Porous roll fluid coating applicator and method

Metered application of coating materials, ranging from room temperature to hot melt coatings and adhesives, through the use of fluid-porous roll applicators operating singly or in multiple units for transfer or direct coating, including simultaneous continuous or intermittent patterns and simultaneous different weight pattern coatings or different material coatings.

The present invention relates to methods of and apparatus for applying or 
coating fluid materials, including but not restricted to hot melt type 
liquids and adhesives of a wide variety of viscosities, to surfaces 
(hereinafter generically referred to as webs), being more particularly 
directed to such coating with the aid of novel porous roll surfaces and 
the like. 
Various types of hot melt and other fluid apparatus and coaters have been 
heretofore employed to provide continuous, intermittent and patterned 
coatings upon web surfaces, including slot nozzle applicators employed 
with metered pumped fluid supply systems, as described in my earlier U.S. 
Pat. Nos. 3,595,204, and 4,277,301, and commutating cylindrical apparatus 
as in U.S. Pat. No. 3,294,060. 
Underlying the present invention, however, is the discovery that great 
flexibility in coating can be obtained through metering the fluid through 
a porous cylindrical shell or roll, enabling both ready direct and 
indirect or transfer coating of one or multiple hot melt or room 
temperature fluids, including hot melts of high viscosity, and with 
reduced pressure drops over prior art techniques, and in continuous, 
intermittent or patterned coatings at will. 
An object of the present invention is to employ the features of this 
discovery to provide, accordingly, a novel method of and apparatus for 
fluid application that enables such and other improved operation through 
the use of porous roll fluid-metering coating. 
A further object is to provide such a new and improved coating applicator 
that enables, also, simultaneous pattern coatings and stripes of different 
fluid coat weights; continuous, pattern and stripe simultaneous coatings 
of dissimilar fluid coating materials; and successive and superimposed 
fluid coatings. 
Other and further objects will be explained hereinafter, such being more 
particularly delineated in the appended claims. 
In summary, from one of its broad viewpoints, the invention embraces a 
method of coating a web with fluid material, that comprises, pumping such 
fluid material with one of continuous and intermittent metered flow along 
a predetermined longitudinal path, exiting the same at a region transverse 
thereto, receiving the transversely exited fluid in a reservoir volume 
extending along and enveloping said path, exiting the fluid from said 
reservoir volume through a porous surface co-extensive with and bounding 
said reservoir volume, relatively rotating the said porous surface and the 
said region of fluid exiting from said path, and applying the fluid 
longitudinally exited through the porous surface to said web while moving 
the web transversely past the same to coat the web with the fluid as 
metered through the pores of the porous surface. In apparatus form, the 
invention contemplates fluid coating apparatus having, in combination, 
means for continuously or intermittently pumping the coating fluid along a 
longitudinally extending conduit terminating in an opening adjusted for 
transversely exiting the fluid, a cylindrical annular reservoir volume 
enveloping the conduit and its opening for receiving the exited fluid, a 
cylindrical porous shell externally bounding the cylindrical reservoir to 
constitute a fluid dispensing roll, means for relatively rotating the 
conduit and its fluid exiting opening and the roll to cylindrically 
distribute the exited fluid along the reservoir volume, and means for 
rotating said roll and applying the fluid dispensed through the porous 
shell to web means drawn transversely past the roll. Preferred and best 
mode embodiments and modifications are hereinafter detailed.

