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Description  |
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DESCRIPTION
1. Technical Field
This invention relates to the treatment of sheet material, especially
textile fabrics, with aqueous treating compositions which are in the form
of a foam so as to minimize the amount of liquid which is applied, and
thus minimize the energy needed to evaporate the volatile portion of the
composition and the size of the ovens needed for this purpose.
2. Background Art
It is well known to foam aqueous treating compositions to facilitate
application to sheet material and to minimize the drying requirements.
Textile fabrics are particularly contemplated, and the preferred
treatments are those involving the application of a resinous binder,
especially those containing dissolved resin such as permanent press
finishes.
One of the difficulties associated with foam application is that it is
necessary to completely collapse the foam in order to avoid the presence
of a foam structure in the final product. This problem is particularly
difficult when the composition which is applied includes a resinous
binder. One way to insure foam collapse is to employ an unstable foam
which is especially formulated to substantially instantaneously collapse
as it contacts the fabric. Unfortunately, it is difficult to control the
amount of material applied to the fabric for this will vary with every
change in the foam, the fabric, and the line speed. Very sophisticated and
expensive apparatus is required, and a computer is needed to control it.
Starting and stopping are particularly difficult and can result in
variations in the treatment which extend over a significant length of the
fabric being treated.
It is also known to apply a layer of a stable foam, as by knife
application, and then pressure applied at the nip of a roller is used to
force the foam to collapse. However, these stable foams do not always
collapse completely, and foam or fibers or both may build up on the
pressure rollers to disturb the textile treating operation.
Disclosure of Invention
In this invention, an aqueous foam composition which is sufficiently stable
to be formed into a layer and to retain this layer form long enough to be
handled, is applied to a sheet material and collapse of the foam structure
is effected or completed by the application of heat. This provides a
controllable foam system in which foam collapse is insured when heat is
applied.
It will be understood that heat is normally employed as a part of the
drying operation, so the treatment is simplified, and the apparatus
requirements are eased. In comparison with instantly collapsing systems,
the simplification of the apparatus is obvious. In comparison with
pressure collapse, one can eliminate precisely controlled pressure rollers
which impose substantial pressure. Unlike the application of an instantly
collapsing foam, the amount of material applied to the fabric is easily
and exactly controlled and change of speed as well as starting and
stopping are easily achieved with minimal modification of the treatment as
the speed of the system is changed. Since the very operation which dries
the foam causes it to collapse, the foam structure is reliably removed
from the final product where it is not desired. For the same reason, build
up of material on the processing apparatus is minimized.
A pressure roller may be employed in this invention to cause penetration of
the foam into the intersticies of a fabric being treated, and some foam
collapse may be induced thereby. However, heat is still relied upon to
remove the foam structure, and the pressure of the roller need not be
appropriate to insure foam collapse. More particularly, pressures of about
20 to 60 psi are normally required for substantially complete cell
collapse, and far less pressure is appropriate herein where the purpose of
pressure application is different.
Heat collapsing foams are different from the usual foams. Normally, a foam
is either poorly stable and collapses quickly when spread on a substrate,
or it is stable and lasts a long time so that is must be mechanically
worked, as by the application of pressure, to cause it to collapse. We
have found that foams may be produced which are relatively stable in the
sense that they can be formed in a layer which remains intact and does not
perceptibly collapse during normal working time on an application machine.
This is advantageous in that the layer can be formed to contain an exact
amount of treating agent which is maintained uniform with time and without
regard to the speed of the machine. In a beaker, the foams in this
invention are stable for periods of from about 5 minutes to about 5 hours,
though this is not a critical factor herein. Despite reasonable stability
at temperatures of from 15.degree. C. to 30.degree. C., the foams collapse
more and more rapidly as the temperature increases. In this invention
practicality requires an oven baking temperature of at least about
150.degree. F., more preferably at least 200.degree. F.
In order to cause foam collapse with increasing temperature, we combine in
the aqueous treating composition which is foamed, a water soluble
surfactant which stabilizes the foam, and a relatively water insoluble
defoamer. The presence of the defoamer at room temperature does not break
the foam because it is poorly soluble, though the foams which are produced
are not as uniformly fine bubbled as are commonly available in the art.
Instead, when the foam is heated, the defoamer becomes more soluble, and
chemically breaks the foam. This is important because it allows the foam
to break where mechanical pressure has not been effective.
The defoamers are preferably surface active agents having a low HLB value
of from 0.1 to 10.0, preferably 0.1 to 7.0, and these are usually fatty
alcohols or ethoxylates thereof with ethylene oxide in small amount so as
to retain water insolubility. The water soluble surfactants which maintain
the foam have an HLB value of more than 8.5 (and at least 3.0 units higher
than the defoamer), usually from 12 to 40. The weight proportions of water
soluble surfactant to defoamer are not critical and may vary from 1 to 10
to 10 to 1, and even more in some instances. One must use enough water
soluble high HLB surfactant to provide a foam which is stable in a layer
long enough to handle, and the water insoluble defoamer must be present in
an amount to break the foam when heated. Inclusion of the defoamer does
impair the foam somewhat, but this is also not important. Foaming is
normally carried out with air to a volume of from 2 to 20 times the
unfoamed volume.
