SILICONE COMPOSITION AND A METHOD FOR ADDITIVE MANUFACTURING A SILICONE ELASTOMER ARTICLE

Abstract

The invention relates to a silicone composition and a method for additive manufacturing a silicone elastomer article. The silicone composition is 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 which is at least partly surface treated, (E) at least one organopolysiloxane having an aryl group E and (F) optionally at least one crosslinking inhibitor F.

Claims

1. A silicone composition for additive manufacturing a silicone elastomer article, wherein said silicone composition is crosslinkable through one or more addition reactions and comprises: (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 which is at least partly surface treated, (E) at least one organopolysiloxane having an aryl group E and (F) optionally at least one crosslinking inhibitor F.

2. The silicone composition according to claim 1 where the organopolysiloxane A comprising, per molecule, at least two C.sub.2-C.sub.6 alkenyl radicals bonded to silicon atoms, comprises: (i) at least two siloxyl units (A.1), which may be identical or different, having the following formula: $\begin{array}{cc}{W}_a{Z}_b{\mathrm{SiO}}_{\frac{4-\left(a+b\right)}{2}}& \left(A\mathrm{.1}\right)\end{array}$ in which: a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3; the symbols W, which may be identical or different, represent a linear or branched C.sub.2-C.sub.6 alkenyl group, and the symbols Z, which may be identical or different, represent a monovalent linear, branched or cyclic alkyl group containing from 1 to 30 carbon atoms, optionally from 1 to 8 carbon atoms, that may be unsubstituted or substituted by one or more halogen atoms optionally fluorine, chlorine and bromine atoms and/or by one or more aryl group optionally phenyl, and optionally chosen from the group formed by methyl, ethyl, propyl, 3,3,3-trifluoropropyl, (ii) and optionally at least one siloxyl unit having the following formula: $\begin{array}{cc}{Z}_c^1{\mathrm{SiO}}_{\frac{4-c}{2}}& \left(A\mathrm{.2}\right)\end{array}$ in which: c=0, 1, 2 or 3, the symbols Z′, which may be identical or different, represent a monovalent linear, branched or cyclic alkyl group containing from 1 to 30 carbon atoms, optionally from 1 to 8 carbon atoms, that may be unsubstituted or substituted by one or more halogen atoms optionally fluorine, chlorine and bromine atoms and/or by one or more aryl group optionally phenyl, and optionally chosen from the group formed by methyl, ethyl, propyl, 3,3,3-trifluoropropyl.

3. The silicone composition according to claim 1 where the organohydrogenopolysiloxane compound B is an organopolysiloxane comprising: (i) at least two siloxyl units and optionally at least three siloxyl units having the following formula: $\begin{array}{cc}{H}_d{Z}_e^3{\mathrm{SiO}}_{\frac{4-\left(d+e\right)}{2}}& \left(B\mathrm{.1}\right)\end{array}$ in which: d=1 or 2, e=0, 1 or 2 and d+e=1, 2 or 3, the symbols Z.sup.3, which may be identical or different, represent a monovalent linear, branched or cyclic alkyl group containing from 1 to 30 carbon atoms, optionally from 1 to 8 carbon atoms, that may be unsubstituted or substituted by one or more halogen atoms such as fluorine, chlorine and bromine atoms and/or by one or more aryl group optionally phenyl, and optionally chosen from the group formed by methyl, ethyl, propyl, 3,3,3-trifluoropropyl, and (ii) optionally at least one siloxyl unit having the following formula: $\begin{array}{cc}{Z}_c^2{\mathrm{SiO}}_{\frac{4-c}{2}}& \left(B\mathrm{.2}\right)\end{array}$ in which: c=0, 1, 2 or 3, the symbols Z.sup.2, which may be identical or different, represent a monovalent linear, branched or cyclic alkyl group containing from 1 to 30 carbon atoms, optionally from 1 to 8 carbon atoms, that may be unsubstituted or substituted by one or more halogen atoms optionally fluorine, chlorine and bromine atoms and/or by one or more aryl group optionally phenyl, and optionally chosen from the group formed by methyl, ethyl, propyl, 3,3,3-trifluoropropyl.

