WO2008125074A2

WO2008125074A2 - Biocompatible radiation-curable formulation for the generative production of medical products, particularly adaptive ear pieces and dental mouldings, by means of image projection systems

Info

Publication number: WO2008125074A2
Application number: PCT/DE2008/000243
Authority: WO
Inventors: Martin Klare; Frank Lindner
Original assignee: Dreve Otoplastik Gmbh
Priority date: 2007-04-12
Filing date: 2008-02-08
Publication date: 2008-10-23
Also published as: WO2008125074A3; DE102007017195A1

Abstract

The invention relates to a radiation-curable, biocompatible formulation comprising: a) at least one or more urethane poly(meth)acrylates, b) at least one or more (poly)(meth)acrylates, or a combination thereof, c) at least one initiator usable for the relevant radiation range, d) at least one or more or a combination of anaerobic and/or aerobic stabilizers, e) and in a particular, clear transparent embodiment, advantageously made of at least >0.1m% surface-modified nanoparticles, f) 0-40m% of fillers, g) 0-5m% of color pigments, h) 0.5m% of typical additives such as UV stabilizers or flow-control additives, wherein the proportion of components a) through h) is 100m% altogether, and the entire formulation lies within the so-called “wetting envelope' of the pre-hardened layer, present in the green-flex mode, of said formulation and has a viscosity of <10 Pas at 23 °C.

Description

Biocompatible, radiation-curing formulation for the generative production of medical products, in particular ear molds and dental moldings, by means of image projection systems

The present invention relates to a low-viscosity, radiation-curing biocompatible formulation for the generative production of medical devices, in particular earmolds and dental moldings, by means of

Image projection systems based on at least two compounds which have free-radically polymerizable (meth) acrylate functions and at least one for the radical polymerization of the above-mentioned. Compounds in the relevant radiation range useful photoinitiator and in a particular embodiment containing surface-modified nanoparticles.

Image projection systems based on emission sources in the visible radiation range are becoming increasingly important in the field of additive manufacturing processes for the production of three-dimensional objects for a variety of reasons. Such systems are an interesting alternative to additive manufacturing processes based on UV laser radiation sources. The use of image projection systems with visible emission range is in comparison to systems, which rely on laser radiation sources for photopolymerization, associated with a significantly lower financial cost in terms of purchase at also reduced maintenance costs. The present invention particularly aims at image projection systems which have a flexible, radiation-permeable conveyor belt by means of which the photopolymerizable formulation is transported into the exposure station. In the exposure station, a Digital Light Processor, hereafter referred to as DLP, projects imagewise the photopolymerizable resin through the radiation-transmissive belt to cure the resin formulation image by image or layer by layer. The DLP unit is mounted above the conveyor belt. After exposing and curing each layer, it is subsequently released from the coating tape by removing the build platform. This process is repeated until the three-dimensional object is generated.

The resin formulations used in such systems are subject to many requirements. On the one hand, such formulations must form a uniform film of material on the conveyor belt. On the other hand, however, then the hardened layer should then easily detach from this and additionally have sufficient mechanical strength to to remain stable on the building platform and the generated object and thus to be able to form three-dimensional objects. Such formulations, for moldings which have no or only a slight inhibiting layer, are described in EP 1717637. However, these formulations have the disadvantage that they are not or only to a very limited extent applicable for medical applications. This is due to the fact that high demands are placed on the generated moldings for medical applications in terms of biocompatibility. In the claimed formulations, however, compounds from, for example, the group of silicone acrylates are used to reduce the pull-off forces between the conveyor belt and the construction platform and for better wetting of the belt. These have a sensitizing effect and are therefore only limited usable for the production of medical devices. The minimization of the withdrawal forces is of particular importance in the aforementioned generative manufacturing processes. For this purpose, the prior art according to several mechanical solutions in US 5,171,490, DE 4125534 Al and DE 102004022600171 described to separate the cured material layer from the reference plane. In this case, the film is moved in the above writings for the purpose of separation, subtracted, unrolled or a slide, stripper or a plate over one side of the slide moves. All of these methods suffer from the disadvantage that additionally mechanically driven components are used, which are error-prone. This is undesirable in view of the robustness of a generative manufacturing process for rapid manufacturing.

