Low-density molding compound
View Patent ↗A molding composition formulation includes a thermoset cross-linkable polymeric resin. Glass microspheroids are present such that upon cure of the resin the resulting article has a linear shrinkage of less than ±0.06% and a density of less than 1.65. An article formed from such a composition is further strengthened by the addition of a surface activating agent bonded to the surface of the glass microspheroids. Conventional particulate fillers when added to an inventive formulation provide enhanced performance when the filler particle has a size sufficiently small to insert within adjacent microspheroid interstitial voids. An unsaturated polyester resin so formed is particularly well suited for the formation of sheet molding compound formulations.
1. A molding composition formulation comprising:
a thermoset cross-linkable polymeric resin; and
glass microspheroids with a mean diameter from 16 to 35 microns that upon cure of said resin yield an article having a linear shrinkage of less than ±0.06%, a density of less than 1.65, and the smoothness of a class-A surface finish.
2. The formulation of claim 1 , wherein said glass microspheroids are present from 4 to 6 total weight percent of the formulation.
3. The formulation of claim 1 wherein said glass microspheroids are solid beads.
4. The formulation of claim 1 , further comprising a surface activating agent bonded to the surface of said glass microspheroids.
5. The formulation of claim 4 , wherein said surface activating agent is a silane.
6. The formulation of claim 4 wherein said surface activating agent further comprises a cross-linkable moiety reactive during the cure of said resin.
7. The formulation of claim 4 wherein said surface activating agent is a heteroatorn functionally terminated thermoplastic coating.
8. The formulation of claim 7 wherein said coating has a heteroatom containing terminus selected from the group consisting of: a tertiary amine-, hydroxyl-, imine- or cyano-molety.
9. The formulation of claim 1 further comprising filler particles such that a filler particle has a particle size that is less than or equal to a diameter D and resides within an interstice formed by proximal glass microspheroids according to
D≦ 2√{square root over (2 r 2 )}−2 r
where r is the average radius of four contiguous microspheroids.
10. The formulation of claim 1 wherein said glass microspheroids have an aspect ratio of normal diameters of between 1 and 1.6.
11. The formulation of claim 1 wherein said resin is a polyester.
12. The formulation of claim 1 wherein said resin is selected from the group consisting of: an epoxy and a polyurethane.
13. A molding composition formulation comprising:
an unsaturated polyester cross-linkable resin;
glass microspheroids having a mean diameter of from 16 to 35 microns;
filler particles having a size that is less than or equal to a diameter D and resides within an interstice formed by proximal glass microspheroids according to
D≦ 2√{square root over (2 r 2 )}−2 r
where r is the average radius of four contiguous microspheroids;
such that cure of said resin yields an article having a linear shrinkage of less than ±0,06%, a density of less than 1.65, and the smoothness of a class-A surface finish.
14. The formulation of claim 13 , wherein said glass microspheroids are present from 4 to 6 total weight percent of the formulation.
15. The formulation of claim 13 , further comprising a surface activating agent bonded to the surface of said glass microspheroids.
16. The formulation of claim 15 , wherein said surface activating agent is a silane.
17. The formulation of claim 15 wherein said surface activating agent further comprises a cross-linkable moiety reactive during the cure of said resin.
18. The formulation of claim 15 wherein said surface activating agent is a heteroatom functionally terminated thermoplastic coating.
19. A process for producing an article from a molding compound formulation of claim 1 and retaining surface quality comprising:
adding a surface activating agent coated glass microspheroid having a mean diameter of from 16 to 35 microns to a molding composition formulation containing a thermoset cross-linkable polymeric resin; and
allowing sufficient time for said resin to cross link.
20. The process of claim 19 wherein said surface activating agent is reactive and cross links to said thermoset cross-linkable resin.