Preparation of film of web-reinforced photopolymerized hydrophilic interpolymer

A process is taught in which a flexible, reinforcing travelling web may be uniformly, thinly transfer-coated, on both sides of the web simultaneously, with a low-viscosity liquid or mixture of monomers which may or may not wet the web, but does not wet the surface of a substrate on which the web and mixture are deposited. The liquid or mixture is first curtain-coated on an applicator curtain against which the web moves in controlled contact. An apparatus is provided for transfer-coating a travelling web with a low-viscosity liquid which is first curtain-coated on an applicator curtain.

BACKGROUND OF THE INVENTION 
This invention relates generally to an apparatus and process for 
transfer-coating a low-viscosity polymerizable liquid from a 
curtain-coated applicator means to either a thin, delicate open-mesh or 
batte web which is embedded in a uniform liquid layer of substantially the 
same thickness as the web, and the liquid is then polymerized; or, to a 
continuous web forming a backing for the liquid. 
This invention particularly relates to the production of a thin, 
web-reinforced sheet or film useful in applications which capitalize on 
the unique properties of a hydrophilic interpolymer. Monomers which are 
polymerized to form the interpolymer may be coated on a thin film of 
corona-treated polyolefin, specifically polyethylene, which is wetted by 
the monomers. Alternatively an open-mesh web or net of a polymer which is 
not wetted by the monomers confines them so as to envelop the net which 
provides reinforcing for the interpolymer. 
Such an interpolymer may be prepared by the copolymerization of a 
low-viscosity liquid mixture of monomers comprising (a) an unsaturated 
carboxylic acid and (b) a salt of the unsaturated carboxylic acid in which 
the majority of the carboxylic groups has been neutralized with an alkali 
metal hydroxide or ammonium hydroxide, in the presence of one or more of 
the following monomers selected from the group consisting of (i) a higher 
alkyl (meth)acrylate (that is, acrylate or methacrylate), (ii) a lower 
alkyl (meth)acrylate, (iii) an alpha-olefin having from 6 to about 18 
carbon atoms, styrene or a substituted styrene, (iv) a cross-linking agent 
which contains two or more ethylenic unsaturations, and (v) 2-hydroxyethyl 
methacrylate or dialkylaminodialkyl (meth)acrylate. These interpolymers 
are known to absorb water and body fluids such as urine and blood, 
rapidly, as disclosed in U.S. Pat. No. 4,167,464, and copending patent 
applications Ser. Nos. 183,616; 389,822; and 427,325, the disclosures of 
which are incorporated by reference thereto as if fully set forth herein. 
The problem is that utilization of these desirable properties of the 
interpolymer is thwarted by the difficulty of incorporating it in a 
product with a suitable woven fabric or non-woven batte made from textile 
fibers because of the peculiar, particular properties of a mixture of 
monomers from which the interpolymer is formed. The term "mixture of 
monomers" is used herein even when the polymer is formed from (a) acrylic 
acid and (b) an alkali metal or ammonium acrylate, and such polymer is 
referred to herein as an interpolymer as these monomers are distinct from 
each other. 
By "fibers" we refer to filamentous elements which are organic natural 
fibers or synthetic fibers such as those produced from spinnerets which 
fibers may be used to form a batte of random or oriented fibers, or to 
form yarn which in turn may be woven into a fabric or netting. In addition 
to the peculiar property of low-viscosity, the liquid has a high 
proclivity to polymerize in the nozzle of a spray gun from which it is 
sprayed, making spray-coating a web of fabric impractical. 
In practice, the interpolymer is prepared by photopolymerizing, preferably 
in the presence of a photoinitiator and a dispersant, (a) from about 10 to 
about 60 percent by weight (wt. %) of acrylic acid, (b) a salt formed by 
neutralization of 40 to 90% of the acrylic acid with an alkali metal 
hydroxide or NH.sub.4 OH, and optionally, (i) less than 25 wt % of a 
higher alkyl (meth)acrylate wherein the alkyl group has from 10 to about 
30 carbon atoms; (ii) less than 30 wt % of a lower alkyl (meth)acrylate 
wherein the alkyl group has from 1 to 8 carbon atoms, a minor amount, or 
none, of the lower alkyl (meth)acrylate being replaced by (meth)acrylic 
nitrile or amide; (iii) hexene or styrene; (iv) less than 10 wt % of a 
cross-linking agent having two to six ethylenically unsaturated groups 
which can be copolymerized with acrylic acid by UV radiation; and (v) from 
5 to 35 weight percent of 2-hydroxyethyl methacrylate or dialkylaminoalkyl 
(meth)acrylate in which each alkyl of the dialkyl groups has 1 to 8 carbon 
atoms, and the other alkyl group has 2 to 6 carbon atoms; so that the 
polymerized film formed contains in excess of 25% water. 