4. The silicone composition according to claim 1 where the silicone composition comprises 0.3-30 wt %, optionally 0.8-20 wt %, optionally 1.0-10.0 wt % and optionally 1.0-7.0 wt % of at least one organopolysiloxane having an aryl group E with respect to the total weight of the silicone composition.

5. The silicone composition according to claim 1 where the organopolysiloxane having an aryl group E is an organopolysiloxane containing siloxyl units of the formula (E-1):
[R.sup.5.sub.pR.sup.6.sub.qSiO.sub.(4−p−q)/2].sub.n  (E-1) in which R.sup.5 and R.sup.6 is independently from each other selected from hydrocarbon-based group containing from 1 to 30 carbon atoms and hydrogen; where n is an integer greater than or equal to 1; p and q are independently 0, 1, 2 or 3; and p+q=1, 2 or 3; provided that the organopolysiloxane having an aryl group E contains at least one aryl group directly bonded to Si atom.

6. The silicone composition according to claim 5, where the hydrocarbon-based group contains from 1 to 24, optionally 1 to 18, optionally 1 to 12, optionally 2 to 8 carbon atoms and is selected from linear, branched or cyclic alkyl and/or alkenyl groups that are unsubstituted or substituted by one or more halogens or an aryl group, and an aryl group that is unsubstituted or substituted by one or more halogens and C.sub.1-C.sub.6-alkyl groups and contains between 6 and 12 carbon atoms.

7. The silicone composition according to claim 1, where the aryl group is chosen from the group formed by xylyl, tolyl and phenyl radicals, optionally phenyl radical.

8. The silicone composition according to claim 1, where at least one of groups R.sup.5 and R.sup.6 is an aryl group and the others are chosen from the group formed by an alkyl group containing from 1 to 8 carbon atoms, optionally methyl or ethyl, and an alkenyl radical containing from 2 to 6 carbon atoms, optionally vinyl group.

9. The silicone composition according to claim 1, where the organopolysiloxane having an aryl group E contains at least one aryl group, optionally a phenyl group, and at least one alkenyl group optionally vinyl group.

10. The silicone composition according to claim 1, where the organopolysiloxane having an aryl group E contains at least one aryl group, optionally a phenyl group, and at least one SiH group.

11. The silicone composition according to claim 1, where the organopolysiloxane having an aryl group E contains at least one aryl group, optionally a phenyl group, at least one alkenyl group optionally vinyl group and at least one SiH group.

12. The silicone composition according to claim 1, where the organopolysiloxane having an aryl group E has the viscosity ranging from 3˜10 000 000 mPas, optionally ranging from 10˜200 000 mPas, optionally 50˜100 000 mPas and 100˜10 000 mPas.

13. The silicone composition according to claim 1, where the reinforcing silica filler D is subjected to hydrophobic surface treatment and optionally is fumed silica.

14. The silicone composition according to claim 1, where the amount of the silica reinforcing filler D is in the range from 2% to 40% by weight, optionally 5% to 35% by weight and optionally 10% to 30% by weight of the total composition.

15. The silicone composition according to claim 1, where the silicone composition comprises, per 100% weight of the silicone composition: from 10 to 95 wt % of at least one organopolysiloxane compound A; from 0.1 to 40 wt % of at least one organohydrogenopolysiloxane compound B; from 5 to 35 wt % of at least one reinforcing silica filler D which is at least partly surface treated; from 0.8 to 20 wt % of at least one organopolysiloxane having an aryl group E; from 0.002 to 0.01 wt % of catalyst e.g. platinum; and from 0.01 to 2 wt % of at least one crosslinking inhibitor F.

