Coating of viscous aqueous gelatin compositions on a continuous web support
AssigneeAgfa-Gevaert
InventorsVictor F. De Beul, Jan H. Van Hove
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Abstract
In an extrusion coating process of the flow-stretch type in which a ribbon of an aqueous gelatin coating composition is extruded through an elongated orifice onto a moving support and becomes stretched and attenuated in thickness between the orifice and support, at least one visco-elasticity enhancing agent is added to the coating composition in sufficient amount as to disproportionately increase the elasticity of the composition compared to its viscosity so as to render the composition stretchable at viscosities which are substantially reduced compared to what would otherwise be necessary for flow-stretch coatability.
Claims10
In a coating process in which a coating composition is forced at a given linear rate out of a narrow extrusion orifice in the form of a ribbon and received on the surface of a continuously moving support spaced from said orifice a distance of about 0.5-1.5 mm, said support travelling at a linear rate of 2-30 times the rate of extrusion of said ribbon, whereby said ribbon is stretched at the same rate in the range of 2-30 times and correspondingly attenuated as it is laid upon said web the improvement wherein said coating composition is aqueous and contains 2-20% by weight of gelatin, and the viscosity and elastic properties of said coating composition are adjusted by the inclusion therein of at least one viscoelasticity-enhancing agent in a proportion within the range of about 1-60% by weight of said gelatin and which is sufficient to impart to said coating composition a viscosity of from 136 to 1000 cps when measured at 38.degree. C. at a shear rate of 1735 s.sup.-1, and a modulus of elasticity .gamma. of 10 to 300 dyne/sq.cm when measured at 38.degree. C. and at 5 Hz, the corresponding range of the relaxation time .tau. being from 0.0045 to 1.0 s.
Dependencies are inferred from the claim text.