Fused deposition modeling method and method to dissolve a high temperature polycarbonate support used in this method

Abstract

The invention pertains to a process for producing a three-dimensional target object by means of fused deposition modeling using a support material made of a composition based on a high temperature polycarbonate, wherein a solvent is used to remove the support material, wherein the solvent comprises 5-10 w% of 3-methoxy-3-methylbutan- 1-ol (MMB) and 5-10 w% of C11-C13 iso-alkanes. The invention also pertains to a method of dissolving an object made of a composition based on a polycarbonate, and to the use of a solvent comprising 5-10 w% of 3-methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of C11-C13 iso-alkanes for dissolving an object made of a composition based on the polycarbonate.

Description

FUSED DEPOSITION MODELING METHOD AND METHOD TO DISSOLVE A HIGHTEMPERATURE POLYCARBONATE SUPPORT USED IN THIS METHODGENERAL FIELD OF THE INVENTIONThe present invention pertains in general to a process for producing a three-dimensional target object by means of fused deposition modeling using a support material made of a composition based on a polymer, wherein a solvent is used to remove the support material, typically by dissolving this material completely, after the target object has been deposited on the support material.BACKGROUND OF THE INVENTIONIn fused deposition modeling (FDM), also fused filament fabrication (FFF), a method from the field of rapid prototyping, a three-dimensional (3D) object is built up layer by layer from a fusible plastic material. Typically, a 3D printer is used for this purpose which is able to print the object layer by layer. The method typically starts with plotting a pattern of dots of the molten plastic material on a surface. The plastic material is typically used in filament form and is generally plotted by extrusion by means of a nozzle, followed by hardening of the material by cooling at the desired position.A shaped article to be realised by means of 3D printing, i.e. the target object, may have geometries, for example undercuts, overhangs and any desired freeform surfaces.These geometrically critical structures cannot be realized easily by the printing of the print material all by itself, but typically entails the use of what is called a support material. While the print material serves to form the target object, the support material serves for mechanical reinforcement, i.e. stabilisation of self-supporting surfaces and structures as shaped parts of the target object through formation of support structures.Typically, the support material may be printed as well in the construction of the actual three-dimensional object and is removed again after the printing. It is a common desirefor the support material to be detachable from the 3D object without damaging it. In principle, there are two known methods for this purpose, viz. mechanical removal and dissolution of the support material, the latter being the preferred method. For this, a suitable solvent has to be used to dissolve the support material. In this way, it is possible to free even sites that are difficult to access due to the shape of the object as formed on the support material. Compared to mechanical detachment of the support material, smoother objects with sharper and finer edges can be obtained. The support material can be removed completely by means of solvent in the detachment. The removal of the support material can be conducted in a simpler manner and within a shorter time. It is also easier to implement an automated process in which the 3D object is first manufactured using print material and support material, whereafter the support material is removed from the target object in the solvent.However, the search for a combination of a suitable support material and solvent that allow removal by means of dissolution without damaging the target object is found to be difficult, given the innumerable volume of already known materials, since various demands have to be fulfilled with regard to suitability as material to be printed and also as material to be detached from the print material by means of the solvent.For the detachment of the support material, it is firstly crucial that the support material to be detached has good solubility in the envisaged solvent. Residue-free removal of the solvent leads to optimal results. The support material must be partly dissolvable at least to such an extent that detachment from the print material used is possible, but the print material used must not itself be attacked by the solvent. The condition of the printed print material, especially with regard to the geometry present and also the surface characteristics, should be conserved. If the support material is dissolved or detached, but the print material is simultaneously partly dissolved or swollen or undergoes an increase in haze or a colour change, for example through formation of white streaks, there is an unsuitable combination of print material, support material and solvent.The print materials used in the FDM method are typically mouldable waxes and thermoplastics, e.g. polyethylene (PE), polypropylene (PP), polylactide (PLA), acrylonitrile-butadiene-styrene (ABS), glycol-modified polyethylene terephthalate (PETG) or else thermoplastic elastomers.For thermoplastics having low melting temperatures, e.g. PLA (150-190° C.), tomoderate melting temperatures, e.g. ABS (210-240° C.), as print materials, suitable soluble support materials have already been identified, for instance high-impact polystyrene (HIPS) or polyvinyl alcohol (PVA). Generally, the processing temperature of the filaments chosen should be much higher than the melting temperature thereof. For PLA, for example, nozzle temperatures of 180-210° C. are advisable.For polymers having a higher melting or processing temperature in FDM printing, for example thermoplastic