Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 ~ e~ 9
~NONWOVEN, COA$~D SUBST~ATES AND METHOD OF
APPLYING A COATING AT HIGH ~ATH
CONCENTRaTION AND LOW ~ET PIC~-UP~
~e¢hnicæl Field
This invention relates to coated materials and
processes for coating fibrous materials. More particularly,
this invention relates to nonwoven, hydrophobic materials
uniformly coated with a wetting agent and having improved
tensile strength. This invention also particularly relates
to a process for uniformly coating a nonwoven, hydrophobic
material with a wetting agent at high bath concentration and
low wet pick-up. In addition, it relates to resulting
nonwoven fabrics which may be either hydrophilic on both sides
or hydrophilic on one side and hydrophobic on the other, in
the latter case exhibiting "one-way valve" properties.
Background of the Invention
Nonwoven, hydrophobic substrates or materials are well
known in the art. Many disposable products such as diapers
and sanitary napkins are constructed with top sheets made of
nonwoven, hydrophobia material. The outer surface of these
top sheets is typically treated with a wetting agent to allow
fluid to more readily penetrate the outer surface for capture
by an underlying absorbent pad. Top sheets made with a
hydrophobic material having an outer surface treated with a
wetting agent are preferred for such applications over top
sheets made with a hydrophilic material because the wetting
agent provides hydrophilic properties to the outer surface to
improve fluid penetration without compromising the desired
hydrophobic properties of the inner surface of the top sheet.
The hydrophobic inner surface retains the penetrated fluid and
inhibits flow back of the penetrated fluid to the outer
surface, thus acting as a "one-way valve".
It is desired to apply the wetting agent to the
nonwoven material in a uniform concentration for aesthetics
and to provide uniform wettability to the outer material.
' ~
Nonwoven materials, however, typically have irregular surfaces
onto which it is difficult to uniformly apply the wetting
agent. This is particularly so if a coating solution having
a high concentration of wetting agent is used. For these
reasons, wetting agents are typically applied by spraying,
direct printing, or roller coating a low concentration
solution of the wetting agent onto the outer surface of the
material. One example of a material treated using
conventional techniques is disclosed in ~nited States Patent
No. 4,585,44~ to Karami.
One disadvantage of coating nonwoven materials using
a low concentration solution is that a large amount of the
solvent (usually water) is typically "picked-up" by the
material. The wet "pick-up" is removed by drying the coated
material to evaporate the solvent. This drying step is
detrimental to the strength and softness of the material, as
it has been observed that the action of wetting and drying a
nonwoven material significantly decreases the tensile strength
of the material. Thus, there is a need in the art for a
method of uniformly applying a wetting agent to a nonwoven
material which results in a uniform application of the wetting
agent on the material without a significant decrease in the
tensile strength of the material.
~u~mary of the In~entio~
The present invention fills the above need by providing
a process for uniformly applying a high concentration solution
of a wetting agent to a fibrous substrate such as a nonwoven
material. The application of a high concentration solution
results in lower wet pick-up by the material, which reduces
subsequent drying of the material and the associatPd loss in
tensile strength. This provides a strong, nonwoven material
having a uniform coating.
Generally described, the present invention provides a
process for coating a material, the process comprising the
steps of introducing a coating solution to a first rotating
roll, the coating solution containing between about 20 and 30
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percent by weight of a wetting agent compound and between
about 70 and 80 percent by weight of a solvent; and passing
the material through a nip defined between the first roll and
a second rotating roll positioned adjacent the first roll,
wherein a portion of the coating solution is applied by the
first roll to a surface of the material in an amount such that
the wetting agent is appliQd to the material in an amount of
between about 0.1 and 0.5 percent by weight of the material,
and the solvent is applied to the material in an amount not
exceeding about 1 percent by weight of the material.
Another aspect o~ the present invention provides a
coated substrate, comprising a nonwoven material and a
substantially uniform coating on a surface of the nonwoven
material. The coating comprises a wetting agent applied to
the nonwoven material in an amount of between about 0.1 and
0.5 percent by weight of the nonwoven material and a solvent
applied to said nonwoven material in an amount not exceeding
about 1 percent by weight of said material.
Thus, it is an object of the present invention to
provide an improved coated material and process for coating
a material.
A further object of the present invention is to provide
a process for coating a fibrous material using a high
concentration coating solution such that wet pick-up and loss
of tensile strength are reduced and drying requirements are
reduced and may be eliminated.
A still further object of the present invention is to
provide a process for coating a fibrous material which does
not require drying of the coated material and yet
microbiological testing confirms that no unacceptable levels
of bacteria are present.
