Breathable barrier

A breathable barrier which includes: PA0 A. a first layer which is a porous sheet having a first side and a second side; and PA0 B. a second layer joined to the first side of the first layer, which second layer is a continuous film of a water-soluble polymeric material, in which: PA1 the film is not microporous in that it is substantially free of voids which connect the two surfaces of the film; PA1 water molecules are capable of being transported through the thickness of the film as a result of the solubility of the water molecules in the polymeric material; and PA1 the film has an average thickness of from about 3 to about 250 microns; wherein the first layer side of the second layer is intimately comingled with at least some of the fibers at the surface of the first side of the first layer, none of the pores at the surface of the first side of the first layer are so large as to significantly adversely affect the barrier properties of the breathable barrier as a consequence of the comingling, and the breathable barrier has a water vapor transmission rate at 37 degrees C. and about 50 percent relative humidity of from about 100 to about 5,000 g/m.sup.2 /24 hours and is impermeable to 0.9 percent by weight saline solution at about 21 degrees C. for a period of at least about one hour at a hydrostatic head of at least about 11.4 cm. In place of a coating, the continuous film can be a preformed film of a water-soluble polymeric material which is laminated to the porous sheet. In preferred embodiments, the water-soluble polymeric material is a poly(vinyl alcohol) and the porous sheet is a meltblown nonwoven web. The disclosed breathable barriers are especially useful as outer covers and baffles in such disposable absorbent articles as diapers, sanitary napkins, and incontinent pads.

CROSS-REFERENCES TO RELATED APPLICATIONS 
The use of a continuous film of a poly(vinyl alcohol) joined to a porous 
substrate having a controlled structure is described and claimed in 
copending and commonly assigned application Ser. No. 925,425 U.S. Pat. No. 
4,713,068, entitled BREATHABLE CLOTHLIKE BARRIER HAVING CONTROLLED 
STRUCTURE DEFENSIVE LAYER, filed of even date in the names of Kenneth Y. 
Wang and Richard S. Yeo, now U.S. Pat. No. 4,713,068. A barrier having at 
least three layers, one of which is a continuous film of a poly(vinyl 
alcohol), is described and claimed in copending and commonly assigned 
Application Ser. No. 925,332, entitled BREATHABLE, MULTILAYERED, CLOTHLIKE 
BARRIER, filed of even date in the names of Ralph V. Braun, Lance Garrett, 
Robert J. Phelan, and Richard S. Yeo. Finally, a baffle for a sanitary pad 
having a central zone of reduced water vapor permeability, which zone can 
result from a continuous film of a poly(vinyl alcohol) joined to the 
baffle material, is described and claimed in copending and commonly 
assigned Application Ser. No. 925,448, entitled BAFFLE HAVING ZONE WATER 
VAPOR PERMEABILITY, filed of even date in the names of Kenneth Y. Wang and 
Richard S. Yeo, now U.S. Pat. No. 4,713,069. 
BACKGROUND OF THE INVENTION 
The present invention relates to a breathable barrier, i.e., a structure 
which is substantially impervious to liquid water but permeable by water 
vapor. More particularly, the present invention relates to a breathable 
barrier which is a porous sheet, such as a nonwoven web, coated with 
poly(vinyl alcohol) or laminated to a poly(vinyl alcohol) film. 
Absorbent articles, especially disposable absorbent articles such as 
diapers, sanitary napkins, bedpads, incontinent pads, and the like are 
well known and important items of commerce. Such articles are capable of 
absorbing and retaining liquid discharges from the body. They typically 
have an outer cover or baffle of a liquid-impermeable plastic film, such 
as a polyethylene or polypropylene film, to prevent retained liquid from 
leaking from the article and soiling items of clothing, bedding, 
furniture, and the like. 
Such liquid-impermeable film prevents, or at least minimizes, leakage by 
establishing a barrier to the passage of liquid from the absorbent article 
in situations where either the capacity of the absorbent article has been 
exceeded or the loading of the target zone exceeded the capacity of the 
absorbent article to wick liquid from the target zone to storage areas. 
Such film, however, suffers from several disadvantages. Because the film is 
impermeable to both liquid and water vapor, the absorbent article feels 
hot when dry and clammy when wet. Such clammy state can cause irritation 
of the skin and even severe dermatological problems, such as diaper rash 
on infants wearing disposable diapers which have been left on too long. In 
fact, diaper rash can develop relatively quickly because of illness or 
changes in diet. In addition, the plastic film employed as the outer cover 
or baffle is severely lacking in aesthetic qualities, especially for such 
products as disposable diapers. 
One proposal for the elimination of such disadvantages is the use of a 
breathable, liquid impermeable barrier as the outer cover or baffle. As 
used herein, the term "breathable" means that the carrier is pervious to 
water vapor; that is, water vapor will pass through the barrier. While 
considerable progress has been made in the development of breathable 
films, such materials typically are lacking in aesthetic qualities. 
Various breathable outer coverings or other materials are known. For 
example, U.S. Pat. No. 3,156,242 discloses a flexible absorbent sheet 
which is useful as a surgical dressing. The backing sheet or outer layer 
of the dressing is either air pervious by nature, such as a microporous 
film, or has had holes or slits formed in it. The example employed a 
perforated polyethylene film. 
U.S. Pat. No. 3,426,754 teaches a breathable medical dressing. Such 
dressing comprises a backing having an open-celled structure, preferably 
coated with a continuous layer of a microporous pressure-sensitive 
adhesive. The backing employs a plastic film to which the desired 
properties have been imparted as a result of special processing 
conditions. The film typically can be prepared from polyolefins, 
polyacetals, polymethylene sulfide, polyethylene sulfide, polyphenylene 
oxide, polyamides, polyesters, and the like. The film possesses an 
open-celled structure, the voids of which are accessible to the outside 
surface by means of passageways which generally are under 5,000 Angstroms, 
e.g., from 100 to 5,000 Angstroms. In addition, such film has a final 
crystallinity of at least 40 percent. 
A porous sheet and a process for making it are described in U.S. Pat. No. 
4,347,844. The sheet is reported to be useful as a water-impermeable, 
vapor-permeable backing sheet for disposable diapers. The sheet contains a 
filler, the particles of which have been broken by the application of a 
compressive force to cause the formation of voids or spaces, i.e., 
micropores, which permit the passage of water vapor through the sheet 
while acting as a barrier to liquid water. The sheet apparently can be 
made of a nonfoamed thermoplastic resin, such as polyethylene and nylon. 
In addition, the patent suggests that the film can be a composite of a 
polyethylene or nylon film and spunbonded polyethylene or polyester. The 
use of a spunbonded material alone does not appear to be within the scope 
of the disclosure. 
Another type of microporous film is described in U.K. Pat. No. GB 
2,115,702B. The patent is directed toward an absorbent article, such as a 
disposable diaper or sanitary napkin, in which the article has a 
vapor-permeable, liquid-impermeable backing sheet. The backing sheet is 
composed of a film produced by mixing 100 parts by weight of a polyolefin 
resin, 28 to 200 parts by weight of a filler, and 10 to 70 parts by weight 
of a liquid or wax-like hydrocarbon polymer, molding the mixture to form a 
film, and then stretching the film laterally and/or longitudinally until 
it has a dimension of more than 1.2 times its original dimension in that 
direction, thereby resulting in the formation of fine pores in the film. 
Examples of polyolefins include polyethylene and polypropylene. A variety 
of fillers can be used, and examples of the hydrocarbon polymer include 
liquid polybutadienes, liquid polybutenes, and hydrogenates of liquid 
polybutadienes, among which saturated polyhydroxy-substituted hydrocarbons 
obtained by hydrogenating hydroxy-terminated liquid polybutadienes are 
preferred. See also U.S. Pat. No. 3,870,593 which describes stretching a 
film containing finely divided particles of a nonhygroscopic inorganic 
salt, such as calcium carbonate, in order to obtain a microporous film. 
The microporous sheet material described in U.S. Pat. No. 3,640,829 also 
involves incorporating within the polymer an inorganic salt which is 
leached out to produce the micropores. 
