Multi-layer rotational moulding
View Patent ↗This invention discloses a multilayer article prepared by rotational molding that comprises: a) a layer A comprising a functionalized fluoropolymer; b) a layer B comprising a non-fluoropolymer containing functional groups; and c) optionally a layer C prepared from a polymer that is dissimilar from that of layer A and that is similar to or dissimilar from that of layer B and is adjacent to layer A and/or layer B and, if present, is characterized in that it has good adhesion to layer A and/or to layer B and is not a blend of layer A and layer B.
1. A multilayer hollow article prepared by rotational moulding that consists of:
a) an inner surface layer A comprising a functionalized fluoropolymer, wherein said functionalized fluoropolymer is a functionalized polyvinylidene fluoride (PVDF) that has been irradiation grafted with maleic anhydride;
an outer surface layer B comprising a non-fluoropolymer containing functional groups, polyester, polyethylene terephthalate, butylene terephthalate, liquid crystal polymer, polycarbonates, acrylics, polyamides, aromatic or aliphatic polyketones, aromatic or aliphatic polyether ketones, or polyphenylene sulfides, polyurethanes, and alloys thereof, characterized in that said layer B polymer has reactive species or end-groups able to create bonds.
2. The multilayer article according to claim 1 wherein each layer has a thickness of at least 0.5 mm.
3. The multilayer rotomoulded article according to claim 1 , wherein said multilayer article is a fuel tank, chemical tank or hydraulic tank.
4. The rotomoulded article according to claim 1 , wherein said layer B comprises a functionalized polyolefin.
5. A process for preparing the multilayer rotomoulded article according to claim 1 by feeding in one shot the material necessary for each one layer.
6. The process of claim 5 for preparing a two-layer rotomoulded article wherein layer B is the outer layer and comprises a non-fluoropolymer containing functional groups composition and layer A is the inner layer and comprises fluoropolymer containing functional groups, said process comprising the steps of:
a) providing a non-fluoropolymer resin composition comprising from 0 to 98 wt % of non-functionalized polymer and from 100 to 2 wt % of functionalised polymer, said non-fluoropolymer having a melting point of less than 145° C.;
b) providing a functional fluoropolymer resin having a melting point of at least 145° C.;
c) physically mixing the resin composition from a) with the resin from b);
d) feeding the mix of step c) in the rotational moulder and keeping under rotation;
e) retrieving the rotomoulded article;
wherein the ratio of the particle diameter of the non-fluorinated polymer composition to that of the fluoropolymer is at most 2:3 and the melting point of the non-fluoropolymer composition is at least 15° C. lower than that of the fluoropolymer.
7. A process for preparing a two-layer rotomoulded article according to claim 1 , wherein layer B is the outer layer and comprises a non-fluoropolymer containing functional groups composition and wherein layer A is the inner layer and comprises a fluoropolymer containing functional groups, said process comprising the steps of:
a) providing the non-fluoropolymer composition for layer B;
b) increasing the peak internal air temperature (PIAT) to a temperature that is from 15 to 50° C. higher than the melting temperature of the composition of layer B in order to fully melt said layer B;
c) adding the composition for layer A using a drop-box or hand addition;
d) increasing the PIAT to a temperature that is superior to the melting temperature of the composition of layer A in order to fully melt said layer A;
e) cooling down the composition to solidify the resins;
f) retrieving the rotomoulded article.
8. The process of claim 7 further comprising a step between steps d) and e) of using a water spray cooling for solidifying the rotomoulded article in order to reduce shrinkage voids.