By a low-viscosity liquid mixture we refer to a liquid which has a 
viscosity in the range from about 2 to about 100 centipoises (cp), more 
specifically from about 8 to about 30 cp, which is referred to herein as 
being `non-viscous` because the mixture defies being coated, so as to form 
a continuous liquid layer, on many a substrate surface if it is not either 
`etched` or especially formed so as to restrict the run-off of the liquid. 
For example, even with the use of a surface active agent or dispersant, the 
mixture of monomers does not wet, but runs off, a laminar substrate of 
nylon, untreated polyester or polyolefin. With a dispersant included in 
the mixture, it wets paper, cotton, wool or polyester surfaces, but only 
with difficulty. A woven fabric of nylon or polyester fibers, such as a 
net, when dipped in the mixture and held so as to hang in a vertical 
position, retains almost none of the mixture even when the interstices of 
the net are only about 1 mm in diameter. Even a non-woven batte of nylon 
or polyester fibers is wetted with difficulty. The problem can best be 
visualized by comparing it to the problem of coating a net with 
concentrated sulfuric acid at room temperature, so that the acid uniformly 
fills the interstices of the net. 
To combat this problem, the '464 patent teaches the use of a wicking aid 
such as a glycol, to improve the rate at which the liquid moves along the 
fibers or film being coated, if the liquid wets them at all. However, even 
with a wicking aid, it is difficult to wet a horizontally supported 
reinforcing nylon net or non-woven nylon batte with the mixture of 
monomers, and we know of no prior art teaching as to how such reinforcing 
might be wetted sufficiently to embed it in a thin, substantially uniform 
liquid layer of the mixture. By "thin" we refer to a thickness from about 
2 mils to about 25 mils thick, and by "substantially uniform" we refer to 
such thickness .+-.20%. 
The addition of cross-linking agents may improve the strength of the 
polymer formed by the action of actinic radiation, but the use of a 
cross-linking agent in an amount sufficient to improve the wettability of 
the reinforcing material adversely affects the desirable properties of the 
polymer formed. Thus, to the extent such wettability may be improved, it 
is accomplished with a choice of dispersants. 
The '464 patent teaches that the interpolymer has particular utility in the 
disposable non-woven industry where there is a need for polymers which 
will absorb and retain water and physiological fluids. In a specific 
example, it teaches a disposable diaper in which fibers of the 
interpolymer, or non-woven agglomerates of its fibers may be included; or, 
in which diaper a film of the interpolymer may be used between a 
fluid-impermeable outer plastic layer and inner fluffy absorbent layer of 
the diaper. There is no teaching of the use of a reinforced film of the 
interpolymer, with the reinforcing web embedded intermediate the upper and 
lower planar surfaces of the film, because there did not exist a practical 
method of making such reinforced embedded film for use in a marketable 
article of commerce. The problem of coping with the peculiar physical 
properties of the mixture of monomers in which the reinforcing material is 
embedded by a method which forms a thin continuous film of the 
interpolymer, had yet to be solved. 
Numerous prior art methods have been devised for coating low viscosity 
liquids on substrates, each of which methods is directed to the solution 
of particular problems presented by the properties of the fluid to be 
coated and the substrate upon which it is to be coated. Brush-coating of a 
web is generally restricted to the application of relatively thick 
coatings of relatively viscous fluids having a viscosity greater than 100 
cp, is known to leave undesirable streaks and other non-uniformities with 
coatings less than 25 mils thick, and is therefore avoided in the coating 
of low-viscosity liquids. Further, when the web is an easily unraveled 
batte, or an easily distorted net of a filament from about 1 mil to about 
10 mils thick, maintaining the integrity of the web becomes a critical 
consideration. 
Most methods for coating low-viscosity liquids in which a web is embedded 
are directed to the production of textiles or textile-like fabrics which 
are unrelated to the web-reinforced articles of this invention both in 
appearance and in function. Moreover, these methods are directed to the 
curtain-coating of a controlled thickness of a polymerizable non-viscous 
fluid, in the range from about 2 mils to about 25 mils, on to a travelling 
web; very few of these are directed to the further problem of stripping or 
delaminating the reinforced polymer film from a substrate not wetted by 
the fluid and upon which substrate the polymer is formed. To our 
knowledge, no prior art method useful for coating a controlled thickness 
of a low-viscosity liquid teaches the use of a stationary curtain-coated 
(with the liquid) applicator curtain with the specific purpose of 
transferring a thin coating to a moving web. 
