THERMOFORMABLE AND SCRATCH-RESISTANT PHOTOPOLYMER COATINGS

Abstract

The present invention relates, in particular, to a coating composition, cross-linkable under the action of UV-visible radiation, which has the advantage of being thermoformable and having excellent scratch and abrasion resistant properties. The present invention also relates to a method for preparing a thermoformable coating, resistant to scratches and abrasion, comprising the cross-linking of a composition according to the invention under the action of UV-visible radiation. The present invention also relates to a method for protecting a substrate against scratches and abrasion, preferably said substrate being thermoformable or thermodrapable. The present invention also relates to a coated article, resistant to scratches and abrasion, preferably a thermoformable or thermodrapable coated article that can be obtained by a method according to the invention, as well as the use of a composition according to the invention to protect a possibly thermoformable or thermodrapable substrate against scratches and abrasion. The present invention also relates to the use of a composition according to the invention for preparing thermoformable coatings, resistant to scratches and abrasion. The present invention further relates to a thermoformable coating, resistant to scratches and abrasion, characterised in that it results from cross-linking under the action of UV-visible radiation at least one composition according to the invention.

Claims

1. A varnish composition, crosslinkable under the action of UV-visible radiation, comprising: A) at least one multifunctional urethane acrylate oligomer comprising 2 to 9 acrylate functions, which is the product of the reaction of a diisocyanate or triisocyanate with a hydroxylated acrylate monomer, preferably with a stoichiometric excess of a hydroxylated acrylate monomer, said hydroxylated acrylate monomer being a random mixture resulting from the reaction of a polyol with a stoichiometric deficiency of acrylic acid, with the proviso that the chain of the diisocyanate or triisocyanate has not been extended beforehand by a polyol, polyester, polyether or polycarbonate comprising residual hydroxyl functions; B) at least one reactive diluent selected from acrylate monomers; and C) at least one photoinitiator suitable for the light source used for the crosslinking; D) optionally at least one surface agent; and E) optionally at least one stabilizing anti-UV agent.

2. The composition as claimed in claim 1, wherein said at least one multifunctional urethane acrylate oligomer comprising 2 to 9 acrylate functions corresponds to the following formula I.sup.A or I.sup.B: ##STR00019## in which: R.sub.1 represents a C1 to C10 aliphatic, mono- or bicyclic C5 to C8 alicyclic or C6 to C13 aromatic radical, preferably C1 to C10 aliphatic or C5 to C8 alicyclic radical optionally substituted with one or more C1-C6 alkyl radicals; R.sub.2 independently represents a linear, branched or cyclic C1-C10 alkyl group, the C1-C10 alkyl chain being able to be optionally interrupted by an ester (—C(═O)O—) or ether (—O—)-function; and each instance of n independently represents a mean number of acrylate functions of between 1 and 4, preferably between 1 and 3, preferably between 1 and 2, preferably 1 for the formula I.sup.A, and between 1 and 3; preferably between 1 and 2, preferably 1 for the formula I.sup.B.

3. The composition as claimed in claim 1, wherein said at least one reactive diluent is selected from diacrylate monomers.

4. The composition as claimed in claim 1, wherein said at least one reactive diluent is a mixture of two acrylate monomers selected from mono-, di-, tetra- or hexacrylate monomers, preferably aliphatic or alicyclic, most preferentially a mixture of two diacrylate monomers, preferably aliphatic or alicyclic.

5. The composition as claimed in claim 1, wherein the multifunctional oligomer is an aliphatic urethane diacrylate, tetracrylate, or hexacrylate, preferably an aliphatic urethane diacrylate.

6. The composition as claimed in claim 1, wherein the multifunctional oligomer is a multifunctional aliphatic urethane acrylate oligomer comprising 6 to 9 acrylate functions.

7. The composition as claimed in claim 1, also comprising a hybrid organic-inorganic reactive diluent that may react by photopolymerization and photosol-gel reaction, of formula
R.sup.4.sub.(4-m)—Si—(R.sup.5).sub.m, in which m represents an integer between 1 and 3; each instance of R.sup.4 independently represents a non-hydrolyzable group covalently bonded to Si via a carbon atom, it being understood that at least one instance of R.sup.4 comprises an unsaturated photopolymerizable group; and each instance of R.sup.5 independently represents a hydrolyzable group selected from C1-C6 alkoxy, C1-C6 acyloxy, a halogen atom or an amino group; preferably C1-C6 alkoxy such as methoxy or ethoxy, preferably methoxy.