It is also an object of the present invention to
provide a coated material which has improved tensile strength
and in one preferred embodiment is hydrophobic on one surface
and hydrophilic on the other, exhibiting one-way valve
properties.
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B~ie~ D~scription of the Drawing3
Figure 1 is a perspective drawing of the "inverted L"
differential offset printer used to apply a coating to a
material in accordance with the present invention.
Figure 2 is a graph showing the percent surface
concentration of the wetting agent on the coated material of
the present invention as a function of cross-direction
position.
Figure 3 is a graph showing the percent surface
concentration of the wetting agent on the coated material of
the present invention as a function o~ machine-direction
position.
Figure 4 is a graph showing the percent surface
concentration of the wetting agent on the coated material of
the present invention as a function of gravure roll speed.
De~ailed Des¢riptio~ of ~he Invention
While the invention will be described in connection
with a preferred embodiment and method, it will be understood
that we do not intend to limit the invention to that
embodiment or method. On the contrary, we intend to cover all
alternatives, modifications, and equivalents as may be
included within the scope of the invention as defined by the
appended claims.
The nonwoven material 18 is preferably a hydrophobic,
nonwoven spunbonded we~ having a basis weight of between about
0.5 and 1.0 ounces per square yard ("osy") although the basis
weight is not known to be critical and may be higher, ~or
example, up to 2.5 osy depending on the desired application.
Such material is well known in the art and may be prepared in
conventional fashion such as illustrated by the following
patents: Dorscher et al. United States PatPnt No. 3,692,618;
Kinnev United States Patent Nos. 3,338,992 and 3,341,394; Levv
United States Patent No. 3,502,538; Hartmann United States
Patent Nos. 3,502,763 and 3,909,009; Dobo et al. United States
Patent No. 3,542,615; Harmon Canadian Patent No. 803,714; and
Appel et al. United States Patent No. 4,340,563. Other
nonwoven materials and methods for ~orming nonwoven materials
are contemplated for use with the present invention.
The wetting agen~ 14 is applied to a surface 50 of the
nonwoven material 18 using the printer 10 to provide
hydrophilic properties to the surface 50. The printer 10 is
preferably a "differential" type printer, with the term
"differential" referring to printers wherein the gravure roll
speed may be varied with respect to the material or line speed
to allow compensation for basis weight changes without
changing the gravure roll. The most preferred printer is that
which is referred to in the art as an "inverted L"
differential offset printer, such as is shown in Fig. 1. The
wetting agent 14 is preferably a non-ionic surfactant. A
preferred wetting agent for use with nonwoven materials having
a basis weight up to about 0.8 osy is "Triton X-102,"
available from Union Carbide. "Gemtex SM-33", available from
Finetex Inc. is a preferred wetting agent for use with
nonwoven materials having a basis weight in exces~ of about
0.8 osy, particularly where "one-way valve" properties are not
necessary. For certain personal care applications, it has
been experienced that a surface concentration of the wetting
agent on the material of between about 0.1 percent to 0.5
percent, broadly and, preferably, between about 0.16 percent
and 0.38 percent is desired. The "fountainless pan" doctor
blade system 44, supplies a uniform application of a solution
containing the wetting agent 14 to the gravure roll 38 in a
conventional manner. The solution is preferably a high
concentration aqueous solution having the wetting agent 14
present in an amount of between about 20 and 100 percent, and
most preferably about 25 percent, by weight of the solution.
The gravure roll 38 is preferably a metal roll of a
type conventionally used in the printing art, and having a
cell pattern known in the art as a "quad" pattern with between
about 300 and 7ao cells per inch and a cell size of between
about 1.5 and 4.0 CBM (cubic billion microns, volume per
square inch). The most preferred gravure roll is one known
g ~ ~
in the art as a 550 (cells p~r inch) quad, 1.7 CBM. The
gravure roll preferably rotates at a speed of between about
20 and 120 percent of the line speed, and most preferably
about 60 percent of the llne speed (line speed is described
below as preferably being between about 300 and 1,500 feet per
minute). A graph showing the percent surface concentration
of the wetting agent as a function of gravure roll speed for
a representative sample is shown in Fig. 4.
