U.S. patent number 3,661,154 [Application Number 04/830,205] was granted by the patent office on 1972-05-09 for water-absorbing material.
Invention is credited to David Torr.
United States Patent |
3,661,154 |
Torr |
May 9, 1972 |
WATER-ABSORBING MATERIAL
Abstract
A sheet which is a blend of water-insoluble fibers and pieces of
film of a dry material which converts to a gel quickly on contact
with a large amount of water. The blend is formed by suspending the
fibers and film pieces in air. The sheet is useful in structures
designed for absorbing body fluids, e.g. disposable diapers.
Inventors: |
Torr; David (Oyster Bay,
NY) |
Family
ID: |
25256532 |
Appl.
No.: |
04/830,205 |
Filed: |
May 26, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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784699 |
Dec 18, 1968 |
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Current U.S.
Class: |
604/368;
604/375 |
Current CPC
Class: |
A61F
13/15577 (20130101) |
Current International
Class: |
A61F
13/15 (20060101); A61f 013/16 () |
Field of
Search: |
;128/284,285,287,290,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Charles F.
Parent Case Text
This application is a continuation-in-part of my application Ser.
No. 784,699 filed Dec. 18, 1968 now abandoned.
Claims
I claim:
1. Process for making water-absorbent products which comprises
forming a blend of cellulose fibers and solid particles of a
material which on contact with 10 times its weight of water loses
its shape rapidly and forms a soft plastic gel, and humidifying
said blend by injecting steam into said blend to improve the
adhesion of said particles to said fibers, the proportion of said
particles in said blend being about 1 to 50 percent.
2. Process as in claim 1 in which said particles are pieces of film
of said material.
3. Process as in claim 1 in which said particles comprise
starch.
4. Process as in claim 1 in which said humidification is effected
by injecting a current of steam into said blend.
5. Process as in claim 4 in which the steam injection is such as to
cause the surfaces of said particles to become adhesive without
destroying their integrity.
6. Process as in claim 5 in which said particles comprise guar.
Description
This invention relates to the production of structures designed for
absorbing body fluids, e.g. diapers, catamenial devices such as
sanitary napkins or vaginal tampons, pads for protecting the bed
against wetting, surgical sheets and surgical and medical
applications.
In one aspect of this invention, there is produced a sheet
comprising a blend of water-insoluble fibers and pieces of film of
a dry material which on contact with water (e.g. on contact with
10, 15, or more preferably 20 or more, times its weight of water at
25.degree. C.) loses its film-like character within a very short
period of time (e.g. less than a minute) and forms a soft plastic
gel. The invention is particularly useful when the water-insoluble
fibers are cellulose fibers and, especially, short cellulose fibers
such as woodpulp cellulose (e.g. bleached sulfite or sulfate pulp)
and when the absorbent product is a diaper, most preferably a
disposable diaper. Thus, unlike ordinary diapers made wholly of
cellulose, which can give up their absorbed urine when pressed or
squeezed, diapers containing the fibers of this invention retain
the moisture in the form of the soft non-fibrous gel and are
therefore more comfortable in use. The gel is harmless and inert to
the body of the wearer.
In the accompanying drawing is
FIG. 1 is a schematic representation of a suitable process,
FIG. 2 is a schematic view, in cross section, of one form of
disposable diaper, and
FIG. 3 is a schematic plan view of a disposable diaper having lines
of weakness for easy tearability of the product.
To form a substantially uniform blend of the pieces of film and the
fibers, the film pieces and the fibers are suspended together in
air or other gas and a layer of the mixture is deposited from the
suspension. About 1 to 50 parts of the film pieces are used per 100
parts of the cellulose fibers; in one preferred form the proportion
of the film pieces is on the order of about 5 to 10 parts per 100
parts of the cellulose fibers. In one embodiment a mass of wood
pulp fibers is broken up in a hammer mill 11 (FIG. 1) and then the
fibers are conveyed from the mill with a current of air to an
air-separating zone such as a cyclone type of separator 12, at the
bottom of which the blend of fibers and film pieces is continuously
collected in fluffy form and continuously deposited as a sheet, 13
of substantially uniform thickness, of said blend on a continuously
moving belt 14. The deposited sheet may be a batt whose thickness
is, say, about 1/4 to 1 inch. Alternatively the airstream carrying
said blend of fibers and film pieces is blown against a moving
continuous screen to form the sheet directly.