U.S. Pat. No. 4,591,523 relates to an apertured, macroscopically expanded, 
three-dimensional polymeric web exhibiting breathability and resistance to 
fluid transmission. The web is reported to have particular utility as a 
breathable barrier for a disposable diaper. The web preferably comprises a 
deeply drawn three-dimensional structure containing a multiplicity of 
debossments of macroscopic cross-section (i.e., visibly perceivable by the 
normal human eye at a perpendicular distance of about one foot), each of 
said debossments originating as an aperture in a first surface of the web 
and having a continuously interconnected side wall extending in the 
direction of a second, remotely located parallel surface of the web. The 
side wall of each debossment terminates to form an end wall in the second 
surface of the web. The end wall includes a multiplicity of apertures, 
each of said apertures being sized and shaped to independently support an 
aqueous fluid meniscus. These smaller apertures in each end wall are so 
spaced relative to all adjacent apertures in the end wall that the aqueous 
fluid menisci supported in the apertures do not contact one another. 
Waterproof products capable of transmitting air and water vapor which have 
fabric-like aesthetic properties are described in U.S. Pat. No. 3,932,682. 
The products are made by spray-spinning filamentary material directly onto 
an open-celled microporous polymer film, such that thermal self-bonding 
occurs between the filamentary material and the film or by spray-spinning 
the filamentary material in the same manner onto an elastic film, 
stretching the resulting product until an open-celled structure is 
produced in the film portion of the product and thereafter heating or heat 
setting the resulting product at substantially constant length to impart 
dimensional stability thereto. Polymers suitable for making films appear 
to be those described in U.S. Pat. No. 3,426,754, discussed hereinabove. 
As already noted, the filamentary material is produced by spray-spinning, 
i.e., meltblowing, directly onto the film. 
U.S. Pat. No. 4,308,303 describes a flocked, foam-coated, 
fibrous-reinforced, water vapor permeable barrier having the appearance of 
fabric and capable of filtering bacteria. The barrier comprises a 
microporous polyolefin film coated on at least one surface with a foamed 
latex polymer, flocked fibers on the exterior surface of said foamed latex 
polymer, and a web of spunbonded fibers on the exterior surface of the 
flocked, foamed latex polymer. The film is rendered microporous by 
stretching a film which contains minute fracture sites or pore-nucleating 
agents such as finely divided filler and/or minute crystalline domains. 
The use of a finely divided, inorganic, water-insoluble, inert filler such 
as calcium carbonate having an average particle size of less than 3 
microns is preferred. 
U.S. Pat. No. 4,560,611 relates to a moisture-permeable, waterproof coated 
fabric. Briefly, a microporous polyurethane layer is formed on a base 
fabric which may be knitted, woven, nonwoven, or the like. The coating 
solution consists of a polar organic solvent solution containing 8 to 25 
percent by weight of a polyurethane elastomer, 0.1 to 10 percent by weight 
of a water repellent agent, 0.2 to 3 percent by weight of a 
polyisocyanate, and 1 to 8 percent by weight of a nonionic surfactant. The 
water repellent agent typically is a fluorine- or silicone-based material. 
The polyisocyanate usually will be any of the well known di- or 
triisocyanates. The polyurethane elastomer can be a polyester or polyether 
polyurethane. 
A somewhat similar approach is described in European Patent Application No. 
85308671.8, Publication No. 0 184 392 A2. A waterproof, moisture-vapor 
permeable unitary sheet material comprises a microporous polymeric matrix 
having pores comprising continuous passages extending through its 
thickness and opening into the opposite surfaces thereof, the passages 
being sufficiently filled with a moisture-vapor permeable, 
water-impermeable, hydrophilic material to prevent the passage of water 
and other liquids through the unitary sheet material while readily 
permitting moisture vapor transmission therethrough, thereby rendering the 
sheet material breathable. Preferably, the average pore size will be less 
than about 10 percent of the thickness of the matrix. By way of example, 
the average pore size for a matrix having a thickness of about 10 to 50 
micrometers typically will be on the order of 1 to 5 micrometers or less. 
By contrast, the average pore size or opening of a woven fabric is about 
the same magnitude as its thickness. A matrix having too large a pore size 
will permit the passage of water therethrough as hydrophilic material 
solidified therein will not sufficiently close the pores against the 
passage of liquid. The matrix can be prepared by known methods from any 
polymeric material which is substantially impenetrable by water. Suitable 
polymeric materials include polyolefins, polyesters, polyamides, and the 
like. The preferred hydrophilic material is polyethylene oxide which 
preferably is polymerized with a polyisocyanate to give a polyurethane. 
U.S. Pat. No. 4,197,371 discloses a water vapor absorbing and transmitting 
sheet material. The sheet material comprises a natural or synthetic rubber 
or a rubber-like polymer having uniformly incorporated therein particles 
of at least one swellable modified polymer. Examples of suitable swellable 
modified polymers include, among others, modified starches and celluloses. 
Apparently, such sheet materials are not suitable for use as an outer 
cover for a disposable absorbent product, e.g., a diaper or sanitary 
napkin. See also U.S. Pat. No. 4,178,271 which describes a similar sheet 
material based on a sheet-like structure of poly(vinyl chloride) or a 
copolymer of vinyl chloride. 
U.S. Pat. No. 3,869,310 describes flexible sheet materials which are 
leather-like. Although the materials allegedly have improved physical 
properties, particular properties, such as water vapor permeability, are 
not discussed. The materials comprise a nonwoven fibrous mat and a 
polymeric impregnant which has a porous structure and is substantially not 
bonded to the fibers of the mat. The materials are obtained by preparing a 
nonwoven fibrous mat composed of fibers prepared from at least two 
different polymeric materials, impregnating the mat with a first liquid 
which is a solvent for one of the polymeric materials and a nonsolvent for 
the other polymeric materials, dissolving the fibers composed of the 
polymeric material which is soluble in the liquid, and coagulating the 
polymer solution resulting from the addition of the first liquid into a 
porous polymeric structure which is substantially not bonded to the 
undissolved fibers by the addition of a second liquid which is a 
nonsolvent for all of the polymeric materials originally present in the 
nonwoven fibrous mat but which is at least partially miscible with the 
first liquid. The list of suitable polymeric materials which can be 
employed includes poly(vinyl alcohol), although the preferred combinations 
of polymeric materials apparently are nylon-6 and polystyrene, nylon-6 and 
polypropylene, poly(ethylene terephthalate) and polystyrene, poly(vinyl 
chloride) and polypropylene, nylon-6 and poly(vinyl acetate), and nylon-6 
and a polyurethane elastomer. One example, however, involved the use of a 
nonwoven mat composed of fibers of poly(vinyl chloride) and poly(vinyl 
alcohol); the first liquid was N,N-dimethylformamide which is a solvent 
for poly(vinyl alcohol) but a nonsolvent for poly(vinyl chloride). 
The use of poly(vinyl alcohol) as a binder for a nonwoven fabric is 
described in U.S. Pat. No. 3,518,041. The nonwoven fabric is composed of 
cellulosic fibers alone or in combination with other natural or synthetic 
fibers. The binder is a poly(vinyl alcohol) resin in film, powder, fiber, 
or other particulate form which is crosslinked in situ with formaldehyde. 
The binder is applied to the fabric as an aqueous solution or poly(vinyl 
alcohol) fibers may be incorporated into the fabric and activated by 
treating the fabric with water. The fabric then is treated with an aqueous 
solution of formaldehyde which contains a catalyst. 
A disclosure somewhat similar to that of the above patent is found in U.S. 
Pat. No. 3,253,715 which describes boil-proof nonwoven filter media. The 
media are prepared by treating a multilayered nonwoven fabric with a 
binder which is an aqueous solution of poly(vinyl alcohol) and a 
polyacrylic acid or crosslinked polyacrylic acid. 
It is interesting to note that, in contrast to U.S. Pat. Nos. 3,518,041 and 
3,253,715, U.S. Pat. No. 3,590,585 describes a composite structure, useful 
as an artificial seaweed, which employs water-decomposable poly(vinyl 
alcohol) filaments to temporarily hold buoyant, water-resistant strands in 
place during handling, transporting, and installing of the product. Also 
of interest in this regard is U.S. Pat. No. 4,304,812 which describes the 
backcoating of an open-weave fabric. Prior to the backcoating step, a 
temporary protective coating is applied to the face of the fabric. After 
backcoating the fabric, the protective coating is removed with a solvent 
medium. Suitable protective coatings preferably are at least partially 
water soluble and include water-soluble poly(vinyl alcohol) or partially 
hydrolyzed poly(vinyl acetate). 
