US-12617955-B2 - Additive production process with a thermoplastic radically cross-linkable construction material

US12617955B2US 12617955 B2US12617955 B2US 12617955B2US-12617955-B2

Abstract

The present invention relates to a method for producing an object in an additive manufacturing process from a precursor and comprises the following steps: I) depositing a layer of a radically cross-linkable construction material, which corresponds to a first selected cross-section of the precursor, on a carrier; II) depositing a layer of a radically cross-linkable construction material, which corresponds to a further selected cross-section of the precursor, on a previously applied layer of the radically cross-linked construction material; III) repeating step II) until the precursor is formed. The radically cross-linkable construction material comprises a thermoplastic radically cross-linkable polyurethane with a urethane group content of ≥5% by weight and a photoinitiator. The radically cross-linkable construction material is also heated to a processing temperature that is greater than the melting point of the radically cross-linkable polyurethane. After step III) the precursor having a temperature of 20° C. is defined as the object, or step IV) is performed: IV) performing a chemical reaction in the precursor obtained after step III) so that the object is obtained.

Inventors

Dirk Achten
Thomas Buesgen
Christoph Tomczyk
Michael Ludewig
Thomas Faecke
Roland Wagner
Florian Stempfle

Assignees

STRATASYS, INC.

Dates

Publication Date: 20260505
Application Date: 20180629
Priority Date: 20170630

Claims (11)