Moreover, compared to prototypes, the cured medical objects must have increased color stability over a longer period of time since they come into contact with the human body surface and are therefore exposed to a wide variety of leaching media. The claimed in EP 1717637 formulations have a combined initiator system, which does not meet the above requirements. Furthermore, there is a need in the field of medical technology, for example for earmolds or implant drilling templates on clear transparent materials. The latter can not be realized with the formulations according to EP 1717637, since in these by both the claimed initiator combinations and the selected concentration ranges of initiators necessarily yellowish discoloration of the materials result. For all the reasons outlined above, there is a need for radiation-curing, biocompatible formulations which, in addition to the process engineering requirements, also meet the requirements for medical products in the cured state. Task of It is the object of the present invention to provide a resin formulation which satisfies the requirements for medical products in the unpolymerized state, the procedural requirements and the molded articles generated therefrom in the final cured state.

Brief Summary of the Invention: The o.g. Radiation-curable formulation requirements for the generative production of medical devices with an image projection system using visible radiation for curing and a coating line for material introduction are solved by a formulation comprising the following components: a) at least one or more urethane poly (meth) acrylates b) at least one or more

(Poly) (meth) acrylates, or a combination of these c) 0.1-4% of at least one initiator useful for the relevant radiation range d) at least one or more or a combination of anaerobic and or aerobic stabilizers e) and in a particular embodiment advantageously at least> 0.1 m% of surface-modified nanoparticles f) 0-40 m% of fillers g) 0-5 m% of color pigments h) 0-5 m% of customary additives such as UV stabilizers or leveling additives, wherein the proportion of the components a) to h) together amounts to 100% and the total formulation lies within the so-called "wetting envelope" of the green-flex mode, precured layer of this formulation and outside the "wetting envelope" of the coating strip and has a viscosity of <10 Pas at 23 ° C.

In addition, in addition to the general requirements for medical devices according to the MPG, the molded articles which have been finally hardened from the above formulation should also fulfill the requirements with regard to cytotoxicity, sensitization and irritation in accordance with DIN EN ISO 10993-1: 2003. The present invention has various advantages in view of the above requirements. By means of image projection systems, the claimed formulation can be used to generate high-quality 3-dimensional moldings, such as ear molds, which on account of the special setting of the adhesion properties of the resin formulation with regard to the "wetting envelopes" of the green body and the conveyor belt can be easily detached from various conveyor belts On the other hand, the above-mentioned invention ensures a robust construction process, as it is advantageous for the rapid manufacturing of medical devices. There is no need compounds such as the silicone acrylates listed in EP 1717637 A2 are used the "wetting envelopes" on o by the setting.-Indicated monomer / Oligomerkombinationen further, to easily solve the components ^"from the conveyor belt. Since these silicone acrylates are often associated with a sensitizing potential, it is very advantageous to be able to dispense with these in medical devices. Furthermore, said class of compound is not always miscible with the preferred methacrylate-based resin systems and thus may

Stability problems of the formulations. The components have sufficient mechanical properties and color stability for the intended use, also with regard to long-term use on / in the human body. In addition, it has surprisingly been found that the reactivities of the resin formulations can be significantly increased by the addition of surface-modified Si0 ₂ nanoparticles. Accordingly, higher results

Curing speeds or hardening depths and thus shortened process times. The latter is significantly beneficial for the field of rapid manufacturing. Furthermore, due to the increased reactivity of the resins, use can be made of lower initiator combinations. This is advantageous for three reasons. On the one hand, initiators such as the 2,4,6- Trimethylbenzoyldiphenylphosphinoxid used in relatively low concentrations and as clear transparent 3-dimensional objects are obtained. In many areas of medical technology, transparency of the shaped bodies, for example in the case of dental implant drilling templates, in order to be able to see the operating area, is necessary. On the other hand, it is known to the person skilled in the art that high concentrations of initiators often lead to discoloration in long-term applications. This is undesirable, for example, in the manufacture of earmolds. In addition, lower concentrations of initiators consequently also lead to lower levels of leachable initiator residual concentrations or initiator fragments. This is advantageous in terms of biocompatibility, such as CT. Hanks et al. described in J.Dent. Res., 70, pp. 1450-1455 (1991) and J. Oral Pathol. , 17, 396-403 (1988) and JL Ferracene, respectively, in J. Oral Pathol., 21, pp. 441-452 (1994).

