METHOD FOR PRODUCING AN OBJECT FROM A PRECURSOR, AND USE OF A RADICALLY CROSSLINKABLE RESIN IN AN ADDITIVE PRODUCTION METHOD

Abstract

A process for producing an object from a precursor comprises the steps of: I) depositing a free-radically crosslinked resin atop a carrier to obtain a ply of a construction material joined to the carrier which corresponds to a first selected cross section of the precursor; II) depositing a free-radically crosslinked resin atop a previously applied ply of the construction material to obtain a further ply of the construction material which corresponds to a further selected cross section of the precursor and which is joined to the previously applied ply; III) repeating step II) until the precursor is formed;
wherein the depositing of a free-radically crosslinked resin at least in step II) is effected by exposure and/or irradiation of a selected region of a free-radically crosslinkable resin corresponding to the respectively selected cross section of the object and wherein the free-radically crosslinkable resin has a viscosity (23 C., DIN EN ISO 2884-1) of 5 mPas to 100000 mPas. In the process the free-radically crosslinkable resin comprises a curable component in which NCO groups and olefinic CC double bonds are present, wherein in the curable component the molar ratio of NCO groups to olefinic CC double bonds is in a range from 1:5 to 5:1.

In the process, after step III) step IV) is further performed: IV) treating the precursor obtained after step III) under conditions sufficient to at least partially trimerize to isocyanurate groups NCO groups present in the free-radically crosslinked resin of the obtained precursor to obtain the object.

The invention further relates to the use of a free-radically crosslinkable resin having a viscosity (23 C., DIN EN ISO 2884-1) of 5 mPas to 100000 mPas in an additive manufacturing process, wherein the resin comprises a curable compound having isocyanurate groups, NCO groups and olefinic CC double bonds. The invention finally relates to a polymer obtainable by crosslinking such a resin.

Claims

1. Process for producing an object from a precursor, comprising the steps of: I) depositing a free-radically crosslinked resin atop a carrier to obtain a ply of a construction material joined to the carrier which corresponds to a first selected cross section of the precursor; II) depositing a free-radically crosslinked resin atop a previously applied ply of the construction material to obtain a further ply of the construction material which corresponds to a further selected cross section of the precursor and which is joined to the previously applied ply; III) repeating step II) until the precursor is formed; wherein the depositing of a free-radically crosslinked resin at least in step II) is effected by exposure and/or irradiation of a selected region of a free-radically crosslinkable resin corresponding to the respectively selected cross section of the precursor and wherein the free-radically crosslinkable resin has a viscosity (23 C., DIN EN ISO 2884-1) of 5 mPas to 100000 mPas, characterized in that the free-radically crosslinkable resin has a curable component in which NCO groups and olefinic CC double bonds are present, wherein in the curable compound the molar ratio of NCO groups to olefinic CC double bonds is in a range from 1:5 to 5:1, and in that, after step III), step IV) is further performed: IV) treating the precursor obtained after step III) under conditions sufficient to at least partially trimerize to isocyanurate groups NCO groups present in the free-radically crosslinked resin of the obtained precursor to obtain the object.

2. Process according to claim 1, characterized in that isocyanurate groups are further present in the curable component, wherein the molar ratio of NCO groups to isocyanurate groups is in a range from 100:1 to 1:2 and in the curable component the molar ratio of olefinic CC double bonds to isocyanurate groups is in a range from 100:1 to 1:5.

3. Process according to claim 1, characterized in that the curable component comprises a curable compound which comprises NCO groups and olefinic CC double bonds, wherein in the curable compound the molar ratio of NCO groups to olefinic CC double bonds is in a range from 1:5 to 5:1.

4. Process according to claim 3, characterized in that the curable component comprises a curable compound comprising isocyanurate groups, NCO groups and olefinic CC double bonds, wherein in the curable compound the molar ratio of NCO groups to olefinic CC double bonds is in a range from 1:5 to 5:1, in the curable compound the molar ratio of NCO groups to isocyanurate groups is in a range from 100:1 to 1:2, and in the curable compound the molar ratio of olefinic CC double bonds to isocyanurate groups is in a range from 100:1 to 1:5.

5. Process according to claim 1, characterized in that the free-radically crosslinkable resin further comprises a free-radical starter and/or an isocyanate trimerization catalyst.

6. Process according to claim 5, characterized in that at least one free-radical starter is selected from the group: -hydroxyphenylketone, benzyldimethylketal, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(4-methoxybenzoyl)diethylgermanium and any combination of at least two thereof and/or the isocyanurate trimerization catalyst is selected from: potassium acetate, potassium acetate in combination with a crown ether, potassium acetate in combination with a polyethylene glycol, potassium acetate in combination with a polypropylene glycol, tin octoate, sodium phenoxide, potassium hydroxide, trioctyl phosphine and/or tributyltin oxide.