8. The composition as claimed in claim 1, comprising at least two acrylate, preferably diacrylate, monomer reactive diluents, in which the reactive diluents/multifunctional oligomer weight ratio is between 1.5 and 3.5, preferably between 1.5 and 3.0, the ratio being calculated taking into consideration the sum by weight of the acrylate monomers.

9. The composition as claimed in claim 1, comprising a diacrylate monomer as reactive diluent, in which the diacrylate monomer/multifunctional oligomer weight ratio is between 1.3 and 1.7.

10. The composition as claimed in claim 1, wherein the photoinitiator is chosen from: type I radical photoinitiators of the family of the acetophenones, alkoxyacetophenones and derivatives such as 2,2-dimethoxy-2-phenylacetophenone and 2,2-diethyl-2-phenylacetophenone; of the family of the hydroxyacetophenones and derivatives such as 2,2-dimethyl-2-hydroxyacetophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone and 2-hydroxy-4′-(2-hydroxypropoxy)-2-methylpropiophenone; of the family of alkylaminoacetophenones and derivatives such as 2-methyl-4′-(methylthio)-2-morpholinopropiophenone, 2-benzyl-2-(dimethylamino)-4-morpholinobutyrophenone and 2-(4-(methylbenzyl)-2-(dimethylamino)-4-morpholinobutyrophenone; of the family of benzoin ethers and derivatives such as benzyl, benzoin methyl ether and benzoin isopropyl ether; of the family of phosphine oxides and derivatives such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), ethyl(2,4,6-trimethylbenzoyl)phenylphosphine oxide (TPO-L) and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylphenylphosphine oxide (BAPO); type II radical photoinitiators of the family of benzophenones and derivatives such as 4-phenylbenzophenone, 4-(4′-methylphenylthio)benzophenone, 1-[4-[(4-benzoylphenyl)thio]phenyl]-2-methyl-2-[(4-methylphenyl) sulfonyl]-1-propanone; the family of thioxanthones and derivatives such as isopropylthioxanthone (ITX), 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 2-chlorothioxanthone and 1-chloro-4-isopropylthioxanthone; the family of quinones and derivatives such as anthraquinones including 2-ethylanthraquinone and camphorquinones; the family of esters of benzoyl formate and derivatives such as methyl benzoylformate; the family of metallocenes and derivatives such as ferrocene, titanium bis(eta 5-2,4-cyclopentadien-1-yl)bis(2,6-difluoro)-3-(1H-pyrrol-1-yl)phenyl) and (cumene)cyclopentadienyl iron hexafluorophosphate; the family of dibenzylidene ketones and derivatives such as p-dimethylaminoketone; the family of coumarins and derivatives such as 5-methoxy and 7-methoxy coumarin, 7-diethylamino coumarin and N-phenylglycine coumarin; photoinitiators of the family of dyes such as triazines and derivatives, fluorones and derivatives, cyanins and derivatives, safranins and derivatives, 4,5,6,7-tetrachloro-3′,6′-dihydroxy-2′,4′,5′,7′-tetraiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one, pyrylium and thiopyrylium and derivatives, thiazines and derivatives, flavins and derivatives, pyronines and derivatives, oxazines and derivatives, rhodamines and derivatives; a mixture of at least two of the abovementioned photoinitiators.

11. The composition as claimed in claim 10, wherein, when the composition also contains a hybrid organic-inorganic reactive diluent, said at least one photoinitiator also contains at least one cationic photoinitiator selected from onium salts, organometallic complexes and non-ionic photoacids, wherein the hybrid organic-inorganic reactive diluent may react by photopolymerization and photosol-gel reaction and corresponds to formula
R.sup.4.sub.(4-m)—Si—(R.sup.5).sub.m, in which m represents an integer between 1 and 3; each instance of R.sup.4 independently represents a non-hydrolyzable group covalently bonded to Si via a carbon atom, it being understood that at least one instance of R.sup.4 comprises an unsaturated photopolymerizable group; and each instance of R.sup.5 independently represents a hydrolyzable group selected from C1-C6 alkoxy, C1-C6 acyloxy, a halogen atom or an amino group; preferably C1-C6 alkoxy such as methoxy or ethoxy, preferably methoxy.

