Suitable free-radical inhibitors/retarders are particularly those which specifically inhibit uncontrolled free-radical polymerization of the formulation outside the desired (irradiated) range. These are crucial for good contour sharpness and imaging accuracy in the precursor. Suitable free-radical inhibitors must be chosen according to the desired free-radical yield from the irradiation/exposure step and the polymerization rate and reactivity/selectivity of the double bond carrier. Suitable free-radical inhibitors are, for example, 2,2-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole), phenothiazine, hydroquinones, hydroquinone ether, quinone alkyds and nitroxyl compounds and mixtures thereof, benzoquinones, copper salts, catechols, cresols, nitrobenzene and oxygen. These antioxidants are preferably used in amounts of 0.001% by weight to 3% by weight, based on the total weight of the free-radically crosslinkable build material.

Embodiments and further aspects of the present invention are elucidated hereinbelow. These may be combined with one another as desired unless the opposite is apparent from the context.

Preferably, the free-radically crosslinkable polyurethane has a melting point or glass transition point of ≥25° C., or preferably ≥30° C., or preferably ≥35° C. to ≤150° C., more preferably ≥40° C. to ≤120° C. (determined by DSC).

The free-radically crosslinkable polyurethane at RT preferably has a viscosity (DIN EN ISO 2884-1) of ≥10 000 mPas, or preferably ≥20 000 mPas, or preferably ≥25 000 mPas, or is a solid.

In a preferred embodiment, the free-radically crosslinkable polyurethane has a melting point or glass transition point (of ≥50° C. (DSC; preferably ≥60° C. to ≤150° C., more preferably ≥80° C. to ≤120° C.); the free-radically crosslinkable polyurethane has a viscosity (DIN EN ISO 2884-1) at the processing temperature of ≤10 000 mPas (preferably ≥50 mPas to ≤8000 mPas, more preferably ≥500 mPas to ≤5000 mPas); and/or the photoinitiator has a half-life for its thermal degradation at the processing temperature of ≥1 hour, or preferably ≥1.5 hours to ≤5 hours, more preferably ≥2 hours to ≤4 hours.

The build material has a pot life at the processing temperature in the presence of the photoinitiator of preferably ≥1 hour, or preferably ≥1.5 hours to ≤5 hours, more preferably ≥2 hours to ≤4 hours. Pot life is understood in the context of the invention to mean the time within which the viscosity of the build resin doubles.

In a further preferred embodiment, in addition to photoinitiators, thermally activatable free-radical donors are also present, for example peroxides, which preferably cause unreacted double bonds to react in a heat treatment process performed in step IV) at temperatures above the recommended decomposition temperatures for these free-radical donors.

In a further preferred embodiment, there are further functional groups in blocked or unblocked form other than free-radically crosslinkable functional groups in the free-radically crosslinkable build material, and these are capable of entering into a reaction other than free-radical crosslinking for increasing mechanical strength in the build material. In the context of the present invention, a reaction for increasing mechanical strength is understood to mean not only a crosslinking reaction but also any other reaction that increases the modulus of elasticity (DIN 53504) of the article obtained by the method of the invention at 20° C. by ≥10% (preferably ≥20%, more preferably ≥50%). An alternative or additional criterion used for this purpose may be an increase in tensile strength (DIN 53504) of the article obtained by the method of the invention at 20° C. by ≥10% (preferably ≥20%, more preferably ≥50%). Examples of such reactions are addition and condensation reactions. As well as the free-radically induced crosslinking and the cooling, mechanical strengthening of the article thus takes place in a third way after these reactions have run.

In a further preferred embodiment, the free-radically crosslinkable build material contains a polyamine component. In a heated build material, it is thus possible for a chemical reaction to take place in the build material (if appropriate in the presence of urethanization catalysts and/or transesterification catalysts). The urethane groups formed by addition may open reversibly, at least in part, under these conditions, as a result of which free NCO groups are available for reaction with the amino groups of the polyamine component to form urea groups. In this way, the average molecular weight of the polyurethane can be increased. In the case of polyamines with an average functionality of >2, the crosslinking density in the build material can be increased further. When the polyurethane has been formed at least partly from polyester polyols, a further reaction that can also proceed is the opening of the ester bonds and reaction with polyamines to give amides. In this way too, it is preferably possible to achieve further curing of the build material after the precursor has been obtained. The same is true when the build material comprises a polyester polymer.