The film pieces may be fed to the airstream in any suitable manner.
For instance, they may be metered into the cyclone (e.g. by means
of a feed screw, or by conveying them while dispersed in another
current of air which is fed to the cyclone chamber, e.g. at the top
thereof, and which may be at a somewhat higher pressure than the
air pressure in the cyclone which itself may be at substantially
atmospheric pressure. The cyclone may be operated under such
conditions that the film pieces, or at least those pieces of larger
size, are broken up to form smaller film pieces therein by the
action of the rapidly moving air, turbulence, and impacts against
the cellulose fiber, against the walls or any baffles of the
chamber or against other film pieces. The film pieces may also be
metered into any conveyor in which the fibers are transported from
the mill to the air stream. They may also be pre-dispersed in the
same airstream used to take up the fibers; that is an airstream
carrying the film pieces can be used to pick up the fibers from the
outlet of the mill. A higher pressure airstream carrying the film
pieces may be discharged in a countercurrent or transverse
direction into a main airstream carrying the fibers so as to create
a localized zone in which the turbulence and the particle impacts
are increased, to produce a blend which may then travel in the
general direction of the main stream of suspended fibers.
To improve the adhesion of the film pieces to the fibers the
mixture thereof may be humidified, preferably by injecting steam
(e.g. saturated steam) into or onto the mixture. Thus a current of
steam may be directed at the deposited sheet 13 e.g. at 16 in FIG.
1) or at the stream of collected fiber-film piece blend at the
bottom of, or just below, the cyclone (e.g. at 17 in FIG. 1), from
one or both sides. The pressure, temperature, speed and width of
the steam current or currents is preferably such as to cause the
surfaces of the film pieces to become adhesive without destroying
their integrity; such conditions can be readily determined by
simple experiment with each particular product.
After deposition of the blend in sheet form the sheet may then be
compacted into the desired thickness (e.g. 1/8 to 1 inch,
preferably about one-fourth to one-half inch) as by passing it
between pressure rolls and may then be cut to a width suitable for
the final product (e.g. for a diaper the width may be, say, 6 to 24
inches).
The sheet (compacted or uncompacted) may be assembled with other
layers to form the final product. For instance, in a typical diaper
this base sheet 19 (FIG. 2) may be covered with a thin
water-permeable layer of soft non-woven fabric 21 (e.g. of bonded
cellulose fibers) or woven or knitted fabric, to form the
body-contacting side of the diaper, and may be covered on its other
side with a water-impermeable or water-repellant material, which
may be, for instance, a preformed film 22 (e.g. of polyethylene) or
may be a coating of water repellant material which may or may not
be air permeable.
To give additional absorbency there may be superimposed, directly
on the base sheet, an additional thickness of a sheet 24 of
cellulose fiber material (or, more preferably, of the blend of
fibers and film pieces). This additional sheet may be narrower than
the base sheet (e.g. it may be 3 to 12 inches wide) and it may be
disposed along the center portion of the diaper at the area most
likely to be wetted. It may be the same thickness as, or thicker or
thinner than, the base sheet.
In one embodiment of this invention, the diaper or other product
may be made more readily disposable by having predetermined tear
lines (i.e. lines where the product, or merely the base sheet, is
weaker, such as lines along which the product is scored,
perforated, partly cut, or merely much thinner). Preferably there
are a plurality of such tear lines extending across the sheet. In
one example, the tear lines 31 (FIG. 3) form a cross made up of two
intersecting perpendicular lines each of which is parallel to a
side of the diaper; of course there may be more than two such
lines. The housewife may then tear the diaper, after use, easily
into a number of smaller, and more easily disposable, portions.
