Thermally expandable thermoplastic microspheres and process for their preparation

1. A process for the manufacture of thermally expandable thermoplastic microspheres, the process comprising:

providing a mixture of monomeric materials suitable for polymerisation to form a thermoplastic polymer and at least one blowing agent,

providing a colloidal silica that is surface-modified with at least hydrophobic organosilane groups;

contacting the mixture of one or more monomers and at least one blowing agent with the surface-modified colloidal silica and forming an o/w emulsion comprising droplets of the mixture of one or more monomers and the at least one blowing agent in an aqueous phase; and

polymerising the one or more monomers in the droplets to form an aqueous slurry and/or wet cake of thermally expandable thermoplastic microspheres,

wherein the colloidal silica is modified with the hydrophobic organosilane groups that are alkylsilyl groups, vinylsilyl groups, and/or phenylsilyl groups, and is further surface-modified with hydrophilic organosilane groups being glycerol propyl silyl groups.

2. The process according to claim 1 , wherein the colloidal silica that is surface-modified with the hydrophobic organosilane groups have a particle size of 2-150 nm, when calculated from the specific surface area (SSA) in m 2 /g according to the formula 2727/SSA.

3. The process according to claim 1 , wherein the colloidal silica that is surface-modified with the hydrophobic organosilane groups has a degree of surface modification (DM) of up to 190%, wherein 190% means an amount of 4.5 μmol hydrophobic organosilane groups per m 2 of the colloidal silica, and wherein DM is calculated according to the equation:

DM

=

N

Sil

⁢

W

CS

×

C

CS

×

SA

CS

in which;

DM is the Degree of Surface Modification in units of μmol m −2

N sil is the quantity of organosilane added to colloidal silica in units of μmol

W CS is the weight of colloidal silica before it is surface modified in units of g (grams)

C CS is the percentage by weight of silica in the colloidal silica before it is surface-modified; and

SA CS is the surface area of the silica in the colloidal silica before it is surface modified, the surface area being calculated by Sears Titration, in units of m 2 g −1 .

4. The process according to claim 1 , wherein a proportion of the degree of surface modification of the hydrophobic organosilane groups/the hydrophilic organosilane groups is from 15%/85% to 60%/40%.

5. The process according to claim 1 , wherein a polymerisation catalyst is also provided.

6. The process according to claim 5 , in which the polymerisation catalyst is an organic peroxide.

7. The process according to claim 5 , in which the polymerisation catalyst is mixed with the surface-modified colloidal silica before contact with the mixture comprising one or more monomeric materials and at least one blowing agent.

8. The process according to claim 1 , in which the aqueous slurry is dewatered to form the wet cake of thermally expandable thermoplastic microspheres.

9. The process according to claim 1 , in which the aqueous slurry and/or wet cake is dried to form dry thermally expandable thermoplastic microspheres.

10. A process for producing expanded microspheres, comprising manufacturing thermally expandable thermoplastic microspheres according to claim 1 , and expanding them by heating.

11. Expanded microspheres obtained by the process of claim 10 .

12. Thermally expandable thermoplastic microspheres obtained by the process according to claim 1 .

13. The thermally expandable thermoplastic microspheres of claim 12 that are in dry form or in the form of an aqueous slurry or a wet cake.

14. A product manufactured using the thermally expandable thermoplastic microspheres of claim 12 .

15. The process according to claim 1 , wherein the alkylsilyl groups are chosen from methylsilyl, dimethylsilyl, trimethylsilyl, propylsilyl, octylsilyl, mercaptopropylsilyl, methacrylamidopropylsilyl and iso-butylsilyl groups.

16. The process according to claim 1 wherein the hydrophobic organosilane groups include propylsilyl groups.

17. The process according to claim 1 wherein the mix of monomeric materials comprises acrylonitrile, methyl methacrylate, and vinylidene chloride, the blowing agent comprises iso-butane, and the emulsion comprises a cross-linker comprising trimethylolpropane tri-(meth)acrylate.

18. The process according to claim 17 wherein a polymerisation catalyst is provided and is di(4-tert-butylcyclohexyl) peroxydicarbonate.

19. A process for the manufacture of thermally expandable thermoplastic microspheres, the process comprising:

providing a mixture of monomeric materials suitable for polymerisation to form a thermoplastic polymer and at least one blowing agent,

providing a colloidal silica that is surface-modified with at least hydrophobic organosilane groups;

contacting the mixture of one or more monomers and at least one blowing agent with the surface-modified colloidal silica and forming an o/w emulsion comprising droplets of the mixture of one or more monomers and the at least one blowing agent in an aqueous phase; and

polymerising the one or more monomers in the droplets to form an aqueous slurry and/or wet cake of thermally expandable thermoplastic microspheres,

wherein the colloidal silica is modified with the hydrophobic organosilane groups that are alkylsilyl groups, vinylsilyl groups, and/or phenylsilyl groups, and is further surface-modified with hydrophilic organosilane groups; and

wherein the colloidal silica that is surface-modified with at least hydrophobic organosilane groups has a degree of surface modification (DM) of up to 190%, wherein 190% means an amount of 4.5 μmol hydrophobic organosilane groups per m 2 of the colloidal silica, and

wherein DM is calculated according to the equation:

D

⁢

M

=

N

sil

⁢

W

CS

×

C

CS

×

SA

CS

in which;

DM is the Degree of Surface Modification in units of μmol m −2 ;

N sil is the quantity of organosilane added to colloidal silica in units of μmol;

W CS is the weight of colloidal silica before it is surface modified in units of g (grams);

C CS is the percentage by weight of silica in the colloidal silica before it is surface-modified; and

SA CS is the surface area of the silica in the colloidal silica before it is surface modified, the surface area being calculated by Sears Titration, in units of m 2 g −1 ; and

wherein a proportion of the degree of surface modification of hydrophobic organosilane groups/hydrophilic organosilane groups is 50%/50%.

20. The process according to claim 19 wherein the mix of monomeric materials comprises acrylonitrile, methyl methacrylate, and vinylidene chloride, the blowing agent comprises iso-butane, and the emulsion comprises a cross-linker comprising trimethylolpropane tri-(meth)acrylate.

21. A process for the manufacture of thermally expandable thermoplastic microspheres, the process comprising:

providing a mixture of monomeric materials suitable for polymerisation to form a thermoplastic polymer and at least one blowing agent,

providing a colloidal silica that is surface-modified with at least hydrophobic organosilane groups;

contacting the mixture of one or more monomers and at least one blowing agent with the surface-modified colloidal silica and forming an o/w emulsion comprising droplets of the mixture of one or more monomers and the at least one blowing agent in an aqueous phase; and

polymerising the one or more monomers in the droplets to form an aqueous slurry and/or wet cake of thermally expandable thermoplastic microspheres,

wherein the colloidal silica is modified with propylsilyl and glycerolpropylsilyl groups,

wherein the mixture of monomeric materials comprises acetonitrile, methylmethacrylate, and vinylidene chloride,

wherein the at least one blowing agent comprises isobutane, and

wherein the emulsion further comprises a cross-linker comprising trimethylolpropane-trimethacrylate, trimethylolpropane tri-acrylate, or combinations thereof.