A method for simultaneously coating multiple thin layers of relatively viscous fluids comprises the adjustment of the pressure gradients in the interface region between two confluent flows. In particular, the pressure gradient along the middle lip is regulated so as to not be excessively positive, in order to position the separating line of the top flow at a particular point on the die lips, thus enhancing stable flow. In one aspect of the method, a step configuration is designed into the die lips so that the downstream lip steps away from the web in the direction of web travel. In another aspect of the method, the pressure gradient at various locations in the bead is controlled by beveling the upstream and downstream lips. In yet a further aspect of the present method, the viscosities of the two liquids being coated are matched at the relevant shear rates to promote good coating quality.
A multilayer coating method is disclosed. The viscosity of an uppermost layer coating composition is adjusted to at least 0.1 Pa.s during coating, while the viscosity of the other layer coating composition is adjusted to at least 0.03 Pa.s, and a plurality of organic solvent-based coating compositions are coated onto a support employing wet on wet.
There is provided a coating method in which an extrusion-type coating head having a plurality of doctor edge surfaces is pressed onto a flexible support laid and running between pass rollers so as to coat the flexible support with a coating composition ejected from a slit, the method comprising the steps of: preparing a lower-layer coating composition so as to have a viscosity of not less than 1 P at rest and a viscosity of not more than 50 cP at a shear rate of 10,000 sec.sup.-1 ; excessively applying the lower-layer coating composition to a surface of the support; scraping a surplus of the lower-layer coating composition by the coating head so that a lower layer is formed; and applying an upper-layer coating composition, which is ejected from the slit, onto the lower layer.
A method of slot extrusion coating is provided that can be used to apply thin coatings using liquid compositions having high percent solids. A window of operability advantageously identifies the limits of a process to provide these thin high solids coatings. The window of operability is determined by obtaining a first graphical curve representing actual values of wet thickness as a function of percent solids level. The critical wet thickness is then identified on the first graphical curve. The window of operability is identified as an area defined by the boundaries: percent solids greater than the point at which critical wet thickness occurs, an actual wet thickness greater than all points above the first graphical curve and equal to or less than the critical thickness.
A method of designing and the resulting thermally stable heated coating die apparatus, the die apparatus including a die having a die geometry and a heating system with heaters and temperature sensors. The method and resultant apparatus provides minimized temperature gradients, flat die lip faces in a die to roll plane and a flat die in a plane perpendicular to die flat lip faces and parallel to substrate width. The method optimizes simultaneously: die geometry, placement of the heaters, placement of temperature sensors, and shielding from operating conditions, using heat transfer and structural numerical modeling and statistical analysis while considering die functionality characteristics, minimum increment of temperature measurement and control accuracy related to minimum acceptable deviation from flatness, coating die material of construction relative to thermo-structural material properties, and desirable coating die material properties.
A method of designing and the resulting thermally stable heated coating die apparatus, the die apparatus including a die having a die geometry and a heating system with heaters and temperature sensors. The method and resultant apparatus provides minimized temperature gradients, flat die lip faces in a die to roll plane and a flat die in a plane perpendicular to die flat lip faces and parallel to substrate width. The method optimizes simultaneously: die geometry, placement of the heaters, placement of temperature sensors, and shielding from operating conditions, using heat transfer and structural numerical modeling and statistical analysis while considering die functionality characteristics, minimum increment of temperature measurement and control accuracy related to minimum acceptable deviation from flatness, coating die material of construction relative to thermo-structural material properties, and desirable coating die material properties.
