Method and apparatus for applying a plurality of superposed layers to a web by curtain coating

Claim 2

In a method of applying to a travelling web a plurality of layers of at least one flowable composition, comprising moving said web along a predetermined pathm, delivering such flowable compositions to a plurality of slot-like orifices to form a plurality of distinct flowing layers of such compositions, flowing said layers into face to face contact with one another to form a composite layer and delivering said composite layer as a free-falling curtain onto said web at a locus extending transversely of said path, said curtain being held in said locus by adherent contact of its lateral edges with curtain guides, said curtain falling on said moving web, the improvement wherein at least one of said plurality of layers has a width greater than the width of the web, and at least one of said plurality of layers has a width smaller than the overall width of the curtain whereby at least one but not all of said plurality of layers are in adherent contact with the curtain guides.

Claim 3

Method according to claim 1, wherein the width of the portion of the curtain that contains all layers is substantially equal to the width of the web.

Claim 4

Method according to claim 1, wherein the width of the portion of the curtain that contains all the layers is smaller than the width of the web.

Claim 5

Method according to claim 3, wherein the web has knurled marginal regions and said width of said portion of the curtain corresponds with the width measured on the web between said knurled marginal regions.

Claim 6

Method according to claim 1, wherein only one layer of the composite curtain has a width sufficient to contact its lateral edges with the curtain guides, all the other layers have a lesser width.

Claim 7

Method according to claim 5, wherein the portion of said one, broader layer that overflows the edges of the web is collected and recirculated.

Claim 8

Method according to claim 5, wherein the rate of flow of said one layer of greater width is greater at the edge regions of the curtain than at the central region of the curtain.

Claim 9

Method according to claim 1, wherein the surface tension of the composition of each layer having a width greater than the web is higher than the surface tension of the composition of each layer of lesser width, thereby to obtain a curtain profile with diverging edges for the region of the curtain containing layers of both widths.

Claim 10

Method according to claim 1, wherein the viscosity of each layer of greater width exceeds the viscosity of each layer of smaller width.

Claim 11

In an apparatus for applying to a moving web a plurality of layers of at least one flowable composition, which comprises means for moving said web along a predetermined path, a plurality of elongate slot-like orifices, means for delivering to such orifices said flowable compositions to form a plurality of distinct flowing layers thereof, means for bringing the layers of coating compositions that have been formed by the flowing of such compositions through said orifice into superposed contact with each other to form a composite layer, and means for delivering the composite layer onto said moving web as a free-falling curtain at locus extending transversely of said path, and curtain guides at the lateral limits of said locus for adherent contact with the lateral edges of said curtain, the improvement wherein at least one of said plurality of slot-like orifices has a length that is substantially equal to the initial distance between the curtain guides, and at least one of said plurality of slot-like orifices is smaller in length than said distance between said guides.

Claim 12

In an apparatus for applying to a moving web a plurality of layers of at least one flowable composition, which comprises means for moving said web along a predetermined path, a plurality of elongate slot-like orifices, means for delivering to such orifices said flowable compositions to form a plurality of distinct flowing layers thereof, means for bringing the layers of coating compositions that have been formed by the flowing of such compositions through said orifice into superposed contact with each other to form a composite layer, and means for delivering the composite layer onto said moving web as a free-falling curtain at locus extending transversely of said path, and curtain guides at the lateral limits of said locus for adherent contact with the lateral edges of said curtain, the improvement wherein at least one of said plurality of slot-like orifices has a length that is substantially equal to the initial distance between the curtain guides, and at least one of said plurality of slot-like orifices is smaller in length than said distance between said guides.

Claim 13

Apparatus according to claim 10, wherein one slot-like orifice alone has a length that equals the distance between the curtain guides, all the other orifices being of lesser length.

Claim 14

Apparatus according to claim 10, wherein at least one orifice having a length that corresponds with the initial distance between the curtain guides has edge regions of increased orifice thickness thereby to produce in operation a rate of flow of composition through the edge region of such orifice that is greater than the rate of flow through the corresponding central region of said orifice.

Claim 15

Apparatus as in claim 10, wherein the centers of said plurality of orifices are disposed in one common central plane.