Catalysts usable in accordance with the invention are those that accelerate the urethanization reaction and also the reverse reaction to give isocyanates and polyols and/or amidation of the urethane bond to give ureas, and/or those that accelerate amidation of ester groups to give amides. Suitable catalysts for the purpose are known to those skilled in the art and may be effective under basic, acidic or neutral pH conditions. In a preferred variant, the transamidation reaction is conducted without the addition of additional catalysts.

Suitable amines for the polyamine component are especially aliphatic polyamines having an average amine functionality of ≥2, preferably symmetric aliphatic polyamines having an average amine functionality of ≥2 (linear or alicyclic polyamines having fixed geometries with respect to their cis or trans configurations).

In a further preferred embodiment, the polyamine component has an average number of Zerewitinoff-active hydrogen atoms of ≥4.

In a further preferred embodiment, the polyamine component contains one or more compounds from the group of: adipic dihydrazide, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, dipropylenetriamine, hexamethylenediamine, hydrazine, isophoronediamine, (4,4′- and/or 2,4′-)diaminodicyclohexylmethane, (4,4′- and/or 2,4′-)diamino-3,3′-dimethyldicyclohexylmethane and N-(2-aminoethyl)-2-aminoethanol.

In a further preferred embodiment, the polyamine component is present in a proportion of ≥0.1% by weight to ≤25% by weight, based on the weight of the build material.

In a further preferred embodiment, the free-radically crosslinkable build material contains blocked or unblocked NCO groups. When the NCO groups are blocked, the method of the invention also includes the step of deblocking these NCO groups. After they have been deblocked, they are available for further reactions.

The blocking agent is chosen such that the NCO groups are at least partly deblocked when heated in the method of the invention. Examples of blocking agents are alcohols, lactams, oximes, malonic esters, alkyl acetoacetates, triazoles, phenols, imidazoles, pyrazoles and amines, for example butanone oxime, diisopropylamine, 1,2,4-triazole, dimethyl-1,2,4-triazole, imidazole, diethyl malonate, ethyl acetoacetate, acetone oxime, 3,5-dimethylpyrazole, ε-caprolactam, N-methyl-, N-ethyl-, N-(iso)propyl, N-n-butyl-, N-isobutyl-, N-tert-butylbenzylamine or 1,1-dimethylbenzylamine, N-alkyl-N-1,1-dimethylmethylphenylamine, adducts of benzylamine onto compounds having activated double bonds such as malonic esters, N,N-dimethylaminopropylbenzylamine and other optionally substituted benzylamines containing tertiary amino groups and/or dibenzylamine, or any desired mixtures of these blocking agents.

In a further preferred embodiment, the free-radically crosslinkable build material contains an isocyanate trimerization catalyst. The trimerization catalyst is preferably 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, trioctylphosphine, tributyltin oxide or a mixture of at least two of the aforementioned catalysts. The reaction for increasing mechanical strength is thus the formation of isocyanurates from free NCO groups. This results in further crosslinking of the build material.

In a further preferred embodiment, the free-radically crosslinkable build material contains groups having Zerewitinoff-active hydrogen atoms and one or more cyclic tin compounds of the formula F-I, F-II and/or F-III:

[Image Omitted]

- wherein:
- D is —O—, —S— or —N(R1)-
  - where R1 is a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical which has up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen or the radical

[Image Omitted]

- - or R1 and L3 together are —Z-L5-;
- D* is —O— or —S—;
- X, Y and Z are identical or different radicals selected from alkylene radicals of formulae —C(R2)(R3)-, —C(R2)(R3)-C(R4)(R5)- or —C(R2)(R3)-C(R4)(R5)-C(R6)(R7)- or ortho-arylene radicals of formulae

[Image Omitted]

- - where R2 to R11 are independently saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or are hydrogen;
- L1, L2 and L5 are independently —O—, —S—, —OC(═O)—, —OC(═S)—, —SC(═O)—, —SC(═S)—, —OS(═O)₂O—, —OS(═O)₂— or —N(R12)-,
  - where R12 is a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical which has up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen;
- L3 and L4 are independently —OH, —SH, —OR13, -Hal, —OC(═O)R14, —SR15, —OC(═S)R16, —OS(═O)₂OR17, —OS(═O)₂R18 or —NR19R20, or L3 and L4 together represent -L1-X-D-Y-L2-,
  - where R13 to R20 are independently saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or are hydrogen.

