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Description  |
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BACKGROUND OF THE INVENTION
Laundry detergents are most commonly available in either liquid or powder
form. In order to use such detergents, the user must measure out a certain
quantity from a supply bottle or box and pour the measured amount into the
clothes washer. In addition, if a fabric softener is desired, the fabric
softener must be separately measured or at least separately deposited into
the washer or dryer. Such multiple products, containers, and measuring can
be messy and, at the very least an inconvenience, particularly for
apartment dwellers who must carry all the necessary containers, etc., to
the laundry area.
In this regard, the prior art discloses a variety of alternative cleaning
products which are intended to provide improved convenience to the
consumer. For example, U.S. Pat. No. 4,356,099 to Davies et al. discloses
a laundry cleaning product comprising a plastic bag containing a liquid
detergent. The bag has a weak seal which is opened by the mechanical
action of the washing machine, thereby releasing the liquid detergent.
U.S. Pat. No. 4,188,304 to Clarke et al. discloses a similar detergent
product comprising a plastic bag containing a particulate detergent. The
bag contains a water-sensitive seal which discharges the contents of the
bag when contacted with water.
U.S. Pat. No. 3,686,075 to Morton discloses a sheet substrate containing a
fabric softener which is to be preferably used in the clothes dryer, but
can also be added to a wash machine during its rinse cycle.
U.S. Pat. No. 4,170,565 to Flesher et al. discloses a laundry product
comprising a detergent composition contained between two layers of a
water-insoluble permeable substrate such as a polypropylene meltblown web.
When contacted by water during the wash cycle, the detergent is dissolved
and permeates through the substrate into the wash water. Most
significantly, at column 1, lines 56-65, Flesher et al. apparently
recognize the potential value of a single layer substrate for delivering
laundry detergent, but concluded it is not feasible because of difficulty
in loading the substrate with a sufficient amount of detergent and the
sticky feel of any product that might be produced.
Therefore there is a need for a laundry cleaning product containing a
sufficient premeasured amount of detergent which is convenient to use and
economical to manufacture.
SUMMARY OF THE INVENTION
It has been discovered that meltblown webs possess a unique ability to
absorb and hold an amount of liquid detergent sufficient to wash a load of
laundry. However, it has also been found that in preparing liquid
detergent formulations to be incorporated into the meltblown web, the
presence of certain detergent enhancing ingredients, such as sodium
citrate, creates an unstable solution and minimizes the total amount of
surfactant that can be added to the detergent formulation. In turn, this
limits the total amount of active detergent solids that can be
incorporated into a meltblown detergent sheet. To overcome this
difficulty, it has been discovered that the total amount of active
detergent solids incorporated into the sheet can be increased if the
sodium citrate and/or other detergent enhancers in the liquid detergent
formulation are independently incorporated into the meltblown web prior to
the balance of the formulation. In this way the creation of an unstable
solution is avoided and the amount of active detergent solids that can be
added to the total detergent formulation is increased by up to about 25
percent.
In general, the invention resides in a method for making a laundry
detergent sheet comprising: (a) forming a meltblown web from molten
thermoplastic meltblown fibers; (b) spraying the meltblown fibers with an
aqueous solution of detergent enhancers, preferably before the meltblown
fibers are formed into a web; (c) saturating the meltblown web with a
solution containing the balance of the liquid detergent formulation; and
(d) drying the web to a water content of about 10 percent or less. For
purposes herein, "detergent enhancers" refers to liquid detergent
formulation ingredients which promote phase separation of the detergent
formulation and includes anti-redeposition agents, water softening agents,
and salts.
The meltblown web can be any meltblown web made from a thermoplastic
polymer having a melting point greater than 110.degree. C. Polymers which
melt at lower temperatures are more likely to melt if exposed to clothes
dryer temperatures. A suitable polymer is polypropylene, which is the most
commonly used polymer for making meltblown webs. However, polymers having
melting points of about 165.degree. C. or greater, and preferably about
200.degree. C. or greater are preferred. Preferred polymers include
poly(ethylene terephthalate), which melts at about 250.degree. C.,
polycaprolactam (nylon 6), which melts at about 220.degree. C.,
poly(butylene terephthalate), which melts at about 221.degree. C., and
polymethyl pentene, which melts at 240.degree. C.