Stated differently, knowing that a thin net or batte (web) cannot be coated 
uniformly with a thin layer of the non-viscous mixture of monomers by 
being dip-coated, or spray coated, or coated from a transfer roll, knife 
over-roll, squeeze roll, or reverse roll such as are conventionally used 
for relatively low-viscosity liquids, and knowing the mixture cannot be 
coated on the thin web by rotagravure coating as is routinely done with 
low-viscosity inks and the like, the particular problem is to embed the 
web, which is wetted by the mixture, in a substantially uniform liquid 
layer from 2 to about 25 mils thick while the web is supported on a 
substrate. In an additional step, after the woven or non-woven web of 
reinforcing material is embedded in the non-viscous mixture, then 
polymerized, the reinforced interpolymer film must be parted from the 
substrate upon which it is polymerized. 
The uniform flow of liquid from weir-like structures including a reservoir 
from which a moving web is coated, the direction of movement of the web 
being transverse to the longitudinal axis of the reservoir, has been 
considered generally difficult to control. Conventional reservoirs with a 
weir, and a curtain supplying liquid across the weir, are known to produce 
non-uniform flow across the length of the weir, which proscribes their use 
where uniformity is essential. Such reservoirs are also known to be 
sensitive to pulsing of the liquid flowed into the reservoir, which 
proscribes their use where a thin film is to be curtain-coated on a web. 
Accordingly, the conventional weir-like structure has been replaced with 
structures such as those disclosed in U.S. Pat. Nos. 3,365,325 and 
3,369,522. 
More recently, U.S. Pat. Nos. 3,587,527; 3,911,174; 4,019,906; 4,075,976; 
4,178,221 and 4,197,812 address particular curtain-coating problems, and 
how they may be solved by obviating the conventional weir-type structure, 
the tendency of droplet formation with a curtain which does not terminate 
in a knife-edge, and other problems. Though none of the disclosures is 
particularly directed to curtain-coating with a low-viscosity liquid, and, 
examples provided are of liquids having substantially higher viscosities 
than 100 cp, it is clear that one skilled in the art when faced with the 
particular aforementioned problems, would not be led to use a curtain 
coated web as an applicator from which the liquid is to be transferred to 
another web. 
Reverting to the '464 patent, it is stated that a film of the monomer 
mixture can be spread on the surface of a suitable substrate to the 
desired thickness, e.g. 1 mil to 25 mil, and then subjected to UV 
radiation for a short time, e.g. 1 second to several minutes. Substrates 
mentioned are Mylar, polyethylene, and paper, inter alia, but it was not 
recognized that the monomer mixture wetted only etched polyethylene and 
that non-corona treated Mylar.RTM. was not wetted at all. Therefore, on 
such non-wettable surfaces, the mixture of monomers cannot be spread by 
conventional methods such as with a Boston-Bradley adjustable blade or by 
spraying. 
Further, since from a practical standpoint, the polymer is formed by 
exposure to UV radiation at a sufficient intensity to effect a cure in a 
short time in the range of from about 20 sec to about 40 secs, it is 
essential that the reinforcing material be substantially permeable to the 
UV radiation. By "substantially permeable" we mean that not enough UV 
radiation is absorbed by the mass of fibers to deleteriously affect their 
properties or those of the interpolymer formed. For example, paper and 
natural organic fibers get too hot to be useful as reinforcing material. 
Thus, to our knowledge, the problem of polymerizing a uniform, thin, 
continuous liquid layer of a non-viscous mixture of plural monomers by 
exposure to ultraviolet radiation, or electron beam radiation where the 
polymer formed is to be reinforced with a substantially uv-permeable 
reinforcing material, is a novel problem which has not been successfully 
solved. 
SUMMARY OF THE INVENTION 
It has been discovered that a flexible reinforcing travelling web may be 
uniformly, thinly transfer-coated, on both sides of the web 
simultaneously, with a low-viscosity liquid such as a mixture of monomers 
which may or may not wet the web, but does not wet the surface of a 
substrate support or conveyor on which the web and mixture are deposited, 
if the mixture is first curtain-coated on an applicator curtain against 
which the web moves in controlled contact. An apparatus is provided for 
transfer-coating a travelling web with a low-viscosity liquid which is 
first curtain-coated on an applicator curtain. 