polyether-etherketone (PEEK), polyetherimide (PEI), Polyphenylsulfon (PPSLI), Polyimide (PI), Polyphenylenesulfide (PPS), Polyketone (PK) polyamides (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET) or else polycarbonate / polybutylene terephthalate blends (PC / PBT), only a few suitable support materials have been identified to date, and these additionally have various disadvantages. Support materials suitable for print materials having low melting temperatures are unsuitable for those having high melting temperatures since the already printed support material would melt again on printing of the print material.US 2013 / 317164 A1 describes maleic anhydride copolymers as support material. This support material is soluble in alkaline aqueous solution. However, owing to its processing temperature, the support material described here is suitable only for printing with ABS. In general, the processing temperatures of print material and support material should not differ too significantly from one another, or there should at least be good thermal stability of the two materials.US 2015 / 028523 A1 describes polyglycolic acid as support material with a heat deflection temperature (HDT-A) of 168°C and a melting temperature of 220°C. This support material is printed in combination with a polysulphone as print material which has an HDT-A of 174°C, a glass transition temperature Tg of 185° C, and a melting temperature of 420°C. However, it is stated that higher temperatures than 300-330°C. already destroy the support material. Moreover, removal of the support material with alkaline aqueous solution is required.Another support material of high thermal stability, known from WO 2015 / 175682 A1, is a carboxylic acid-functionalized copolymer, but this can likewise be dissolved only in alkaline aqueous solution.In addition, there is also a known water-soluble support material, polyvinyl alcohol(Tg=85° C.) from 3D Systems (Rock Hill, South Carolina, USA) which according to the manufacturer is only compatible with nylon and PLA. However, the high tendency to absorb water / moisture in the case of water-soluble materials is also disadvantageous since storage of such materials with exclusion of moisture and sufficient drying prior to printing are necessary.EP 3452530B1 discloses various polycarbonates that are suitable as support materials in FDM. These materials are stable even at particularly high processing temperatures of above 250° C, or even higher, such that they can be used with print materials having a particularly high processing temperature, for example with PEEK having a processing temperature of 370 - 400°C. A disadvantage is that the polycarbonates need to be dissolved in tetrahydrofuran (THF). Although THF is a regarded as an acute nontoxic solvent, chronic exposure is suspected of causing cancer. Also, it easily penetrates the skin causing rapid dehydration and is highly flammable. Next to this, it has a tendency to form the explosive compound 2-hydroperoxytetrahydrofuran upon reaction with air. Another option is to use ethylacetate, but this solvent has the disadvantage that upon contact it irritates the skin, eyes, nose and throat. Long-term exposure can affect the liver and kidneys.OBJECT OF THE INVENTIONIt is an object of the invention to devise a new fused deposition modeling process, using a novel combination of a support material and solvent for this support material that overcomes disadvantages of the prior art.SUMMARY OF THE INVENTIONIn order to meet the object of the invention a process for producing a three-dimensional target object by means of fused deposition modeling using a support material for the target object, the support material being made of a composition based on a copolycarbonate, wherein the copolycarbonate contains one or more monomer units of the formula (1a)in which R1is hydrogen or a Ci- to C4-alkyl radical, R2is a Ci- to C4-alkyl radical, n is 0, 1 , 2 or 3, (1 b), (1c) and / or (1d)(1b) (1c) (1d) in which R3is a Ci- to C4-alkyl radical, aralkyl radical or aryl radical, and / or of the formula (1e)in which R19is hydrogen, Cl, Br or a Ci- to C4-alkyl radical, R17and R18are the same or different and are each independently an aryl radical, a Ci- to Cw-alkyl radical or a Ci- to Cw-alkylaryl radical, and where X is a single bond, -CO-, -0-, a Ci- to Ce-alkylene radical, a C2 to Cs-alkylidene radical, a C5- to C12 cycloalkylidene radical or a C6- to C12 arylene radical, which may optionally be fused to further aromatic rings containing heteroatoms, n is a number from 1 to 500, m is a number from 1 to 10, and p is 0 or 1 ,wherein a solvent is used to dissolve the support material after the target object has been deposited on this support material, wherein the solvent comprises 5-10 w% of 3- methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of Cn-Cn iso-alkanes. The remainder of the solvent is not critical and may be any liquid that is miscible with MMB such as water, glycol, di-butylether, a polyglycolether such as dipropyleneglycol dimethyl ether, or any other liquid non reactive with the copolycarbonate.Surprisingly, it has been found that the particular copolycarbonate, which is a so called hight temperature polycarbonate, as known from EP 3452530B1 , and thus is extremely difficult to dissolve (needing THF as described in the ‘530 patent) can be dissolved in a solvent based on the very mild active ingredient MMD. This is indeed very surprising since MMD is known not to be able dissolve even the regular (low temperature) polycarbonates. MMD is so mild that it is used i.a. in consumer products for cleaning and skin care. It is not able to dissolve materials typically used for FDM such as PEEK, PEI, PA, PBT and PET.It is noted that CN 111032320 (assigned to Kao Corporation) mentions the potential use of MMB in a composition to solve a FDM support. However, apart from the fact that it is indicated in paragraph

