,

[0278] 5 parts by weight of hydrocarbon resin (CAS 9017-27-0),

[0279] 1.1 parts by weight of additional ingredients, such as additives and dyes (A),

[0280] 81 to 82 parts by weight of a binder (B) which is a SIS triblock copolymer having a styrene content of about 15% and a diblock fraction of about 19%, and

[0281] 0 to 1 parts by weight of a stabilizer (S).

[0282] In a given example, the amount of stabilizer varies within the range of 0 to 1 part by weight, and the excess is correspondingly offset by the amount of binder.

[0283]

[0284] Table 5: SIS rubber based formulations with ascorbyl palmitate compared with a formulation without any additional stabilizer and with a formulation with an equimolar amount of BHT as reference, and the respective crosslinking start times.

[0285] In the absence of additional stabilizers, crosslinking was observed after a measurement time of 5 min. Reference ascorbic acid was incompatible with the test formulation and therefore could not be tested. Using BHT, the crosslinking onset time increased from 5 min to 16 min. Ascorbyl palmitate (AP) had an effect on the crosslinking onset time that was more than five times that of an equimolar amount of BHT, indicating higher thermal stability and better manufacturability in the extrusion process (Table 5).

[0286] Example 6

[0287] In this example, the type of plasticizer and the type and concentration of stabilizer were varied. The material in plate form was produced according to the method mentioned above with the following test composition:

[0288] 10 parts by weight of hexanediol diacrylate (HDDA) as an ethylenically unsaturated compound;

[0289] 2 parts by weight of benzil dimethyl ketal (BDK) as a photoinitiator;

[0290] 21 parts by weight of a liquid plasticizer, i.e., polybutadiene or a bio-based plasticizer;

[0291] 1 part by weight of additional ingredients such as additives and dyes (A);

[0292] 64 to 66 parts by weight of a binder (B) having a styrene content of about 25% and a large

[0293] An SBS triblock copolymer (thus based on SBS rubber) with a diblock fraction of about 10%; and

[0294] 0 to 1.5 parts by weight of a stabilizer (S).

[0295] In the given examples, the amount of stabilizer varied in the range of 0 to 1.5 parts by weight, and the excess was offset accordingly by the amount of binder. The type of stabilizer and the type of plasticizer were varied. The rheological measurement time was 30 min respectively.

[0296]

[0297] Table 6: SBS rubber based formulations tested with different types of stabilizers in combination with different types of plasticizers.

[0298] The reference ascorbic acid was not compatible with the test formulation and therefore could not be tested. The crosslinking onset time of the inventive stabilizers ascorbyl palmitate and tocopherol was found to be increased also in the presence of different types of liquid plasticizers such as polybutadiene or bio-based plasticizers compared to sample 6.1 without any additional stabilizer (Table 6).

[0299] Example 7

[0300] Kneading tests were carried out using a ThermoFisher Scientifc Haake kneading device equipped with a Haake PolyLab OS RheoDrive 7 control unit, a HaakeRheomix 600OS heating and kneading chamber with a roller rotor R600. Torque and sample temperature were recorded using software PolySoft, version 2.1.0.1. For the measurements, a temperature of 180°C was applied. The measurements were carried out for 60 min each. The components as solids were added to the kneading device and allowed to mix in the kneading device.

[0301] As a sample, 50 g of the following composition were used:

[0302] 99 to 100 parts by weight of a binder (B) which is an SBS triblock copolymer (thus based on SBS rubber) having a styrene content of about 25% and a diblock fraction of approximately 10%; and

[0303] 0 to 1.0 parts by weight of a stabilizer (S).

[0304] In a given sample, the amount of stabilizer varied from 0 to 1.0 part by weight, and the excess was offset accordingly by the amount of binder.

[0305]

[0306] Table 7: Formulations based on SBS rubber with different types of stabilizers tested in kneading tests.

[0307] The increase in torque indicates that the SBS rubber begins to crosslink due to insufficient stability. In the absence of additional stabilizers, an increase in torque is observed within the first 10 min of the measurement time. Using BHT as a stabilizer, an increase in torque is detected after heating at 180°C for 28 min. Using ascorbyl palmitate, the best results were achieved, where crosslinking was observed after 50 min. The reference ascorbic acid was incompatible with the test formulation and therefore could not be tested.