It has further been discovered that a travelling web, particularly an 
open-mesh web, which has been transfer-coated as described immediately 
hereinabove may then be photopolymerized by intense uv-radiation, if flow 
of the mixture on the substrate support or conveyor is restricted by the 
web, and the web is substantially permeable to the uv-radiation used, 
though the open-mesh web is formed from a polymer which is not wetted by 
the mixture. 
It is accordingly a general object of this invention to provide a process 
for embedding a thin, easily distorted or unraveled web in a substantially 
uniform thin liquid layer from about 2 to about 25 mils thick, the liquid 
being characterized as having a viscosity in the range from about 2 cp to 
99 cp. Such a process is also applicable to coating a thin corona-treated 
polyethylene film with such a layer which upon polymerization forms a thin 
hydrophilic film backed by the polyethylene film. 
It is another general object of this invention to provide a 
transfer-coated, web-reinforced photopolymerized film of uniform thickness 
made from at least two photopolymerizable monomers present as a mixture 
confined by the web which is placed on a conveyor, though the mixture does 
not wet either the web or the conveyor. 
It is a more specific object of this invention to provide a net-supported 
film from about 2 to about 15 mils thick, of a hydrophilic interpolymer 
formed by uv-radiation curing (polymerization), preferably in the presence 
of a photoinitiator and a dispersant, of a mixture of (i) about 50 to 90 
percent by weight (wt %) of acrylic acid in which from 60 to 90% of the 
carboxylic groups have been neutralized with an alkali metal hydroxide or 
NH.sub.4 OH, (ii) 0 to 25 wt % of a higher alkyl (meth)acrylate wherein 
the alkyl group has from 10 to about 30 carbon atoms, and, (iii) 0 to 30 
wt % of a lower alkyl (meth)acrylate wherein the alkyl group has from 1 to 
8 carbon atoms, 0 to 50% of said lower alkyl (meth)acrylate being replaced 
by (meth)acrylic nitrile or amide. 
It is another specific object of this invention to provide a novel 
apparatus for the purpose of curtain-coating an applicator curtain from a 
reservoir with a weir-like structure, so that a low-viscosity liquid 
having a viscosity greater than 2 cp but less than about 100 cp, 
gravitatingly flowed along the applicator curtain, can then be 
transfer-coated upon a travelling web such as a net while the net is 
supported on a moving substrate, though the mixture does not wet either 
the net or the substrate, and which apparatus effectively produces a 
substantially uniform liquid layer of the mixture in the range from about 
2 to about 25 mils thick, in which liquid the net is submerged. 
It is still another specific object of this invention to provide an 
oxygen-permeable burn-wound dressing which has particularly desirable 
properties with respect to the transport and absorption of body fluids 
generated in proximity to the wound, for which dressing it is critical 
that the thickness of the reinforced film be in the range from about 2 to 
about 25 mils. 
It is a further specific object of this invention to provide an article for 
personal use, such as a diaper, sanitary napkin or the like, comprising a 
woven or non-woven synthetic fiber web which physically confines a mixture 
of monomers to be photopolymerized, though the web is formed from a 
polymer not wetted by the mixture and absorbs none of the mixture; which 
web when embedded in the interpolymer must have a substantially uniform 
thickness of from 2 to about 25 mils; and, when the web is a net, because 
the net is uv-permeable, it functions as a reinforcing material which 
physically confines the mixture of monomers to prevent its flow so that it 
can be uv-radiation-polymerized without deleteriously affecting the 
reinforcing material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In one preferred embodiment, this invention relates generally to embedding 
a thin delicate open-mesh web ("net") in a uniform layer of low-viscosity 
liquid, having a viscosity in the range from about 2 cp but not exceeding 
100 cp; after which the liquid-embedded net may be treated as desired. The 
net may be formed from a polymer the surface of which is wetted by the 
liquid, in which case the liquid is held in and around the net by surface 
tension and other forces, facilitating the embedding of the net in the 
liquid. Alternatively, the net may be formed from a polymer the surface of 
which is not wetted by the liquid, as is the case with polyethylene, 
polyester and nylon net, yet the liquid is physically confined within and 
around the net. In the most preferred embodiment, such non-wetted nets are 
preferred for their strength and a process is taught for continuously 
producing a net-reinforced, thin polymeric sheet or film, particularly 
useful as a burn wound dressing or sanitary napkin, by using a known 
interpolymer composition in a UV-fiber-fixable process. By 
"UV-fiber-fixable process" I refer to a process in which the interpolymer 
adheres to certain natural or synthetic resinous fibers forming the web, 
and which will bond these plural fibers together, the interpolymer being 
formed when a mixture of plural monomers is exposed to UV radiation and 
which interpolymer after being so fixed, may be removed from a substrate 
on which it is formed because the monomers do not wet the substrate, 
whether or not they wet the net. Stated differently, the release property 
of the UV-polymerized interpolymer is attributable to the surface of the 
substrate upon which it is formed and not to the effect of a particular 
component of the interpolymer. 