[0033] that MMB is preferably not added to the composition at all, there is no mention that this solvent would be suitable for dissolving polycarbonates, let alone the high temperature polycarbonates as defined here above. Next to this, from this Chinese application it is known that the MMB is used a potential additive to an alkali metal hydroxide solution, whereas in the present invention, it was found that the polycarbonates as claimed can be dissolved without using such aggressive alkali solutions. Thus, an aspect of the invention is to use MMB in the absence of an alkali metal hydroxide.The invention also embodied in a method of dissolving an object made of a composition based on a copolycarbonate as defined here above, comprising submerging the object in a solvent that comprises 5-10 w% of 3-methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of C11-C13 iso-alkanes, and leaving the object until it is dissolved, as well as in the use of a solvent comprising 5-10 w% of 3-methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of C11-C13 iso-alkanes, for dissolving an object made of a composition base d on a copolycarbonate as defined here above.DEFINITIONSA polycarbonate is any polymer prepared by polymerization of diols in the presence of phosgene or a similar carbonate generating agent.A copolycarbonate is a copolymer prepared by copolymerization of one diol with a different diol (including different diols based on the same basic diol molecule, but differing in substituents) in the presence of phosgene or a similar carbonate generating agent.The solvent 3-methoxy-3-methylbutan-1-ol or MMB, also denoted as 3-methoxy-3- methyl-1-butanol, 3-methyl-3-methoxybutanol and 3-methoxy-3-methylbutanol, is a mild detergent and cleaner. It is a clear, colourless and completely water-soluble liquid with a mild odour.A liquid hydrocarbon is a hydrocarbon which under normal atmospheric pressure is a liquid at room temperature. Liquid hydrocarbons are used as component in lubricants, as a lubricating oil in metal working fluids, or as a carrier for actives or additives, and as a component in water treatment additives, such as defoamers for detergents and coatings.An iso-alkane is any branched-chain alkane, preferably one having a methyl group attached to the penultimate carbon atom of the main chain, such as for example an alkane having only one branch point with one hydrogen atom on the branch point and two methyl groups on the branch point.C11-C13 iso-alkanes have on average from 11 to 13 C atoms in their molecules and are often used in washing and cleaning products for consumer use, since they are non- hazardous and (almost) odourless.A composition based on a polymer is understood to mean a composition that contains at least 50% by weight of the polymer, preferably at least 60% by weight, more preferably at least 75% by weight, most preferably at least 80 or 85% by weight up to 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98, 99 or even 100%.An aqueous carrier is a protic carrier that is freely miscible with water at room temperature, preferably between 10°C and up to at least 70°C.FURTHER EMBODIMENTS OF THE INVENTIONAccording to the invention, the solvent next to 3-methoxy-3-methylbutan-1-ol comprises one or more liquid hydrocarbons. It was found that hydrocarbons can be advantageous to function as an aprotic solvent in addition to the protic MMD. The one or more liquid hydrocarbons comprise iso-alkanes, in particular C11-C13 iso-alkanes.The solvent may comprise a protic or an aprotic carrier. An aprotic carrier has less risk of chemical reaction or other unwanted interference with the copolycarbonate.Further preferred are copolycarbonates which contain one or more monomer units of the formula (1a) in which R1is hydrogen or a Ci- to C4-alkyl radical, R2is a Ci- to C4- alkyl radical, n is 0, 1, 2 or 3.Most preferred for use in the present invention is a copolycarbonate that has been prepared from the monomers 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (Bisphenol TMC) and 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A).Preferably, the copolycarbonate has a Vicat temperature (VST / B120) as determined according to ISO 306:2013 of at least 150°C, preferably at least 175°C, or even further preferably at least 180°C, most preferably at least 200°C. Such a polycarbonate is available, for example, under the APEC® name from Covestro Deutschland AG.In yet a further embodiment, the copolycarbonate is dissolved under the action of ultrasound. Ultrasound decreases the amount of time needed to dissolve a given object made of the copolycarbonate as defined here above, at a given temperature of the solvent.In an embodiment of the method of dissolving an object made of a composition based on a polycarbonate, the solvent is heated to a temperature of between 40 and 90°C, preferably between 40 and 60°C. These temperatures have been found to beadvantageously suitable for arriving at dissolution of the polycarbonates in a relatively short amount of time, not needing an excessive amount of energy and keeping the level of any volatiles escaping to a minimum.All of the above embodiments also correspond to embodiments of the method of dissolving an object made of a composition based on a polycarbonate, and the use of a solvent comprising in combination 3-methoxy-3-methylbutan-1-ol and one or more Cn- C13 iso-alkanes for dissolving an object made of a composition based on a polycarbonate.The invention will now be further explained using the following specific example.EXAMPLEA 3D print was made using the polymer PEI 1010 (Polyether Imide Ultern 1010, an amorphous thermoplastic with a glass transition temperature of 217 °C), which was printed on a support made of so called high temperature resistant polycarbonate (HTPC), available as Addigy FPC SOL1 from Covestro, Germany, which is a polycarbonate based on bisphenol A / bisphenol TMC as described in EP 3452530B1 , having a Vicat temperature of about 205 °C. The overall dimensions of the 3D printed object were 30 mm x 30 mm x 30 mm, standing on a PC-HT support of equal dimensions.After the printing process was finished and the object cooled down to room temperature, the object while still being connected to its HTPC support was put in an ultrasonic bath filled with the mild cleaner liquid Safeco Fresh (obtainable from Eco-Point International, Halsteren, The Netherlands), containing 5-10 w% of the active ingredient 3-methoxy-3- methylbutan-1-ol (MMB), 5-10 w% of C11-C13 iso-alkanes and dipropyleneglycol dimethyl ether as an inert solvent for the MMB and iso-alkanes, and having a temperature of about 45 °C. Within 5 hours the support dissolved completely, while leaving the printed target object intact.Depending on the dimensions of the support, in particular its thickness, complete dissolution in this mild solvent, at relatively low temperatures will take between 20minutes for small supports (having a thickness of about 1 mm) and 24 hours for larger supports.It was confirmed that a regular polycarbonate only gets soft in the cleaner fluid but does not dissolve.