The process for making meltblown webs is well known in the art and is used
extensively for manufacturing a wide variety of commercial nonwoven
products. Representative examples of the meltblowing process are described
in U.S. Pat. No. 3,978,185 to Buntin et al. dated Aug. 31, 1976; U.S. Pat.
No. 4,298,649 to Meitner dated Nov. 3, 1981; and U.S. Pat. No. 4,100,324
to Anderson et al. dated July 11, 1978, all herein incorporated by
reference. For purposes of meltblowing, it is preferred that the apparent
viscosity of the polymer as it leaves the die tip be about 500 poise or
less, most preferably from about 150 to about 300 poise. Higher apparent
viscosities provide lower throughputs which are generally unsatisfactory
for commercial operation. Increased throughputs can be achieved by
lowering the apparent viscosity, which can be lowered either by lowering
the molecular weight of the polymer or by raising the temperature of the
polymer. It will be appreciated, however, that other meltblowing processes
will produce webs suitable for purposes of this invention. The meltblown
web can be combined or laminated to other supporting webs, such as
spunbonded webs, in order to impart strength or other attributes to the
product.
The basis weight for a single sheet of the untreated meltblown base webs of
this invention can range from about 80 to about 300 grams per square
meter. Preferably the basis weight will be from about 110 to about 250,
and most preferably about 160 grams per square meter. Basis weights lower
than the abovesaid range lack sufficient pore volume to hold the amount of
liquid detergent necessary to wash a load of laundry at a reasonable sheet
size. Basis weights greater than the abovesaid range are too difficult to
convert. It is within the scope of this invention, however, to incorporate
more than one ply into the product to increase the detergent load.
The size of the meltblown web can be from about 200 to about 2000 square
centimeters, preferably from about 600 to about 1,000 square centimeters,
and most preferably about 800 square centimeters. The minimum size of the
web is limited by the amount of liquid detergent the web can absorb and
hold. The maximum size is determined by consumer acceptance, convenience
and packaging considerations. It is preferred that the meltblown web be
pattern bonded to maintain integrity during use. Pattern bonding is
commonly performed during manufacture of meltblown webs by hot embossing
or ultrasonic bonding of the newly formed web.
The liquid detergent formulations useful for making products in accordance
with this invention can be any liquid detergent which is suitable for
cleaning laundry. As is well known in the detergent arts, these
formulations typically contain a large number of components such as
surfactants, fragrances, brighteners, dyes, solubilizers, pH adjusters,
and detergent enhancers.
Specific detergent enhancers which can be added to the meltblown web in
accordance with this invention include sodium citrate, carboxymethyl
cellulose, EDTA salts, sodium carbonate, sodium silicate, phosphates,
alumino silicates, nitrilotriacetic acid salts, sodium borate, poly(vinyl
alcohol), poly(vinyl acetate), and polyvinyl pyrrolidone. The amount of
each of the foregoing ingredients will vary widely depending upon the
specific detergent formulation. However, in general, the detergent
enhancers can be present in the following amounts (grams per sheet): water
softeners (0-20); and anti-redeposition agents (0-5). Other ingredients
which can also be included are: pH control agents (0-10); enzymes (0-5);
and brighteners (0-3).
The detergent ingredients which can be incorporated into the meltblown web
after the detergent enhancers have been added primarily include the active
detergent solids, such as surfactants such as nonionic, anionic,
amphoteric, and cationic surfactants. Other phase-compatible ingredients
can also be included with the active detergent solids, such as
stabilizers, pH control agents, brighteners, enzymes, dyes, etc.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic view of a meltblowing process for incorporating the
detergent enhancers into the meltblown web in accordance with this
invention.
FIG. 2 is a schematic view of a method for saturating the meltblown web
with the balance of the liquid detergent formulation.