The tin compounds of the formulae F-I, F-II and F-III are thermally labile. Below a certain temperature, they do not exhibit industrially useful catalytic activity for the reaction of NCO groups with functional groups bearing Zerewitinoff-active hydrogen atoms. The reactions in question here are especially urethanizations and urea formations. Above a certain temperature, however, there is a significant rise in catalytic activity. Without being limited to a theory, it is assumed that then the ligands completely or partially dissociate Sn center and therefore the Sn center is available as a catalyst. The catalysts may therefore be referred to as thermally latent catalysts. Because the NCO groups present in the build material do not react below this temperature, the build material is also easy to reuse.

In the cases in which the tin compounds of the formulae F-I, F-II and/or F-III have ligands with free OH radicals and/or NH radicals, the catalyst can be incorporated into the product in the polyisocyanate polyaddition reaction. A particular advantage of these incorporable catalysts is their markedly reduced fogging behavior.

The different methods of preparation for the tin(IV) compounds for use in accordance with the invention or their tin(II) precursors are described inter alia in: J. Organomet. Chem. 2009 694 3184-3189, Chem. Heterocycl. Comp. 2007 43 813-834, Indian J. Chem. 1967 5 643-645 and in literature cited therein.

The content of the tin compounds of the formulae F-I, F-II and/or F-III in the build material may be made dependent on the type of isocyanates on which the build material is based. For instance, when NCO groups bonded to an aromatic carbon atom are dominant, the content may be ≤100 ppm, based on the total weight of the build material. When NCO groups bonded to an aliphatic carbon atom are dominant, the content may be ≤3000 ppm, based on the total weight of the build material.

There are preferably unblocked NCO groups in the build material.

NCO-reactive compounds having Zerewitinoff-active hydrogen atoms that are used may be any compounds known to those skilled in the art and having an average OH or NH functionality of at least 1.5. These may be, for example, low molecular weight diols (for example ethane-1,2-diol, propane-1,3- or -1,2-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol), triols (for example glycerol, trimethylolpropane) and tetraols (for example pentaerythritol), short-chain amino alcohols, polyamines, but also higher molecular weight polyhydroxyl compounds such as polyether polyols, polyester polyols, polycarbonate polyols, polysiloxane polyols, polyamines and polyether polyamines, and also polybutadiene polyols.

A further preferred embodiment provides that as the cyclic tin compound one or more of the following compounds is employed:

4,12-di-n-butyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

4,12-di-n-butyl-2,6,10,14-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

2,4,6,10,12,14-hexamethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

4,12-di-n-octyl-2,6,10,14-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

4,12-di-n-octyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

4,12-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

1,1-dichloro-5-methyl-5-aza-2,8-dioxa-1-stannacyclooctane,

1,1-diisopropyl-5-methyl-5-aza-2,8-dioxa-1-stannacyclooctane,

1,1-dibenzoyl-3,3,7,7-tetramethyl 5-n-octyl-5-aza-2,8-dioxa-1-stannacyclooctane,

1,1-dibenzoyl-5-n-octyl-5-aza-2,8-dioxa-1-stannacyclooctane,

1,1-bis(p-dodecylphenylsulfonyl)-5-n-octyl-5-aza-2,8-dioxa-1-stannacyclooctane,

2-benzoyloxy-6-octyl-4,8-dioxo-1,3,6,2-dioxazastannocan-2-yl benzoate

or mixtures thereof.

In a further preferred embodiment, the free-radically crosslinkable build material contains groups having Zerewitinoff-active hydrogen atoms and in that the blocking agent is an isocyanate or the blocking agent is selected such that, after deblocking of the NCO group, no release of the blocking agent as a free molecule or as part of other molecules or molecular moieties takes place. In that case, the after the deblocking, the functional groups obtained can react with compounds having at least two Zerewitinoff-active hydrogen atoms, such that an increase in mechanical strength or crosslinking occurs. In this respect, deblocking of the NCO groups in the context of the present invention need not necessarily mean that an NCO group is obtained again. Instead, this may also mean that a functional group such as an acyl cation group can be obtained after deblocking, which reacts with other functional groups having Zerewitinoff-active hydrogen atoms to form a covalent bond.

