Silicone compositions for producing elastomeric molded parts by means of ballistic methods
3D printing of curable silicone cam positions is made possible by employing a mixture of Si—H-functional silicon compounds and silicon compounds bearing aliphatically unsaturated groups, a hydrosilylation catalyst, and a combination of a reinforcing filler and a rheological agent containing polar groups, exhibiting shear thinning behavior.
1. A crosslinkable silicone rubber composition for the 3D printing of silicone components in the ballistic additive DOD method, comprising:
(A) 50% to 95% by weight of at least one linear organosilicon compound having at least two aliphatically unsaturated groups per molecule,
(B) 1% to 10% by weight of at least one organosilicon compound having at least two SiH groups per molecule,
and optionally, in addition to (A) and (B),
(G) at least one organosilicon compound having at least two aliphatically unsaturated groups and at least two SiH groups per moleculep;
or, in place of (A)+(B)+(G),
(G′) 50%-95% by weight of at least one organosilicon compound having at least two aliphatically unsaturated groups and at least two SiH groups per molecule;
(C) 0.1 to 500 ppm by weight of at least one metal-containing hydrosilylation catalyst, based on the content of the metal of the metal-containing hydrosilylation catalyst relative to the overall silicone rubber composition;
and
(D) 1% to 30% by weight of at least one reinforcing material, in combination with
(E) 0.01% to 2% by weight of a rheological agent which contains polar groups and is selected from (E1), (E2) and (E3) and mixtures thereof:
(E1) epoxy group-functional compounds,
(E2) (poly)ether group-functional compounds;
(E3) (poly)ester group-functional compounds,
where two or more of epoxy, ether, and ester groups are optionally present in a single molecule; and
(F) 0% to 30% by weight of auxiliaries other than (D) and (E),
wherein the relaxation time τ of the silicone rubber composition at 25° C. is within the range
0 seconds<τ≤10 seconds,
where τ is calculated from formula (III):
η( t )=η max +(η 0 −η max )*EXP(− t /τ), (III)
where
η(t) is the viscosity at time t at 25° C.,
η max denotes the maximum viscosity at 25° C. attained within a given time when shearing at a shear rate of 0.5 s −1 has stopped,
η 0 is the viscosity measured immediately after shearing at 25 s −1 , and
EXP means the e function,
with the proviso that the viscosity η MP1 of the silicone rubber composition comprising all the constituents except for constituent (E) is not more than 300,000 mPa·s.
2. The silicone rubber composition of claim 1 , wherein the relaxation time τ of the silicone rubber composition is within the range:
0 seconds<τ≤7 seconds.
3. The silicone rubber composition of claim 1 , wherein the relaxation time τ of the silicone rubber composition is within the range:
0 seconds<τ≤5 seconds.
4. The silicone rubber composition of claim 1 , wherein (E) is an epoxy-functional organic compound (E1).
5. The silicone rubber composition of claim 1 , wherein (D) is selected from the group consisting of fumed silica, precipitated silica, and mixture thereof.
6. The silicone rubber composition of claim 1 , which is crosslinkable by initiation by UV or UV-VIS radiation.
7. The silicone rubber composition of claim 1 , wherein, for every one gram of constituent (D), there is at least 0.1 μmol to at most 100 mmol of polar groups of constituent (E).
8. A process for producing an elastomeric shaped body, comprising forming the shaped body a silicone rubber composition of claim 1 by means of a ballistic additive DOD method (3D printing).
9. An elastomeric shaped body produced by means of ballistic additive DOD methods (3D printing) employing the crosslinkable silicone composition of claim 1 .