U.S. patent number 3,923,592 [Application Number 05/493,251] was granted by the patent office on 1975-12-02 for process for manufacturing a flushable fibrous sheet material for use in sanitary products.
This patent grant is currently assigned to Riegel Textile Corporation. Invention is credited to Joseph H. Angel, Donald K. George.
United States Patent |
3,923,592 |
George , et al. |
December 2, 1975 |
Process for manufacturing a flushable fibrous sheet material for
use in sanitary products
Abstract
A process for producing a fibrous sheet material suitable for
use in sanitary products and wherein there is provided in the sheet
material a high molecular weight water soluble polymeric material
which serves to effect bonding together of the fibers to avoid
disintegration of the sheet through normal use in sanitary
products, but which permits flushing of the sanitary products after
use by dispersing the polymeric particles and the fibers in the
flushing water. In accordance with the process, the polymeric
material, in finely ground form, is introduced into the white water
system of the paper machine and permitted to remain therein for a
limited time, sufficient to permit hydration and swelling of the
polymeric particles to assure their retention in the fibrous sheet,
but insufficient for the polymer to dissolve in the water or be
lost through the paper machine wire.
Inventors: |
George; Donald K. (Aiken,
SC), Angel; Joseph H. (Columbia, SC) |
Assignee: |
Riegel Textile Corporation (New
York, NY)
|
Family
ID: |
26790163 |
Appl.
No.: |
05/493,251 |
Filed: |
July 31, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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95388 |
Dec 4, 1970 |
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Current U.S.
Class: |
162/168.1;
162/183; 162/187; 162/190; 604/364; 604/368; 604/376 |
Current CPC
Class: |
D21H
17/36 (20130101); D21H 23/00 (20130101); D21H
17/27 (20130101) |
Current International
Class: |
D21H
17/00 (20060101); D21H 17/27 (20060101); D21H
17/36 (20060101); D21H 23/00 (20060101); D21H
003/40 (); D21H 003/00 (); A61F 013/18 () |
Field of
Search: |
;162/168,169,190,158,183,185,187 ;128/284 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lindsay, Jr.; Robert L.
Attorney, Agent or Firm: Parrott, Bell, Seltzer, Park &
Gibson
Parent Case Text
This application is a continuation of our earlier-filed copending
application Ser. No. 95,388, filed Dec. 4, 1970, now abandoned.
Claims
That which is claimed is:
1. A process for producing a cellulosic sheet suitable for use in
flushable sanitary products and being resistant to disintegration
in use, and in which the sheet is formed on the machine wire of a
paper machine, comprising incorporating in the white water system
of the paper machine a high molecular weight water soluble
polymeric material in finely ground particulate form which hydrates
and swells rapidly in cold water and which has cold water soluble
components, said polymeric material being sufficiently finely
ground to pass through a 50 mesh screen, permitting said polymeric
material to remain in the white water for about three to 90 seconds
to effect hydration and swelling of the polymeric particles but
avoiding an excessive residence time in the white water sufficient
to dissolve the water soluble polymer components or permit loss of
the hydrated particles through the paper machine wire, forming on
the paper machine wire a cellulosic fiber sheet containing the
swollen polymeric particles, and subsequently drying the cellulosic
sheet produced on the paper machine with the water soluble
polymeric particles contained therein effecting bonding together of
the cellulosic fibers in a sufficiently strong manner to prevent
breaking of the bond through normal use in the sanitary products,
but permitting flushing of the sanitary products after use by
dispersing the polymeric particles and the cellulosic fibers in the
flushing water.
2. A process as defined in claim 1 and in which the polymeric
material is permitted to remain in the white water system between
about five seconds and 40 seconds.
3. A process as defined in claim 1 and in which the polymeric
material is polyvinyl alcohol.
Description
The present invention relates to an improved process for
manufacturing a flushable fibrous sheet material which is suitable
for use as a cover sheet in sanitary products and which is
resistant to disintegration in normal use.
In U.S. Pat. No. 3,370,590, issued Feb. 27, 1968 to Kenneth C.
Hokanson and Donald K. George, there is disclosed a process for
preventing undesirable loosening and matting on the surface of
paper products when subjected to friction; the particular paper
product being used as a cover sheet in flushable sanitary products
such as disposable diapers, sanitary napkins, etc. The improved
non-matting or non-loosening properties of the paper sheet in that
case were obtained by forming the sheet of special rayon fibers on
a paper making machine and impregnating the sheet by spraying or
the like, before drying or complete drying, in situ, on the machine
with a high molecular weight water soluble polymeric material, such
as polyvinyl alcohol, pressing the sheet after impregnation and
then drying of the sheet.
In the improved process of the present invention which uses high
molecular weight water soluble polymeric chemicals, we have found
that it is not necessary to apply the chemicals to the preformed
moist sheet by spraying or the like, as specified in the above
prior Hokanson et al patent.
