The invention relates to thermally expandable thermoplastic microspheres comprising a polymer shell made from ethylenically unsaturated monomers encapsulating a propellant, said ethylenically unsaturated monomers comprising from 40 to 70 wt % of acrylonitrile, from 5 to 40 wt % of methacrylonitrile, from 10 to 50 wt % of monomers selected from the group consisting of esters of acrylic acid, esters of methacrylic acid and mixtures thereof, and said propellant comprising at least one of methane, ethane, propane, isobutane, n-butane and neo-pentane. The invention further relates to the production and use of the microspheres.
1. Thermally expandable thermoplastic microspheres comprising a polymer shell made from ethylenically unsaturated monomers encapsulating a propellent, said ethylenically unsaturated monomers consisting essentially of from 40 to 70 wt % of acylonitrile, from 5 to 40 wt % of methacrylonitrile, from above 20 to 50 wt % of acrylate monomers selected from the group consisting of methyl acrylate, ethyl acrylate and mixtures thereof, and from 0.1 to 10 wt % of one or more crosslinking multifunctional monomers, and said propellant consisting essentially of n-butane.
2. The microspheres as claimed in claim 1 , wherein said ethylenically unsaturated monomers comprises from 45 to 65 wt % acrylonitrile.
3. The microspheres as claimed in claim 1 , wherein said ethylenically unsaturated monomers comprises from 10 to 35 wt % of methacrylonitrile.
4. The microspheres as claimed in claim 1 , wherein said acylate monomers are ethyl acrylate.
5. The microspheres as claimed in claim 1 , wherein said acrylate monomers are methyl acrylate.
6. The microspheres as claimed in claim 1 , wherein T start is from 50 to 110° C.
7. The thermally expandable thermoplastic microspheres according to claim 1 , wherein said ethylenically unsaturated monomers consist essentially of from 45 to 65 wt % of acrylonitrile, from 10 to 35 wt % of methacrylonitrile, from above 20 to 40 wt % of acrylate monomers selected from the group consisting of methyl acrylate, ethyl acrylate and mixtures thereof, and from 0.1 to 10 wt % of one or more crosslinking multifunctional monomers.
8. Aqueous slurry comprising thermally expandable thermoplastic microspheres according to claim 1 .
9. The aqueous slurry as claimed in claim 8 further comprising at least one thickener being an at least partially water soluble polymer selected from the group consisting of starch, gums, celluloses, chitins, chitosans, glycans, galactans, pectins, mannans, dextrins, co-polymers made from monomers comprising acrylic acid or salts thereof, homo- and co-polymers made from monomers comprising esters or amides of acrylic acid, homo and co-polymers made from monomers comprising methacrylic acid, esters or amides thereof, rubber latexes, poly(vinyl chloride) and copolymers, poly(vinyl esters) and co-polymers, poly(vinyl alcohol), polyamines, polyetyleneimine, polyethylene/polypropylene oxides, polyurethane, aminoplast, phenoplast precondensates and polyamidoamine epichlorohydrin resins.
10. Process for the production of thermally expandable microspheres comprising polymerising ethylenically unsaturated monomers in the presence of a propellant to yield microspheres comprising a polymer shell encapsulating said propellant, said ethylenically unsaturated monomers consisting essentially of from 40 to 70 wt % of acylonitrile, from 5 to 40 wt % of methacrylonitrile, from above 20 to 50 wt % of acylate monomers selected from the group consisting of methyl acrylate, ethyl acrylate and mixtures thereof, and from 0.1 to 10 wt % of one or more crosslinking multifunctional monomers, and said propellant consisting essentially of n-butane.
11. Expanded microspheres obtained by expending the thermally expandable thermoplastic microspheres according to claim 1 .
12. Printing ink comprising the thermally expandable thermoplastic microspheres according to claim 1 .
13. Process for the production of paper comprising the steps of adding thermally expandable thermoplastic microspheres to a stock containing cellulosic fibres, dewatering the stock on a wire to obtain paper, and drying the paper by applying heat and thereby also raising the temperature of the microspheres sufficiently for them to expand and increase the bulk of the paper, said expandable thermoplastic microspheres comprising a polymer shell made from ethylenically unsaturated monomers encapsulating a propellant, said ethylenically unsaturated monomers consisting essentially of from 40 to 70 wt % of acylonitrile, from 5 to 40 wt % of methacrylonitrile, and from above 20 to 50 wt % of acylate monomers selected from the group consisting of methyl acrylate, ethyl acrylate and mixtures thereof, and from 0.1 to 10 wt % of one or more crosslinking multifunctional monomers, and said propellent consisting essentially of n-butane.
14. The process as claimed in claim 13 , wherein the thermally expandable microspheres are added in the form of an aqueous slurry comprising said thermally expandable microspheres.
15. The thermally expandable thermoplastic microspheres according to claim 1 , wherein said ethylenically unsaturated monomers consist of from 40 to 70 wt % of acrylonitrile, from 5 to 40 wt % of methacrylonitrile, from above 20 to 50 wt % of acrylate monomers selected from the group consisting of methyl acrylate, ethyl acrylate and mixtures thereof, and from 0.1 to 10 wt % of one or more crosslinking multifunctional monomers.