METHOD FOR MANUFACTURING A SILICONE ELASTOMER ARTICLE USING A 3D PRINTER

Abstract

The invention relates to an additive manufacturing method for producing a three-dimensional elastomer silicone article. The elastomer silicone article is built up layer by layer by printing a silicone composition crosslinkable by addition reactions comprising at least one organopolysiloxane-polyoxyalkylene copolymer with a 3D printer selected from an extrusion 3D printer or a material jetting 3D printer.

Claims

1. Method for additive manufacturing a silicone elastomer article comprising: 1) printing a first silicone composition on a substrate with a 3D printer selected from an extrusion 3D printer or a material jetting 3D printer to form a first layer, 2) printing a second silicone composition on the first or previous layer with the said 3D printer to form a subsequent layer and 3) optionally repeating 2) with independently selected silicone composition for any additionally layer needed and 4) allowing the first and subsequent layers to crosslink, optionally by heating, to obtain a silicone elastomer article, wherein said silicone compositions are crosslinkable through addition reactions and comprise: (A) at least one organopolysiloxane compound A comprising, per molecule at least two C.sub.2-C.sub.6 alkenyl radicals bonded to silicon atoms, (B) at least one organohydrogenopolysiloxane compound B comprising, per molecule, at least two hydrogen atoms bonded to an identical or different silicon atom, (C) at least one catalyst C consisting of at least one metal or compound, from the platinum group, (D) at least one reinforcing silica filler D, (E) at least one organopolysiloxane-polyoxyalkylene copolymer E, and (F) at least one crosslinking inhibitor F.

2. Method according to claim 1 wherein the silicone compositions comprise at least 0.3% weight of at least one organopolysiloxane-polyoxyalkylene copolymer E with respect to the total weight of silicone composition.

3. Method according to claim 1 wherein the silicone compositions comprise from 0.6% to 4% weight of at least one organopolysiloxane-polyoxyalkylene copolymer E with respect to the total weight of silicone composition.

4. Method according to claim 1 wherein the silicone compositions further comprise one or more hydroxyl functional silicone resins.

5. Method according to claim 1 wherein at least one silicone composition comprises per 100% weight of the silicone composition: from 55 to 80% weight of at least one organopolysiloxane compound A, from 0.1 to 4% weight of at least one organohydrogenopolysiloxane compound B, from 5 to 40% weight of at least one reinforcing silica filler D, from 0.3 to 4% weight of at least one organopolysiloxane-polyoxyalkylene copolymer E, from 0.0002 to 0.01% weight of platinum and from 0.01 to 0.2% weight of at least one crosslinking inhibitor F.

6. Method according to claim 1 wherein the 3D printer is an extrusion 3D printer.

7. Method according to claim 6 wherein in the extrusion 3D printer the silicone compositions are extruded through a nozzle with an average diameter comprise from 50 to 2000 m, optionally from 100 to 800 m and optionally from 100 to 500 m.

8. Method according to claim 7 wherein when printing the distance between the nozzle and the substrate or the previous layer is comprised from 70 to 130%, optionally from 80 to 120% of the nozzle average diameter.

9. Method according to claim 1 wherein no energy source as heat or radiation is applied during or between 1) to 3) prior to the printing of at least 10, optionally 20 layers.

10. A silicone elastomer article produced by the method as claimed in claim 1.

11. A silicone composition crosslinkable through addition reactions as set forth in claim 1 with a 3D printer, optionally selected from an extrusion 3D printer or a material jetting 3D printer.

Description

EXAMPLES

[0243] Addition-crosslinking silicone compositions are prepared and printed using an extrusion 3D printer according with disclosure.

Raw materials

LSR Composition 1

[0244] A mixer is loaded with: [0245] 29 parts dimethylpolysiloxane oil blocked at both ends by Me.sub.2ViSiO.sub.1/2 units, having a viscosity of 60000 mPa.Math.s [0246] 29 parts of a dimethylpolysiloxane blocked at both ends by Me.sub.2ViSiO.sub.1/2 units, having a viscosity of 100000 mPa.Math.s [0247] 26 parts of silica fumed with a specific surface area measured by the BET method of 300 m.sup.2/g and 7 parts of hexamethyldisilazane.