The reaction is preferably performed until ≤50%, preferably ≤30% and more preferably ≤20% of the blocked isocyanate groups originally present in the curable component are still present. This can be determined by surface IR spectroscopy. It is further preferable that, after step IV), ≥50%, ≥60%, ≥70% or ≥80% of the NCO groups deblocked in the curable component react with the compound having at least two Zerewitinoff-active hydrogen atoms.

Here too, NCO-reactive compounds having Zerewitinoff-active hydrogen atoms that are used may be any compounds known to those skilled in the art and having an average OH or NH functionality of at least 1.5. These may be, for example, low molecular weight diols (for example ethane-1,2-diol, propane-1,3- or -1,2-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol), triols (for example glycerol, trimethylolpropane) and tetraols (for example pentaerythritol), short-chain amino alcohols, polyamines, but also higher molecular weight polyhydroxyl compounds such as polyether polyols, polyester polyols, polycarbonate polyols, polysiloxane polyols, polyamines and polyether polyamines, and also polybutadiene polyols.

In a preferred embodiment, the blocking agent is selected from the group consisting of organic isocyanates, lactams, glycerol carbonate, a compound of the general formula (I):

[Image Omitted]

in which X is an electron-withdrawing group, R¹and R²are independently the radicals H, C₁-C₂₀-(cyclo)alkyl, C₆-C₂₄-aryl, C₁-C₂₀-(cyclo)alkyl ester or amide, C₆-C₂₄-aryl ester or amide, mixed aliphatic/aromatic radicals having 1 to 24 carbon atoms which may also be part of a 4- to 8-membered ring and n is an integer from 0 to 5,

or a combination of at least two of these.

The electron-withdrawing group X may be selected from any substituents which result in CH acidity of the α-hydrogen. These may include, for example, ester groups, amide groups, sulfoxide groups, sulfone groups, nitro groups, phosphonate groups, nitrile groups, isonitrile groups, polyhaloalkyl groups, halogens such as fluorine, chlorine or carbonyl groups. Preference is given to nitrile and ester groups, particular preference being given to methyl carboxylate and ethyl carboxylate groups. Also suitable are compounds of the general formula (I) wherein the ring optionally contains heteroatoms, such as oxygen, sulfur or nitrogen atoms. The activated cyclic ketone of formula (I) preferably has a ring size of 5 (n=1) and 6 (n=2).

Preferred compounds of general formula (I) are cyclopentanone 2-carboxymethyl ester and -carboxyethyl ester, cyclopentanone-2-carbonitrile, cyclohexanone 2-carboxymethyl ester and -carboxyethyl ester or cyclopentanone-2-carbonylmethyl. Particular preference is given to cyclopentanone 2-carboxymethyl ester and -carboxyethylester and cyclohexanone 2-carboxymethyl ester and -carboxyethyl ester. The cyclopentanone systems are easily obtainable industrially by a Dieckmann condensation of dimethyl adipate or diethyl adipate. Cyclohexanone 2-carboxymethyl ester can be prepared by hydrogenation of methyl salicylate.

Further preferred blocking agents are glycerol carbonate, lactams such as ε-caprolactam or isocyanates themselves. The NCO group to be blocked can react with the NCO group of the blocking agent to form a uretdione. The reverse reaction results in reformation of the NCO groups which react with the available chain extenders. It is particularly preferable when the blocking agent and the compound having the NCO group to be blocked are identical. In that case, blocking comprises a dimerization of the relevant compound. This and the reaction with polyol and polyamine are shown by way of example in the scheme which follows.

In a further preferred embodiment, step II) simultaneously illuminates and/or irradiates a multitude of energy beams the selected area of the layer of the free-radically crosslinkable build material corresponding to the respectively selected cross section of the precursor. Accordingly, this embodiment covers the additive manufacturing method of DLP technology when the multitude of energy beams generates the image to be provided by exposure and/or irradiation via an array of individually controllable micromirrors.