Claims

CLAIMS1 . A process for producing a three-dimensional target object by means of fused deposition modeling using a support material for the target object, the support material being made of a composition based on a copolycarbonate, wherein the copolycarbonate contains one or more monomer units of the formula (1a)in which R1is hydrogen or a Ci- to C4-alkyl radical, R2is a Ci- to C4-alkyl radical, n is 0, 1 , 2 or 3, (1 b), (1c) and / or (1d)(1b) (1c) (id) in which R3is a Ci- to C4-alkyl radical, aralkyl radical or aryl radical, and / or of the formula (1e)in which R19is hydrogen, Cl, Br or a Ci- to C4-alkyl radical, R17and R18are the same ordifferent and are each independently an aryl radical, a Ci- to Cw-alkyl radical or a Ci- to Cw-alkylaryl radical, and where X is a single bond, -CO-, -O-, a Ci- to Ce-alkylene radical, a C2 to Cs-alkylidene radical, a C5- to C12 cycloalkylidene radical or a C6- to C12 arylene radical, which may optionally be fused to further aromatic rings containing heteroatoms, n is a number from 1 to 500, m is a number from 1 to 10, and p is 0 or 1 , wherein a solvent is used to dissolve the support material after the target object has been deposited on this support material, characterised in that the solvent comprises 5- 10 w% of 3-methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of C11-C13 iso-alkanes.

2. A process according to any of the preceding claims, characterised in that the copolycarbonate contains one or more monomer units of the formula (1a) in which R1is hydrogen or a Ci- to C4-alkyl radical, R2is a Ci- to C4-alkyl radical, n is 0, 1 , 2 or 3.

3. A process according to claim 2, characterised in that the copolycarbonate has been prepared from the monomers 1 ,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (Bisphenol TMC) and 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A).

4. A process according to any of the preceding claims, characterised in that the copolycarbonate has a Vicat temperature (VST / B120) as determined according to ISO 306:2013 of at least 150°C, preferably at least 200°C.

5. A process according to any of the preceding claims, characterised in that the copolycarbonate is dissolved under the action of ultrasound.

6. A method of dissolving an object made of a composition based on a copolycarbonate as defined in claim 1 , comprising submerging the object in a solvent that comprises 5-10 w% of 3-methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of C11-C13 iso-alkanes, and leaving the object until it is dissolved.

7. A method according to claim 6, characterised in that the solvent is heated to a temperature of between 35 and 90°C.

8. A method according to claim 7, characterised in that the solvent is heated to a temperature of between 40 and 60°C.

9. The use of a solvent comprising 5-10 w% of 3-methoxy-3-methylbutan-1-ol (MMB) and 5-10 w% of Cn-Cn iso-alkanes for dissolving an object made of a composition based on a copolycarbonate as defined in claim 1.

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