The fibers may be of any material desired, such as wool, glass, or 
cellulosic materials including cotton, rayon, and wood pulp, but are 
preferably the synthetic fibers produced from fiber-forming polymers 
including polyamides, polyacrylonitrile, polyesters, polyurethanes, 
polyethylene, polypropylene, polyvinylidene chloride and the like, as long 
as the fibers of the web (net or batte) are substantially permeable to UV 
radiation. Since both the natural and synthetic fibers, if present either 
in substantial bulk and density as a batte or as a yarn heavier than about 
10 mils in diameter to form the net, are generally not sufficiently 
UV-permeable under the conditions of UV-polymerization used in a 
commercial process, the web used herein is necessarily a delicate batte or 
net. 
By "delicate" batte we refer to a batte which can be unraveled or pulled 
apart with a force of 8 ounces or less, exerted by attaching a weight by 
means of a clamp 1 inch wide to the hanging batte. Typically, such a batte 
will weigh less than 50 g/m.sup.2, and preferably from about 10 to about 
25 g/m.sup.2. By "delicate" net we refer to a net formed with a filament 
from about 45 to about 150 denier, or 2 to about 10 mils in diameter, and 
preferably from 2 to 5 mils in diameter, the interstices of the net being 
in the range from about 5 mils to about 0.25 inch in diameter, and the net 
is easily visibly distorted by a force of 8 ounces or less, exerted as 
before. 
Since the fibers, whether woven as a net or non-woven as formed in a random 
or oriented batte, are embedded, that is completely submerged, in the 
interpolymer, the surface area of the interpolymer where it is in contact 
with the fibers, when added to the remaining surface area of the 
interpolymer including that area which is exposed to the atmosphere, is 
greater than the surface area of the fibers. This physical criterion, 
along with the appearance of the reinforced interpolymer film, serves to 
distinguish the reinforced article formed by the process of this invention 
from prior art reinforced articles in which the interpolymer was used. For 
example the interpolymer was formed on a continuous corona-treated 
Mylar.TM. polyester film, or etched polyethylene film, which formed a 
backing (substrate) for one planar surface of the interpolymer. 
It is generally preferred to prepare a thin web of non-woven batte of 
fibers using a continuous fiber technique as shown in Belgian Pat. No. 
608,646, or by the use of short lengths of fibers, that is, fibers having 
an average length of about 0.125 to about 0.5 inch, and the fibers are 
placed horizontally so that the thickness of the batte is less than about 
25 mils. If the thickness of the batte is more than 25 mils it may be 
compressed to a predetermined thickness in the range from about 2 to about 
25 mils, from 2 to about 10 mils being more preferred. 
Through fibers may be used as a non-woven batte in this invention, it is 
preferred to employ a yarn made from synthetic fibers, which yarn is woven 
or otherwise formed into netting preferably having interstices in the 
range from about 10 mils to about 50 mils in average diameter, the yarn 
itself having a diameter corresponding approximately to the thickness of 
the liquid to be confined within and upon the net. Further description of 
the invention will be made with respect to the use of a nylon or polyester 
net reinforcement, these being the most preferred reinforcing materials. 
Referring now to the drawing, and particularly to FIGS. 1 and 2 thereof, 
there is shown a liquid reservoir means indicated generally by reference 
numeral 10 set transversely with respect to a longitudinally extending 
endless conveyor belt referred to herein as a conveyor S. Liquid L is 
pumped by a metering pump (not shown), the liquid entering through a 
supply tube 11 having plural through-passages 12 in open fluid 
communication with the interior of a walled trough 13 having a wall 14 
extending peripherally on three of its sides, and the wall is preferably 
reinforced exteriorly with angle iron 15 which may be used to mount the 
trough. The passages 12 serve to supply the liquid substantially uniformly 
along the length of the trough 13, near the bottom thereof. 