16. The silicone composition according to claim 1, where the silicone composition comprises, per 100% weight of the silicone composition: from 20 to 85 wt % of at least one organopolysiloxane compound A; from 0.1 to 15 wt % of at least one organohydrogenopolysiloxane compound B; from 10 to 30 wt % of at least one reinforcing silica filler D which is at least partly surface treated from 1.0 to 15 wt % of at least one organopolysiloxane having an aryl group E; from 0.0002 to 0.01 wt % of catalyst e.g. platinum; and from 0.01 to 1 wt % of at least one crosslinking inhibitor F.

17. The silicone composition according to claim 1, where the organopolysiloxane having an aryl group E has refractive index above 1.405, optionally ranging from 1.41˜1.6, optionally from 1.43˜1.58.

18. The silicone composition according to claim 1, where the amount of aryl group is from 2% to 70% by weight, optionally 5% to 62%, and optionally 10% to 58%, based on the total weight of organopolysiloxane having an aryl group E.

19. A 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 additional layer needed and 4) allowing the first and subsequent layers to crosslink, optionally by heating, to obtain a silicone elastomer article, wherein at least one layer of said silicone composition is the silicone composition as defined in claim 1.

20. The Method according to claim 19 where the 3D printer is an extrusion 3D printer.

21. A silicone elastomer article produced by the method as claimed in claim 19.

22. A product comprising a silicone composition crosslinkable through one or more 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

[0204] Addition-crosslinking silicone compositions are prepared and printed using an extrusion 3D printer according with disclosure.

Raw Materials

[0205]

TABLE-US-00001 TABLE 1 Raw materials Chemical description or structure A-1 Vinyl terminated Polydimethylsiloxane, viscosity: 1500 mPa•s, vinyl content: 0.26 wt % A-2 Vinyl terminated Polydimethylsiloxane, viscosity: 600 mPa•s, vinyl content: 0.38 wt % B-1 Poly(methylhydrogeno)(dimethyl)siloxane with SiH groups in-chain and end-chain (α/ω), viscosity: 300 mPa•s, SiH content: 4.75 wt % B-2 Poly(methylhydrogeno)(dimethyl)siloxane with SiH groups in-chain and end-chain (α/ω), viscosity: 25 mPa•s, SiH content: 20 wt % B-3 Poly(methylhydrogeno) (dimethyl)siloxane with end-chain (α/ω) SiH groups, viscosity: 8.5 mPa•s, SiH content: 5.5 wt % C-1 Pt catalyst: Platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Pt content: 10 wt %) D-1 Treated silica, CAS NO: 68988-89-6 E-1 Methyl phenyl polysiloxane, viscosity: 75 mPa•s, refractive index: 1.4912 [00004] E-2 Methyl phenyl polysiloxane, viscosity: 40 mPa•s, refractive index: 1.492 [00005] E-3 Methyl phenyl polysiloxane, viscosity: 1360 mPa•s, refractive index: 1.534 [00006] E-4 Methyl phenyl polysiloxane, viscosity: 10000 mPa•s, refractive index: 1.543 E-5 Methyl phenyl polysiloxane, viscosity: 40 mPa•s, refractive index: 1.473 [00007] E-6 Methyl phenyl polysiloxane, viscosity: 90 mPa•s, refractive index: 1.553 [00008] E-7 Methyl phenyl polysiloxane, viscosity: 413 mPa•s, refractive index: 1.578 [00009] E-8 Vinyl phenyl polysiloxane viscosity: 200 mPa•s, refractive index: 1.551, phenyl content: 56 wt % [00010] E-9 Methyl vinyl phenyl polysiloxane viscosity: 60 mPa•s, refractive index: 1.474, phenyl content: 27.1 wt % [00011] E-10 Methyl vinyl phenyl polysiloxane viscosity: 1900 mPa•s, refractive index: 1.532 [00012] E-11 Vinyl phenyl polysiloxane viscosity: 5 mPa•s, refractive index: 1.502, phenyl content: 40.1 wt % [00013] E-12 Methyl vinyl phenyl polysiloxane viscosity: 3000 mPa•s, refractive index: 1.443, phenyl content: 20% [00014] E-13 Methyl vinyl phenyl polysiloxane viscosity: 800 mPa•s, refractive index: 1.46, phenyl content: 15% [00015] E-14 Methyl vinyl phenyl polysiloxane viscosity: 3000 mPa•s, refractive index: 1.46, phenyl content: 15% [00016] F-1 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, CAS NO.: 2554-06-5 [00017] F-2 Ethynylcyclohexanol, CAS NO.: 78-27-3 [00018]  G-1 Non-reactive methyl polysiloxane, viscosity: 50 mPa•s