In a further preferred embodiment, in step II), the deposited layers of the free-radically crosslinked build material are heated to a temperature above the melting point of the free-radically crosslinkable polyurethane. The temperature may be ≥10° C. to ≤100° C., preferably ≥20° C. to ≤80° C. and more preferably ≥30° C. to ≤60° C. above the melting point of the free-radically crosslinkable polyurethane ascertained by DSC. In this way, the third subsequent curing mechanisms in particular as described above can proceed faster and/or more comprehensively.

In a preferred embodiment of the method of the invention, in step IV), the performing of the chemical reaction includes heating to a temperature above the melting point of the free-radically crosslinkable polyurethane. Preferably, the performing of the chemical reaction is performed with heating above room temperature RT of 23° C., preferably at a temperature within a range from 50 to 200° C., or preferably within a range from 60 to 180° C., or preferably within a range from 80 to 150° C.

The present invention further provides a system for producing an article in an additive manufacturing method from a precursor, comprising a carrier that can be raised counter to the direction of gravity, a build unit comprising a molten build material below the carrier and an irradiation and/or exposure unit for irradiating and/or exposing molten build material below the carrier, wherein the build material comprises a thermoplastic free-radically crosslinkable polyurethane and a photoinitiator.

In a preferred embodiment, the free-radically crosslinkable polyurethane has in the system has a melting point of ≥50° C. (DSC; preferably ≥60° C. to ≤240° C., more preferably ≥80° C. to ≤180° C.);

the free-radically crosslinkable polyurethane has a viscosity (DIN EN ISO 2884-1) at the processing temperature of ≤10 000 mPas (preferably ≥50 mPas to ≤8000 mPas, more preferably ≥500 mPas to ≤5000 mPas);

the photoinitiator has a half-life for its thermal degradation at the processing temperature of ≥1 hour, or preferably ≥1.5 hours to ≤5 hours, more preferably ≥2 hours to ≤4 hours; and/or

there are further functional groups in blocked or unblocked form other than free-radically crosslinkable functional groups in the free-radically crosslinkable build material, and these are capable of entering into a reaction other than free-radical crosslinking for increasing mechanical strength in the build material. For details with regard to these functional groups and their reactions, to avoid repetition, reference is made to the above remarks relating to the method of the invention.

The present invention further relates to the use of a free-radically crosslinkable build material in an additive manufacturing method at a processing temperature of ≥50° C., wherein the free-radically crosslinkable build material comprises a thermoplastic free-radically crosslinkable polyurethane having a urethane group content of ≥5% by weight and a photoinitiator. For details with regard to the build material including preferred variants and ranges, to avoid repetition, reference is made to the above remarks relating to the method of the invention.

The present invention likewise relates to a polymer obtainable from the free-radical crosslinking of a thermoplastic free-radically crosslinkable polyurethane having a urethane group content of ≥5% by weight, where the free-radically crosslinkable polyurethane is heated to a processing temperature greater than the melting point of the free-radically crosslinkable polyurethane and where there are further functional groups in blocked or unblocked form other than free-radically crosslinkable functional groups in the free-radically crosslinkable polyurethane, and these enter into a crosslinking reaction other than free-radical crosslinking in the build material. For details with regard to the build material including preferred variants and ranges, to avoid repetition, reference is made to the above remarks relating to the method of the invention.

The present invention finally relates to a coating comprising a polymer of the invention. The coating is preferably a paint or an adhesive.

The present invention is more particularly elucidated by the figures that follow, without being limited thereto. The drawings show:

FIG. 1 a system of the invention in the performance of the method of the invention,

FIG. 2 a further system of the invention in the performance of the method of the invention.

In the system shown in FIG. 1, a reservoir vessel 100 provides a molten build material 200. The reservoir vessel 100 is appropriately thermally insulated and/or has a controlled heating device in order to heat the molten build material 200 to a predetermined temperature. By means of a pump 300, the molten build material 200 reaches the build unit 400. The molten build material is present there in the form of a layer 210, the thickness of which correlates with the thickness of a layer of the precursor 700 to be built up layer by layer. It is likewise preferable that the build unit 400 is thermally insulated and/or has a controlled heating device in order that the layer 210 remains in the molten state. The base of the build unit 400 is formed by a transparent base 410 manufactured from quartz glass, for example. By means of a carrier 500, the precursor 700 to be built up, which is bonded thereto, is moved counter to the direction of gravity, symbolized in FIG. 1 by the arrow pointing upward. An exposure unit 600 exposes the layer 210 of the molten build material in accordance with the respective cross section of the precursor to be built up. This is symbolized in FIG. 1 by “hv”.