7. Process according to claim 1, characterized in that in the resin the molar ratio of NCO groups to Zerewitinoff-active H atoms is 500.

8. Process according to claim 1, characterized in that the curable component has a number-average molecular weight M.sub.n of 200 g/mol to 5000 g/mol.

9. Process according to claim 1, characterized in that in step IV) the treating of the precursor obtained after step III) under conditions sufficient to at least partially trimerize to isocyanurate groups NCO groups present in the free-radically crosslinked resin of the obtained precursor comprises a heating of the body to a temperature of 60 C.

10. Process according to claim 1, characterized in that the surface of the precursor obtained after step III) and/or of the object obtained after step IV) is contacted with a compound comprising Zerewitinoff-active H atoms, wherein water occurring as natural atmospheric humidity in the atmosphere surrounding the precursor and/or the object is excluded.

11. Process according to claim 1, characterized in that: the carrier is arranged inside a container and is vertically lowerable in the direction of the gravitational force, the container contains the free-radically crosslinkable resin in an amount sufficient to cover at least the carrier and crosslinked resin deposited atop the carrier, before each step II) the carrier is lowered by a predetermined distance so that above the uppermost ply of the construction material viewed in the vertical direction a layer of the free-radically crosslinkable resin is formed and in step II) an energy beam exposes and/or irradiates the selected region of the layer of the free-radically crosslinkable resin corresponding to the respectively selected cross section of the precursor.

12. Process according to claim 1, characterized in that: the carrier is arranged inside a container and is vertically raisable counter to the direction of the gravitational force, the container provides the free-radically crosslinkable resin, before each step II) the carrier is raised by a predetermined distance so that below the lowermost ply of the construction material viewed in the vertical direction a layer of the free-radically crosslinkable resin is formed and in step II) a plurality of energy beams simultaneously expose and/or irradiate the selected region of the layer of the free-radically crosslinkable resin corresponding to the respectively selected cross section of the precursor.

13. Process according to claim 1, characterized in that: in step II) the free-radically crosslinkable resin is applied from one or more printing heads corresponding to the respectively selected cross section of the precursor and is subsequently exposed and/or irradiated.

14. Use of a free-radically crosslinkable resin having a viscosity (23 C., DIN EN ISO 2884-1) of 5 mPas to 100000 mPas in an additive manufacturing process, characterized in that the resin has a curable compound which comprises isocyanurate groups, NCO groups and olefinic CC double bonds, wherein the molar ratio of NCO groups to olefinic CC double bonds is in a range from 1:5 to 5:1, in the curable compound the molar ratio of NCO groups to isocyanurate groups is in a range from 100:1 to 1:2, and in the curable compound the molar ratio of olefinic CC double bonds to isocyanurate groups is in a range from 100:1 to 1:5.

15. Polymer obtainable by crosslinking of a resin having a viscosity (23 C., DIN EN ISO 2884-1) of 5 mPas to 100000 mPas, characterized in that the resin comprises a curable component comprising NCO groups and olefinic CC double bonds, wherein the molar ratio of NCO groups to olefinic CC double bonds is in a range from 1:5 to 5:1.

Description

EXAMPLES

[0111] The invention is more particularly elucidated with reference to the examples which follow but without any intention to limit the invention thereto.

[0112] The formulations of free-radically crosslinkable resins reported in the tables 1 and 2 were produced. The data in the table relate to parts by weight unless otherwise stated. Entries designated with a V are comparative examples.

TABLE-US-00001 TABLE 1 1 2 Isocyanate 1 56 70 Isocyanate 2 14 Acrylate 1 30 30 Photoinitiator 1 0.8 wt % of the acrylate 0.8 wt % of the acrylate Inhibitor 0.08 wt % of the acrylate 0.08 wt % of the acrylate KOAc catalyst 1.5 wt % of isocyanates 1 1.5 wt % of isocyanate 1 and 2

TABLE-US-00002 TABLE 2 Formulation 3 4 5 6 7 8 9 V2 V3 10 Components g g g g g g g g g g Isocyanate 1 30 15 21 10.5 15 21 15 11 Isocyanate 3 15 10.5 21 Isocyanate 4 6 Isocyanate 5 10 Acrylate 1 9 9 9 6 9 21 9 Acrylate 2 9 9 9 Photoinitiator 2 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Catalyst 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9
Isocyanate I: reaction product of the 1,6-HDI trimer with hydroxyethyl acrylate and the following idealized structure:

##STR00001##

Isocyanate 2: NCO-terminated, polyether-modified HDI prepolymer (Desmodur N3100 Covestro Deutschland AG)
Isocyanate 3: aliphatic polyisocyanate, low viscosity HDI trimerisate (Desmodur N3600 Covestro Deutschland AG)
Isocyanate 4: Isophorone diisocyanate (Desmodur Covestro Deutschland AG)
Isocyanate 5: aliphatic, mostly linear isocyanate-functional prepolymers of a polyether based on hexamethylene diisocyanate (Desmodur XP 2617 Covestro Deutschland AG)
Acrylate 1: 1,6-hexanediol diacrylate (analytical quality obtained from Sigma-Aldrich)
Acrylate 2: isobornyl acrylate (analytical quality obtained from Sigma-Aldrich)
Photoinitiator 1: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; TPO (obtained from Sigma-Aldrich)
Photoinitiator 2: 2-hydroxy-2-methylpropiophenone; Darocur 1173 (obtained from Sigma-Aldrich)
Inhibitor: BBOT: 2,2-(2,5-thiophenediyl)bis(5-(1,1-dimethylethyl))benzoxazole; UV blocker (obtained from Sigma-Aldrich)
Catalyst: potassium acetate+18-crown-6 crown ether in diethylene glycol (components obtained from Sigma-Aldrich and mixed in the ratio: 0.148 g of potassium acetate+0.485 g of 18-crown-6 ether+3.115 g of diethylene glycol.

[0113] The resin formulation Autodesk Standard Clear Prototyping Resin PR48 was chosen for the comparative example V1. This resin formulation contains about 40 weight % of the aliphatic urethane acrylate Ebecryl 8210, about 40 weight % of the ethoxylated pentaerythritol tetraacrylate Sartomer SR 494, TPO as a photoinitiator, about 20 weight % of the monofunctional urethane acrylate Rahn Genomer 1122 as a reactive diluent and Mayzo OB+ (2,2-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole)) as a UV blocker.

[0114] All listed formulations were, unless described otherwise, mixed by adding all components in the order given by the recipe in a Thinky ARE 250 Speedmixer for 2 minutes at 2000 rpm.

[0115] Formulations 1 and 2 according to the invention and the formulation of the comparative example V1 were used to produce standard S3 test bars for tensile tests on an Autodesk Ember DLP-based 3D printing apparatus. The wavelength for the exposure was 405 nm. The individual layers of the test bars were arranged parallel to the tensile direction. The layer thickness was 50 m in each case. The exposure time was 5 s/layer.

[0116] The precursors produced from formulations 1 and 2 were subsequently heated for 30 minutes at 130 C. in a forced-air drying cabinet.

[0117] The thus obtained test bars had the properties reported in the table 3 below.

TABLE-US-00003 TABLE 3 V1 1 2 Modulus of elasticity [GPa], DIN 53504 1 1.3 1.2 Tensile strength [MPa], DIN 53504 34 48 48 Elongation at break [%], DIN 53504 5.4 4.4 5.1 Glass transition temperature [ C.], DSC, 20 K/min 15 70 70

[0118] Examples 1 and 2 according to the invention, when compared to comparative example V1, show a significantly higher tensile strength at comparable elongation at break.

[0119] The formulations 3 to 10 according to the invention and the comparative formulations V2 and V3 were coated onto a glass plate using a doctor knife as 400 micrometer thick layers and pre-cured using UV lamps (gallium-doped mercury lamp and undoped mercury lamp) at a line speed of 5.0 m/min and a radiation dose of 1400 mJ/cm.sup.2. After that the precursors obtained from the formulations 3 to 10 according to the invention and the comparative formulations V2 and V3 were heated at 180 C. for 10 minutes in a forced-air drying cabinet.

[0120] Using a Fischerscope HC100C apparatus from Fischer Technology Inc., USA the microhardness and according to DIN EN ISO 14577-1b using the force-indentation curve the Martens hardness were determined for the coatings thus obtained and listed in table 4.

[0121] Furthermore, the optical appearance of the coatings thus obtained was described and also listed in table 4.

[0122] After curing at the given UV dose all samples are self-supporting, i.e. there is no flow of the samples from the glass plate visible even after vertical positioning of the plates. This self-supporting is an indicator for a rapid sufficient modulus generation which enables the production of an article according to the invention.

TABLE-US-00004 TABLE 4 3 4 5 6 7 8 9 V2 V3 10 Martens 126 128 126 154 140 161 157 brittle brittle 101 hardness not not [N/mm.sup.2] determinable determinable optical clear clear clear clear clear clear clear cloudy clear clear appearance

[0123] The results of table 4 clearly show that particularly good results and compatible, transparently cured products are achieved with the components according to the invention, whereas the comparative examples are brittle and frequently cloudy. In contrast to the comparative examples the mixtures according to the invention contain isocyanate groups and double bond carriers in at least one formulation component (in this case, isocyanate 1). Surprisingly this leads to a stabilization of the otherwise incompatible (as shown in V2 and V3) networks which form from polyisocyanurate and poly(meth)acrylate groups.