Detailed description of the invention:

In the following, "(meth) acrylate" is always used

Acrylates and methacrylates understood. Under

In the text which follows, "(poly) (meth) acrylate" is understood as meaning mono- or polyfunctional acrylates and methacrylates.

Diacrylates, triacrylates, tetraacrylates,

Pentaacrylates, dimethacrylates, trimethacrylates,

Called tetramethacrylates and pentamethacrylates. Preferably, the mixture according to the invention contains:

a) 10-80 m% of one or a combination of urethane poly (meth) acrylates having a functionality of n <6 and a viscosity of <30 Pas at 23 ⁰ C b) 4- 89 .tau..sub.n% of at least one or a combination of several poly ( meth) acrylates having a functionality of n <5 and a viscosity <10 Pas at 23 ⁰ C, or a combination of one or more

(Poly) (meth) acrylates and at least one monomeric (meth) acrylate having a viscosity of <5 Pas at 23 ⁰ C c) 0.1-3.5% m usable at least one or a combination of the relevant radiation range initiators d) 0.0001-0.5 m% of at least one or more or a combination of anaerobic and / or aerobic stabilizers e) 0-40 m% surface-modified nanoparticles having a particle size of <100 nm and in a particular embodiment advantageously at least> 10 m% surface-modified Nanoparticles with a particle size of <30 nm f) 0-40 m% of fillers g) 0-5 m% of color pigments h) 0-5 m% of customary additives such as UV stabilizers or leveling additives, the proportion of the components being to h) 100% together and the total formulation lies within the so-called "wetting envelope" of the green-flex mode, precured layer of this formulation and outside the "wetting envelope" of the coating tape and has a <10 Pas at 23 ° C ,

Suitable compounds of component a) are, for example, urethane (meth) acrylates having a functionality of n <4. These are known to the person skilled in the art and can be prepared in a known manner, for example by reacting a polyurethane with (meth) acrylic acid to give the corresponding urethane (meth) acrylate, or by reacting an isocyanate-terminated prepolymer with hydroxymethacrylates. Corresponding methods are e.g. known from EP 0579503.

Urethane methacrylates are also commercially available and are sold, for example, under the name PC-Cure® by the company Piccadilly Chemicals, under the product name CN 1963 by the company Sartomer and under the name Genomer® by the company Rann. Preferred urethane (meth) acrylates used are those which have been prepared with a functionality of n <4 from aliphatic starting materials, in particular the isomer mixture 7, 7, 9- (or 7, 9, 9) obtained from HE (M) A and TMDI -) trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-diol-di (meth) acrylate. The in the formulations according to the invention as Examples of components (b) of poly (meth) acrylates having a functionality of n <5 are di (meth) acrylates of (n) -alkoxylated bisphenol A such as bisphenol A ethoxylate (2) di (meth) acrylate, bisphenol A ethoxylate (4) di (meth) acrylate, bisphenol A propoxylate (2) di (meth) acrylate, bisphenol A propoxylate (4) di (meth) acrylate and di (meth) acrylates of (n) -alkoxylated bisphenol F such as bisphenol F-ethoxylate (2) di (meth) acrylate and bisphenol F-ethoxylate (4) di (meth) acrylate, bisphenol F-propoxylate (2) di (meth) acrylate, bisphenol F-propoxylate ( 4) di (meth) acrylate 1,3-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, ethylene glycol di (meth) acrylate, neopentyldi (meth) acrylate, polyethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate and tetraethylene glycol di (meth) acrylate and 1,4-butanediol di (meth) acrylate. Such products are commercially available, for example from Sartomer. It is also possible to use allyl (meth) acrylate, methyl, ethyl, n-propyl, n-butyl, isobutyl, n-hexyl, 2-ethylhexyl, n-octyl, n-decyl, n- Dodecyl, isobornyl, isodecyl, lauryl, stearyl (meth) acrylate, 2-hydroxyethyl, 2- and 3-hydroxypropyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate and cyclohexyl (meth) acrylate and ethyl (meth) acrylate can be used. As component (c) all types can be used as photoinitiators, which form free radicals with the corresponding irradiation. Known photoinitiators are compounds of benzoins, benzoin ethers, such as benzoin, benzoin methyl ether, benzoin ethyl ether and benzoin isopropyl ether, benzoinphenyl ether and benzoin acetate, acetophenones, such as acetophenone, 2, 2-dimethoxyacetophenone, and 1,1-dichloroacetophenone, benzil, benzil ketals, such as benzil dimethyl ketal and benzil diethyl ketal. Anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert. Butylanthraquinone, 1-chloroanthraquinone and 2-amylanthraquinone, triphenylphosphine, benzoylphosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide (lutirine TPO) and bis (2,4,6-trimethylbenzoylphenyl) phosphine oxide, benzophenones such as benzophenone and 4,4'-bis (N, N'-dimethylamino) benzophenone, thioxanthones and xanthones, acridine derivatives, phenazine derivatives, quinoxaline derivatives or 1-phenyl-1,2-propanedione-2-O-benzoyloxime, 1-aminophenyl ketones or 1 Hydroxyphenyl ketones such as 1-hydroxycyclohexyl phenyl ketone, phenyl (1-hydroxyisopropyl) ketone and 4-isopropylphenyl (1-hydroxyisopropyl) ketone.