1 . A method of producing an article in an additive manufacturing method from a precursor, comprising: I) depositing a first layer of a free-radically crosslinked build material corresponding to a first selected cross section of the precursor on a carrier; II) depositing a further layer of the free-radically crosslinked build material corresponding to a further selected cross section of the precursor onto the first layer or another previously applied layer of the free-radically crosslinked build material; III) repeating step II) until the precursor is formed; wherein the depositing of the free-radically crosslinked build material at least in step II) comprises exposing and/or irradiating a selected region of a free-radically crosslinkable build material corresponding to the respectively selected cross section of the precursor; wherein the carrier is disposed within a container providing the free-radically crosslinkable build material, wherein the carrier is vertically raisable counter to the direction of gravity and wherein the carrier is additionally raised by a predetermined distance prior to each step II), such that a layer of the free-radically crosslinkable build material forms below a lowermost layer of the build material as viewed in a vertical direction; wherein the free-radically crosslinkable build material comprises a thermoplastic free-radically crosslinkable polyurethane having a urethane group content of ≥15% by weight to ≤30% by weight and a photoinitiator; and wherein the free-radically crosslinkable build material comprises an isocyanate trimerization catalyst; wherein the free-radically crosslinkable build material is heated in step II) to a processing temperature greater than a melting point, determined by dynamic differential calorimetry, first heating, at a heating rate of 20 K/min, of the free-radically crosslinkable polyurethane; wherein the free-radically crosslinkable polyurethane has a melting point, determined by dynamic differential calorimetry, first heating, at a heating rate of 20 K/min, of ≥50° C.; and wherein, after step III), the article is formed by allowing the precursor to cool to a temperature of about 20° C., or wherein, after step III), the article is formed by performing step IV): IV) performing a chemical reaction in the precursor obtained after step III) to obtain the article.
2 . The method as claimed in claim 1 , wherein the free-radically crosslinkable build material comprises further functional groups in blocked or unblocked form other than free-radically crosslinkable functional groups that are reactive towards functional groups other than free-radically crosslinkable functional groups for increasing mechanical strength in the build material.
3 . The method as claimed in claim 2 , wherein the free-radically crosslinkable build material comprises a polyamine component.
4 . The method as claimed in claim 2 , wherein the free-radically crosslinkable build material comprises blocked or unblocked NCO groups.
5 . The method as claimed in claim 4 , wherein the free-radically crosslinkable build material comprises groups having Zerewitinoff-active hydrogen atoms and one or more cyclic tin compounds of the formula F-I, F-II, F-III, or a combination thereof: 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 optionally comprises heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen or the radical 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 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 optionally comprise 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) 2 O—, —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 optionally comprises heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen; L3 and L4 are independently —OH, —SH, —OR13, a halogen, —OC(═O)R14, —SR15, —OC(═S)R16, —OS(═O) 2 OR17, —OS(═O) 2 R18 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 optionally comprise heteroatoms from the group of oxygen, sulfur, nitrogen, or are hydrogen.
6 . The method as claimed in claim 4 , wherein the free-radically crosslinkable build material contains groups having Zerewitinoff-active hydrogen atoms and further comprising a blocking agent wherein 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.
7 . The method as claimed in claim 1 , wherein, in step II), a multitude of energy beams simultaneously exposes and/or irradiates the selected region of the additional layer of the free-radically crosslinkable build material corresponding to the respectively selected cross section of the precursor.
8 . The method as claimed in claim 1 , wherein, in step IV), the performing of the chemical reaction includes heating to a temperature above the melting point of the free-radically crosslinkable polyurethane.
9 . The method as claimed in claim 1 , wherein the free-radically crosslinkable polyurethane at the processing temperature has a viscosity of ≤10,000 mPas based on DIN EN ISO 2884-1.
10 . The method as claimed in claim 1 , wherein the photoinitiator at the processing temperature has a half-life for its thermal degradation of ≥1 hour.
11 . The method as claimed in claim 1 , wherein the isocyanate trimerization catalyst is contained in the free-radically crosslinkable build material to increase a Martens hardness value of the free-radically crosslinked build material.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a national stage application under 35 U.S.C. § 371 of PCT/EP2018/067557, filed Jun. 29, 2018, which claims the benefit of European Application No. 17179206.2, filed Jun. 30, 2017, each of which is incorporated herein by reference. BACKGROUND Coating compositions which cure by two independent processes are generally referred to as dual-cure systems. The binder components present generally have different functional groups which under suitable conditions generally undergo crosslinking with one another independently of one another. Customary prior art dual-cure systems have radiation-curable and thermally curable groups, wherein particularly advantageous properties are obtained when using isocyanate and hydroxyl groups as thermally crosslinking functions. However the disadvantage of such solutions is that the reactivity of the NCO groups and/or the presence of catalysts for the second curing mechanism limits the pot life of the coating composition. One class of dual-cure systems contains blocked isocyanates. After a deblocking at a suitable temperature, the NCO groups are available for reactions with polyols. Disadvantages of the use of blocked isocyanates are the typically high viscosity for blocked isocyanates and the typically very high deblocking temperature. In coating applications and for use as adhesives, dual-cure systems can have advantages in so-called shadow curing. This is to be understood as meaning a curing mechanism which proceeds not photochemically but rather, for example, thermally. The coating or adhesive composition can then undergo further curing even in the case of substrates having complex shapes with regions that are shaded with respect to an exposure lamp. Several main groups of dual-cure technology are in existence in the coatings and adhesives sectors: two different free-radical starters (UV and thermal), UV and moisture post-curing, UV and PUR-2K curing and cationically catalyzed UV and thermal curing. For example Berlac AG markets a dual-cure lacquer system under the name Berlac 082.907 in which a reaction between NCO groups and OH groups is triggered first before the system is subjected to UV curing. A further conceivable application of dual-cure systems is in additive manufacturing methods (“3D printing”). Additive manufacturing methods refer to those methods by which articles are built up layer by layer. They therefore differ markedly from other methods of producing articles such as milling or drilling. In the latter methods, an article is processed such that it takes on its final geometry via removal of material. Additive manufacturing methods use different materials and processing techniques to build up articles layer by layer. One group of additive manufacturing methods uses free-radically crosslinkable resins which in some cases obtain their final strength in the formed article via a second curing mechanism. Examples of such methods are stereolithography methods and the so-called DLP method derived therefrom. For 3D printing, the disadvantages of conventional dual-cure systems in respect of pot life mean that an unused build material is difficult to reuse and the planned build times for a product cannot exceed the pot life. What would therefore be desirable would be 3D printing methods in which the disadvantages mentioned do not occur. WO 2016/181402 A1 discloses a method of producing a polymeric three-dimensional object by printing a photopolymerizable material in the melt to give an object having a memorizable first form which is deformable to a metastable form and which can transform to the first form above a trigger temperature of the polymer. In an experiment described, a polycaprolactone is reacted with isocyanatoethyl methacrylate and the resulting macromonomer is processed at 90° C. as a melt in a 3D printer using UV light (385 nm) to form an article. Further prior art documents are WO 2016/181149 A1 (“Method for making an object”), WO 2015/200189 A1 (“Three-dimensional objects produced from materials having multiple mechanisms of hardening”), WO 2016/039986 A1 (“Build materials having a metallic appearance for 3D printing”) and US 2001/0025061 A1 (“Thermally-stable photopolymer composition and light transmissive device”). SUMMARY It is an object of the present invention to at least partly overcome at least one disadvantage of the prior art. It is a further object of the invention to provide an additive manufacturing method in which the articles to be produced from a build material with more than one mechanism for increasing mechanical strength are obtainable in a very cost-efficient and/or individualized and/or resource-efficient manner, especially in terms of the reusability of build material. The object is achieved in accordance with the invention by a method as claimed in claim 1. Advantageous developments are specified in the subsidiary claims. They may be combined as desired, unless the opposite is unamb