12. The composition as claimed in claim 1, wherein the surface agent is a silicone-based or acrylic copolymer-based surface agent.

13. The composition as claimed in claim 1, also comprising at least one UV stabilizer selected from UV absorbers and sterically hindered amines.

14. The composition as claimed in claim 1, which composition is crosslinkable in the absence of solvent.

15. The composition as claimed in claim 1, characterized in that it comprises: (i) A) 30 to 50% by weight, preferably 35 to 45% by weight, of an aliphatic urethane diacrylate (such as CN981®, CN9001® or CN991®), tetracrylate (such as CN9276®), or hexacrylate (such as CN9210® or EB1290) oligomer, preferably an aliphatic urethane diacrylate oligomer such as CN981®; B) an aliphatic diacrylate monomer such as SR238®, as reactive diluent, at an amount of 40 to 60%, preferably 45 to 55% by weight; C) 1 to 10%, preferably 3 to 7% by weight of a radical photoinitiator as defined in claim 10; preferably a type I radical photoinitiator, most preferentially 1-hydroxycyclohexylphenyl ketone (Irgacure 184®); D) optionally 1 to 10% by weight of a surface agent; and E) optionally 1 to 10% by weight of a UV stabilizer; the sum of the percentages of all the components being equal to 100% of the total weight of the composition subjected to crosslinking; and wherein the diacrylate monomer/multifunctional oligomer weight ratio is between 1.3 and 1.7; (ii) A) 20 to 50% by weight, preferably 20 to 40% by weight, of an aliphatic urethane diacrylate (such as CN981®, CN9001® or CN991®), tetracrylate (such as CN9276®), or hexacrylate (such as CN9210® or EB1290) oligomer, preferably an aliphatic urethane diacrylate oligomer such as CN981®; B) a mixture of two aliphatic or alicyclic diacrylate monomers, such as SR238® and SR833S®, as reactive diluents, at an amount of 50 to 70%, preferably 55 to 70% by weight; C) 1 to 10%, preferably 3 to 7% by weight of a radical photoinitiator as defined in claim 10; preferably a type I radical photoinitiator, most preferentially 1-hydroxycyclohexylphenyl ketone (Irgacure 184®); D) optionally 1 to 10% by weight of a surface agent; and E) optionally 1 to 10% by weight of a UV stabilizer; the sum of the percentages of all the components being equal to 100% of the total weight of the composition subjected to crosslinking; wherein the diacrylate monomers/multifunctional oligomer weight ratio is between 1.5 and 3.5, preferably between 1.5 and 3.0; the sum by weight of the two reactive diluents being taken into consideration for calculating this ratio; and the acyclic aliphatic diacrylate monomer (such as SR238®) and the alicyclic diacrylate monomer (such as SR833S®) are present in a weight ratio of 40/60 to 90/10, preferably 45/55 to 85/15; or (iii) A) 45 to 65%, preferably 50 to 60% by weight of an aliphatic urethane oligomer having a functionality of greater than or equal to 6; preferably an aliphatic urethane hexacrylate, octacrylate or nonacrylate oligomer; B) 25 to 45%, preferably 30 to 40%, by weight of an aliphatic diacrylate monomer as reactive diluent; C) 5 to 15%, preferably 5 to 7% by weight of a radical photoinitiator as defined in claim 10; preferably a type I radical photoinitiator; D) optionally 1 to 10% by weight of a surface agent, preferably from the class of silicones; and E) optionally 1 to 10% by weight of a UV stabilizer; the sum of the percentages of all the components being equal to 100% of the total weight of the composition subjected to crosslinking.

16. A process for preparing a scratch-resistant and abrasion-resistant thermoformable varnish, said process comprising the formation of said varnish by crosslinking the composition of claim 1 under the action of UV-visible radiation.