Referring to FIGS. 1A and 1B, a preferred porous roll applicator 
construction is illustrated for continuously or intermittently pumping the 
coating fluid from a single supply port at a rotary joint union 2 along a 
longitudinally extending conduit 2' terminating in a transversely radially 
extending opening 2" within a cylindrical inner supply roll conduit 4--the 
inlet 2' extending preferably axially along the roll 4 and the opening 2" 
exiting fluid transversely therefrom. A coaxial cylindrical annular 
reservoir cavity or volume 6 envelops the inner roll conduit 4 and 
receives the exited fluid at 2". The reservoir volume 4 is coaxially 
externally bounded by a cylindrical porous shell 8, as of sintered metal, 
screening or the like, as later more fully described, with the conduit 4 
and its fluid exiting opening 2" being relatively rotatable to distribute 
the fluid within and along the reservoir to keep the same filled and 
applying fluid uniformly longitudinally along the porous shell 8. The 
porous shell may, for example, be of uniform sintered metal construction, 
say 20 micron pores, as in FIG. 3A, or may employ multiple varying or 
different porosity (and weight) shells as in FIG. 3B, such as a 10 micron 
outer shell occupying, say, 10% of the total shell thickness, and a 100 
micron inner concentrate shell portion of 100 microns, constituting the 
balance of the shell thickness. The differential micron construction will 
reduce the pressure drop for high viscosity materials such as 
10,000-30,000 cps at room temperature, when metered through the porous 
metal shell. The outer surface of the porous shell roll 8 may be varied 
not only in degree of porosity, but also in surface preparation or extent, 
as at 8' in FIG. 1A, to introduce predetermined patterns in the coating, 
such as the repeat coating horizontal stripes or longitudinal side stripes 
and intermittent horizontal stripes of FIG. 4A. The patterns may be 
metered into the surface of the roll by special etching after the surface 
pores have been machined closed. 
While porous sintered metal cylinders have heretofore been used for the 
very different applications of air film as bearing rolls, wicks and filter 
cartridges and the like, suitable sintered stainless steel, Monel and 
similar porosities of 10, 20 or 40 microns in shell thickness of the order 
of 3/8 inch have been successfully employed for this very different usage 
as a viscous fluid metering coating roll. Among such are the Series 1400 
of Mott Metallurgical Corporation of Farmington, Conn. This unique usage 
is more clearly delineated in FIGS. 5A and 5B, showing the porous 
apparatus roll 8 used for transfer and direct coating to moving webs, 
respectively. In FIG. 5A, the porous roll 8 is rotated in contact with a 
rubber-coated steel mandrel or similar applicating roll 10 that transfers 
the coating fluid from the porous dispensing roll 8 to the web 
(so-labelled) as it moves between the roll 10 and the lower laminating 
roll 12, rotating oppositely to the roll 10. The laminating roll insures 
positive web contact against the applicating roll for fluid transfer. The 
porous roll 8 rotates oppositely to the transfer or applicating roll 10 
and preferably either with the same surface speed thereof or synchronously 
therewith, or proportional thereto (including fractional speed). The 
applicating roll operates at web speed or at a slightly less speed to 
create a smeared surface. Typical speed can be as low as 95% of web speed. 
In FIG. 5B, on the other hand, the porous roll 8 itself directly contacts 
the web as the same moves between the roll 8 and an oppositely rotating 
lower laminating roll 12 which insures positive contact of the web with 
the porous roll. In such direct coating usage, the porous roll 8 runs 
synchronous to the web speed for pattern print coating; or at a slightly 
less speed for full width coating or continuous stripes (longitudinal in 
web direction) to create a smeared surface. The systems of FIGS. 5A and 5B 
permit full, or continuous, stripe and pattern coatings in single weight 
coats. 
A more complete system for that schematically shown in FIG. 5A is shown in 
FIG. 6 applied to the illustrative example of hot melt adhesives as of the 
types described in said patents or other well-known coatings of this type, 
fed from a hopper 1 through a filter 3 to a positive displacement metering 
pump 5 (such as that of said patents) to supply fluid at 7 to a three-way 
valve 9 (as, for example, of the type described in my U.S. Pat. No. 
4,565,217) that supplies the rotary union inlet 2 of the porous roll 
system 8. A return feed back to the filter input is shown at 11. The 
metering pump 5 is controlled by a digital pump drive 13 which is 
connected to a web reference magnetic pick up sensor 15 contacting the web 
to synchronize the pump speed with the web speed. Examples of full or 
continuous coatings and continuous longitudinal stripe and intermittent 
horizontal stripe patterns are shown in FIGS. 7A and 7B. 