LSR Base Composition

Example 1-34

[0206] In example 1, all of the raw materials is mixed according to weight ratio. 53.97 parts of vinyl terminated polydimethylsiloxane A-1 and 16.67 parts of A-2 are mixed with 23.07 part of D-1. 0.38 part of F-1 is added and then mixed sufficiently. 2.27 parts of an organohydrogenopolysiloxane B-1, 1.81 parts of an organohydrogenopolysiloxane B-2 and 1.81 parts of an organohydrogenopolysiloxane B-3 are added and stirred, following with 0.017 part of C-1 to obtain Example 1. Example 10 and 21 are prepared likewise according to the above process with varying ratios of raw materials as shown in tables 2-1 and 2-2. No organopolysiloxane having an aryl group is contained in Examples 1, 10 and 21.

[0207] In example 2, all of the raw materials are mixed according to weight ratio shown in table 2-1. 53.97 parts of A-1 and 16.67 parts of A-2 are mixed with 23.07 parts of D-1. 0.38 part of F-1 is added and then mixed sufficiently. 2.27 parts of an organohydrogenopolysiloxane B-1, 1.81 parts of an organohydrogenopolysiloxane B-2 and 1.81 parts of an organohydrogenopolysiloxane B-3 are added and stirred, following with 0.017 part of C-1 and 1 part of E-1 to obtain example 2. Example 3-9, example 11-20, example 22-35 are also prepared likewise according to the above process with varying ratios of raw materials as shown in table 2-1 and 2-2.

3D Printing Process Based on Curable Method

[0208] The 3D printing process was carried out by using ULTIMAKER 2+ equipment. The Mixture of example 35 was used as printing materials. Printing process is as follows: I. Loading silicone materials in extruder;
II. Level adjustment of printing platform and printing parameter setting;
III. Strat printing via extruder layer by layer.
Wherein, parameters of printing is below:
Diameter of nozzle: 0.84 mm
The distance between nozzle and platform: 0.5 mm.
The printing process and sample were observed, finding that each layer formed smoothly and shape printed was kept very stable.

Properties Assessment

[0209] According to the invention, assessment results of the prepared samples are listed in the table 2-1 and table 2-2.

[0210] Viscosity: according to ASTM D445, the viscosity of the sample mixture is tested at 25° C., the detail of testing conditions can be seen in the table 2-1 and 2-2, in which, for example, the expression Viscosity-20 (7#, 20 rpm) means that the viscosity is measured at 20 rpm by using spindle 7, and likewise Viscosity-2 (7#, 2 rpm) means the viscosity measured at 2 rpm by using spindle 7.

[0211] Thixotropic Index: A fluid is thixotropic to have a low viscosity when stirred at high speed and high viscosity at low speed. The thixotropic index is obtained by measuring the viscosity at two speeds that differ by a factor of 10 (for example 2 and 20 rpm) at room temperature. Herein, the ratio between Viscosity-2 and Visocisty-20, i.e. (Viscosity-2/Visocisty-20), defines how well the fluid will hang or resist sagging under gravity. At rest, the fluid will not flow, but when subjected to shear or pressure, it flows easily. The higher thixotropic ratio, the stronger thixotropy of the non-Newtonian fluid is.

[0212] Hardness: according to ASTM D2240, the hardness of cured samples are tested at 25° C., the details of testing conditions can be seen in the table 2-1 and 2-2. The cured sample was obtained under 150° C. for 30 min.