17. The process as claimed in claim 16, wherein the source of UV or visible radiation is an LED or a discharge lamp.

18. (canceled)

19. A process for protecting a support from scratches and abrasion, said support preferably being thermoformable or thermally drape-formable, said process comprising the following successive steps: a) coating a surface of an optionally thermoformable or thermally drape-formable support with a varnish composition as claimed in claim 1; b) curing the varnish composition covering the coated surface of the support by crosslinking said composition under the action of UV-visible radiation; and c) in the case in which said support is thermoformable or thermally drape-formable, optionally shaping the varnished support by thermoforming or thermal drape forming.

20.-23. (canceled)

24. A scratch-resistant and abrasion-resistant varnished article, which is preferably thermoformable or thermally drape-formable, able to be obtained by a process as claimed in claim 16.

25. (canceled)

26. A scratch-resistant and abrasion-resistant thermoformable varnish, characterized in that it results from the crosslinking, under the action of UV-visible radiation, of at least one composition as defined in claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0289] FIG. 1: A) Diagram of the motorized applicator fitted with a set of bars for the deposition of varnish films applied on PMMA sheets, used in examples 1 to 6. B) UV-visible conveyor for crosslinking the varnish.

[0290] FIG. 2: Code for classifying coating adhesion results according to standard ASTM D 3559.

[0291] FIG. 3: Comparative scratch resistance tests between the 3 varnishes of example 2, and 2 commercial varnishes. A). Depth of the scratch (μm). B) Force (N) at which (i) the first damage and (ii) the ruining of the sample are observed.

[0292] FIG. 4: Scratch resistance tests of the 4 varnishes of example 3: Force (N) at which (i) the first damage and (ii) the ruining of the sample are observed.

[0293] FIG. 5: Scratch resistance tests of the 4 varnishes of example 4: Force (N) at which (i) the first damage and (ii) the ruining of the sample are observed.

[0294] FIG. 6: Comparative scratch resistance tests of the varnishes b and e of example 4. A). Depth of the scratch (μm). B) Force (N) at which (i) the first damage and (ii) the ruining of the sample are observed.

[0295] FIG. 7: Scratch resistance tests of the 4 varnishes of example 5. A). Depth of the scratch (μm). B) Force (N) at which (i) the first damage and (ii) the ruining of the sample are observed.

[0296] FIG. 8: Thermoforming/thermal drape forming test of sample 280415A from example 6.

[0297] FIG. 9: Comparative adhesion tests of several varnish compositions according to the invention, by the crosscut test according to standard D3359.

[0298] Table 1: Different data obtained following scratching by a durometer. The images corresponding to the 1st damage and to the ruining are obtained by reflected light microscopy. The depth of penetration of the tip was determined by optical profilometry. The width of the deformation is calculated by the Gwyddion software.

EXAMPLES

Example 1—Application of Varnish and Scratch Resistance and Adhesion Properties—General Protocol

[0299] The preparation of the crosslinked varnished according to the process of the invention was carried out under the following experimental conditions: [0300] The homogeneous liquid formulations were deposited by a motorized applicator on PMMA “ShieldUp®” sheets (Arkema). A set of calibrated bars was used in order to control the thickness of the films (cf. FIG. 1A). [0301] The polymerization of the film of varnish composition deposited on the surface of the PMMA sheets was carried out at room temperature, without the addition of solvent, using a UV Qurtech industrial-grade conveyor after three to four passes (cf. FIG. 1B). The source of UV irradiation is an H microwave lamp. The lamp was used at 100% of its intensity. Each sample received 1.34 J/cm.sup.2 during one pass.

[0302] The crosslinked varnish films were then tested for their scratch resistance.

[0303] The thickness of the films is measured by contactless optical profilometry. For this purpose, an Altisurf 500 (Altimet) measuring apparatus fitted with an Altiprobe Optic sensor (350 μm probe working at 5 mm from the surface) was used. The sensor is moved so as to scan a segment of a few centimeters (Z=f(X) profile measurement or profilometry).

[0304] With the aim of rapidly obtaining characterization of the scratch so as to validate or invalidate a formulation, scratch tests were carried out by a motorized CLEMEN durometer fitted with a spherical diamond-tipped cone (R=100 μm). The latter is brought into contact with the surface of the sample and moved in a straight line. The force exerted by the tool on the coating surface can be adjusted by means of a mobile weight of 0 to 1500 g, i.e. from 0 to 15 N. The PMMA samples are 2.5 cm×7.5 cm or 7.5 cm×8 cm and 4 mm thick.