U.S. Pat. No. 3,597,307 describes a supple sheet material which is composed 
of a fibrous nonwoven web and a polyurethane filler. The fibers of the web 
can be prepared from poly(vinyl alcohol) and the amount of the filler can 
be up to 30 percent by weight, based on the weight of the sheet material. 
Although the sheet material is stated to have a good water vapor pick-up 
value, it is not known if the material is permeable to water vapor. See 
also U.S. Pat. No. 4,006,052. 
U.S. Pat. No. 3,891,487 discloses a decorative laminate which has a textile 
backing, a crushed, thermoset plastic foam bonded thereto, and a 
transparent polymeric film overlaying the foam. The film preferably is 
cast from a latex; suitable materials for preparing the latex include 
poly(vinyl alcohol). The film can be made breathable by mechanically 
foaming the latex before casting, mechanically puncturing the film, using 
chemical blowing agents, or dissolving or digesting out temporary fillers 
placed in the latex before it is cast. The textile backing apparently can 
be either woven or nonwoven. The decorative laminate is useful as, for 
example, a simulated oil painting, and clearly is not intended to be 
contacted by water. 
Microporous coated fabrics are described in U.S. Pat. No. 4,226,906. 
Microporosity apparently results from the use of clustered microspheres. 
The microspheres may be synthetic or naturally occurring. If the former, 
they are prepared by bonding individual microspheres in a matrix which is 
insoluble in the coating composition; the bonding agent for such matrix 
can be, for example, poly(vinyl alcohol). However, the patent does not 
appear to teach the use of poly(vinyl alcohol) in the preparation of 
microporous coated fabrics when naturally occurring microspheres are used; 
in such case, the coating composition was based on poly(vinyl chloride) 
and the fabric was a nonwoven polyester. 
U.S. Pat. No. 4,415,617 discloses a base fabric for the manufacture of 
embroidery and lace. The base fabric is a nonwoven web of poly(vinyl 
alcohol) fibers which has been processed in such a manner as to convert 
one surface of the web into a gas-permeable film comprising 
thermoplasticized and rehardened, flattened fibers and portions of fibers. 
The base fabric then can be dissolved away from embroidery stitched 
thereon by exposing the fabric to water at a temperature of about 100 
degrees C. 
U.S. Pat. No. 4,454,191 describes a waterproof and moisture conducting 
fabric coated with a hydrophilic polymer. The fabric can be a woven, knit, 
felt, or nonwoven material which is composed of natural, synthetic, or 
mineral fibers. The fabric itself must be permeable to water vapor. The 
fabric is sealed with a hydrophilic polymer which is capable of absorbing, 
transporting, and releasing water molecules. Such capability results from 
the presence in the polymer of hydrophilic groups, such as hydroxy, amino, 
ether, and carboxy groups. Thus, suitable polymers include those prepared 
from hydroxyalkyl acrylates, the acrylic or methacrylic esters of 
polyalkylene oxides or polyalkylenimides, and the like. Other suitable 
polymers include modified vinyl alcohol resins, regenerated cellulose, a 
poly(vinyl chloride) having built-in monomers which have powerful 
hydrophilic groups, copolymerizates of vinyl chloride and vinyl acetate in 
which the acetate groups have been hydrolyzed to hydroxy groups, and 
polyurethanes having excess hydroxy or amino groups. 
A somewhat related disclosure is found in German Published Patent 
Application No. 3417909 A1, which describes the use of a water-soluble 
poly(vinyl alcohol) film in the resorbent material of a sanitary pad. The 
film reportedly prevents soiling of clothing while permitting sanitary 
disposal of the used article. There appears to be no mention of the 
characteristics of the film or where and how the film is placed in the 
pad. 
It perhaps should be mentioned that there is a relatively large body of 
literature on the preparation of microporous films, only a relatively 
small portion of which has been discussed hereinabove. While a detailed 
discussion of such body of literature is beyond the scope of this section, 
a limited number of additional, representative references perhaps should 
be mentioned for the sake of completeness. Such references include, by way 
of illustration only, U.S. Pat. Nos. 4,247,498, 4,519,909, 4,257,997, 
4,452,845, 4,539,256, 3,843,761, 3,679,538, 4,430,278, 4,289,832, 
4,384,023, 4,472,328, 4,197,148, U.K. Published Patent Application No. GB 
2,103,537A, Japanese Published Patent Application No. 57-142323, and 
European Patent Application Nos. 84307198.6, Publication No. 0 141 592 A2, 
and 83305161.8, Publication No. 0 105 629 A2. 
Although various of the breathable barriers described above have proven 
useful in such absorbent articles as disposable diapers and sanitary 
napkins, there still is a need for an effective breathable outer cover or 
baffle which has a clothlike feel and can be manufactured cheaply in large 
quantities. 
SUMMARY OF THE INVENTION 
It therefore is an object of the present invention to provide a breathable 
barrier. 
Another object of the present invention is to provide a breathable barrier 
which is suitable for use as an outer cover or baffle for a disposable 
absorbent article. 
A further object of the present invention is to provide a breathable 
barrier which is clothlike in appearance and feel. 
These and other objects will be apparent to one having ordinary skill in 
the art from a reading of the specification and claims which follow. 
Accordingly, the present invention provides a breathable barrier which 
comprises: 
A. a first layer which is a porous sheet having a first side and a second 
side; and 
B. a second layer joined to said first side of said first layer, which 
second layer comprises a continuous film of a water-soluble polymeric 
material, in which: 
said film is not microporous in that it is substantially free of voids 
which connect the two surfaces of said film; 
water molecules are capable of being transported through the thickness of 
said film as a result of the solubility of said water molecules in said 
polymeric material; and 
said film has an average thickness of from about 3 to about 250 microns; 
wherein the first layer side of said second layer is intimately comingled 
with at least some of the fibers at the surface of said first side of said 
first layer, none of the pores at the surface of said first side of said 
first layer are so large as to significantly adversely affect the barrier 
properties of said breathable barrier as a consequence of said comingling, 
and said breathable barrier has a water vapor transmission rate of 37 
degrees C. and about 50 percent relative humidity of from about 100 to 
about 5,000 g/m.sup.2 /24 hours and is impermeable to 0.9 percent by 
weight saline solution at about 21 degrees C. for a period of at least 
about one hour at a hydrostatic head of at least about 11.4 cm. 
The present invention also provides a breathable barrier which comprises a 
porous sheet laminated on at least one side to a film of a water-soluble 
polymeric material, in which: 
said film is not microporous in that it is substantially free of voids 
which connect the two surfaces of said film; 
water molecules are capable of being transported through the thickness of 
said film as a result of the solubility of said water molecules in said 
polymeric material; and 
said film has an average thickness of from about 3 to about 250 microns; 
wherein sad breathable barrier has a water vapor transmission rate at 37 
degrees C. and about 50 percent relative humidity of from about 100 to 
about 5,000 g/m.sup.2 /24 hours and is impermeable to 0.9 percent by 
weight saline solution at about 21 degrees C. for a period of at least 
about one hour at a hydrostatic head of at least about 11.4 cm. 
The present invention still further provides a breathable barrier which 
comprises: 
A. a first layer which is a porous sheet having a first side and a second 
side; and 
B. a second layer joined to said first side of said first layer, which 
second layer comprises a continuous film of a poly(vinyl alcohol), in 
which: 
said film is not microporous in that it is substantially free of voids 
which connect the two surfaces of said film; and 
said film has an average thickness of from about 3 to about 250 microns; 
wherein the first layer side of said second layer is intimately comingled 
with at least some of the fibers at the surface of said first side of said 
first layer, none of the pores at the surface of said first side of said 
first layer are so large as to significantly adversely affect the barrier 
properties of said breathable barrier as a consequence of said comingling, 
and said breathable barrier has a water vapor transmission rate at 37 
degrees C. and about 50 percent humidity of from about 100 to about 5,000 
g/m.sup.2 /24 hours and is impermeable to 0.9 percent by weight saline 
solution at about 21 degrees C. for a period of at least about one hour at 
a hydrostatic head of at least about 11.4 cm. 