[0248] The whole is heated at 70 C. under agitation for 1 hour and then devolatilised, cooled and stored as Base 1 of the composition 1

[0249] To 45 parts of this Base 1 is then added in a speed mixer: [0250] Platinum metal which is introduced in the form of an organometallic complex at 10% by weight of Platinum metal, known as Karstedt's catalyst diluted in a vinyl oil. [0251] 3 parts: dimethylpolysiloxane oil having vinyl groups in the chain and at the chain ends and having a viscosity of 1000 mPa.Math.s [0252] 2 parts of a dimethylpolysiloxane oil having vinyl groups in the chain and at the chain ends and having a viscosity of 400 mPa.Math.s

[0253] The composition called LSR composition 1 part A is mixed during one minute at 1000 rounds per minute in the speed mixer. The Pt content is 5 ppm

[0254] To 45 parts of this Base 1 is then added in a speed mixer: [0255] 1.3 parts of an organohydrogenopolysiloxane MQ resin comprising SiH groups [0256] 0.5 parts of a linear organohydrogenopolysiloxane comprising Si H groups in the chain and at chain ends and containing approximately 20% by weight of groups Si H [0257] 1.5 parts of a dimethylpolysiloxane oil having vinyl groups in the chain and at the chain ends and having a viscosity of 400 mPa.Math.s [0258] 1.6 parts: dimethylpolysiloxane oil having vinyl groups in the chain and at the chain ends and having a viscosity of 1000 mPa.Math.s [0259] 0.08 parts of ethynyl-1-cyclohexanol-1 as crosslinking inhibitor.

[0260] The composition called LSR composition 1 part B is mixed during one minute at 1000 rounds per/minute in the speed mixer

[0261] Addition-crosslinking compositions used in the examples are prepared by mixing the LSR composition 1 parts A & B in a ratio 1:1 already comprising silica as thixotropic agent with different components listed below that improve the threshold effect.

[0262] PEG 400 is poly(ethylene glycol) monolaurate, CAS Number 9004-81-3 purchased from Sigma Aldrich.

[0263] Bluesil SP 3300 obtained Bluestar Silicones, CAS Number 68937-55-3 corresponds to Me.sub.3SiO[Me.sub.2SiO].sub.75[MeSi((CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.22(OCH.sub.2CH.sub.2CH.sub.2).sub.22OH)O].sub.7SiMe.sub.3.

[0264] Silsurf Q20308 purchased from Siltech Corporation, polyether MQ resin where some of the methyl groups are replaced with polyalkyleneoxide chains, viscosity at 25 C. 800 mPa.Math.s.

[0265] Silsurf Q25315-O purchased from Siltech Corporation, polyether MQ resin where some of the methyl groups are replaced with polyalkyleneoxide chains, viscosity at 25 C. 500 mPa.Math.s.

[0266] LSR composition 1 part A with different amounts of the above components have been evaluated in rheological tests

TABLE-US-00001 TABLE 1 Tested compositions (weight %) LSR Part A Sample Composition 1 PEG 400 SP 3300 Q20308 Q25315 Part A 100 0 0 0 0 Composition 1 PEG-05 99.5 0.5 0 0 0 PEG-1 99 1 0 0 0 PEG-2 98 2 0 0 0 SP-05 99.5 0 0.5 0 0 SP-1 99 0 1 0 0 SP-2 98 0 2 0 0 Q20-05 99.5 0 0 0.5 0 Q20-1 99 0 0 1 0 Q20-2 98 0 0 2 0 Q25-05 99.5 0 0 0 0.5 Q25-1 99 0 0 0 1 Q25-15 98.5 0 0 0 1.5

Rheological Test Descriptions

Viscosity Ratio and Tan(Delta) Ratio

[0267] A rotational rheometer (DHR-2TA INSTRUMENTS) was used to define the rheological behavior of samples. An equivalent shear thinning test was performed using cone-plate (25 mm, 2, gap=51 m) to define a viscosity ratio which allows users to evaluate the material's performance in 3D printing. The ratio is computed with the dynamic viscosity at low and high shear rate: 0.5 and 25 s.sup.1 respectively. The time required to get the measure is 60 s at different shear rate. A high value of viscosity ratio means that material is able to product 3D objects with high quality (Table 2).