The action of light results in free-radical crosslinking of the molten build material in a predetermined region of the layer 210 with deposition of a layer 710 onto a previously deposited layer of the free-radically crosslinked build material. Subsequently, the carrier 500 is raised by a predetermined distance and the layer 210 is completed by means of the pump 300. In this way, the precursor 700 to be built up is obtained from individual layers. Since already formed parts of the precursor 700 are no longer being heated, the temperature thereof falls, and solidification results in further mechanical consolidation. FIG. 1 does not show how the precursor 700 is optionally subjected to thermal aftertreatment, resulting in further consolidation.

In the system shown in FIG. 2, a reservoir vessel 100 provides a build material 220 in pellet form. The reservoir vessel 100 may be thermally insulated and/or have a controlled heating device in order to heat the build material 220 to a predetermined temperature. By means of a heatable extruder screw 310, the build material molten thereby reaches the build unit 400. The molten build material is present there in the form of a layer 210, the thickness of which correlates with the thickness of a layer of the precursor 700 to be built up layer by layer. It is preferable that the build unit 400 is thermally insulated and/or has a controlled heating device in order that the layer 210 remains in the molten state. The base of the build unit 400 is formed by a transparent base 410 manufactured from quartz glass, for example. By means of a carrier 500, the precursor 700 to be built up, which is bonded thereto, is moved counter to the direction of gravity, symbolized in FIG. 2 by the arrow pointing upward. An exposure unit 600 exposes the layer 210 of the molten build material in accordance with the respective cross section of the precursor to be built up. This is symbolized in FIG. 1 by “hv”.

The action of light results in free-radical crosslinking of the molten build material in a predetermined region of the layer 210 with deposition of a layer 710 onto a previously deposited layer of the free-radically crosslinked build material. Subsequently, the carrier 500 is raised by a predetermined distance and the layer 210 is completed by means of the pump 300. In this way, the precursor 700 to be built up is obtained from individual layers. Since already formed parts of the precursor 700 are no longer being heated, the temperature thereof falls, and solidification results in further mechanical consolidation. FIG. 2 does not show how the precursor 700 is optionally subjected to thermal aftertreatment, resulting in further consolidation.

EXAMPLES
General Details

All percentages, unless stated otherwise, are based on percent by weight (% by weight).

The ambient temperature of 23° C. at the time of conducting the experiments is referred to as RT (room temperature). When reference is made hereinafter to heating, this means that the build material is brought to a temperature above RT.

The methods detailed hereinafter for determining the relevant parameters were employed for performing/evaluating the examples and are also the methods for determining the parameters relevant in accordance with the invention in general.

Determination of Phase Transitions by DSC

The phase transitions were determined by means of DSC (differential scanning calorimetry) with a Mettler DSC 12E (Mettler Toledo GmbH, Giessen, Germany) in accordance with DIN EN 61006. Calibration was effected via the melt onset temperature of indium and lead. 10 mg of substance were weighed out in standard capsules. The measurement was effected by two heating runs from −50° C. to +150° C. at a heating rate of 20 K/min with subsequent cooling at a cooling rate of 320 K/min. Cooling was effected by means of liquid nitrogen. The purge gas used was nitrogen. The values reported are each based on the evaluation of the 1st heating curve, since changes in the sample in the measurement process at high temperatures are possible in the reactive systems being examined as a result of the thermal stress in the DSC. The melting temperatures T_mwere obtained from the temperatures at the maxima of the heat flow curves. The glass transition temperature T_gwas ascertained from the temperature at half the height of a glass transition step.

Determination of Infrared Spectra

The infrared spectra were measured on a Bruker FT-IR spectrometer equipped with an ATR unit. For the relative measurement of the change in the free NCO groups on films, a Bruker FT-IR spectrometer (Tensor II) was used. The sample was contacted with the platinum ATR unit. The contacted area of the sample was 2×2 mm. In the course of measurement, the IR radiation penetrated 3-4 μm into the sample according to wavenumber. An absorption spectrum was then obtained from the sample. In order to compensate for nonuniform contacting of the samples of different hardness, a baseline correction and a normalization in the wavenumber range of 2600-3200 (CH2, CH3) was performed on all spectra. The interpolation of the “free” NCO group was performed in the wavenumber range of 2170-2380.