[0213] Tensile strength and Elongation at break: according to ASTM D412, tensile strength and elongation at break of cured samples are tested at 25° C., the details of testing conditions can be seen in the table 2-1 and 2-2. The cured sample was obtained under 150° C. for 30 min.

[0214] Tear strength: according to ASTM D642, tear strength of cured samples are tested at 25° C., the details of testing conditions can be seen in the table 2. The cured sample was obtained under 150° C. for 30 min.

[0215] Transparency assessment: observation method is employed to assess transparency of the samples. In the table 2-1 and 2-2, more marks “+” indicates higher transparency. Different transparency of the samples can be seen in FIG. 1.

[0216] Oil bleeding assessment: The samples are placed on the white paper and stay at room temperature for one week. Oil spots can be seen if the sample exhibits oil bleeding phenomenon. More marks “+” indicates the more oil bleeding on the surface of samples. Accordingly, the mark “NO” means no oil bleeding spots are observed.

TABLE-US-00002 TABLE 2-1 Formulas and test results of curable silicone compositions Raw material Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 A-1 53.97 53.97 53.97 53.97 53.97 53.97 53.97 53.97 53.97 57.28 A-2 16.67 16.67 16.67 16.67 16.67 16.67 16.67 16.67 16.67 7.05 B-1 2.27 2.27 2.27 2.27 2.27 2.27 2.27 2.27 2.27 2.16 B-2 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.72 B-3 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.72 C-1 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017 D-1 23.07 23.07 23.07 23.07 23.07 23.07 23.07 23.07 23.07 24.59 E-1 0 1 2 0 0 0 0 0 0 0 E-2 0 0 0 1 2 0 0 0 0 0 E-3 0 0 0 0 0 1 2 0 0 0 E-4 0 0 0 0 0 0 0 1 2 0 E-5 0 0 0 0 0 0 0 0 0 0 E-6 0 0 0 0 0 0 0 0 0 0 E-7 0 0 0 0 0 0 0 0 0 0 F-1 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.36 F-2 0 0 0 0 0 0 0 0 0 0.095 G-1 0 0 0 0 0 0 0 0 0 4.9 Total 100 101 102 101 102 101 102 101 102 100 SiH/Si- 1.38 1.38 1.38 1.38 1.38 1.38 1.38 1.38 1.38 1.42 alkenyl (mole ratio) Test results Viscosity-2, 243000 358000 514000 440000 700000 506000 680000 300000 360000 397000 mPa .Math. s, (7#, 2 rpm, 25° C. ) Viscosity-20, 88600 118000 164000 129000 200000 142000 199000 109000 132000 105000 mPa .Math. s, (7#, 20 rpm, 25° C.) Thixotropic 2.74 3.03 3.13 3.41 3.5 3.56 3.42 2.75 2.73 3.78 Index Hardness/ NA NA NA NA NA NA NA NA NA NA Shore. A Tear NA NA NA NA NA NA NA NA NA NA strength/ N/mm Tensile NA NA NA NA NA NA NA NA NA NA strength/MPa Elongation NA NA NA NA NA NA NA NA NA NA at break/% Transparency NA NA NA NA NA NA NA NA NA NA Oil NA NA NA NA NA NA NA NA NA NA bleeding Raw Material Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20 A-1 57.28 57.28 57.28 57.28 57.28 57.28 57.28 57.28 57.28 57.28 A-2 7.05 7.05 7.05 7.05 7.05 7.05 7.05 7.05 7.05 7.05 B-1 2.16 2.16 2.16 2.16 2.16 2.16 2.16 2.16 2.16 2.16 B-2 1.72 1.72 1.72 1.72 1.72 1.72 1.72 1.72 1.72 1.72 B-3 1.72 1.72 1.72 1.72 1.72 1.72 1.72 1.72 1.72 1.72 C-1 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017 D-1 24.59 24.59 24.59 24.59 24.59 24.59 24.59 24.59 24.59 24.59 E-1 2 0 0 0 0 0 0 0 0 0 E-2 0 1 2 0 0 0 0 0 0 0 E-3 0 0 0 1 2 0 0 0 0 0 E-4 0 0 0 0 0 1 2 0 0 0 E-5 0 0 0 0 0 0 0 2 0 0 E-6 0 0 0 0 0 0 0 0 2 0 E-7 0 0 0 0 0 0 0 0 0 2 F-1 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 F-2 0.095 0.095 0.095 0.095 0.095 0.095 0.095 0.095 0.095 0.095 G-1 4.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9 Total 102 101 102 101 102 101 102 102 102 102 SiH/Si- 1.42 1.42 1.42 1.42 1.42 1.42 1.42 1.42 1.42 1.42 alkenyl (mole ratio) Test results Viscosity-2, 560000 520000 632000 564000 648000 436000 454000 486000 400000 498000 mPa .Math. s, (7#, 2 rpm, 25° C. ) Viscosity-20, 122600 114000 120000 123000 127000 107000 102000 110000 80000 103800 mPa .Math. s, (7#, 20 rpm, 25° C.) Thixotropic 4.57 4.56 5.27 4.59 5.1 4.07 4.45 4.42 5 4.8 Index Hardness/ 40 NA 51 NA 50 NA 52 39 43 36 Shore. A Tear 32 NA 32.3 NA 33 NA 24.3 30 29 28.8 strength/ N/mm Tensile 5.36 NA 7.1 NA 5.79 NA 6.77 5.5 5 4.62 strength/MPa Elongation 347 NA 250 NA 259 NA 273 346 312 304 at break/% Transparency ++++ NA NA NA + NA ++ +++++ +++++ ++++ Oil NO NA + NA +++ NA NO NO NO NO bleeding * NA means not applicable or not determined.