One transverse side of the trough provides a weir means indicated generally 
by reference numeral 20, formed by a transverse lip 21 having a flattened 
upper surface over which the liquid overflows substantially uniformly at a 
preselected rate set by the metering pump and correlatable to the 
thickness of the liquid layer in which a net 40 is to be embedded. A 
clamping means such as an elongated clamping plate 22 extends beneath the 
lip so as to clamp one transverse (upper) edge of an applicator curtain 
means 30 between the plate and lip 21 when clamping screws 31 are 
tightened. The applicator curtain 30 hangs vertically and is trained under 
a hold-down edge means 33, such as a wire or rod means. The wire or rod 33 
is positioned transversely to the direction of movement of the net 40 on 
conveyor S. The portion of the applicator curtain under the wire or rod 
extends in a horizontal plane as horizontal portion 36, coextensively upon 
the substrate S. Thus liquid L flowing over the lip 21 gravitates along 
the vertical portion 37 of the applicator curtain forming a curtain of 
liquid which is slowed as it descends, by the applicator curtain. 
A "feathering" member 35, preferably made from a strip of fabric, is draped 
across the lip 21 and is removably affixed thereupon, extending along the 
entire length of the lip 21, with the lower portion of the strip 35 in 
overlapping contact with the applicator curtain 30 along a smoothing zone 
38 contiguous to the lip. The feathering means thus serves to feather and 
distribute the overflowing liquid more uniformly across the vertical 
portion of the applicator curtain 30. Without the feathering means 35, 
liquid L overflowing the lip 21 is found to flow unevenly across the 
vertical portion of the curtain. 
The net 40 is fed along the surface of the conveyor S and in 
liquid-transferable contact with the applicator curtain 30. The height of 
the rod or wire 33 above the conveyor S is preset so as to be only 
slightly greater than the thickness of the net, so as to allow formation 
of a uniform liquid layer of preselected thickness. It is preferred to set 
the rod or wire at a height in the range from about 1 mil to about 5 mils 
greater than the thickness of the net as viewed in side elevation, and 
most preferred to set it about 1 to 2 mils greater. The conveyor S thus 
provides a means for continuously transporting the net 40 beneath and away 
from the reservoir to permit the transfer of a layer of liquid from the 
applicator curtain onto the net. 
Because the applicator curtain is preferably a woven fabric, the liquid L 
wets both sides of it and gravitates to the net 40, and is transferred to 
it substantially uniformly because of the peculiar wiping contact of the 
web 40 with the wetted applicator curtain 30 so a to form liquid-embedded 
net 42. 
To ensure even greater uniformity of the liquid layer in which the net is 
embedded so that both the upper and lower surfaces of the net are coated 
with a lamina of liquid, a dressing means 50, such as a roller, brush or 
pad, is disposed in contact with the upper surface of the horizontal 
portion 36 of the applicator curtain, the force exerted by the dressing 
means 50 being established by a little trial and error, as is expected to 
be done in the art. 
The net 40 travels from beneath the horizontal portion 36 embedded in an 
uniformly thin liquid layer, and as embedded net 42 travels to a 
subsequent processing step. In the most preferred embodiment the net 42 on 
the conveyor S is conducted under an intense UV radiation source having an 
intensity at least 100 watts/inch for a short period of time sufficient to 
form the interpolymer which coats all surfaces of the net. 
The quantity of liquid applied to the net is substantially correlatable to 
the thickness of the net to be embedded therein because the viscosity of 
the liquid is such that the liquid not held by the net will run off the 
net and the substrate's surface. Since a very thin layer of liquid less 
than about 1 mil thick is most preferably formed as a lamina both above 
and below the embedded net 42, the weight of the liquid always exceeds the 
weight of the net 40 and is generally several times greater, depending 
upon the physical properties of the web 40 and the liquid in which it is 
to be embedded. 
Since the mixture of monomers most preferred for use in this invention is 
essentially permeable to UV radiation, a photoinitiator is used such as is 
disclosed in the '464 patent, a preferred amount being in the range from 
about 0.1 to about 1% by wt of the liquid. In addition, there may be 
included an air cure promoter, cross-linking agents and the like, as is 
known in the art. 
In addition to the foregoing essential monomeric components of the mixture, 
minor amounts, that is, less than 5% by wt of the liquid, of additional 
monomers may be added to tailor the physical and chemical properties of 
the interpolymer. Among these additional monomers are 1,2-monoolefinically 
unsaturated nitriles, monoolefinically unsaturated amides including 
N-alkyl(meth)acrylamides, N-alkyol (meth)acrylamides, N-alkoxy 
(meth)acrylamides, and the like, disclosed in the '464 patent. 
If desired, pigments may be added to the liquid and also inert fillers such 
as talc, but it should be recognized that these absorb UV light to a 
greater or lesser degree, and will slow the curing process, and may heat 
the curing resin to an unacceptably high temperature. It is preferred to 
maintain the temperature during polymerization in the range from about 
65.degree. C. to about 130.degree. C., and a temperature in the range from 
70.degree. to 90.degree. C. is most preferred. 