[0268] The thixotropic behavior is also determined by the tan(delta) ratio corresponding to G/G, (where G and G are the loss and storage moduli respectively) for each sample at several structural times (10, 100 and 1000 s) (Table 3).

TABLE-US-00002 TABLE 2 Viscosity Ratio Sample (Pa .Math. s) at [0.5 s.sup.1] (Pa .Math. s) at [25 s.sup.1] Ratio Part A 1302 48 27 Composition1 PEG-05 3752 117 32 PEG-1 3953 119 33 PEG-2 3826 93 41 SP-05 4223 108 39 SP-1 6592 143 46 SP-2 7443 117 63

[0269] The results of Table 2 show the shear thinning ability of samples through the viscosity value. We observe that the SP-1 and SP-2 mixtures have a higher viscosity ratio (>45) compared to other mixtures (<45). This allow users to print high viscous mixtures despite elastic part increasing.

TABLE-US-00003 TABLE 3 Thixotropic behaviorTan(delta) at 10, 100 and 1000s (1 radiant/s) G/G G/G G/G Tan(delta) at 10 s Tan(delta) at 100 s Tan(delta) at 1000 s Part A 1.96 1.44 0.75 Composition1 PEG-05 0.88 0.45 0.25 PEG-1 0.86 0.42 0.23 PEG-2 0.86 0.43 0.24 SP-05 0.86 0.48 0.27 SP-1 0.74 0.37 0.21 SP-2 0.67 0.32 0.19

[0270] We observe that the SP-1 and SP-2 formulations are extraordinarily elastic (low tan(delta)) compared with PEG-05, PEG-1 and PEG-2 formulations. The SP-05 sample shows the same rheological behavior that formulations with PEG (PEG-05, PEG-1 and PEG-2). These observations are especially true for 10 and 100 s. It allows users to print at high speed with a good bearing of 3D object.

[0271] Yield Stress, Restructuring Time and G at Rest.

[0272] Yield Stress:

[0273] The yield stress in 3D printing will characterize the ability of the material to keep a constant shape under the pressure of the successive layer of material. On a rheometer ARES G2 from TA with a conic upper geometry (25 mm, 0.1002 rad, stainless steel) and a plan lower geometry (25 mm, stainless steel), a stress growth procedure is applied in transient mode. A constant shear rate of 0.1 s.sup.1 is imposed for 60 seconds, the stress will growth constantly with the time. To avoid histological interactions a soak time of 300 s is performed. The sampling rate is 50 points/s. The yield stress value finally associated with a formulation is the maximum stress value measured.

[0274] Restructuring Time:

[0275] During the extrusion through the syringe during printing, the material is destructured (the yield stress is overpassed). The material becomes fluid and after a characteristic time at rest (on the plate) the material recovers its previous state. That's the thixotropic effect. This characteristic time is called the restructuring time. On a rheometer ARES G2 from TA with a conic upper geometry (25 mm, 0.1002 rad, stainless steel) and a plan lower geometry (25 mm, stainless steel). First the sample is pre-sheared in conditioning sample mode with a constant shear rate of 3 s.sup.1 for 10 s. Secondly in dynamic mode, an oscillation time measure of the storage modulus (G) is conducted for 700 sat a 0.1% strain (value acquired with a linear range measure) at a 1 rad/s frequency. The value associated with the formulation is the time of the cross point of the tangent from the first points line (5 first seconds) and the tangent from the last points line (100 last seconds) on the G curve.

[0276] G at Rest:

[0277] This value characterizes the state of the material at rest and its processability. With the same methods as in restructuring time the value at rest of G at 700 s is taken.