The transfer roll 24 is preferably a rubber roll of a
type conventionally used in the printing art, and having a
durometer hardness of between about 60 and 85. The gravure
roll 38 is spaced apart from the transfer roll 24 such that
in operation a desired amount of the coating solution
transfers to ~he transfer roll for subsequent application to
the nonwoven material. The distance between the transfer roll
24 and the gravure roll 38 which defines the nip 39 is
preferably between about 1/16 and 1/2 inch to achieve the
desired surface concentration, and is op~imally about 3/16
inch when applying the coating solution to nonwoven materials
having a basis weight of about 0.7 osy. The transfer roll 24
preferably rotates at a rate which advances the material at
a line speed of between about 300 and l,500 feet per minute,
with an optimum line speed of about 5~0 feet per minuteO The
bac~ing roll 20 is preferably either a metal or rubber roll
of a type well known in the printing art, having a durometer
hardness of about 90. The backing roll 20 rotates at a rate
which provides the same line speed as the transfer roll 24.
The spacing between the backing roll 20 and the transfer roll
20 which defines the nip 30 is preferably between about 1/4
and 3/4 inch and is optimally about 3/8 inch whPn coating
nonwoven materials having a basis weight of about 0.7 osy.
By using the differential printer 10 for coating the
nonwoven material 18, the resulting coated material 34 has a
more uniform coating of wetting agent and has improved tensile
strength over conventionally prepared coated materials. In
order to evaluate the effect of coating a nonwoven material
using a high concentration bath or solution, a representative
3 9
sample was produced by applying a 25 percent by weight "Triton
X-102" aqueous solution to a 0.7 osy nonwoven, hydrophobic
material. The solution was applied using an "inverted L"
differential offset printer producing a line speed of 500 fpm
and a gravure roll speed of 300 fpm (60% line speed). The wet
pick-up for the representative sample was determined to be
about 0.9 percent and the average surface concentration of the
wetting agent was about 0.3 percent solids (coat weight). No
drying was necessary. This yielded a uniform distribution of
about 0.24 grams of coating solution per square yard.
With reference to Figs. 2 and 3, one can see
graphically the uniformity of the surface concentration of the
wetting agent on the representative sample in the
cross-direction (Fig. 2) and in the machine-direction (Fig.
3). The representative sample exhibited overall a 5.0 percent
coefficient of variation in surface concentration across the
material, and materials of the invention will generally
exhibit a coefficient of variation in surface concentration
of 10.0 percent or less. Loss in tensile strength for the
representative sample was determined (in accordance with
~TM-6200) by comparing the tensile strength of treated
material with untreated material for the same cross-direction
or deckle position. Material treated in accordance with the
present invention experienced a 5 percent loss in tensile
strength. This compares with a typical tensile strength loss
of at least 21 percent for coated materials prepared utilizing
spray treatment and treatments requiring secondary drying over
steam cans.
The printing process of the present invention coats the
material from the transfer roll; therefore, only one side of
the coated material is hydrophilic, while the other side is
hydrophobic. Hydrophilic material is wettable material that
produces less than 20 mililiters of runo~f; hydrophobic
material produces greater than 20 mililiters of runoff. A
material having a hydrophilic and hydrophobic surface rapidly
allows fluid to pass through and does not allow it to flow
back. Thus, such material acts as a "one way valve." It has
been observed that materlals having basis weights between 0.5
and 1.0 osy which are treated in accordance with the present
invention behave as one way valves when, after treatment, they
are not wound up into roll form in a manner that causes
contact between opposing sides of the material. It has also
been observed that when materials having a basis weight of
less than about 0.85 osy are rolled up after application of
the wetting agent, some of the wetting agent transfers to the
untreated side, producing a two-sided h~ydrophilic material.
The time required for the wetting agent to transfer to the
untreated side being dependent upon the basis weight.
Materials having a basis weight greater than about 0.85 osy
remain one way valves in sheet or roll form. If two sided
hydrophilic behavior is desired for materials having a basis
weight in excess of 0.85 osy, a conventional four roll
differential printer (dual printer) may be utilized to apply
the wetting agent to both sides.
Micropore filtration testing of materials treated in
accordance with the invention showed reduced levels of Class
I, Class II and Class III bacteria when compared with
untreated materials. Class I included Bacillus sp,
Corynebacterium, other gram positive rods, mold and yeast
(other than Candida albicans). Class II included
Staphylococcus sp. (other than S. Aureus), Psuedomonas sp.
(other than P. ~eruginosa), Enterobacteriaceae (other than E.
Coli and Salmonella sp.), other gram positive cocci,
Oxidative-Fermentative bacteria, and other gram negative rods.
Class III included Staphylococcus aureus, Escherichia coli,
Pseudomonas aeruginosa, Salmonella sp., and Candida albicans.
While the control had a total CFU of 17, none of the treated
samples exceeded 10 CFU.
The foregoing description relates to preferred
embodiments of the present invention, and modifications or
alterations may be made without departing from the spirit and
scope of the invention as defined in the following claims.
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