Use of mixtures of polyvinyl alcohol with less polar polymers as support structure in 3D printing process

Abstract

A process of manufacturing a three-dimensional object includes a step of depositing and solidifying molten polyvinyl alcohol to form a support structure; and a step of depositing and solidifying a molten thermoplastic polymer on the support structure to form a three-dimensional preform. The support structure has a mixture of at least 50% by weight of polyvinyl alcohol and at most 50% by weight of at least one polymer of polyvinyl butyral, polylactid acid, ethylene-vinylalcohol-vinylacetate terpolymer, vinyl acetate-vinyl pyrrolidone copolymer, acrylonitrile-butadiene-styrene terpolymer, polycaprolactone, vinyl acetate-vinyl caprolactame copolymer, and polyvinyl alcohol having a degree of hydrolysis DH of 30-65%. The support structure can be dissolved to form the three-dimensional object.

Claims

1. A process of manufacturing a three-dimensional object, the process comprising: depositing and solidifying a molten polyvinyl alcohol composition to form a support structure; and depositing and solidifying a molten thermoplastic polymer on the support structure to form a three-dimensional preform, wherein the molten polyvinyl alcohol composition is a mixture of at least 50% by weight of a first polyvinyl alcohol having a degree of hydrolysis of 60-99% and at least one polymer selected from the group consisting of polyvinyl butyral, polylactic acid, ethylene-vinylalcohol-vinylacetate terpolymer, vinyl acetate-vinyl pyrrolidone copolymer, acrylonitrile-butadiene-styrene terpolymer, polycaprolactone, vinyl acetate-vinyl caprolactame copolymer, and a second polyvinyl alcohol having a degree of hydrolysis of 30-65%.

2. The process according to claim 1, wherein the polyvinyl alcohol having a degree of hydrolysis of 60-99% has a vinyl acetate content of at least 10 mol %.

3. The process according to claim 1, wherein the polyvinyl alcohol having a degree of hydrolysis of 60-99% has a degree of polymerization of at least 200-3000.

4. The process according to claim 1, further comprising removing the support structure by dissolving the support structure in water and/or alcohol to obtain the three-dimensional structure.

5. The process according to claim 1, wherein the molten composition comprising a polyvinyl alcohol is deposited at a temperature of at least 170° C.

6. The process according to claim 1, wherein the thermoplastic polymer is deposited on the support structure at a temperature of at least 140° C.

7. The process according to claim 1, wherein the thermoplastic polymer is selected from the group consisting of polylactic acid, acrylonitrile-butadiene-styrene copolymer, a polyamide, a polycarbonate, polyethylene terephthalate, a polyethylene terephthalate copolymer, a polyhydroxyalkanoate, a wood filled composite, a metal filled composite, a carbon fiber filled composite, polyvinylbutyral, a thermoplastic elastomer, a thermoplastic polyurethane, a polyolefin, a polyproplyene, acrylonitrile styrene acrylate, a polyacrylate, a polymethacrylate, polystyrene, polyoxymethylene, and a mixture thereof.

8. The process according to claim 1, wherein the polyvinyl alcohol having a degree of hydrolysis of 60-99% comprises as repeating units vinyl alcohol, vinyl acetate and up to 20 mol % of further olefinic monomers.

9. The process according to claim 1, wherein the composition comprising a polyvinyl alcohol having a degree of hydrolysis of 60-99% further comprises up to 20% by weight based on the total weight of the composition of one or more plasticizers selected from the group consisting of water, glycerine, diglycerine, sorbitol, ethylene glycol, diethylene glycol, polyethylene glycol, pentaerythritol, dipentaerythritol, propylene glycol, trimethylolpropane, di-trimethylolpropane and triethanolamine.

10. The process according to claim 1, wherein the polyvinyl alcohol composition comprises the polyvinyl alcohol different from the polyvinyl alcohol having a degree of hydrolysis of 60-99% and the different polyvinyl alcohol comprises one or more grades of polyvinyl alcohol, differing in vinyl acetate content and/or degree of polymerization and/or degree of hydrolysis and/or viscosity.