Any commercially available medium pressure mercury (Hg) lamp source of 
radiation in the range from about 2000 .ANG. to about 5000 .ANG., which 
supplies from about 100 to about 300 watts/in is preferred for exposing 
the liquid, and the irradiation may be accomplished in stages if so 
desired. The atmosphere during irradiation may be an inert gas, but air is 
preferred. Since the UV source and means for exposing the web 42 are well 
known in the art, no further details are necessary and are not illustrated 
in the drawing. 
In the best mode, this invention is carried out with a polyester net on 
which an interpolymer is preferably formed with (i) acrylic acid in which 
from about 80 to 100% of the carboxylic groups have been neutralized; (ii) 
a higher alkyl (meth)acrylate having the structure 
##STR1## 
wherein R.sup.1 represents hydrogen or methyl, and R.sup.2 represents 
alkyl having from about 10 to about 18 carbon atoms, for example, isodecyl 
methacrylate, lauryl methacrylate, stearyl methacrylate and the like; 
(iii) a lower alkyl (meth)acrylate having the structure 
##STR2## 
wherein R.sup.1 has the same connotation as hereinabove, and R.sup.3 
represents alkyl having from 1 to about 8 carbon atoms, for example, 
methyl acrylate, ethyl methylacrylate and the like, present in an amount 
in the range from about 7 to about 17 wt % of the mixture of monomers, a 
minor portion of which lower alkyl (meth)acrylate may be replaced with 
(meth)acrylic nitrile or amide; and, (iv) from about 0.01 to about 5 wt % 
of a photoinitiator. 
Another low-viscosity mixture of monomers consists essentially of 
(a) 90 to 99.9wt % of acrylic acid in which 50 to 100 percent of the 
carboxylic groups have been neutralized with an alkali metal or ammonium 
hydroxide prior to polymerization, 
(b) 0.1 to 10 wt % of a cross-linking agent which contains two or more 
ethylenic unsaturations, 
(c) 0.01 to 5 wt % of a photoinitiator, based on the total weight of 
acrylic acid and cross-linking agent, and 
(d) a sufficient amount of water so that the resulting film contains 25 to 
45 wt % of water. 
Still another mixture of monomers consists essentially of 
(a) 70 to 95 wt % of acrylic acid in which from 70 to 100 percent and more 
preferably 80 to 100 percent, of the carboxylic groups have been 
neutralized with an alkali metal hydroxide or ammonium hydroxide prior to 
polymerization, and 
(b) 5 to 30 wt % of a comonomer selected from the group consisting of an 
alphaolefin having 6 to 18 carbon atoms, styrene or a substituted styrene. 
Yet another mixture of monomers consists essentially of 
(a) 65 to 95 wt % of acrylic acid in which from 60 to 100 percent of the 
carboxylic groups have been neutralized with an alkali metal hydroxide or 
ammonia base prior to polymerization, 
(b) 5 to 35 wt % of a comonomer selected from the group consisting of 
2-hydroxyethyl methacrylate and dialkylaminoalkyl (meth)acrylate wherein 
each alkyl of the dialkyl groups has 1 to 8 carbon atoms, and the other 
alkyl group has 2 to 6 carbon atoms, 
(c) 0.01 to 5 wt %, based on the total weight of the monomers, of a 
photoinitiator, 
(d) 0 to 5 wt %, based on the total weight of the monomers, of a 
cross-linking agent which contains two or more ethylenic unsaturations, 
and, 
(e) a sufficient amount of water so that the resulting film contains 25 to 
45 wt % of water. 
Upon polymerization, the interpolymer may be dried in a convection oven to 
adjust the water content which is preferably at least 10 wt % based on the 
weight of the web-reinforced film. If so dried, the volume of the 
interpolymer shrinks and the surface is not planar but slightly 
undulating, depending upon mainly the degree of drying and the 
characteristics of the web. The uv-cured web-reinforced interpolymer may 
be stripped from the substrate and rolled, as is conventionally done. 
The reinforced web has a firm feel and ample strength for use in "personal 
care" end products such as diapers, sanitary napkins and the like, and is 
especially desirable for burn-wound dressings. 
It should be noted that whether the web is wetted by the foregoing mixture 
of monomers, or not, the surface of the conveyor S is not wetted, so that 
after the interpolymer is formed, the web-reinforced sheet or film may be 
dry-stripped from the substrate S. 