Mixtures which are useful herein are disclosed, though not to provide a
heat collapsing foam, in the application of Christian Guth and Jorg Binz,
Ser. No. 058,047, filed July 16, 1979 and now abandoned, and the
disclosure of this application is incorporated herein by reference.
The invention will be more fully understood from a consideration of the
accompanying drawings in which several forms of the invention are
illustrated in diagrammatic form. In these drawings:
FIG. 1 shows the knife application of a foam layer which may be compressed
into the fabric by optional rollers and then heated to collapse any
remaining foam structure.
FIG. 2 is similar to FIG. 1 except that a floating knife is used to apply
the foam and force the foam into the intersticies of the fabric which is
treated;
FIG. 3 shows the foam being applied to a fabric during a vertical pass
thereof between horizontally positioned rollers; and
FIG. 4 shows the foam layer transferred to a tile being coated.
Referring more particularly to FIG. 1, a fabric 10 is unwound from a supply
roller 11 and is passed over a supporting table 12 beneath a knife 13
which is spaced above the fabric. Foam is placed behind the knife where it
piles up as indicated at 14 and passes beneath the knife to form a layer
15. The fabric 10 with the foam layer 15 thereon may be permitted to pass
directly into the oven 16 where the foam simultaneously collapses and
dries, and the treated fabric is then wound up on roller 17.
In some instances it is desired to cause the treating composition to more
uniformly penetrate the fabric 10, and this is achieved by using the
optional rollers 18 which are shown in phantom. Very little pressure is
needed, and the foam does not normally fully collapse as a result of
roller pressure. However, more uniform penetration is obtained when
desired, and the heat encountered in oven 16 completes the collapse of the
foam.
In FIG. 2, the fabric 10 runs under tension against the edge of knife 13.
This forces a smaller amount of foam into the fabric which is then dried
and collapsed in the oven 16. It will be noted that like numbers are
applied to like parts to ease the burden of understanding.
FIG. 3 shows a vertical pass of the fabric 10 between rollers 19 which are
horizontally arranged. The foam may be piled up on one or both sides of
the fabric, depending upon whether the fabric is to be treated on one or
both sides. Again, the pressure applied by the rollers need not be
sufficient to completely collapse the foam, and the oven not shown in FIG.
2 would function to simultaneously dry the foam and collapse it so that
the puffiness created by residual foam structure in the final product
would not be present.
FIG. 4 illustrates a transfer process in which the foam 20 is piled up
above rollers 21 and 22 with roller 21 being of nonadhesive material so
that the layer of foam which is formed adheres to roller 22. This foam
layer 23 is then transferred to a tile which is passed beneath roller 22
on belt 24 which runs around rollers 25 and 26. A roller 27 supports the
tile 28 as it passes beneath roller 22 where it is coated with the
transferred foam layer 23. The coated tile is then baked to collapse the
foam in oven 29. In this system, since the foam is dried and collapsed at
the same time, its penetration into a porous tile is minimized. This is
particularly advantageous in the application of coatings and layers of
adhesive.
It is desired to stress that many variations are permissible within the
scope of this invention. Thus, the foam may be clear, dyed, or pigmented.
The surface being treated may be imperforate, like paper, or it may be an
ordinary textile fabric. The treatment may involve bleaching, dyeing, or
various other treatments, especially including permanent press finishing
in which the aqueous treating composition includes a dissolved aminoplast
resin.
BEST MODE FOR CARRYING OUT THE INVENTION
This invention will now be illustrated in the following specific example
which shows a typical permanent press application which constitutes the
area in which this invention is presently considered to have its greatest
impact.
EXAMPLE
The following is an illustrative composition which can be foamed and
applied to drapery and table cloth fabrics in order to impart wash and
wear properties to the fabrics.
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Component Percent by Weight
______________________________________
1-Ethylene-vinyl acetate aqueous
emulsion copolymer containing 75 pts.
vinyl acetate, 25 pts. ethylene, 3 pts.
N-methylol allyl carbamate, and 2 pts.
acrylamide and having a solids
content of 45% 7
2-Dimethylol dihydroxy ethylene
urea (40% solids in water)
50
3-High density polyethylene
softener (25% solids in water)
10
4-Aqueous emulsion polymer of
methacrylic acid (25% solids)
30
5-Sodium lauryl sulfate
(30% solids in water)
1
6-Emulsion of water-soluble foam
stabilizer and water-insoluble
defoamer (notel) 2
______________________________________
Note 1
This mixture is provided by emulsifying 65 parts of coco fatty acid amide
and 65 parts of cetyl alcohol in 865 parts of water with the aid of 5
parts of stearyl alcohol ethoxylated with 20 moles of ethylene oxide per
mole of alcohol.
The above aqueous composition is foamed to a cup weight of 200 grams per
liter (a blow ratio of about 4:1) and is applied to the fabric using a
pair of rolls which apply very little pressure to force the foam into the
fabric. The wet impregnated fabric contains uncollapsed cells and is dried
by baking which serves to complete cell collapse. Two baking schedules are
typical, e.g., 4 minutes at 280.degree. F. and 30 seconds at 360.degree. F
.
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