Description

EXAMPLES

(1) Measurement of Degree of Hydrolysis:

(2) Degree of hydrolysis: indicates percentage of vinyl acetate unit saponified to vinyl alcohol unit and it is calculated by following equation. EV standards for Ester Value which is the number of mg KOH needed to neutralize the acid released from the ester by saponification in 1 g of substance and it is measured according to EN ISO 3681.
Degree of hydrolysis: =100×(100−0.1535×EV)/(100−0.0749×EV)

(3) Measurement of Vinyl Acetate Content

(4) The vinyl acetate content is calculated from the degree of hydrolysis hydrolysation (DH) by following equation.
Vinyl acetate content=100−DH

(5) Measurement of Degree of Polymerization

(6) The degree of polymerization is measured according to JIS K6727. Specifically, it may be calculated by the equation below from the limiting viscosity [η] (unit: L/g) measured in water at 30° C. after resaponification and purification of the PVOH.
Degree of polymerization=([η]×10000/8.29).sup.(1/0.62)

(7) Viscosity:

(8) For the measurements 4 wt % solutions in distilled water were prepared. The measurements were performed in a falling ball viscometer according to DIN 53 015.

(9) Measurement of Moisture Uptake

(10) The moisture uptake of each sample was determined by placing a defined quantity of pellets of each compound into a climate chamber at 23° C. and a relative humidity of 50%. The weight increase was measured over time. For comparison the moisture uptake after 14 days is used.

(11) Measurement of Melt Flow Rate

(12) The melt flow rate of the PVOH compounds was measured with a Gottfert MP-D machine by heating 6 g of material at 190° C. for 5 minutes before putting a load of 21.6 kg on the piston. The measurement was started after an additional pre-running time of 1 minute.

(13) Preparation of PVOH Compositions for 3D Printing

(14) PVOH compositions were prepared by compounding in a twin screw extruder as described in WO 03/020823 A1. Optionally filaments with a diameter of 1.75 mm or 2.85 mm, respectively, for 3D printing tests by fused filament fabrication (FFF) technology were extruded with a Dr. Collin 30 mm single screw extruder by a process commonly known to those skilled in the art. Alternatively, compounding and filament extrusion was carried out with a DSM Xplore micro compounder MC 15.

(15) Dual Material 3D Printing Adhesion Test

(16) To determine the adhesion strength of the PVOH compositions on polylactic acid (PLA) as a main printing material, a circular 3-layer sandwich structure was 3d printed on a Felix Pro 1 printer with filaments extruded from the PVOH compounds. The printing temperature for PLA was 190° C. and the printing temperature for the PVOH compounds was 205° C. The printing speed for both materials was set to 25 mm/s and the printing layer thickness to 150 μm. From the bottom the specimen consists of 3×150 μm of PLA followed by 2×150 μm of PVOH compound followed by 4×150 μm of PLA. The area of each adhesion interface is 2.35 cm.sup.3. The adhesion strength was determined by measuring the force required to delaminate the 3d printed specimen in a tensile testing machine. An average value was calculated from at least five measurements. The result reflects the adhesion strength of the weakest interface.

Comparative Example 1

(17) PVOH with a 4% solution viscosity of 5.0 mPa.Math.s and a degree of hydrolysis: of 74% was prepared. The melt flow rate (190° C., 21.6 kg) is 15.7 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 2.1%. In the 3d printing adhesion test a force of less than 20 N is required to delaminate the 3d printed specimen. The low melt flow rate makes printing at high rate difficult and the low adhesion strength results in frequent issues during 3d printing due to detachment of the printed object from the support structures.

Comparative Example 2

(18) To the PVOH described in comparative example 1, 5 wt. % of trimethylolpropane was added to increase the plasticizer content. The melt flow rate (190° C., 21.6 kg) is 46.7 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 3.8%. The increased melt flow rate allows printing at higher rate than comparative example 1. However, the significantly increased moisture absorption decreases shelf life of the filament when exposed to air.

Comparative Example 3

(19) PVOH with a 4% solution viscosity of 5.5 mPa.Math.s and a degree of hydrolysis of 88% was prepared. The melt flow rate (1.90° C., 21.6 kg) is 2.3 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 2.1%. In the 3d printing adhesion test a force of less than 20 N is required to delaminate the 3d printed specimen. The low melt flow rate makes printing at high rate difficult and the low adhesion strength results in frequent issues during 3d printing due to detachment of the printed object from the support structures.

Comparative Example 4

(20) To the PVOH described in comparative example 3, 3 wt. % of trimethylolpropane was added to increase the plasticizer content. The melt flow rate (190° C., 21.6 kg) is 9.7 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 2.7%. The increased melt flow rate allows printing at somewhat higher rate than comparative example 3. However, the increased moisture absorption decreases shelf life of the filament when exposed to air.