Multiple width porous roll applicators may also be provided as shown in 
FIG. 2, illustrating multiple inlet supply ports and rotary union 2, 
multiple width successive inner supply rolls 4, with successive section 
separators 4' between adjacent rolls separating the respective successive 
reservoir cavities and porous roll shell sections. FIG. 4B illustrates 
typical exemplary multiple width repeat coating patterns. 
Turning to the before-mentioned flexibility of the invention to enable 
stripe or other pattern coatings of different coat weights simultaneously 
or full, stripe or pattern coatings of dissimilar fluid coating materials 
simultaneously, reference is made to the schematic application 
modification of FIG. 5C, dealing with such differential or different 
material coatings. This design would permit stripes or pattern coatings of 
different coat weights simultaneously. The combination of two porous rolls 
permits applying layer upon layer of two identical or dissimilar fluids 
side by side, or the same fluid applied at different coat weights, to meet 
a specific customer coating pattern. In FIG. 5C, the porous roll 8 (with a 
pattern #1, for example) is shown contacting one upper side portion of the 
oppositely rotating applicator roll 10 between which and the laminating 
roll 12, the web is moved. A second porous roll 8' (pattern #2 or 
different coating weight or material, for example) simultaneously contacts 
the opposite side of the applicator roll 10. The porous rolls 8 and 8' can 
run synchronously with or at fractional differential speed to the 
applicating roll 10 which, in turn, may, if desired, run at a fractional 
differential speed to that of the web. 
A complete system for such different material or differential operation is 
shown in FIG. 8, wherein the second porous roll 8' is shown fed from a 
second positive displacement metering pump 5', feeding at 7' a second 
3-way valve 9' for inputting the second porous roll assembly 8', and with 
a return line 11' to the input of the filter 3. The pump 5 feeding the 
porous roll 8 is shown as a dual discharge metering pump with supply lines 
7 and 7A. FIG. 9 illustrates an exemplary pattern coating of intermittent 
differential weight stripe (supply line 7'--say, 2 mil coating) and 
continuous longitudinal side stripes (supply lines 7 and 7A--say, 1 mil 
coating). 
As previously noted, the flexibility of the invention also extends to 
multiple coatings of two different fluid coating materials, one over the 
other as in FIG. 11. The system of FIG. 10 enables this with a structure 
similar to that of FIG. 8, but involving separate material hoppers 1 and 
1' and pumps 5 and 5', as shown for the different fluid materials. 
The porous roll applicating technique of the invention is useful with 
room-temperature liquids and with hot melt type liquids, at operating 
temperatures of 350.degree. F., and fluid coating applications of other 
temperature ranges. This can be accomplished by installing heating 
elements within the porous roll assembly, or using the porous metal 
material 8 as an electrical conductor/resistor, receiving heating current. 
Typical material used for resistance heat would be Nichrome metal. 
Industrial applications for hot melt pattern coatings are required, for 
example, in the cigarette industry. Typically, the attachment of the 
filter covering paper, known as tipping paper, joining the filter element 
to the cigarette, requires parameter/rectangular adhesive pattern with the 
center area open, without adhesive. Present cigarette making machines are 
operating up to 7,000 cigarettes per minute, which represents the drying 
limitation of conventional polyvinyl resin adhesive. Any further increase 
in line speed prevents succesful adhesive attachment and drying of the 
cigarette components. Hot melt coating used with the present invention in 
place of the resin adhesive permits a further increase in production 
speed. The hot melt will be applied at a low coating thickness, such as 1 
mil, in order to obtain satisfactory bond of the cigarette components. 
In addition to coatings previously described, the invention is particularly 
useful with room temperature materials such as silicones, polyvinyl 
acetates and other adhesive coatings, and with hot melts such as the 
etholene vinyl package sealing materials. 
Further modifications will also occur to those skilled in this art, and 
such are considered to fall within the spirit and scope of the present 
invention as defined in the appended claims.