TABLE-US-00003 TABLE 2-2 Raw materials Example 21 Example 22 Example 23 Example 24 Example 25 A-1 56.71 56.71 56.71 56.71 56.71 A-2 6.97 6.97 6.97 6.97 6.97 B-1 2.13 2.13 2.13 2.13 2.13 B-2 1.7 1.7 1.7 1.7 1.7 B-3 1.7 1.7 1.7 1.7 1.7 C-1 0.016 0.016 0.016 0.016 0.016 D-1 24.31 24.31 24.31 24.31 24.31 E-3 0 0.5 5 8 10 F-1 0.36 0.36 0.36 0.36 0.36 F-2 0 0 0 0 0 G-1 6.1 6.1 6.1 6.1 6.1 Total 100 100.5 105 108 110 Test results Viscosity-2, mPa .Math. s, 362000 524000 900000 1056000 1132000 (7#, 2 rpm, 25° C.) Viscosity-20, mPa .Math. s, 83600 108000 158000 165000 173000 (7#, 20 rpm, 25° C.) Thixotropic Index 4.33 4.85 5.7 6.4 6.54 Raw materials Example 26 Example 27 Example 28 Example 29 Example 30 A-1 57.28 57.28 57.28 57.28 57.28 A-2 7.05 7.05 7.05 7.05 7.05 B-1 2.16 2.16 2.16 2.16 2.16 B-2 1.72 1.72 1.72 1.72 1.72 B-3 1.72 1.72 1.72 1.72 1.72 C-1 0.017 0.017 0.017 0.017 0.017 D-1 24.59 24.59 24.59 24.59 24.59 E-8 2 0 0 0 0 E-9 0 2 4.8 7.2 0 E-10 0 0 0 0 2 E-11 0 0 0 0 0 E-12 0 0 0 0 0 E-13 0 0 0 0 0 E-14 0 0 0 0 0 F-1 0.36 0.36 0.36 0.36 0.36 F-2 0.095 0.095 0.095 0.095 0.095 G-1 4.9 4.9 4.9 4.9 4.9 Total 102 102 104.8 107.2 102 Test results Viscosity-2, mPa .Math. s, 472000 586000 538000 526000 545000 (7#, 2 rpm, 25° C.) Viscosity-20, mPa .Math. s, 114600 138400 127000 121000 122200 (7#, 20 rpm, 25° C.) Thixotropic Index 4.12 4.23 4.24 4.34 4.46 Hardness/ Shore. A 39 40 NA NA 43 Tear strength/ N/mm 15 34 NA NA 33 Tensile strength/ MPa 4 6 NA NA 5 Elongation at break/% 284 399 NA NA 302 Transparency +++++ +++++ ++++ + + Oil bleeding NO NO NO NO NO Raw materials Example 31 Example 32 Example 33 Example 34 Example 35 A-1 57.28 57.28 57.28 57.28 47 A-2 7.05 7.05 7.05 7.05 5.78 B-1 2.16 2.16 2.16 2.16 1.77 B-2 1.72 1.72 1.72 1.72 1.41 B-3 1.72 1.72 1.72 1.72 1.41 C-1 0.017 0.017 0.017 0.017 0.0139 D-1 24.59 24.59 24.59 24.59 20.17 E-8 0 0 0 0 0 E-9 0 0 0 0 0 E-10 0 0 0 0 0 E-11 2 0 0 0 0 E-12 0 2 0 0 1.64 E-13 0 0 2 0 0 E-14 0 0 0 2 0 F-1 0.36 0.36 0.36 0.36 0.3 F-2 0.095 0.095 0.095 0.095 0.078 G-1 4.9 4.9 4.9 4.9 20.43 Total 102 102 102 102 100 Test results Viscosity-2, mPa .Math. s, 472000 700000 790000 648000 276000 (7#, 2 rpm, 25° C.) Viscosity-20, mPa .Math. s, 110600 156000 161400 150000 57800 (7#, 20 rpm, 25° C.) Thixotropic Index 4.27 4.49 4.89 4.32 4.77 Hardness/ Shore. A 28 41 42 43 NA Tear strength/ N/mm 1.8 31 31 34 NA Tensile strength/ MPa 0.8 4.9 5.7 5.2 NA Elongation at break/% 61.7 333 365 331 NA Transparency +++++ ++++ +++ +++ NA Oil bleeding NO NO NO NO NA