The present invention yet further provides a breathable barrier which 
comprises a porous sheet laminated on at least one side to a film of a 
poly(vinyl alcohol), in which: 
said film is not microporous in that it is substantially free of voids 
which connect the two surfaces of said film; and 
said film has an average thickness of from about 3 to about 250 microns; 
wherein said breathable barrier has a water vapor transmission rate at 37 
degrees C. and about 50 percent relative humidity of from about 100 to 
about 5,000 g/m.sup.2 /24 hours and is impermeable to 0.9 percent by 
weight saline solution at about 21 degrees C. for a period of at least 
about one hour at a hydrostatic head of at least about 11.4 cm. 
In preferred embodiments, the porous sheet or first layer is a nonwoven 
web. In other preferred embodiments, the porous sheet is a meltblown or 
spunbonded web. In still other preferred embodiments, the porous sheet is 
a meltblown or spunbonded web which is composed of polyolefin fibers, 
e.g., polyethylene or polypropylene fibers. In yet other preferred 
embodiments, the film of a water-soluble polymeric material or second 
layer is substantially insoluble in water having a temperature less than 
about 50 degrees C. 
The present invention additionally provides a multilayer absorbent article 
in which at least one layer is a breathable barrier as described and 
claimed herein. 
In preferred embodiments, the absorbent article is a disposable diaper, a 
sanitary napkin, or an incontinent pad.

DETAILED DESCRIPTION OF THE INVENTION 
As used herein, the term "breathable barrier" means a material which is 
permeable to water vapor as measured by the water vapor transmission rate 
at 37 degrees C. and about 50 percent relative humidity, but which is 
impermeable to 0.9 percent by weight of saline solution at about 21 
degrees C. for a period of at least about one hour at a hydrostatic head 
of at least about 11.4 cm. The material is permeable to water vapor for 
the purposes of the present invention if it has a water vapor transmission 
rate at 37 degrees C. and about 50 percent relative humidity of from about 
100 to about 5,000 g/m.sup.2 /24 hours. 
As a matter of convenience, the terms "porous sheet" and "first layer" are 
used interchangeably throughout this specification, with occasional 
cross-referencing. The same is true of the terms "continuous film" or 
"film" or variations thereof and "second layer." 
In the broadest interpretation of the present invention, the porous sheet 
or first layer can be any porous material which is desired to be converted 
to a breathable barrier. Thus, such porous sheet can be a paper substrate, 
woven web, knitted fabric, spunlaced material, bonded carded web, needle 
punched material, stitch bonded fabric, meltblown web, spunbonded web, 
coformed web, or the like. Preferably, however, the porous sheet will be a 
nonwoven web. Most preferably, the porous sheet will be a spunbonded, 
meltblown, or coformed nonwoven web. 
Various methods for making porous sheets are, of course, well known to 
those having ordinary skill in the art and need not be discussed herein. 
For the most preferred porous sheets, however, representative methods are 
described in, for example, U.S. Pat. Nos. 3,016,599, 3,755,527, 3,704,198, 
3,849,241, and 4,100,324, and 3,692,618, all of which are incorporated 
herein by reference. With respect to coformed webs, it perhaps should be 
noted that the web in general will consist of primary web-forming fibers 
with secondary fibers or particles dispersed therein. 
The material from which the porous sheet is prepared is not known to be 
critical, provided that there is sufficient adhesion between the porous 
sheet and the polymeric material. That is, the second layer must be joined 
to the first layer. Moreover, it should be appreciated by one having 
ordinary skill in the art that the levels of adhesion for any given porous 
sheet may differ, depending upon the nature of the polymeric material and 
whether it is applied as a solution or as a preformed film. Although the 
use of a supplemental adhesive, i.e., an adhesive material different from 
the polymeric material, is contemplated and comes within the scope of the 
present invention, such use is not preferred. In any case, whether or not 
adhesion is sufficient for any given combination of porous sheet material 
and polymeric material is readily determined by one having ordinary skill 
in the art without a need for undue experimentation. Moreover, when 
insufficient adhesion is observed, one having ordinary skill in the art, 
following the guidelines contained herein, can easily determine conditions 
under which sufficient adhesion will be achieved. 
When the porous sheet is a nonwoven web, the preferred materials for the 
preparation of the web are polyolefins. For the purposes of the present 
disclosure, the term "polyolefin" is meant to include any polymeric 
material a major constituent of which, i.e., at least 50 percent by 
weight, is a polyolefin. Thus, the term includes homopolymers, copolymers, 
and polymer blends. 
Copolymers can be random or block copolymers of two or more polyolefins (or 
two or more different polyolefin monomeric precursors) or of one or more 
polyolefins and one or more nonpolyolefin polymers. Similarly, polymer 
blends can utilize two or more polyolefins or one or more nonpolyolefin 
polymers. As a practical matter, homopolymers and copolymers and polymer 
blends involving only polyolefins are preferred, with homopolymers being 
most preferred. 
Examples of polyolefins include polyethylene, polystyrene, poly(vinyl 
chloride), poly(vinyl acetate), poly(vinylidene chloride), poly(acrylic 
acid), poly(methacrylic acid), poly(methyl methacrylate), poly(ethyl 
acrylate), polyacrylamide, polyacrylonitrile, polypropylene, 
poly(1-butene), poly(2-butene), poly(1-pentene), poly(2-pentene), 
poly(3-methyl-1-pentene), poly(4-methyl-1-pentene), 
1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, 
polychloroprene, and the like. 
The preferred polyolefins are those prepared from unsaturated hydrocarbon 
monomers, with polyethylene and polypropylene being most preferred. 
The size and thickness of the porous sheet are not critical. However, those 
having ordinary skill in the art should appreciate that it may be 
necessary to alter film thicknesses or materials if very thin or very 
thick porous sheets are employed. The present invention is unique in part 
because it permits the use of relatively thin films or second layers 
without sacrificing barrier properties. Thus, one goal of the present 
invention is to keep the films relatively thin. Thus, some experimentation 
may be required to optimize the performance of the resulting breathable 
barrier upon changing the thickness of the porous sheet or first layer. In 
addition, some porous sheets may exhibit partial barrier characteristics 
to liquid water, which characteristics should be taken into consideration 
when planning film thicknesses. In fact, the presence of such 
characteristics in the first layer is both desirable and preferred. 
By way of illustration, satisfactory breathable barriers have been prepared 
using nonwoven spunbonded or meltblown porous sheets as first layers. 
Spunbonded basis weights have varied from about 13.6 to about 102 g per 
square meter, or g/m.sup.2, and meltblown basis weights have varied from 
about 3.4 to about 102 g/m.sup.2. 
As already stated, the second layer is a continuous film of a water-soluble 
polymeric material. Such film can be a preformed film which is joined or 
laminated to the porous sheet or first layer by any suitable method known 
by those having ordinary skill in the art, such as thermal bonding, 
chemical or adhesive bonding, solvent bonding, ultrasonic bonding, and the 
like. Of course, the joining method should not significantly adversely 
affect the solubility of water molecules in the film or the barrier 
properties of either the film or the porous sheet. Alternatively, and 
preferably, the second layer of continuous film can be formed in situ from 
an aqueous coating on the porous sheet or first layer. Because the in situ 
formation of the second layer is preferred, most of the discussion which 
follows is directed thereto. 
When the continuous film or second layer is formed in situ on the porous 
sheet or first layer, the structure of the porous sheet, e.g., the sizes 
of the pores at the surface of the porous sheet on which the film will be 
formed, is of concern only in the sense that none of such pores can be so 
large as to interfere with the formation of the continuous film in such a 
manner as to significantly adversely affect the barrier properties of the 
breathable barrier. It is important to note that perfection is not 
required; it is necessary only that those film imperfections which are 
present do not result in a significant deterioration of the barrier 
properties, especially with respect to liquid water. 