[0305] By virtue of the characterizations by the durometer, it is possible to obtain the normal force that induces the first damage, the ruining of the film, and the width and depth of the deformation at a given pressure (table 1).

[0306] The adhesion of the varnish films to the substrate may also be tested according to the “cross-cut” test of standard ASTM D 3359. Briefly, the standardized procedure consists in producing a series of scratches spaced apart by approximately 1 mm (for films of thickness≤50 μm) and of a length of approximately 20 mm. Once the series of scratches has been completed, the surface of the substrate is very lightly brushed with a soft brush to eliminate any fragments of film which might have become detached. The procedure is repeated, this time producing a series of parallel scratches perpendicular to the first series, so as to obtain a grid of scratches. After eliminating any debris/fragments of coating from the surface of the substrate with the soft brush, a piece of adhesive tape is applied to the center of the grid of scratches (adhesive side in contact with the varnish coating). Ensure good contact between the adhesive tape and the surface of the substrate, if necessary by pressing the tape firmly using an eraser. After 90±30 s of application, remove the adhesive tape by grasping one end and by pulling it rapidly while maintaining an angle as close to 180° as possible. Inspect the region of the grid of scratches and evaluate the adhesion of the varnish using the classification provided for this purpose (cf. FIG. 2).

[0307] For the varnish films according to the invention, the procedure for measuring adhesion was slightly modified as follows: a special cut by a large handle, producing two series of perpendicularly-crossed lines in the form of crosshatching is made over ¾ of the surface of the film. A 3M scotch tape (2.5 N/m) standardized according to the cross-cut test is applied and removed, the cutting region is then evaluated to determine the adhesion. The scotch tape was used twice for each sample. The adhesion of the films to the PMMA ShieldUp is measured 12 hours after polymerization by a cross-cut test according to standard ASTM D 3359. A standardized 3M scotch tape (2.5 N/m) was used. The comparative results for several samples of different composition are given in FIG. 9 (samples A1 to G1).

TABLE-US-00004 Films SR238 ® CN981 ® CN9276 ® I184 ® I250 ® BYK3505 TCDDA MAPTMS A1 51.4 39.5 — 5.0 — 4.0 — — B1 45.8 35.2 — 5.0 — 4.0 10.0 — C1 30.8 23.7 — 5.0 — 4.0 36.6 — D1 30.5 23.4 — 5.0 7.0 4.0 — 30.0 E1 51.4 — 39.6 5.0 — 4.0 — — F1 45.8 — 35.2 5.0 — 4.0 10.0 — G1 30.7 — 23.6 5.0 — 4.0 36.7 —

Example 2—Comparative Study with Commercial Varnishes

[0308] Three different varnishes were produced, all using the diacrylate monomer reactive diluent SR238®: [0309] a purely organic-based varnish “A2” [0310] a purely organic-based varnish “B2” with the addition of a second diacrylate monomer reactive diluent [0311] a hybrid-based varnish “C2” with the addition of a hybrid reactive diluent

[0312] The compositions of each of these varnishes are as follows (the values are expressed as % by weight relative to the total weight of the composition):

TABLE-US-00005 Films SR238 ® CN981 ® I184 ® I250 ® BYK3505 TCDDA MAPTMS A2 51.4 39.5 5.0 — 4.0 — — B2 30.8 23.7 5.0 — 4.0 36.6 — C2 30.5 23.4 5.0 7.0 4.0 — 30.0

[0313] The reactive diluent/oligomer (SR238/CN981) weight ratio was 1.3.

[0314] The different varnishes were applied with the calibrated bar, each one on a ShieldUp® (Arkema) PMMA sheet, and were polymerized under UV in a single step at room temperature (25° C.) without addition of solvent. The thickness of the liquid film is 10 μm+−1 μm, evaluated by contactless optical profilometry. The measurement of the thickness is important insofar as the behavior of the varnish film depends heavily thereon.

