Copolymer for use in a digital manufacturing process

Abstract

Copolymers for use in a digital manufacturing process, in particular support materials for use in a digital manufacturing process comprising such copolymers. More particularly, the invention is directed to a copolymer, a support material based on the the copolymer, the use of the copolymer in a digital manufacturing process, a method for preparing the copolymer and a method for building a 3D-model by using a support material comprising the copolymer.

Claims

1. A copolymer comprising a plurality of carboxyl monomer units derived from methacrylic acid monomers (MM); a plurality of phenyl monomer units; a plurality of first carboxylate ester monomer units derived from alkyl (meth-)acrylate monomers; and a plurality of second carboxylate ester monomer units derived from ethylhexyl acrylate monomers; wherein the first and the second carboxylate ester monomer units differ in their structural formula, wherein relative amounts of the monomer units are as follows: 35-45 wt % of the carboxyl monomer units derived from methacrylic acid monomers (MAA); 25-30 wt % of the phenyl monomer units; 10-15 wt % of the first carboxylate ester monomer units derived from alkyl methacrylate monomers, 12-20 wt % of the second carboxylate ester monomer units derived from ethylhexyl acrylate monomers; based on a weight of the copolymer.

2. The copolymer according to claim 1, wherein the first carboxylate ester monomer units are derived from methyl methacrylate monomers (MMA).

3. The copolymer according to claim 1 wherein the relative amounts add up to 100 wt % to give a tetrapolymer.

4. The copolymer according to claim 1 having a glass transition temperature Tg in the range of 90° C. to 140° C., measured according to ISO 11357-2:2013-05.

5. The copolymer according to claim 1, wherein a number average molecular weight (Mn) of the copolymer is in the range of 50,000-70,000 g/mol, determined by gel permeation chromatography according to DIN 55672-1:2016-03.

6. The copolymer according to claim 1, wherein a weight average molecular weight (Mw) of the copolymer is in the range of 90,000 to 140,000 g/mol, determined by gel permeation chromatography according to DIN 55672-1:2016-03.

7. The copolymer according to claim 1 wherein carboxyl groups are present along a carbon chain of the copolymer and are linked at least partly in each case with a side group of a neighboring monomer unit within the carbon chain with formation of intramolecular anhydride structures.

8. The copolymer according to claim 1, wherein the copolymer is soluble under stirring in alkaline solution of pH 13 (0.1M NaOH) at 167° F. (75° C.) within less than 50 min.

9. A support material for a digital manufacturing system wherein the support material comprises a copolymer according to claim 1.

10. The support material according to claim 9 provided as a filament strand.

11. The copolymer according to claim 1, wherein the phenyl monomer units are derived from styrene monomers.

12. The copolymer according to claim 1, wherein the copolymer has a glass transition temperature Tg in the range of 94° C. to 120° C., measured according to ISO 11357-2:2013-5.

13. The support material according to claim 9, wherein the support material comprises at least 80% by weight of the copolymer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The Figures show

(2) FIG. 1 the differential scanning calorimetry (DSC) curve of the polymer according to Example 1, including one repetition of the heating/cooling cycle (heat flow over temperature);

(3) FIG. 2 the Fourier-transform infrared spectrum (FTIR) of the polymer according to Example 1.

EXAMPLES

Example 1

(4) The following starting materials were mixed in the indicated relative amounts in a stirred tank reactor:

(5) TABLE-US-00001 MAA 40.00 wt-% Styrene 29.75 wt-% 2-ethylhexyl acrylate 17.50 wt-% MMA 12.75 wt-%

(6) Radical polymerization was started by dissolving 1.706 kg of Fujifilm V-59 free radical initiator in 315 kg of ethanol in a different stirred tank reactor under nitrogen atmosphere at 75° C. 450 kg of the monomeric starting material mixture were constantly and evenly added to the reaction solution over the course of 90 minutes. Polymerization was performed at a temperature of 78° C. for 14 hours. The resulting dissolved polymer was worked-up in a planetary roller extruder at temperatures of 200-260° C. at extrusion rates between 5 and 30 kg/h, in order to remove the solvent, monomeric residues and residues of the radical starter. The resulting polymer melt was cooled and pelletized.

(7) Example 1 gives a copolymer according to the present invention (Expl.1).