[0217] Different aryl-containing organopolysiloxanes (alkyl phenyl polysiloxanes here) are used to improve thixotropic properties of the silicone composition. As can be seen from the above tables, the structure of the organopolysiloxane having an aryl group, viscosity and refractive index have influences on thixotropic properties. As for a certain formulation of the silicone composition, with the increasing amount of alkyl phenyl polysiloxanes, thixotropic properties normally become better. But, unduly high amount of alkyl phenyl polysiloxane in some cases has risk of oil bleeding for the cured products. The preferred alkyl phenyl polysiloxane has additionally vinyl and/or SiH group which can involve polyaddition reaction to avoid oil bleeding but keep better thixotropic properties for 3D printing.

[0218] Different alkyl phenyl polysiloxanes are used to improve thixotropy of the silicone composition. The viscosity ratio at different speed of rotation is employed to assess thixotropy, which is derived from change of shear force accompanied with viscosity change of thixotropic liquid. The higher thixotropic index means better thixotropy. According to table 2-1, compared with example 1, examples 6 and 7 exhibit better thixotropy because of the addition of methyl phenyl polysiloxane E-3. The same results can be obtained in the examples 12 to 17, when compared with example 10. Meanwhile, the different contents of methyl phenyl polysiloxane E-3 are added in the examples 22-25, indicating that the thixotropy becomes better with increasing E-3 content.

[0219] In some cases, methyl phenyl polysiloxane may have a negative effect such as oil bleeding problem like examples 15 as may be adverse to some specific applications. With polysiloxane with both phenyl and vinyl group (example 26-35), however, a good thixotropic property without oil bleeding problem is obtained. Besides, by using polysiloxane with both phenyl and vinyl group, transparent product can be obtained in example 26, 27 and 31.