[0315] The scratch resistance of the varnish films obtained was tested using a Clemen Elcometer 3000 durometer, and was compared to that of two commercial varnishes: CETELON® and MOMENTIVE®, which are varnishes for application to transparent plastic parts, which are not thermoformable and can only be applied once the part has been thermoformed. The Cetelon® varnish is based on nanosilica+organic acrylic network, crosslinked under UV. The Momentive® varnish is based on an inorganic silicone network, thermally crosslinked. The results are presented in FIG. 3.

[0316] It can be seen that the 3 varnishes according to the invention have better performance in terms of scratch resistance than the 2 commercial varnishes. Indeed, the first damage for the 2 commercial samples is observed earlier (at a lower force) than for the varnishes according to the invention. The depth of the scratch is also greater for the commercial varnishes than for the varnishes of the invention.

[0317] In addition, it is observed that compared to the varnish “A2”, which only contains a single reactive diluent (SR238®), the addition of a second, reactive diluent, either organic (TCDDA) or hybrid (MAPTMS), improves the scratch resistance properties of the varnishes obtained in this way. For example, at F.sub.N=4 N (maximum force reached), “B2” shows greater scratch resistance and shallower penetration of the ball (4 μm).

[0318] Comparative thermoforming/thermal drape forming tests were carried out: the 3 varnishes according to the invention are thermoformable (no cracking for a high deformation stress), while the 2 commercial varnishes are not thermoformable.

[0319] The other drawback of the 2 commercial varnishes is that they must be used with a solvent (70% by weight), whereas no solvent was used for the application and polymerization of the 3 varnishes according to the invention.

Example 3—Purely Organic-Based Varnish Compositions—Addition of a Second Reactive Diluent

[0320] Four different varnishes were produced, all using the diacrylate monomer reactive diluent SR238® and a surface agent (BYK302®).

[0321] The compositions of each of these varnishes are as follows (unless indicated otherwise, the values are expressed as % by weight relative to the total weight of the composition):

TABLE-US-00006 Thickness Films SR238 ® CN9276 ® I184 ® BYK302 TCDDA (μm) A3 59.2 35.0 5.0 0.8 — 9.5 B3 53.13 31.07 5.0 0.8 10.0 10.0 C3 46.82 27.38 5.0 0.8 20.0 11.0 D3 42.9 21.3 5.0 0.8 30.0 11.0

[0322] The reactive diluent/oligomer (SR238/CN9276) weight ratio was 1.7.

[0323] The different varnishes were applied with the calibrated bar, each one on a ShieldUp® (Arkema) PMMA sheet, and were polymerized under UV in a single step at room temperature (25° C.) without addition of solvent.

[0324] The scratch resistance of the varnish films obtained was tested using a Clemen Electometer 3000 durometer. The results are presented in FIG. 4.

Example 4—Purely Organic-Based Varnish Compositions—Different Reactive Diluent/Oligomer Weight Ratios

[0325] Five different varnishes were produced, all using the diacrylate monomer reactive diluent SR238® and the urethane acrylate oligomer CN9276®.

[0326] The compositions of each of these varnishes are as follows (unless indicated otherwise, the values are expressed as % by weight relative to the total weight of the composition):

TABLE-US-00007 SR238/ CN9276 weight Films SR238 ® CN9276 ® I184 ® BYK302 BYK3505 ratio A4 53.2 41 5 0.8 — 1.3 B4 53.2 41 5 — 0.8 1.32 C4 59.2 35 5 0.8 — 1.71 D4 59.2 35 5 — 0.8 1.71 E4 51.4 39.5 5 4.0 — 1.32

[0327] The different varnishes were applied with the calibrated bar, each one on a ShieldUp® (Arkema) PMMA sheet, and were polymerized under UV in a single step at room temperature (25° C.) without addition of solvent.

[0328] The scratch resistance of the varnish films obtained was tested using a Clemen Elcometer 3000 durometer. The results for the formulations a to d are presented in FIG. 5. The comparative results between formulations b and e are presented in FIG. 6.

[0329] In both the weight ratio cases studied (SR238/CN9276=1.3 or 1.7), the addition of a surface agent made it possible to improve the scratch behavior of the crosslinked varnish.