Comparative Example 5

(21) PVOH with a 4% solution viscosity of 4.8 mPa.Math.s and a degree of hydrolysis of 88% was prepared. The melt flow rate (190° C., 21.6 kg) is 13.1 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 2.0%. In the 3d printing adhesion test a force of less than 20 N is required to delaminate the 3d printed specimen. The low melt flow rate makes printing at high rate difficult and the low adhesion strength results in frequent issues during 3d printing due to detachment of the printed object from the support structures.

Example 1

(22) To the PVOH described in comparative example 1, 10 wt. % of vinyl acetate-vinyl pyrrolidone copolymer (BASF Sokalan VA64 P) was added. The melt flow rate (190° C., 21.6 kg) is 42.6 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 2

(23) To the PVOH described in comparative example 1, 20 wt. % of vinyl acetate-vinyl pyrrolidone copolymer (BASF Sokalan VA64 P) was added. The melt flow rate (190° C., 21.6 kg) is 66.7 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 3

(24) To the PVOH described in comparative example 1, 30 wt. % of vinyl acetate-vinyl pyrrolidone copolymer (BASF Sokalan VA64 P) was added. The melt flow rate (190° C., 21.6 kg) is 153.8 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 4

(25) To the PVOH described in comparative example 1, 20 wt. % of a PVOH grade with a degree of hydrolysis of 50% and a 10% solution (methanol/water 1:1) viscosity of 9.5 mPa.Math.s was added. The melt flow rate (190° C., 21.6 kg) is 89.1 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 2.9%. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. An even higher melt flow rate could be achieved than in comparative example 2 and with lower moisture absorption, which is beneficial for a longer shelf life of the filament. Support structures printed with this compound are soluble in water at 25° C.

Example 5

(26) To the PVOH described in comparative example 1, 5 wt. % of polycaprolactone (Sigma-Aldrich) was added. The melt flow rate (190° C., 21.6 kg) is 49.0 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 6

(27) To the PVOH described in comparative example 1, 10 wt. % of polycaprolactone (Sigma-Aldrich) was added. The melt flow rate (190° C., 21.6 kg) is 65.3 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 7

(28) To the PVOH described in comparative example 1, 5 wt. % of ABS (Terluran GP-35, INEOS Styrolution) was added. The melt flow rate (190° C., 21.6 kg) is 25.5 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 8

(29) To the PVOH described in comparative example 1, 5 wt. % of PLA (NatureWorks Ingeo 6202D) was added. The melt flow rate (190° C., 21.6 kg) is 26.7 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at higher rate than comparative example 1 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 9

(30) To the PVOH described in comparative example 3, 5 wt. % of PLA (NatureWorks Ingeo 6202D) was added. The melt flow rate (190° C., 21.6 kg) is 4.3 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing at somewhat higher rate than comparative example 3 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 10

(31) To the PVOH described in comparative example 3, 10 wt. % of a PVOH grade with a degree of hydrolysis of 50% and a 10% solution (methanol/water 1:1) viscosity of 9.5 mPa.Math.s was added. The melt flow rate (190° C., 21.6 kg) is 14.0 g/10 min and the moisture absorption at 23° C. and 50% relative humidity after 14 days is 2.2%. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing higher rate than comparative example 3 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. An even higher melt flow rate could be achieved than in comparative example 4 and with lower moisture absorption, which is beneficial for a longer shelf life of the filament. Support structures printed with this compound are soluble in water at 25° C.

Example 11

(32) To the PVOH described in comparative example 5, 5 wt. % of a PVOH grade with a degree of hydrolysis of 50% and a 10% solution (methanol/water 1:1) viscosity of 9.5 mPa.Math.s was added. The melt flow rate (190° C., 21.6 kg) is 18.1 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing higher rate than comparative example 5 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.

Example 12

(33) To the PVOH described in comparative example 5, 10 wt. % of a PVOH grade with a degree of hydrolysis of 50% and a 10% solution (methanol/water 1:1) viscosity of 9.5 mPa.Math.s was added. The melt flow rate (190° C., 21.6 kg) is 26.3 g/10 min. In the 3d printing adhesion test a force of more than 20 N is required to delaminate the 3d printed specimen. The increased melt flow rate allows printing higher rate than comparative example 5 and the higher adhesion strength allows for reliable printing without detachment of the support structures from the main object. Support structures printed with this compound are soluble in water at 25° C.