Example 2

(8) The following starting materials were mixed in the indicated relative amounts in a stirred tank reactor:

(9) TABLE-US-00002 MAA 40.00 wt % Styrene 35.00 wt % n-Butyl acrylate 25.00 wt %

(10) The reaction conditions were the same as indicated for example 1.

(11) Example 2 affords a copolymer as known in the state of the art, for comparison purposes (Expl.2).

Example 3

(12) The Tg of Expl. 1 was determined according to ISO 11357-2:2013-05. The corresponding differential scanning calorimetry (DSC) curve of the polymer according to Example 1 is depicted in FIG. 1. The x-axis represents the temperature [° C.] and the y-axis the endotherm/exotherm [mW/mg]. Curve 1 shows a first heating sequence of a sample (25.1 mg) from 25° to 250° C. (10 K/min), followed by cooling which is shown in curve 2 (solid lines). The repetition cycle of heating 3 and cooling 4 is displayed in the same diagram (dashed lines). Temperature range and heating rate were the same. Measuring was performed on a Netzsch DSC 214 Polyma device in N.sub.2 atmosphere (40.0 ml/min).

(13) One endothermic (heating) or exothermic (cooling) change was registered per curve. The following onset/mid/and end temperatures were determined:

(14) TABLE-US-00003 Curve Onset Mid End 1 101.5 110.2 118.6  2  98.2 109.3 118.5  3 106.7 114.1 121.0° 4  96.6 108.1 108.1  Mean 110.4

(15) The midpoint of each endo-/exothermic change is indicated as a vertical mark in FIG. 1. The exothermic change was observed between 108° C. and 115° C. giving a mean Tg value of 110.4° C. The Tg of Expl. 2 was determined under the same conditions and was found to be slightly lower with a mean 109.9° C.

Example 4

(16) The number average molecular weight (Mn) and the weight average molecular weight (Mw) of Expl. 1 and Expl. 2 were determined via gel permeation chromatography GPC in THF against polystyrene standards according to DIN 55672-1:2016-03.

(17) TABLE-US-00004 Expl. 1 number average molecular weight (Mn)  60.80 kg/mol weight average molecular weight (Mw) 109.90 kg/mol % Expl. 2 number average molecular weight (Mn)  60.60 kg/mol weight average molecular weight (Mw) 119.80 kg/mol

Example 5

(18) The IR spectrum of Example 1 was measured in order to assess the presence of carboxyl groups along a carbon chain of the copolymer linked at least partly with a side group of a neighbouring monomer unit by forming intramolecular anhydride structures. In addition to the absorbance at 1699.67 cm.sup.1, which is characteristic for the acyl moiety of the carboxyl groups, the spectrum shows absorbance peaks at 1726 cm.sup.1, 1756 cm.sup.−1 and 1800 cm.sup.−1. These are indicators for intramolecular anhydride structures within the copolymer.

Example 6

(19) Dissolvability of the compounds according to Expl. 1 and Expl. 2 in alkaline solution was assessed in the following experimental set-ups: 2 g of the copolymer were pressed into the shape of a disk having a diameter of 40 mm and a thickness of 1.5 mm. the sample disks were placed in 350 mL aqu. NaOH solution (pH 13, 0.1 mM) at 70° C. under constant stirring (500 rpm) in an alternative set-up, the sample disks were placed in 350 mL “3D Wash” solution (pH 10.5, commercially available from Traxer GmbH, preparation according to the supplier's instructions) at 70° C. under constant stirring (500 rpm).

(20) The time required to substantially dissolve and disperse the support structure was measured. When subject to treatments at pH 13, the sample disks of Expl. 1 were completely dissolved within 44 min. The resulting solution was clear, colourless and fibre-free. When subject to the dissolvability test in “3D Wash” at pH 10.5, the disks of Expl. 1 were completely dissolved after 90 min. The resulting solution was clear, colourless and almost fibre-free. Accordingly, the support materials of the present disclosure are capable of being removed from 3D models with short residence time in the alkaline aqueous solutions.

(21) In contrast, when subject to treatments at pH 13, the sample disks of Expl. 2 were not dissolved before 53 min. The copolymer according to the invention, therefore, has preferable properties for use as support material.