In the case of the most preferred porous sheet, i.e., a meltblown web, it 
is estimated that, in order to obtain generally satisfactory barrier 
properties, each of at least about 50 percent of the pores at the surface 
to be coated of the meltblown porous sheet should have a cross-sectional 
area of less than about 3.2.times.10.sup.-8 m.sup.2, with none of such 
pores being so large as to prevent the formation of the continuous film in 
such a manner as to significantly adversely affect the barrier properties 
of the breathable barrier. Moreover, it is believed that optimum barrier 
properties should be possible with meltblown webs when essentially none of 
the pores at such surface has a cross-sectional area in excess of about 
3.2.times.10.sup.-8 m.sup.2. Because of the numerous combinations of 
porous sheets and water-soluble polymeric materials which are possible, 
however, it is not feasible to do more than offer the foregoing guidelines 
with respect to the pore size distribution of the porous sheet. 
When the polymeric material is applied to the porous sheet as an aqueous 
solution to form a continuous film in situ, it must, of course, be capable 
of forming a continuous film under the conditions of application. In 
general, the polymeric material can be any water-soluble polymeric 
material which, in addition to the foregoing requirement, will form a film 
which: 
is not microporous in that it is substantially free of voids which connect 
the two surfaces of the film; 
is capable of transporting water molecules through the thickness of the 
film as a result of the solubility of said water molecules in the 
polymeric material; and 
has an average thickness of from about 3 to about 250 microns. 
These film characteristics also apply to the preformed film which is 
laminated to the porous sheet. 
An important aspect of the present invention is the fact that a film 
employed herein, whether preformed or formed in situ, is not a microporous 
film as that term has been used in the art. That is, a film utilized in 
the present invention does not have voids or micropores which connect the 
two surfaces of the film. In a microporous film, the interconnecting voids 
provide a pathway for the transport of water molecules from one surface to 
another, the driving force being the differences in relative humidities at 
the two surfaces. A film employed in the present invention, however, 
utilizes a different mechanism, namely: water molecules must be soluble in 
the film and capable of being transported by means of such solubility from 
one surface of the film to the other. 
As already noted, the average thickness of the second layer should be in 
the range of from about 3 to about 250 microns. Preferably, the average 
thickness of the second layer will be in the range of from about 3 to 
about 100 microns, more preferably from about 3.4 to about 50 microns, and 
most preferably from about 5 to about 25 microns. 
If a third layer is present which also is a continuous film of a 
water-soluble polymeric material, and the third layer is joined to the 
second layer, than both the second and third layer thicknesses can be 
reduced. Under these conditions, the preferred range for the thicknesses 
of each such layer is from about 1.5 to about 85 microns, with a range of 
from about 1.5 to about 12 microns being more preferred. The most 
preferred thickness range for each of the two adjacent film layers is from 
about 1.5 to about 10 microns. 
It should be noted that average film thickness is involved, not maximum 
film thickness. Because of the inherent relative roughness of the surfaces 
of many porous sheets, and nonwoven webs in particular, film thickness 
typically varies over the area constituting the second layer. This 
necessitates dealing with average film thickness. Moreover, the average 
film thickness is an adequate measure of the amount of the continuous film 
which constitutes the second layer. Stated differently, some variability 
or imprecision in film thickness is acceptable since the barrier 
properties of the film do not appear to be extremely sensitive to film 
thickness. 
A related problem is the difficulty of accurately measuring film thickness, 
unless the film is preformed. For the purposes of the present invention, 
it is sufficient if film thickness is only estimated. A reasonable 
estimate of the thickness of a film can be made from the amount of add-on 
of the PVOH resin or PVOH composition if the density of the resin or 
composition is known. With the poly(vinyl alcohol) resins employed in the 
examples, it was found that each g/m.sup.2 of add-on was approximately 
equivalent to 0.85 micron of film thickness. 
In general, the water-soluble polymeric materials suitable for use in the 
present invention can be either natural or synthetic, and the former group 
of materials can be modified, if desired, to achieve particular 
properties. The natural and modified natural materials included, by way of 
illustration only, agar, carragenan, corn starch, guar gum, gum arabic, 
gum karaya, gun tragacanth, locust bean gum, potato starch, wheat starch, 
rice starch, tapioca, casein, gelatin, pectin, sodium alginate, xanthan 
gum, aminoalkyl starches, dextran, hydroxyalkyl starches, hydroxyethyl 
cellulose, hydroxypropyl cellulose, methyl cellulose, sodium carboxymethyl 
cellulose, and the like. 
Examples of synthetic water-soluble polymeric resins include poly(vinyl 
alcohol), polyacrylamides, poly(acrylic acid), poly(methacrylic acid), 
polyethyleneimine, Mannichsubstituted polyacrylamides, 
poly(dimethylaminoethyl methacrylate), polyalkylene polyamines, 
poly(vinylbenzyltrimethylammonium chloride), poly(diallyldimethylammonium 
chloride), poly(glycidyltrimethylammonium chloride), poly(ethylene oxide), 
poly(N-vinyl-2-pyrrolidinone), methyl vinyl ether-maleic anhydride 
copolymers and lower alkyl esters thereof, and the like. 
In many cases, it may be necessary to include a crosslinking agent in order 
to obtain the requisite film properties. However, suitable crosslinking 
agents and their uses are well known to those having ordinary skill in the 
art. 
The use of synthetic water-soluble materials is preferred, with poly(vinyl 
alcohol) being most preferred. Because poly(vinyl alcohol) is most 
preferred and was used in the examples, the material and its use are 
described in greater detail below. However, such description is not to be 
construed as in any way limiting either the spirit or the scope of the 
present invention. 
As is well known in the art, poly(vinyl alcohol), from which the second 
layer most preferably is prepared, is a synthetic water-soluble polymeric 
material. There are, however, numerous grades of poly(vinyl alcohol), many 
of which have different solubility characteristics in water. For example, 
some grades are soluble in water at ambient temperature, while others are 
soluble in water only at elevated temperatures. At the present time, 
though, there are no known limitations with respect to the grade or nature 
of the poly(vinyl alcohol) employed in the preparation of the second 
layer. 
Poly(vinyl alcohol), for convenience often referred to hereinafter as PVOH, 
is produced by the hydrolysis of poly(vinyl acetate). PVOH is available 
commercially in several grades which differ in degree of polymerization 
and degree of hydrolysis. In general, the degree of polymerization will 
vary from about 500 to about 2,500; the corresponding molecular weights 
are from about 22,000 to about 110,000. The degree of hydrolysis usually 
will vary from about 85 percent to essentially 100 percent (e.g., 99.7 
percent minimum hydrolysis). In addition, some modified PVOH materials 
also are available, such as so-called tackified grades which are borated 
PVOH resins (see U.S. Pat. No. 3,135,648). 
Typical of the commercially available PVOH resins are the VINOL.RTM. resins 
available from Air Products and Chemicals, Inc., Polymer Chemicals, 
Allentown, Pa. Preformed PVOH films also are commercially available, such 
as the MONO-SOL.RTM. 1-100 series from Mono-Sol Division, Chris Craft 
Industries, Gary, Ind. 
Preferably, the PVOH resin will have a relatively high degree of 
hydrolysis, typically essentially completely hydrolyzed, since such a 
resin does not require the use of a crosslinking agent. 
Although resins having a lower degree of hydrolysis can be employed with 
satisfactory results, such resins may require the addition of a 
crosslinking agent in the aqueous solution of PVOH with which the porous 
sheet is coated, depending upon the use intended for the breathable 
barrier, since such resins often are quite soluble in water at ambient 
temperature. However, inclusion of a crosslinking agent is not required, 
even for such resins. 
One of the remarkable aspects of the present invention is the fact that 
such resins can be used to prepare satisfactory breathable barriers. There 
are a number of porous sheets, meltblown webs in particular, which exhibit 
barrier properties with respect to liquid water. Such barrier properties, 
however, generally are insufficient to permit such porous sheets to serve 
by themselves as breathable barriers having the properties associated with 
the barriers of the present invention. Nevertheless, such sheets, when 
joined with a continuous film of a water-soluble polymeric material as 
provided herein, yield barriers having properties which exceed the sum of 
the properties of the individual components making up the barrier. That 
is, there is a kind of synergy which results from the combination of a 
porous sheet having significant barrier properties with a continuous film 
of a water-soluble polymeric material as provided by the present 
invention. For some applications, the porous sheet permits the use of 
polymeric materials which are quite soluble in water at ambient 
temperature. As a practical matter, however, it is preferred that such 
continuous film is substantially insoluble in water having a temperature 
less than about 50 degrees C. 