Determination of Viscosity

All viscosity measurements were made with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (Germany) to DIN EN ISO 3219.

Determination of Modulus of Elasticity

The modulus of elasticity was ascertained on cured polymer films in a tensile test to DIN 53371.

Determination of Hardness

Microhardness was determined by means of a Fischerscope H100C instrument, and Martens hardness was calculated by means of DIN EN ISO 14577-1b using the force-indentation curve.

Determination of Pot Life

Pot life was determined as the time until doubling of the viscosity at processing temperature.

Determination of the Half-Life of the Photoinitiator

The half-life of the photoinitiator at processing temperature was determined as a 10% solution in d8-toluene at processing temperature. Degradation was determined using initiator-specific signals of the product spectrum by means of 1H or 13C NMR spectroscopy.

Starting Compounds

- Polyisocyanate A: HDI trimer (NCO functionality >3) with an NCO content of 23.0% by weight by test method M105-ISO 11909, sourced from Covestro AG as Desmodur® N3600. The viscosity is about 1200 mPa·s at 23° C. (DIN EN ISO 3219/A.3).
- Polyisocyanate B: HDI uretdione (NCO functionality >2) with an NCO content of 21.8% by weight by test method M105-ISO 11909, sourced from Covestro AG as Desmodur® N3400. The viscosity is about 175 mPa·s at 23° C. (DIN EN ISO 3219/A.3).
- Isophorone diisocyanate (IPDI), functionality: 2, sourced from Covestro AG as Desmodur® I.
- Hexamethylene diisocyanate (HDI), functionality: 2, sourced from Covestro AG as Desmodur® H.
- Hydroxyethyl methacrylate (HEMA), sourced from Sigma Aldrich.
- Polytetrahydrofuran having a number-average molecular weight of about 1000 g/mol (PolyTHF1000), sourced from Sigma Aldrich.
- Ebecryl® 4101, urethane acrylate, viscosity at 25° C. about 7000 mPas, number-average molecular weight about 1100 g/mol, functionality about 3, sourced from Allnex.
- Ebecryl® 4141, urethane acrylate, viscosity at 25° C. about 10 000 mPas, number-average molecular weight about 700 g/mol, functionality about 2, NCO content about 12%, sourced from Allnex.
- Butylhydroxytoluene (BHT), sourced from Sigma Aldrich.
- 2-(2-Dimethylaminoethoxy)ethanol, with an OH number of about 421 mg KOH/g, sourced from Huntsman Corporation as Jeffcat® ZR-70.
- Dibutyltin dilaurate (DBTL) sourced from TIB Chemicals as TIB KAT 218.
- 2-Hydroxy-2-methylpropiophenone photoinitiator, sourced from IGM Resins as Omnirad® 1173.
  
  Preparation of the Trimerization Catalyst K Used:

2-(2-Dimethylaminoethoxy)ethanol having an OH number of 421 mg KOH/g was reacted with an equimolar amount of isocyanate, based on OH number, of polyisocyanate A (about 23% by weight of isocyanate) by dropwise addition with stirring and cooling at room temperature until no OH was detectable any longer and the isocyanate concentration after titration was <0.5%.

Preparation of the Noninventive Urethane Acrylate C1

To 58.26 g of the oligomeric starting polyisocyanate A1 at room temperature was added, while stirring, 41.67 g of hydroxyethyl methacrylate, as were 0.05 g of BHT and 0.02 g of DBTL, followed by heating to 50° C. for 3 h and then stirring until the isocyanate concentration was <0.5%. Cooling to room temperature and stirring for a further 5 h gave a clear, highly viscous urethane acrylate having a viscosity of 1250 mPas at 75° C.

Preparation of the Inventive Urethane Acrylate C2*

To 59.75 g of the oligomeric starting polyisocyanate B at room temperature was added, while stirring, 40.18 g of hydroxyethyl methacrylate, as were 0.05 g of BHT and 0.02 g of DBTL, followed by heating to 50° C. for 3 h and then stirring until the isocyanate concentration was <0.5%. Cooling to room temperature gave a urethane acrylate that was solid at 23° C. and had a viscosity of 330 mPas at 75° C. Urethane content: about 18%.