[0330] The increase in the concentration of surface agent from 0.8 to 4.0% by weight results in an even more scratch-resistant varnish (shallower penetration of the tip of the durometer for the varnish containing 4.0% of BYK3505).

Example 5—Purely Organic-Based Varnish Compositions—Addition of a Second Reactive Diluent

[0331] Four different varnishes were produced.

[0332] The compositions of each of these varnishes are as follows (unless indicated otherwise, the values are expressed as % by weight relative to the total weight of the composition):

TABLE-US-00008 Films SR238 ® CN9276 ® CN981 ® I184 ® BYK3505 TCDDA Thickness A5 51.4 0 39.5 5.0 4.0 0 10 μm B5 45.8 0 35.2 5.0 4.0 10.0 10 μm C5 51.4 39.5 0 5.0 4.0 0 10 μm D5 45.8 35.2 0 5.0 4.0 10.0 11 μm

[0333] The reactive diluent/oligomer (SR238/CN9276 or SR238/CN981) weight ratio was 1.3.

[0334] The different varnishes were applied with the calibrated bar, each one on a ShieldUp® (Arkema) PMMA sheet, and were polymerized under UV in a single step at room temperature (25° C.) without addition of solvent.

[0335] The scratch resistance of the varnish films obtained was tested using a Clemen Elcometer 3000 durometer. The results are presented in FIG. 7.

[0336] In both the weight ratio cases studied (SR238/CN9276=1.3 or 1.7), the addition of a surface agent made it possible to improve the scratch behavior of the crosslinked varnish.

[0337] The increase in the concentration of surface agent from 0.8 to 4.0% by weight results in a more scratch-resistant varnish (shallower penetration of the tip of the durometer for the varnish containing 4.0% of BYK302).

Example 6—Thermoforming/Thermal Drape-Forming

[0338] There are several possible methods of thermoforming

1) Drape Forming

[0339] (i) the sheet (PC or PMMA) is placed in an oven to soften the plastic. For the PC, ˜5 min at 200° C. [0340] (ii) the sheet is “manually” moved over a mold. The sheet begins to deform by gravity. [0341] (iii) a countermold is placed on the hot sheet and gives the definitive shape to the part. Cooling for 3 min before removing from the mold.

2) Compression Molding

[0342] The sheet is heated and directly shaped in a press. This process is reserved for the most complex geometries that require greater elongation of the plastic.

3) Relaxation

[0343] This is forming by gravity in an oven. The advantage of this process is to remove a stress maximum (plastic memory) from the part, but it is carried out on very small series (long cycle time).

[0344] In the present example, the thermoforming tests were carried out by the “2D” drape-forming process on PMMA substrates coated with a varnish according to the present invention.

[0345] Substrates: PMMA Shieldup (Arkema), 5 mm thick, dimensions 300×300 mm, coated with varnish 280415A 16, 18 and 19 μm thick.

[0346] The composition of this varnish is detailed in the table below (unless indicated otherwise, the figures are expressed as % by weight relative to the total weight of the composition):

TABLE-US-00009 Film SR238 ® CN981 ® I184 ® BYK3505 TCDDA 280415A 30.7 23.6 5.0 4.0 36.7

[0347] The reactive diluent/oligomer (SR238/CN981) weight ratio was 1.3.

Tested on:

[0348] Mold 1: “2D light”: Four Sat—Fritzmeier 524017 mold

[0349] Mold 2: “2D strong” Strada light guide

[0350] Thermoforming conditions for all tests carried out: “2D” drape-forming process (cf. detail of the process above). Placing in oven at 140° C. for 10 min before thermoforming.

[0351] Results: the samples were successfully thermoformed without any cracking of the varnish, as illustrated in FIG. 8.

REFERENCE LIST

[0352] 1. EP 0 035 272 [0353] 2. Belon et al., Macromol. Mater. Eng., 2011, 296(6), 506-516 [0354] 3. Belon et al., J. polym. Sci.: Part A: Polymer Chemistry, 2010, 48(19), 4150-4158 [0355] 4. WO 2013/171582 [0356] 5. WO 94/22968 [0357] 6. EP 0 276 501 [0358] 7. EP0 249 201 [0359] 8. WO 97/12945 [0360] 9. EP 0 008 127