To produce the film pieces, a solution of the highly absorbent
material may be cast as a layer onto any suitable casting surface
and then dried and stripped from the casting surface. The casting
surface may be a rotating drum which may be heated to drive off the
solvent (which is preferably aqueous). The film may be stripped
intact and then (with or without rolling it up for intermediate
storage or transit) sent to a zone where it is broken mechanically,
or cut, to form pieces of substantially the same thickness as the
original film. Or the film may be broken or cut up during the
stripping operation or during the solvent removal. The film may
have visible pores; in one form it has substantially uniformly
distributed fine holes, about one-half mm or less in diameter,
extending through the film and has the appearance of a network
having a total hole area of the same order of magnitude as the
solid material of the film, e.g. a hole area one-third to twice the
solid area. Or the films may be substantially nonporous to the
naked eye.
The areas of the film pieces which are fed to the air stream may
be, for instance, from about one-twentieth or one-fourth square
inch (e.g. a square piece about one-half by one-half inch) to about
20 square inches (e.g. a rectangular piece about 5 by 4 inches). In
the airstream the larger pieces (particularly when the film is
relatively brittle) are broken up by impacts, as previously
described, and the smaller pieces may also be broken.
Starch (particularly cooked or gelatinized starch) has been found
to be a very suitable material for making the film. An excellent
material is starch which has been cooked in dilute aqueous acetic
acid and then cast from the same solvent. Starches of various
types, e.g. potato starch, corn starch, rice starch, tapioca
starch, etc. may be used. Another suitable material is guar which
is a natural gum of polysaccharide character, soluble in cold
water. Chemically guar is a galactomannan and is believed to
consist essentially of a straight chain of d-mannose units, linked
to each other by means of beta (1-4) glycosidic linkages, the chain
having single-membered d-galactose side branches; the branches are
found on alternate mannose units. The guar may be the natural
product or a chemically modified type such as the self-complexing
guars. The guar may be admixed with other hydrophilic materials,
e.g. with a proportion of a cold-water-swelling starch such as
pre-gelatinized starch or a chemically modified starch.
It is within the broader scope of the invention to employ as all or
part of the film material other polysaccharide gums, pectin, algin
or highly water-absorbent polymeric materials which form gels
quickly on contact with large amounts of water. Also the
polysaccharide gum may be of the chemically modified type; among
the known chemical modifications are oxidation, esterification such
as acetylation, carboxylation, etherification such as methylation,
amination, phosphation or sulfation; other possible derivatives
contain carboxyalkyl, cyanoalkyl or hydroxyalkyl substituents.
The following examples of the preparation of films given to
illustrate this invention further. All proportions are by weight
unless otherwise indicated, in the examples and in the rest of the
application. In the examples all pressures are atmospheric unless
otherwise indicated.
EXAMPLE 1
5 to 10 grams of raw potato starch powder (standard food grade) are
dispersed with agitation in 100 grams of water at room temperature
and the resulting translucent mixture is heated to a temperature
just below the boiling point (e.g. 93.degree.-98.degree. C.) and
maintained at that temperature for 4 hours during which time the
mixture becomes viscous but is still pourable. It is cast onto a
glass plate to form a thin layer of the material and thoroughly
dried in an oven, in air, at about 50.degree. C. The resulting dry
film is stripped, while remaining intact and flat, from the plate
with the aid of a scraper (e.g. a spatula).
Various thickness of films (ranging from about 0.001 to 0.02 inch)
are produced according to the above method by varying the thickness
of the casting on the plate. The thinner films, in this particular
experiment, are visibly (and substantially uniformly) porous, while
the thicker ones are non-porous to the naked eye.
EXAMPLE 2
Example 1 is repeated using dilute acetic acid (e.g. of 1 to 5
percent concentration) in place of water. In comparison with
Example 1, the resulting product has an increased water-absorption
and forms a firmer gel with water.
It will be appreciated that in the cyclone separator the gaseous
dispersion of fibers and film pieces is whirled to cause the
mixture of fibers and film pieces to separate from the air and
settle in fluffy form.
The process of this invention has shown a remarkable ability to
combine the dry polymeric material of high water absorption (e.g.
the film pieces of the starch material) with the cellulose fibers.