Suitable crosslinking agents are those known in the art, such as glyoxal; 
formaldehyde; urea-formaldehydes; melamine-formaldehydes; metal compounds, 
such as cupric ammonium complexes; chromium complexes, organic titanates, 
and dichromates; and the like. When required, a crosslinking agent usually 
is employed in an amount in the range of from about 1 to about 5 percent 
by weight, based on the weight of PVOH in the aqueous solution, although 
higher or lower amounts can be employed if desired. 
In addition to the use of chemical crosslinking agents as discussed above, 
the formed PVOH film can be crosslinked by radiation, such as electron 
beam radiation, ultraviolet radiation, and the like. The formed PVOH film 
also can be crosslinked thermally by heating the film to a temperature in 
excess of 100 degrees C. The preferred temperature range is from about 120 
to about 180 degrees C. In the preferred temperature range, the 
crosslinking time typically is about one hour. Thermal crosslinking is 
preferred over the inclusion of a chemical crosslinking agent in the 
coating solution, especially when the breathable barrier is to be used in 
a disposable absorbent article such as a diaper or sanitary napkin. 
Because flexibility of the breathable barrier often is a required 
characteristic, it may be either necessary or desirable to include a 
plasticizer in the PVOH coating solution. Suitable plasticizers in general 
are any of the known plasticizers for PVOH, such as glycerol, the 
poly(oxyethylene) diols, pentaerythritol, 1,2,6-hexanetriol, sorbitol, 
formamide, urea, and the like. Glycerol has been found to be a 
particularly useful plasticizer and is preferred. Thus, a plasticizer can 
be present in an amount of from 0 to about 50 percent by weight, based on 
the weight of PVOH employed, although somewhat higher amounts perhaps can 
be used, depending upon the polymeric material and its molecular weight 
range. When employed with PVOH resins, the plasticizer preferably will be 
present in an amount of from about 15 to about 25 percent by weight. 
Some care must be exercised in the use of plasticizers, however. While 
plasticizers can increase film flexibility and enhance film formation, 
they also can adversely affect the liquid water barrier characteristics of 
the breathable barrier, especially when used at unusually high levels. 
Thus, the plasticizer level in general should be kept to the minimum level 
which is consistent both with film formation and flexibility requirements 
and the desired properties of the breathable barrier. 
As indicated hereinbefore, the PVOH or other water-soluble polymeric 
material preferably is applied to the porous sheet as an aqueous solution. 
Application usually is made at ambient temperature and pressure, although 
such conditions are not mandatory. Indeed, any combination of temperature 
and pressure can be employed, although for reasons of economics and 
convenience, ambient temperature and pressure are preferred. The 
concentration of polymeric material in the solution is not known to be 
critical and usually is a matter of convenience. In practice, when the 
polymeric material is PVOH, concentrations of from about 4 to about 12 
percent by weight are typical. The preferred concentration range is from 
about 5 to about 10 percent by weight as employed in the examples. 
The method of application is not known to be critical and largely is a 
matter of convenience. Thus, the PVOH solution can be applied by spraying, 
dipping, brushing, doctor blade, roller, Meyer rod, and the like. In 
addition, a single coat or multiple coats can be applied. Moreover, if 
multiple coats are applied, the application solution does not have to be 
the same for each application. The several solutions can utilize different 
concentrations of the same water-soluble polymeric material, the presence 
or absence of such compounds as crosslinking agent and plasticizer, 
different polymeric materials at the same or different concentrations, or 
combinations of any of the foregoing variations. 
After the aqueous solution of water-soluble polymeric material has been 
applied to the porous sheet, the sheet is dried by removing water, 
preferable at an elevated temperature. The removal of water generally 
results in the formation of a film of the polymeric material. If a 
subsequent porous sheet is to be applied adjacent to the film, such 
application can be done before drying has been completed and is preferred 
in cases where the polymeric material has adhesive properties. If desired, 
multiple coatings of the polymeric material solution can be applied, with 
the last-applied coating serving as the adhesive layer. 
Finally, additives other than crosslinking agents and plasticizers can be 
incorporated into the aqueous coating solution or film of polymeric 
material, if desired. Such additives include binders, extenders, fillers, 
pigments, dyes, defoamers, preservatives, fungicides, wetting agents, 
deodorants, fluorescent agents, and the like. 
It may be noted at this point that the porous sheet can be a single layer 
or a composite of two or more layers. Moreover, the breathable barrier can 
be a composite of more than the two layers required by the present 
invention. Composite structures are, in fact, preferred since the use of 
multiple layers permits one to taylor the breathable barrier for any 
desired combination of barrier properties, including water vapor 
transmission rate, and aesthetic properties. 
By way of illustration of multilayer constructions for the barrier, when 
the barrier is to be used as the baffle in a sanitary napkin, the barrier 
can be a composite of a thermally bonded carded web, a second layer as 
provided by the present invention, and a meltblown web first layer, with 
the meltblown web being the inner or body side layer. Alternatively, the 
bonded carded web can be replaced with a spunbonded web. 
For disposable diaper or incontinent pad applications, an example of a 
suitable outer cover is a composite of a first meltblown web as the first 
layer, two layers of a film as provided by the present invention, a third 
layer of a film as provided by the present invention to serve as an 
adhesive for the next layer which is a second meltblown web, and a final 
layer which is a spunbonded web. Each meltblown web can have a basis 
weight of, for example 17 g/m.sup.2, and the spunbonded web can have a 
basis weight of, for example, 23.8 g/m.sup.2, with the spunbonded web 
being the outermost layer. That is, the first meltblown layer is placed 
next to the absorbent batt within the disposable diaper or incontinent 
pad. Of course, other constructions are possible and come within the 
spirit and scope of the present invention. 
The present invention is further described by the examples which follow 
which illustrate certain preferred embodiments. Such examples are not to 
be construed as in any way limiting either the spirit or scope of the 
present invention. In the examples, all temperatures are in degrees 
Celsius and all amounts are in parts by weight, unless indicated 
otherwise. 
In the examples, the water vapor transmission rate was determined in 
accordance with ASTM Method E 96-80, Standard Test Methods for Water Vapor 
Transmission of Materials, Procedure 12. The apparatus employed was a 
Vapometer (Catalog No. 68-1, Thwing-Albert Instrument Company, 
Philadelphia, Pa.). The apparatus consisted of a two-inch (about 5.1-cm) 
deep aluminum cup having a flanged top with a neoprene rubber gasket. The 
inner diameter of the flange was 2.5 inches (about 6.4 cm). About 100 ml 
of water was added to the cup and a sample of the breathable barrier to be 
tested was sealed mechanically over the open end of the cup and weighed. 
The sample-cup assembly was placed in an oven at 37 degrees C. and about 
50 percent relative humidity. Periodic weighings of the sample-cup 
assembly permitted calculation of the water vapor transmission rate 
(WVTR). 
The effectiveness of the coated porous sheet as a barrier to liquid water 
was measured by INDA Standard Test 80.7-70 (82), INDA Standard Test for 
Saline Repellency of Nonwovens, often referred to as the Mason Jar Test. 
The test liquid was 0.9 percent by weight saline solution. In both tests, 
the coated porous sheet was oriented inwardly, i.e., with the porous sheet 
closest to the saline solution. 
EXAMPLE 1 
An approximately five percent by weight aqueous solution of poly(vinyl 
alcohol) was prepared by dispersing the resin in water at ambient 
temperature and heating the mixture at about 96 degrees with moderate 
agitation until the resin dissolved. The poly(vinyl alcohol) employed was 
VINOL.RTM. 165 (Air Products and Chemicals, Inc., Polymer Chemicals, 
Allentown, Pa.). According to information supplied by the manufacturer, 
the resin was in excess of 99.3 percent hydrolyzed and a 4 percent by 
weight aqueous solution of the resin at 20 degrees had a viscosity of 
55-65 cps. The resulting solution then was allowed to cool to ambient 
temperature. 