[0308] Example 8

[0309] The test composition as mentioned in Example 1 was used. The printing plate precursors were developed according to the procedure described in the section Evaluation of Printing Plates. For evaluation of resistance to UV light and cracking, the developed printing plates were then further irradiated (machine type: Combi FIII (Flint Group Germany GmbH, Germany), UVA exposure time: 40 min, UVA intensity: 11 mW / cm 2 , UVA tube type: Philips TL 60W / 10-R, UVC exposure time: 40min, UVC intensity: 13mW / cm 2 , UVC tube type: Philips TUV 75W HO G75 T8, UVA and UVC post-exposure started simultaneously). On a piece of solid printed area of ​​5×8 cm, an edge (0.2 mm) was cut in the middle of the long side with a knife. The sheet was bent at an angle of 180° in such a way that the cut could propagate along the relief layer (on the carrier foil). After 5 minutes, the total length of the cracked relief layer along the bend minus the initial cut length was measured. Cracks that did not follow the original cut (e.g. started in the middle of the bend due to brittleness) were also taken into account.

[0310]

[0311] Table 8: Tear test of BHT stabilizer and AP stabilizer

[0312] Longer tears indicate poor stability after extended UV exposure. The best results with no tearing were achieved with ascorbyl palmitate. The tearing was more pronounced with an equimolar amount of BHT. The longest tearing was observed without additional stabilizers.

[0313] Example 9

[0314] Several carbamate derivatives from ascorbic acid (AA) were synthesized and used in test compositions similar to those previously mentioned in Example 1. The reaction mixture was used completely without purification and was simply added to the plate preparation during homogenization in toluene solution. The stoichiometric amounts of the reactants were calculated in such a way that a concentration of 1 wt% of the carbamate derivatives was obtained in the plate preparation, assuming complete conversion of the reactants. For each synthesis of the entries in Table 9 below, 1.0 molar equivalents (eq.) 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 preparation in toluene solution. The procedure for plate precursor production was followed as mentioned above. The solution was cast on a carrier sheet, and a trace amount of THF / ethanol was evaporated with toluene during the drying step of the plate precursor.

[0315] However, for the reference (Ref.) in Table 9 below, the same procedure was followed but without the addition of AAD.

[0316] Detailed procedures for example regarding item 1: 1.84g n-butyl isocyanate (0.0186mol, 2eq.), 1.61g L-ascorbic acid (0.0093mol, 1eq.) and 0.294g di-n-butyltin dilaurate (0.000465mol, 0.05eq.) are suspended in 7gTHF and stirred at 60°C for 5 hours. The reaction progress is monitored by thin layer chromatography (silica gel 60F254, Aldrich, solvent: dichloromethane: ethanol 3:1, Rf (retention factor, ascorbic acid)=0.02, Rf (product)=0.70). The compound is visualized on a TLC plate by staining with Seebach solution (a mixture of phosphomolybdic acid hydrate, cerium sulfate (IV), sulfuric acid and water). In order to quench the reaction, 10mL ethanol is added to the mixture.

[0317]

[0318]

[0319] Table 9: Testing of carbamate derivatives

[0320] Molecular weight (MW) (g / mol) of the monofunctional derivative (MF) and the difunctional derivative (BF). Different isomers are possible. The calculated octanol-water coefficient (OWc) is identical for the possible monofunctional carbamate isomers. * Not determined (nd). Onset time t (Δη* / Δt≥1 Pa) / min (OT).

[0321] Exemplary IR spectroscopy measurements of the dried crude product:

[0322] L-Ascorbic acid (reference)

[0323] 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 .

[0324] Item 1—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(butylcarbamate)

[0325] IR(ATR):nd.

[0326] Item 2—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(tosylcarbamate)

[0327] IR(ATR):nd.

[0328] Item 3—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(phenylcarbamate)

[0329] 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 .

[0330] Item 4—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((3-(triethoxysilyl)propyl)carbamate)

[0331] IR(ATR):nd.

[0332] Item 5—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(tert-butylcarbamate)

[0333] IR(ATR):nd.

[0334] Item 6—6-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)-4,9-dioxo-5,8-dioxa-3,10-diazadodecane-1,12-diyl bis(2-methylacrylate)

[0335] 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 .

[0336] Item 7—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((2-(4-vinylphenyl)propan-2-yl)carbamate)

[0337] IR(ATR):nd.

[0338] Item 8—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(cyclohexylcarbamate)

[0339] 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 .

[0340] Item 9—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((trimethylsilyl)carbamate)

[0341] IR(ATR):nd.

[0342] Item 10—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(octadecylcarbamate)

[0343] 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 .

[0344] Item 11—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis((4-isopropylphenyl)carbamate)

[0345] 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 .