Thus in a run in which starch film pieces were supplied to the
cyclone separator together with the cellulose fibers, the final
product appeared to be quite uniform, without any detectable
separation of, or even any readily visible evidence of the presence
of, the starch. In this process the starch or other polymeric film
pieces of high water absorption may be replaced in whole or in part
by short fibers or filaments of the same material. Such fibers or
filaments may be obtained by extruding the material in a thick
viscous condition (e.g. a viscous aqueous solution of the starch
material, which may be a chemically modified starch) through fine
orifices and passing the extruded filaments into, for example, a
heated evaporative zone; for instance the viscous solution may be
extruded into air and onto a moving belt which conveys the extruded
filaments into a drying oven. The resulting substantially dry
fibers or filaments may then be cut to the desired length, e.g.
one-eighth to one-half inch or more. The diameters of these fibers
or filaments may be, for instance, about 0.0005 to 0.002 inch or
more. An extruded film of the starch or other polymeric material
(which may be plasticized) may also be cut into thin strips to form
filaments of the desired width (e.g. 0.005 to 0.2 inch or
more).
The cellulose fibers used for making the sheet are usually
relatively short, e.g. about one-sixteenth to one-half, preferably
about one-eighth to one-half inch in length. Wood pulp fibers such
as bleached sulfite pulp or "wood fluff" are suitable, for
instance. It is within the broader scope of the invention to use
other fibers, such as non-cellulose fibers which retain their
fibrous structure when wet, alone or in admixture with the
cellulose fibers. In the sheet the fibers are preferably
non-aligned.
The humidification technique described above may be applied to
blends of fiber and the particulate water-absorbing material in
which the latter is in a form other than film pieces, e.g.
spray-dried beads, granules, powder, fibers, etc., instead of, or
in admixture with, film pieces. The humidified (e.g. steamed) blend
may be suitably dried in various ways, as by passing it through a
spray tower, or in an oven, and/or by a stream of hot air.
It is advantageous to assembly the humidified blend with the other
layers previously mentioned (for example with the waterproof layer
22 and/or the layer 21) before the blend is dried, or after only
partial drying. At this stage the blend tends to adhere to said
other layers; this avoids, or reduces, slippage between the
cellulose fiber layer containing the somewhat tack, moist,
particulate water-absorbing material (in the form of film pieces,
beads, granules, powder, fibers, etc.) and the waterproof layer 22.
The preferred waterproof layer is of polyethylene film and may be
of the type whose surfaces (or at least the surface which is in
contact with the blend of cellulose fiber and water-absorbing
particulate material) have been pretreated in well known manner to
make them printable (e.g. by corona discharge treatment) and more
wettable. The precise residual moisture content for best adhesion
can be determined readily by experiment. In making the assemblage
the layers can be brought together in any suitable fashion as by
passing the layers together between pressure rolls, after which the
assemblage may be dried.
The water-absorbing particulate materials of types other than film
pieces (e.g. beads, granules, powder, fibers, etc.) may be combined
with the cellulose or similar fibers by the same techniques and in
the same proportions as described above for the film pieces.
Another technique for obtaining a blend of the cellulose fibers and
the water-absorbing material is by spraying a mist of a solution of
the water-absorbing material in a liquid solvent into the
suspension of cellulose fibers in the airstream. For instance, a 5
percent aqueous solution of a mixture of equal parts of guar gum
and starch may be injected into the cyclone previously described,
in such proportions as to provide, say, 2 to 5 percent of the
water-absorbing, solid material based on the weight of the
cellulose. It will be understood that more concentrated solutions
may be used, particularly when the solutions are heated so as to
reduce their viscosity prior to spraying. The resulting blend may
be dried partially so as to obtain a moist mixture having superior
adhesion to the adjacent layers (e.g. the waterproof layer).
Another technique for combining the cellulose fibers and the
water-absorbing material is by combining a foamed solution of the
water-absorbing material with the cellulose fibers. The foam may be
prepared, for example, by beating a gas into the solution (e.g. in
an Oakes device, to produce a foam having very fine air bubbles).
The cellulose fibers may be mixed with the solution prior to
foaming or after foaming and a sheet may be formed of the foamy
mixture, or the foam of the solution of water-absorbing material
may be applied to one or both sides of a layer of cellulose.
It is understood that the foregoing detailed description is given
merely by way of illustration and that variations may be made
therein without departing from the spirit of the invention. The
"abstract" given above is merely for the convenience of technical
searchers and is not to be given any weight with respect to the
scope of the invention.
* * * * *