DETAILED DESCRIPTION OF THE DRAWING
Directing attention to FIG. 1, the invention will be described in greater
detail. Shown is a process for making meltblown webs utilizing a plurality
of meltblowing die tips 5. These die tips are variously referred to as
"heads" or "banks." The die tips substantially extend across the width of
the forming fabric 6, which travels in a continuous loop around rolls 7
and 8, at least one of which is suitably driven. Each of the die tips is
supplied with molten polymer from an extruder and a source of compressed
air. The extrudate is broken up by the compressed air to form
discontinuous molten fibers which are deposited onto the traveling forming
wire to form the web. Shown in FIG. 1 for purposes of illustration are
three die tips in series, but for purposes of this invention any number
can be used depending upon the throughput from each die tip, desired
production speeds, and the basis weight of the meltblown web product. Each
die tip can be accompanied by an aqueous quench shower or spray 10 as
shown which serves to set the molten polymer fibers into a nonwoven
fibrous network. The quench shower is generally directed at the extruded
fibers between the extrusion die and the forming fabric. It can, however,
also be directed at the newly-formed web between banks. After formation,
the resulting meltblown web 13 is preferably passed through a hot
embossing roll nip 15 to thermally bond the web and enhance its integrity.
The web is then wound up on a suitable roll 16 for further processing or
converting.
In accordance with this invention, one or more of the quench sprays
comprise an aqueous solution or dispersion of detergent enhancers and/or
other detergent formulation ingredients as previously described. The
concentration of each ingredient will vary with the specific detergent
formulation, the particular ingredient, the number of quench sprays, the
line speed, the basis weight of the meltblown web, etc.
It is preferred that the detergent formulation ingredients be incorporated
into the meltblown web only via quench sprays accompanying the
intermediate die tips and not via the first and/or last die tip(s). The
reason for this preference is that some of the detergent ingredients can
cause stickiness, which is better confined to the central portion of the
meltblown web rather than being present on the surface(s). Therefore,
referring to FIG. 1, the preferred detergent ingredient-containing quench
would be quench spray 10'. However, for purposes of this invention, all
quench sprays can contain one or more detergent ingredients.
FIG. 2, shows a supply roll 21 of the meltblown web material, which
contains certain detergent ingredients as described in connection with
FIG. 1, to be saturated with the balance of the liquid detergent
formulation. Preferably the web has been thermally pattern-bonded to
provide sufficient integrity to withstand a wash and dry cycle without
disintegrating. The web 22 is passed through a series of tension control
rolls 23A, 23B, 23C, and 23D and passed over a slotted bar applicator 25
which is filled with an aqueous solution containing the balance of the
detergent formulation, primarily containing the active detergent solids.
As used herein, a "slotted bar" applicator includes applicators having
slots, holes, or other orifices which serve to deposit the solution onto
the surface of the web, such as by coating, injecting, printing, and the
like. The solution is deposited onto the web through a slot 26 to saturate
the web with the solution. The rate at which the solution is applied to
the web will depend upon the line speed, the detergent composition, the
absorbency of the web, etc. Other means for incorporating the solution
into the web are also suitable, however. The solution can be applied to
either or both sides of the web.
After leaving the slotted bar applicator, the saturated web 31 passes
through a controlled nip between nip rolls 32 and 33 which serves to
enhance the even distribution of the solution throughout the web.
The treated web then passes through a dryer 35, preferably an air flotation
dryer, which removes substantially all (up to about 95 percent) of the
available moisture, which includes alcohol and water. More typically the
moisture removal will be on the order of about 80 percent. The product
leaving the dryer contains concentrated liquid detergent having a gel-like
consistency, yet the web has an acceptable feel.
After drying, the dried web passes around a tension control roll 36, a pull
roll 37, a slitter roll 38, a Mount Hope roll 39, and a rewind drive roll
40. The web is thereby wound onto the rewind roll 41 for subsequent
converting and packaging operations.
It will be appreciated that the foregoing discussion, given for purposes of
illustration, is not to be construed as limiting the scope of this
invention.
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