In an analogous manner, a dilute aqueous solution of a water-soluble 
film-forming polymer such as polyvinyl alcohol or polyethylene oxide, 
having a viscosity in the range from about 10 to 99 cp, is transfer-coated 
on a randomly oriented batte transported on an endless conveyor belt 
(substrate). The batte is wetted by the dilute solution, and the wetted 
batte is dried on the belt. This method is particularly adapted for 
coating a 5% solution of Polyox.TM. WSR N-10 polyethylene oxide having an 
approximate molecular weight of 100,000 and a viscosity in the range 10-20 
cp (at 25.degree. C.); or, a 5% solution of WSR N-80 having a mol wt of 
200,000 and a viscosity of 55-95 cp. Though undiluted polyvinyl alcohol 
has a viscosity in the range from about 25,000 to about 35,000 cp the 
diluted solution has a viscosity less than 100 cp. 
The invention is further described in the following illustrative examples 
in which particular low-viscosity liquids are transfer-coated on thin 
webs. 
EXAMPLE 1 
A 9 gallon stainless steel (316) air-tight mix tank equipped with a 
motor-driven agitator and an internal cooling coil, is used to prepare a 
first solution (A) by charging the tank with 7.654 kg of 45% aqueous KOH, 
4.427 kg of glacial acrylic acid and 1.116 kg of demineralized water, the 
acid being metered in over about 30 mins to maintain the temperature below 
about room temperature (75.degree. F.). A premixed solution (B) of 0.781 
kg glacial acrylic acid, 36.3 g of Irgacure.TM.651, 225 g of 
Pluronic.TM.F-38, 104 g of polyethyleneglycol diacrylate (PEGDA), 282 g 
methyl methacrylate, and 114 g lauryl methacrylate is added to the mix 
tank. After the mixture is well-mixed, the tank is evacuated and the 
vacuum broken with nitrogen until the pressure is 25 psig. This evacuation 
and pressurizing may be repeated. 
The mixture of monomers in the tank has a specific gravity of about 1.2 and 
a viscosity of about 15 cp measured with a Brookfield viscometer, Model 
LVT at 60 rpm. This mixture is pumped to a reservoir of a coating line 
equipped with an applicator curtain and coating head 11 ins wide. The 
conveyor belt is a glass fiber reinforced silicone rubber which passes at 
a speed of about 10 ft/min under 8 medium pressure Hg arc lamps having a 
total power of 1400 watts/inch, and thereafter, through convection drying 
ovens for adjusting the moisture level of the UV-cured hydrophilic polymer 
film. 
A web of corona-treated embossed polyethylene film, 2 mils thick, is 
transported on the belt in contact with the applicator curtain from which 
it is coated with a substantially uniform liquid layer of monomers 1.8 
mils thick. The liquid wets the surface of the PE film and is held thereon 
while it is exposed to the uv-radiation. 
The interpolymer film contains 681 parts per million (ppm) of residual 
monomers and has a water content of 30.7%. This film absorbs 24 times its 
weight of a simulated urine solution containing 1% sodium salt. The 
hydrophilic film adheres strongly to the polyethylene backing and is not 
delaminated. It is especially suitable for the liner of a diaper. 
EXAMPLE 2 
In an analogous manner as in example 1 hereinabove, this mixture of 
monomers is coated onto a Travis #501 nylon net made from 70 denier yarn 
with a 26.times.32/in.sup.2 count, which net is supported on the conveyor 
belt moving at about 3 ft/min in the same equipment as used in example 1 
hereinabove. Varying thickness of film are produced in the range from 
about 2 mils to about 10 mils by adjusting the rate at which the mixture 
is metered to the reservoir and the speed of the conveyor belt. 
The net-supported interpolymer is easily delaminated from the conveyor 
belt. The net is found to be completely embedded in the interpolymer with 
no uncoated surface of the net visible. Heavier denier yarn is preferably 
used for thicker hydrophilic films which typically contain from about 30 
to about 50% water and less than 1000 ppm of unreacted monomers. The water 
content is adjusted by further drying, depending upon the choice of 
particular application for the net-reinforced film. Longer periods of 
polymerization may be used to decrease the unreacted monomers to within 
the range from about 10 to about 200 ppm. 
EXAMPLE 3 
In a manner analogous to that described hereinabove, the mixture of 
monomers is coated on a randomly oriented batte of glass fibers. Other 
mixtures of monomers prepared from recipes given hereinabove are also 
transfer-coated on continuous thin films of treated polyethylene, 
open-mesh nylon webs, and battes, all of which may be polymerized and 
delaminated from the conveyor belt, as described hereinbefore.