TABLE-US-00004 TABLE 4 Results Yield Stress Restructuring G at rest Sample (Pa) time (s) (kPa) Part A 525 210 18 Composition 1 PEG-05 1627 50 180 PEG-1 1697 48 182 PEG-2 1482 45 152 SP-05 2596 61 300 SP-1 3112 59 352 SP-2 2836 58 370 Q20-05 948 80 52 Q20-1 2110 72 255 Q20-2 3207 62 282 Q25-05 1910 61 232 Q25-1 2156 57 306 Q25-15 2090 57 306

3D Printing Tests

[0278] A homemade 3D printer, build from FDM (Fused deposition Modelling) type, was used to product 3D objects using fluid materials (from low to high Newtonian viscosity). The 3D printer has a high XYZ movement precision (10 m). The 3D printer was controlled by computer using open-source Repetier and slic3r software. A pneumatic dispenser (ULTIMUS V-NORDSON EFD) was used to control the addition-crosslinking silicone composition deposition.

[0279] Fluid deposition is performed with simple (or coaxial) cartridge(s) connected to a nozzle (and static mixer for coaxial cartridges) (NORDSON EFD).

[0280] The average nozzle diameter used, equal to the thickness of the layer, is 400 m.

[0281] The pressure used is 5.5 bars for the base composition, 6 bars for the PEG-05, PEG-1, PEG-2 and SP-05 compositions and 6.5 bars for SP-1 and SP-2 compositions.

[0282] A single layer has the following dimensions (50 mm; 400 m; 400 m). The distance between the nozzle and the building plate or the previous layer is comprised from 350 to 450 m. The printing speed is adjusted to 10 mm/s. A 10 s stop is done between each layer printing.

[0283] No heat or radiation is applied.

[0284] We have measured the maximum number of layers that can be printed without distorsion or collapse of the structure using the LSR composition 1 prepared by mixing the LSR composition 1 parts A & B in a ratio 1:1 where different amounts of PEG 400 or organopolysiloxane-polyoxyalkylene copolymers (SP3300 or Q20308) have been added.

TABLE-US-00005 TABLE 5 3D printing observationMaximum layers printed with 400 m each layer Sample Layers with 10 s stop LSR Composition 1 15 LSR Composition 1 with 20 0.25% weight PEG400 LSR Composition 1 with 19 0.5% weight PEG400 LSR Composition 1 with 22 1% weight PEG400 LSR Composition 1 with 25 0.25% SP3300 LSR Composition 1 with 28 0.5% weight SP3300 LSR Composition 1 with 34 1% weight SP3300 LSR Composition 1 with 26 0.5% weight Q20308

[0285] When 0.5% weight of SP 3300 or Q20308 is added to the LSR composition 28 or 26 layers can be printed without distorsion or collapse of the structure compared to 15 where the LSR composition is used. PEG 400 is less effective, only 19 layers can be printed.

Curing of Printed Dumbbell Shaped Specimen

[0286] Dumbbell specimen have been printed with the same printer and operations than disclosed before and allowed to crosslink for 72 hours at ambient temperature.

Mechanical Characterization:Tensile Test Description on Dumbbell Specimen

[0287] A tensile testing machine (AGS-X SHIMADZU) with 10 kN cell, pneumatic flat grips (5 bars) and mechanical extensometer, was used to define mechanicals properties of samples. Tests according to ASTM test (D412) were performed on printed dumbbell shaped specimen (thickness2 mm) for each formulation to determine the Young Modulus E, the elongation at break and the stress at break. Results are presented on table 6.

TABLE-US-00006 TABLE 6 Mechanical behaviorGeneral description Elongation Stress at E at break break Sample (MPa) (%) (MPa) LSR Composition 1 2.0 697 42.3 LSR Composition 1 2.3 771 57.2 with PEG-0.25% weight LSR Composition 1 2.2 759 49.2 with PEG-0.5% weight LSR Composition 1 1.9 814 51.1 with PEG-1% weight LSR Composition 1 2.3 645 37.4 with SP-0.25% LSR Composition 1 2.8 644 45.7 with SP-0.5% weight LSR Composition 1 2.2 681 36.8 with SP-1% weight

[0288] The results of table 6 show the mechanicals properties for each composition. The Young's modulus, elongation at rupture and stress at rupture are not different compared to the silicone base. This very good results allow users to print 3D objects which will get the same mechanical properties as objects products by molding.