In the mixtures according to the invention as component (d) as the anaerobic inhibitor or stabilizer 2,2,6, 6-tetramethylpiperidin-1-yloxy (free radical) and as aerobic stabilizers known in the art compounds such Hydroquinone monomethyl ether are added. As component (e) Si0 ₂ nanoparticles as they are, for example. Sold by the company. Clariant under the brand Highlink, are used. In this case, particles with particle sizes <50 nm and preferably with particle sizes <25 nm and very preferably with particle sizes <15 nm are used. These particles are surface-modified by means of acid hydrolysis using silanization reagents known to those skilled in the art, for example 3-trimethoxysilylpropyl methacrylate. For this purpose, the stabilized in alcoholic solution nanoparticles are placed in a round bottom flask and adjusted with an acid to a pH of 2.5. With stirring, the (meth) acrylated silane is added. The solution thus prepared is stirred for> 6 h. Subsequently, a corresponding monomer is added and the solvent removed under vacuum in a rotary evaporator. As component (f), the fillers known to those skilled in the art, such as those sold for example by Degussa under the name Aerosil®, may be present in the formulations according to the invention.

If necessary, the components according to the invention may also contain, as components (g) and (h), the color pigments, leveling agents, UV stabilizers, wetting agents and dyes known to those skilled in the art. In the context of the invention, particularly suitable dyes are anthraquinone dye Preparations, such as those sold by the Bayer company under the name Macrolex.

It has surprisingly been found that by adding the o.g. Surface-modified nanoparticles, the reactivity of the claimed resin mixtures can be significantly increased upon irradiation by means of image projection systems based on visible radiation. As a measure of the resin reactivity, the depth of cure was chosen as a function of the logarithm of the irradiation time for the following test. For this purpose, about 100 ml of the resin mixture of example formulation 1 were irradiated with an image projection unit from Optoma for different lengths of time.

Example formulation 1:

90.7-xm% 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,1,6-diol dimethacrylate xm% surface-modified SiO ₂

(Particle size 13 nm)

8.9 m% triethylene glycol dimethacrylate 0.4 m% 2,4,6-trimethylbenzoyldiphenylphosphine oxide 0.3 m% 2- (2H-benzotriazol-2-yl) -p-cresol

0.002 m% 2, 2, 6, 6-tetramethylpiperidin-1-yloxy

(free radical) The resin surface was located exactly in the focal plane of the irradiation unit, here 40 cm away from the lens. By way of example, the increase in the depth of cure as a function of the duration of irradiation on a clear transparent resin, which was provided with surface-modified nanoparticles in the concentration range of 0-15% by volume, is shown in FIG. It can be seen from Figure 1 that by adding the nanoparticles, especially at concentrations> 10 m%, the depth of cure increases significantly.