A polypropylene meltblown web sample having a nominal basis weight of about 
34 g/m.sup.2 and a measured basis weight of 38 g/m.sup.2 was coated with 
the above PVOH solution by means of a brush. The coated sample was air 
dried overnight at ambient temperature. The poly(vinyl alcohol) add-on was 
17 g/m.sup.2. The coated sample passed the Mason Jar Test and gave a water 
vapor transmission rate of 1171 g/m.sup.2 /24 hours. A comparable, 
uncoated sample having a nominal basis weight of about 34 g/m.sup.2 gave a 
WVTR of 2518 g/m.sup.2 /24 hours and failed the Mason Jar test. 
EXAMPLE 2 
The procedure of Example 1 was repeated six times at six different PVOH 
add-on levels. The results are summarized in Table 1. 
TABLE 1 
______________________________________ 
Sample 
Nom. Meas. PVOH Mason Jar 
No. Basis.sup.a 
Basis.sup.b 
Add-on.sup.c 
Test WVTR.sup.d 
______________________________________ 
2A 34 36 4 Passed 2959 
2B 34 37 9 Passed 1277 
2C 34 31 31 Passed 1048 
2D 34 31 40 Passed 1183 
2E 34 31 58 Passed 978 
2F 34 39 151 Passed 742 
______________________________________ 
.sup.a Nominal basis weight in g/m.sup.2. 
.sup.b Measured basis weight in g/m.sup.2. 
.sup.c In g/m.sup.2. 
.sup.d Water vapor transmission rate in g/m.sup.2 /24 hours. 
EXAMPLE 3 
The procedure of Example 1 was repeated, except that the polypropylene 
meltblown web sample was replaced with polypropylene spunbonded web 
samples of varying basis weights. The results are summarized in Table 2. 
TABLE 2 
______________________________________ 
Sample 
Nom. Meas. PVOH Mason Jar 
No. Basis.sup.a 
Basis.sup.b 
Add-On.sup.c 
Test WVTR.sup.d 
______________________________________ 
3A 34 -- 0 Failed 2788 
3B 34 -- 10 Failed 2000 
3C 34 40 12 Failed 2037 
3D 42 -- 0 Failed 2927 
3E 42 41 13 Failed 2175 
3F 51 -- 0 Failed 1990 
3G 51 44 13 Failed 2278 
3H 68 -- 0 Failed 2798 
3I 68 64 12 ND.sup.e 
ND 
______________________________________ 
.sup.a Nominal basis weight in g/m.sup.2. 
.sup.b Measured basis weight in g/m.sup.2 (not all samples were measured) 
.sup.c In g/m.sup.2. 
.sup.d Water vapor transmission rate in g/m.sup.2 /24 hours. 
.sup.e Not determined. 
The results of Examples 1-3, inclusive, demonstrate the fact that the PVOH 
film and the porous substrate upon which it is formed are interdependent. 
That is, choices regarding the nature of the aqueous PVOH coating solution 
are in part dependent upon the nature of the porous substrate to be 
coated. Meltblown webs are less porous than spunbonded webs at any given 
basis weight. Thus, the sizes of pores at the surfaces of spunbonded webs 
tend to be significantly larger than those of meltblown webs. 
Consequently, the thickness of the PVOH film joined to a spunbonded web in 
general needs to be substantially thicker than for a meltblown web of the 
same basis weight. The failure of coated spunbonded webs to pass the Mason 
Jar Test also is related to the ability of the PVOH resin to bridge the 
pores or openings at the surface of the porous substrate during the 
film-forming process. Adding a plasticizer to the PVOH resin usually has a 
positive effect on such bridging ability. 
The next example is a repeat of Example 3, except that a plasticizer was 
included in the aqueous resin solution. 
EXAMPLE 4 
The procedure of Example 3 was repeated, except that the aqueous PVOH resin 
solution also contained approximately 1 percent by weight glycerol (25 
percent by weight, based on the dry weight of the PVOH resin). The results 
are summarized in Table 3. 
TABLE 3 
______________________________________ 
Sample 
Nom. Meas. Film Mason Jar 
No. Basis.sup.a 
Basis.sup.b 
Add-On.sup.c 
Test WVTR.sup.d 
______________________________________ 
4A 34 -- 0 Failed 2788 
4B 34 42 57 Passed 1173 
4C 42 -- 0 Failed 2927 
4D 42 50 54 Passed 739 
4E 51 -- 0 Failed 1900 
4F 51 49 59 Passed 748 
4G 68 -- 0 Failed 2798 
4H 68 71 52 Passed 742 
4I 102 -- -- Failed 2808 
4J 102 109 77 Passed 960 
______________________________________ 
.sup.a Nominal basis weight in g/m.sup.2. 
.sup.b Measured basis weight in g/m.sup.2. 
.sup.c In g/m.sup.2. 
.sup.d Water vapor transmission rate in g/m.sup.2 /24 hours. 
Because the coated samples in Example 4 all had high levels of film add-on, 
it is difficult to determine to what extent the presence of a plasticizer 
contributed to the 100 percent Mason Jar Test pass rate observed in 
Example 4. Experience has shown, though, that the presence of a 
plasticizer greatly enhances the bridging ability of the resin during film 
formation and minimizes or eliminates cracks and holes in the formed film. 
However, the amount of plasticizer must be selected with some care, 
depending upon the application, as shown by Examples 5-8, inclusive. 
EXAMPLE 5 
The procedure of Example 1 was repeated twice, except that the PVOH 
solution also contained about 3.5 percent by weight glycerol, or about 76 
percent by weight based on the weight of PVOH resin, and the PVOH solution 
was applied to the meltblown web by means of a No. 22 Meyer rod. The 
results obtained are summarized in Table 4. 
TABLE 4 
______________________________________ 
Sample Film Mason Jar 
No. Add-On.sup.a Test WVTR.sup.b 
______________________________________ 
5A 8.3 Failed 2908 
5B 8.4 Failed 2521 
______________________________________ 
.sup.a In g/m.sup.2. 
.sup.b Water vapor transmission rate in g/m.sup.2 /24 hours. 
While some water-soluble polymeric materials may be capable of withstanding 
the presence of as large an amount of plasticizer as was employed in 
Example 5, VINOL.RTM. 165 does not appear to be one of them unless a 
crosslinking agent is added to impart additional film integrity. Moreover, 
the effect observed in Example 5 was not altered by placing the film 
between two porous substrates, as shown in the next three examples. 
EXAMPLE 6 
A meltblown polypropylene web having a nominal basis weight of about 34 
g/m.sup.2 was coated with resin solution of Example 5 by means of a No. 22 
Meyer rod. A spunbonded polypropylene web having a nominal basis weight of 
about 34 g/m.sup.2 was immediately layed over the coated surface of the 
meltblown web. The resulting composite was air dried. The film add-on was 
6.5 g/m.sup.2. Three samples of the composite thus obtained were subjected 
to the Mason Jar Test; only one passed. The composite gave a water vapor 
transmission rate of 2471 g/m.sup.2 /24 hours. 
EXAMPLE 7 
The procedure of Example 6 was repeated, except that the film add-on was 
5.6 g/m.sup.2. The resulting composite failed the Mason Jar Test and gave 
a water vapor transmission rate of 2534 g/m.sup.2 /24 hours. 
EXAMPLE 8 
The procedure of Example 6 was repeated, except that the nominal basis 
weight of each of the two webs was 25 g/m.sup.2 and the film add-on was 
5.6 gm.sup.2. The resulting composite failed the Mason Jar Test and gave a 
water vapor transmission rate of 2923 g/m.sup.2 /24 hours. 
EXAMPLE 9 
The procedure of Example 1 was repeated, except that the PVOH resin was a 
mixture of 50 percent by weight VINOL.RTM. 165 and 50 percent by weight 
VINOL.RTM. 205 (Air Products and Chemicals, Inc. Polymer Chemicals, 
Allentown, Pa.) and the meltblown web sample was coated by means of a No. 