[0346] Item 12—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(m-tolylcarbamate)

[0347] 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 .

[0350] Item 13—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(phenethylcarbamate)

[0351] 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 .

[0352] Item 14—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(dodec-11-en-1-ylcarbamate)

[0353] IR(ATR):nd.

[0354] Item 15—1-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)ethane-1,2-diylbis(naphthalene-1-ylcarbamate)

[0355] 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 .

[0356] Item 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-diyl bis(2-methylacrylate)

[0357] IR(ATR):nd.

[0358] 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-azatridec-12-en-1-yl)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), the composition comprising: a free 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 Adhesive (B), the adhesive is a thermoplastic elastomer block copolymer, the thermoplastic elastomer block copolymer has a first monomer unit (Mu1), the first monomer unit being derived from a vinyl aromatic monomer, and a second monomer unit (Mu2), the second monomer unit being derived from an olefin monomer and / or a diene monomer; or a combination thereof; The stabilizer (S1) is a hydroxytetraonic acid (HTAD) derivative.

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

3. The composition according to claim 1 or 2, wherein the stabilizer (S1) has a predicted log octanol-water coefficient as calculated from Log Kow (WSKOW v 1.68 estimate) in EPI Suite v4.11, and wherein the predicted log octanol-water coefficient (OWc) is 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 according to any one of the preceding claims, further comprising a second stabilizer (S2), the second stabilizer being selected from one of the following categories: phenols, phenols and acrylates, thioethers, hindered amines, phenols and amines, amines, thioetheramines, multifunctional amines and acrylates, more preferably, wherein the second stabilizer (S2) is one of the following: 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, 3,3'-didodecyl thiodipropionate, 1,5,8,12-Tetrakis[4,6-bis(N-butyl-N-1,2,2,6,6-pentamethyl-4-piperidinylamino)-1,3,5-triazine-2-yl]-1,5,8,12-tetraazadodecane, 2',3-bis[[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyl]]propionylhydrazide, Bis[4-(2-phenyl-2-propyl)phenyl]amine, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-ylamino)phenol, A tertiary amine and an acrylate, preferably 1H-aza 2,2-bis[[(1-oxo-2-propen-1-yl)oxy]methyl]butylhexahydro-1H-azepine -1-propionate.

5. A composition according to any one of the preceding claims, wherein The 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, most preferably 200-430 g / mol.

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

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

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

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

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

13. A composition according to any one of the preceding claims, Wherein the binder (B) is a diblock copolymer or a triblock copolymer having a diblock fraction in the range of 5%-50%, preferably 5%-30%, more preferably 8%-28%, even more preferably 10%-24%.

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

15. A composition according to any one of the preceding claims, wherein the composition further comprises a plasticizer (P), the plasticizer being a bio-based plasticizer, preferably a vegetable oil, a fatty acid, and / or a fatty acid ester of mono- and polyfunctional alcohols; wherein the 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 %; wherein preferably, The bio-based plasticizer is characterized by a UV transmittance at 365 nm of a 33 wt% solution of the plasticizer in n-hexane of higher than 15%, preferably higher than 25%, more preferably higher than 50%, even more preferably higher than 60%; and / or The bio-based plasticizer is selected from the group consisting of 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 the preceding claims, wherein the stabilizer is an ascorbic acid derivative (AAD).

17. A method for producing a relief precursor (RP), comprising the steps of: extruding a photosensitive composition according to any one of the preceding claims through to form an extruded photosensitive layer; The extruded layer is applied to a dimensionally stable support (L1).

18. A relief precursor (RP) for being developed into a relief (RS), said relief precursor (RP) comprising: A dimensionally stable support body (L1); A photosensitive layer (L2), the photosensitive layer (L2) comprising the photosensitive composition according to any one of claims 1-16.

19. A relief (RS) developed from a relief precursor according to any one of the preceding claims, preferably for use as a printing sleeve or a printing blanket.

20. Use of a stabilizer (S1) to improve the extrusion stability of a mixture and / or to enhance the thermal stability of a second stabilizer (S2) as a thermal stabilizer, the stabilizer (S1) being a vitamin or a vitamin derivative, preferably ascorbyl palmitate (AP), preferably wherein the second stabilizer (S2) is selected from one of the following categories: phenols, phenols and acrylates, thioethers, hindered amines, phenols and amines, amines, thioetheramines, multifunctional amines and acrylates, more preferably wherein the second stabilizer (S2) is butylated hydroxytoluene (BHT).

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