It follows that the addition of the surface-modified nanoparticles can increase the reactivity and consequently increase the speed of the construction process. This is particularly important in rapid manufacturing processes, which are much more critical than rapid prototyping processes to assess in terms of construction time, of great importance. For example, in the generative production of ear molds, a process in which many parts that can be used in medical technology must be produced in a short time, this can be regarded as very advantageous.

In the following, use examples for resin mixtures according to the invention in clear and opaque beige (with different values for the elongation at break), as they can be used for the production of ear molds, are listed. Example Formulation 2 of a Clear Transparent Resin

77.3% m% 7,7, 9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-diol dimethacrylate

13.4 m% surface-modified SiO ₂

(Particle size 13 nm)

8.9 m% triethylene glycol dimethacrylate 0.4 m% 2,4,6-trimethylbenzoyldiphenylphosphine oxide 0.3 m% 2- (2H-benzotriazol-2-yl) -p-cresol 0.002 m% 2, 2, 6, 6 -Tetramethylpiperidin-1-yloxy

(free radical)

Example Formulation 3 of a Beige Opaque Resin with Low Elongation:

83.62 m% 4-tuply ethoxylated bisphenol A dimethacrylate 11.43 m% 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-diol dimethacrylate 4 , 25 m% 1, 4-butanediol dimethacrylate

0.7% bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide

0.43 m% iron oxide pigment

0.03 m% 2- (2H-benzotriazol-2-yl) -p-cresol Example formulation 4 of a beige opaque resin with higher elongation:

64.06m% 4-D ethoxylated bisphenol A dimethacrylate 11.9m% aliphatic urethane triacrylate

10.0% tetrahydrofurfuryl methacrylate

6.4% by weight of hydroxypropyl methacrylate 4.95% by weight of dodecyl methacrylate

2.65% 7,7, 9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,1,6-diol dimethacrylate

1.5% bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide

The physico-chemical parameters for the three o.g. Usage examples are shown in Tab. All viscosity measurements were carried out at 23 ° C. using a CVO 120 rheometer from Bohlin Instruments. The determination of the bending strengths, moduli of elasticity and strains was carried out in accordance with EN ISO 178 (1996) using a Zwick 1 test machine from Zwick.

Table 1: Mechanical values of the formulations according to the invention Elastic Modulus, Bending Strength Elongation at Break Viscosity N mm ^"2 % by% Pas N mm ^{" 2} Example 2 3044 155 7 3, 16 Example 3 2083 112 7 0, 68 Example 4 1906 108 13 0, 44

Compared with the values for materials for the traditional production of ear molds (Tab. 2) by means of the PNP method, it can be seen that the o.g. Formulations advantageously provide significantly higher values for modulus of elasticity and flexural strengths. The elongation at break are somewhat lower for example 2 and example 3, and for example 4 as comparable.

Tab.2: Mechanical values of commercially available products for the production of ear pieces e ^ria - ^l modulus of elasticity, bending strength elongation at break

N mm ^"2 speed, N mm ^{" 2} % oplast S / IO, blue 1513 81 ΪÖ nsparent, Lot. 201504 oplast S / IO, reddish 1527 84 13 nons., Lot. 301531 oplast S / IO, colorless 1602 88 11 not transparent, lot. 203523 oplast S / IO, brown, lot. 1374 74 14

540

For the generative production of such medical devices with image projection systems, which have a flexible, radiation-permeable conveyor belt, by means of which the photopolymerizable formulation is transported into the exposure station, it was further surprisingly found that the formulations according to the invention are not as follows "Wetting Envelope" of the conveyor belt, but in the "Wetting Envelope" of the green body or the precured layer are located. In the context of the process, this results in a very advantageous manner that uncured resin wets the pre-hardened component when separating the build platform from the transport foil and is easily detached from the conveyor belt. Accordingly, the pull-off forces between the component and conveyor belt decrease, resulting in a more stable construction process. This is due to the fact that even fragile structures of the component in this "separation process" are less detached from the build platform, and the wetting behavior of the different resin variants on different substrates was tested using the wetting envelope Envelopes can be used to predict whether a given liquid, whose surface tension components are known, will completely wet the solid it was tested in. For the representation of the wetting envelope, the determination of the polar and disperse surface energy was reversed dispersive fractions were determined by the method of Owens, Wendt, Rabel, Kaelble (OWRK), which is known to the person skilled in the art and described in the literature.The instrument used was the drop shape analyzer (DSA100) from Krüss Diiodomethane, pentanediol and Water used as test liquids. To determine the wetting envelope, it was calculated at which polar and dispersive fraction of the liquid a value of cos φ = 1 results for the investigated solid. The angle φ represents the contact angle of the drop contour, which forms on the surface to be examined. The plot of the polar component versus the disperse component results in a curve for cos φ = 1 that starts from the origin (0/0), goes through a maximum and finally hits the x-axis again. The area enclosed by this curve is the wetting envelope. All fluids whose data are within this range will wet the corresponding solid.