22 Meyer rod. According to information supplied by the manufacturer, the 
VINOL.RTM. 205 resin was 87.0-89.0 percent hydrolyzed and a 4 percent by 
weight aqueous solution of the resin at 20 degrees had a viscosity of 5-6 
cps. The nominal basis weight of the web was 34 g/m.sup.2 and the measured 
basis weight was 39 g/m.sup.2. The PVOH add-on was 5.9 g/m.sup.2. Two out 
of three samples of the composite passed the Mason Jar Test and the 
composite gave a water vapor transmission rate of 2095 g/m.sup.2 /24 
hours. 
EXAMPLE 10 
The procedure of Example 1 was repeated, except that different PVOH resins 
were employed, actual basis weights of the samples were not calculated, 
and the PVOH solution was applied by means of a Meyer rod. The 
characteristics of the several PVOH resins employed are summarized in 
Table 5, based on information provided by the manufacturer (Air Products 
and Chemicals, Inc., Polymer Chemicals, Allentown, Pa.), and the results 
obtained are summarized in Table 6. 
TABLE 5 
______________________________________ 
Resin Percent Hydrolyzed 
Viscosity.sup.a 
______________________________________ 
VINOL .RTM. 125 
99.3 26-30 
VINOL .RTM. 165 
99.3 55-65 
VINOL .RTM. 107 
98.0-98.8 5.4-6.5 
VINOL .RTM. 205 
87.0-89.0 5-6 
______________________________________ 
.sup.a In cps, of a 4 percent by weight aqueous solution at 20 degrees C. 
TABLE 6 
______________________________________ 
Sample Nom. VINOL .RTM. 
PVOH Mason Jar 
No. Basis.sup.a 
Resin Add-On.sup.b 
Test.sup.c 
WVTR.sup.d 
______________________________________ 
10A 34 -- 0 0/3 3170 
10B 34 125 4 2/3 2366 
10C 34 165 4 2/3 2922 
10D 34 107 6 3/3 2004 
10E 34 205 4 3/3 2695 
.sup. 10F.sup.e 
34 205 4 .sup. 2/3.sup.f 
2991 
______________________________________ 
.sup.a Nominal basis weight in g/m.sup.2. 
.sup.b In g/m.sup.2. 
.sup.c Number of trials which passed/number of trials run. 
.sup.d Water vapor transmission rate in g/m.sup.2 /24 hours. 
.sup.e Heat treated at 120 degrees C. for 80 minutes to thermally 
crosslink the PVOH. 
.sup.f One trial leaked around the rim of the jar. 
Sample 10E of Example 10 is of particular interest since it illustrates one 
of the unexpected results from using water-soluble polymeric materials in 
accordance with the present invention. Both the resin and the film formed 
from the resin are soluble in water at ambient temperature. Yet, the 
sample passed the Mason Jar test. In the test, the sample was oriented 
with the meltblown web toward the inside of the jar and, as a consequence, 
was in direct contact with the water. Because the meltblown web itself 
acts as a partial barrier to the passage of water through it, the web acts 
as a protective layer for the film and significantly extends the period of 
time over which the film can remain intact in the presence of water. Thus, 
the film and the porous substrate in combination can, depending upon the 
characteristics of the substrate, exhibit a kind of synergism in which the 
barrier properties of the combination exceed the barrier properties of the 
components of the combination. That is, the meltblown web by itself fails 
the Mason Jar Test, and the film by itself is soluble in water and would 
dissolve within the time period over which the test is run. In 
combination, however, the meltblown web and water-soluble film are able to 
pass the Mason Jar Test if oriented properly with respect to the direction 
of the aqueous challenge. Since such a resin may not be suitable for all 
applications, it is preferred that the continuous film portion of the 
barrier of the present invention have a somewhat reduced water solubility; 
that is, it is preferred that such film be substantially insoluble in 
water having a temperature less than about 50 degrees C. 
EXAMPLE 11 
The procedure of Example 1 was repeated, except that the coating solution 
was an eight percent by weight solution of VINOL.RTM.125 in water, the 
meltblown web had a nominal basis weight of 25 g/m.sup.2, and the coating 
solution was applied by means of a No. 22 Meyer rod. The coated sample was 
dried at about 140 degrees for two minutes. The PVOH add-on was 5.3 
g/m.sup.2. The sample passed the Mason Jar Test and gave a water vapor 
transmission rate of 1761 g/m.sup.2 /24 hours. 
EXAMPLE 12 
The procedure of Example 11 was repeated, except that a second coating of 
the PVOH solution was applied over the first coating after the sample had 
been dried; the total PVOH add-on was 7.1 g/m.sup.2. The sample passed the 
Mason Jar Test and gave a water vapor transmission rate of 1348 g/m.sup.2 
/24 hours. 
EXAMPLE 13 
The procedure of Example 11 was repeated, except that the PVOH solution was 
replaced with a 10 percent by weight aqueous solution of VINOL.RTM. SH-72 
(Air Products and Chemicals, Inc., Polymer Chemicals, Allentown, Pa.). 
According to information supplied by the manufacturer, the resin was a 
tackified (borated) grade derived from VINOL.RTM.165. The viscosity of a 
10 percent by weight aqueous solution of the resin at 25 degrees C. was 
reported to be 3800-5500 cps. The PVOH add-on was 7.7 g/m.sup.2. The 
sample passed the Mason Jar Test and gave a water vapor transmission rate 
of 1714 g/m.sup.2 /24 hours. 
EXAMPLE 14 
The procedure of Example 11 was repeated, except that the PVOH solution 
also contained 1 percent by weight glycerol, or about 12 percent by 
weight, based on the weight of PVOH. The add-on of the PVOH composition 
was 5.3 g/m.sup.2. The sample passed the Mason Jar Test and gave a water 
vapor transmission rate of 2392 g/m.sup.2 /24 hours. 
The polypropylene meltblown web employed in Examples 11-14, inclusive, was 
examined by scanning electron microscopy. The coated samples obtained from 
Examples 11-14, inclusive, also were examined by scanning electron 
microscopy. 
FIG. 1 is a representation of a plane view scanning electron micrograph 
(SEM) of the meltblown web used in Examples 11-14, inclusive, taken at a 
magnification of 200.times.. The porous nature of the web is clearly 
evident. 
FIG. 2 is a representation of a plane view SEM of the coated sample of 
Example 13, taken at a magnification of 200.times.. The continuous nature 
of the film and the comingling phenomenon described earlier are apparent. 
FIG. 3 is similar to FIG. 2, except that the sample is that of Example 12. 
The effectiveness of two coats in giving a much more substantial film is 
apparent, even though the total film add-on is about the same for both 
samples. 
FIGS. 4-8, inclusive, are representations of cross-sectional view SEMs of 
the coated samples of Examples 11, 13, and 14, taken at either of two 
magnifications, as summarized in the following table: 
______________________________________ 
FIG. Magnification 
Example 
______________________________________ 
4 1000.times. 
11 
5 200.times. 
14 
6 1000.times. 
14 
7 200.times. 
13 
8 1000.times. 
13 
______________________________________ 
The figures illustrate the very thin nature of the resulting films and the 
comingling phenomenon described earlier. 
EXAMPLE 15 
A 1.5-mil poly(vinyl alcohol) film was edge-bonded thermally to a meltblown 
polypropylene web having a basis weight of 25 gsm. Edge bonding was 
accomplished with a Model 14P Thermal Impulse Heat Sealing Machine 
(Vertrod Corp., Brooklyn, N.Y.); both the dwell and heat settings were 
about 4. The film was a MONO-SOL 1-000 series film (Mono-Sol Division, 
Chris Craft Industries, Inc, Gary, Ind.) having a water vapor transmission 
rate of 1719 g/m.sup.2 /24 hours. A spunbonded polypropylene web then was 
thermally bonded to the other side of the film. The resulting composite 
passed the Mason Jar Test, and gave a water vapor transmission rate of 
1780 g/m.sup.2 /24 hours. 
Having thus described the invention, numerous changes and modifications 
thereof will be readily apparent to those having ordinary skill in the art 
without departing from the spirit or scope of the invention.