To determine the proportions of

Interfacial tension (IFT) of the resins was used in two ways. On the one hand, the pendant drop method was used, with which the interfacial tension of the liquids was determined. On the other hand, a drop of the resin was added to PTFE and determines the contact angle of the drop contour. With the specific contact angle, the interfacial tension of the resin, and the known surface properties of PTFE, the OWRK equation was used to calculate the polar and dispersive fractions of the interfacial tension of the resin. As resin variants, use examples 2 and the unfilled variants example 3 and 4 were chosen. The Provisions of the so-called "wetting envelopes" of the transport foil, as used in the commercially available unit V-Flash from the company 3DSystems, and the position of the interfacial tension of the liquid use examples 2 to 4 are shown in Fig.2 The green compacts were fabricated in a clear transparent silicone mold with 50 flashes in the Sonolux PR (Dreve), the surface of the component that was not delimited by the silicone mold , was covered with the transport film of the V-Flash and the results are shown in Table 3.

3: Interfacial tension (IFT) of Use Examples 2 to 4

Resins Density, IFT, Polar proportion, Disperser β g / cm ³ mN / m mN / m mN / rr

Example of application 2 1.16 36.83 4.5 32.3 Example of use 3 1.12 39.57 5.4 34.2

Application Example 4 1.09 35.8 5.3 30.5

Claims

Claims:

A radiation-curable formulation for the generative production of medical products with an image projection system which utilizes visible radiation for curing and preferably a coating tape for material introduction, comprising the following components: a) at least one or more urethane poly (meth) acrylates b) at least one or more

(Poly) (meth) acrylates, or a combination of these c) at least one initiator useful for the relevant radiation range d) at least one or more or a combination of anaerobic and / or anaerobic stabilizers e) and in a particular embodiment preferably at least> 0, lm % surface-modified nanoparticles f) 0-40m% of fillers g) 0-5m% of color pigments h) 0.5m% of conventional additives such as UV stabilizers or flow control additives, the proportion of components a) to h) together being 100m% and the total formulation is within the so-called "wetting envelope" of the located in the Green-Flex mode, pre-cured layer of the formulation and has a viscosity of <10 Pas at 23 ⁰ C.

2. Formulation according to claim 1, comprising the following components: a) 10-80m% of one or a combination of urethane poly (meth) acrylates having a functionality of n <5 and a viscosity of <30Pas at 23 ° C b) 4-89m % of at least one or a combination of several (poly) (meth) acrylates having a functionality of n <5 and a viscosity <10 Pas at 23 ⁰ C, or a combination of one or more

(PoIy) (meth) acrylates and at least one monomeric (meth) acrylate having a viscosity of <5 Pas at 23 ⁰ C c) 0, l-3m% of at least one or a combination for the relevant radiation range usable initiators d) 0, 0001 -0, 5m% of at least one or more or a combination of anaerobic and / or aerobic stabilizers e) 0-40m% surface-modified nanoparticles with a particle size of <100nm, preferably at least <10m% surface-modified nanoparticles with a particle size of <30nm f) 0- 40m% of fillers g) 0-5m% of color pigments h) 0-5m% of conventional additives such as UV stabilizers or flow control additives, wherein the proportion of components a) to h) together is 100m% and the total formulation within the so-called " wetting envelope "in Green Flex mode, precured layer of this formulation is and has a viscosity <10 Pas at 23 ⁰ C.