Moreover, we have discovered that a more efficient impregnation of
the sheet may be obtained by introducing the polymeric chemicals,
e.g., polyvinyl alcohol, directly into the white water circulating
on the paper machine on which the paper sheet is produced. In this
improved process, the polymeric material we employ is in finely
divided particulate forms and is dispersed in the white water
before or after it is mixed with the fiber stock and before
formation of the paper sheet.
In U.S. Pat. No. 2,402,469, issued June 18, 1946 to William Craig
Toland and Benjamin B. Burbank, a process is disclosed wherein
particles of polyvinyl alcohol polymer are mixed with pulp fibers
and thereafter formed into a fibrous sheet. However, the process
disclosed is for the purpose of providing wet strength properties
in the sheet rather than providing a water dispersible or flushable
sheet, and the polymer particles employed are previously washed in
cold water and added to the pulp in a hydrated state.
In accordance with the present invention, a fibrous sheet which is
resistant to disintegration in normal use and which has dispersible
or flushable properties in water is obtained by adding the finely
ground polymer material to the white water system of the paper
machine and by allowing the same to remain in the white water for a
prescribed limited amount of time, sufficient to effect hydration
and swelling of the polymeric particles but avoiding an excessive
residence time in the white water sufficient to dissolve the water
soluble polymer components or permit loss of the hydrated particles
through the paper machine wire.
The polymers which are useful in the process of this invention for
producing the improved flushable sheet product comprise high
molecular weight polymers that swell rapidly in cold water as they
hydrate but have limited solubility in cold water. By the term
limited cold water solubility, it is understood that such polymers
are soluble to a limited extent in cold water, having components or
fractions which are insoluble in cold water as well as components
or fractions which are cold water soluble. An illustrative example
is a high molecular weight polyvinyl alcohol, e.g., Air Reduction
Company's Vinol 325, or National Starch and Chemical Covol 9835.
These polymers, when added to the white water, or to the white
water-stock mixture before the sheet is formed, swell rapidly and
become tacky so that when the sheet is formed on the wire, the
polymer particles have become too large to pass through the screen
and will stick to the fibers and are carried on to the drying
section of the paper machine. As the temperature of the paper is
raised on the dryers and the water begins to evaporate, the
swollen, hydrated polymer particles shrink and bond the fibers
together very effectively at fiber crossover points.
For the process of the present invention, the high molecular weight
polymers should be finely ground before being used. In practice,
the polymer particles should be ground sufficiently to pass a 50
mesh screen and a more desirable degree of fineness would be a
polymer powder, of which approximately 80% will pass through a 100
mesh screen and 20% will pass through an 80 mesh screen.
It is also important that the polymer powder be introduced into the
white water system at the proper place so that sufficient contact
time is allowed in the white water for the water soluble polymer
particles to hydrate and become swollen. Furthermore, it is
important that an excessive residence time in the white water be
avoided so that the polymer cannot dissolve. We have found that
when the polymer is allowed a minimum residence in the white water
system of three seconds, the particles will swell sufficiently to
be substantially retained on the sheet and will do a satisfactory
bonding job. When the particles are allowed to remain in the white
water system for times exceeding approximately 90 seconds, the
particles will tend to become so soft that the hydrated particles
will be substantially lost through the wire and will no longer
efficiently bond the sheet together. A preferable time of contact
for the particles in the white water would be between five and
forty seconds.
The finely divided polymer may be added alone directly to the white
water or it may be added as a slurry in a watermiscible solvent in
which the polymer is not itself soluble. In practice, the polymer
may be conveniently added as a slurry in isopropanol or ethylene
glycol by metering the slurry through a positive displacement pump
into the white water trays on the paper machine.
When a sheet of flushable paper is formed in this manner and bonded
together according to the new process, the resulting sheet can be
easily redispersed in water. When such a sheet is immersed in cold
water, such as in a toilet, and is agitated, the high molecular
weight water soluble polymer softens as it hydrates and swells and
will allow the fiber-to-fiber bonding to be weakened so that the
fibers can slide apart and the sheet can disperse when slightly
agitated as, for example, when it is flushed through the trap of
the toilet.
The process of our invention yields a sheet in which the polymeric
material is more uniformly distributed since the polymeric material
is thoroughly mixed with the fiber before the sheet is formed.
Also, it allows more economical operation of the paper machine
since no additional water has to be added to and removed from the
sheet.
The following illustrative Examples 1 and 2 will serve to explain
the process of this invention more fully, and to illustrate its
advantages over processes (Examples 3 to 7) which are not in
accordance with the invention:
EXAMPLE 1
To the circulating white water system of a paper machine to which
sixty pounds per minute of 1.5 denier, 12 millimeter self-bonding
hollow rayon fiber is being metered, 2.4 pounds per minute of a 25%
by weight slurry of isopropanol and a high molecular weight
polyvinyl alcohol ground to pass an 80 mesh screen is added at a
point where eight seconds of contact results before sheet
formation. The resulting dried sheet is strong and extremely
abrasion resistant but can be easily softened by crushing,
embossing, or creping to yield a drapable, cloth-like material
which retains a high percentage of its dry strength when wettted,
but which disperses rapidly into component fibers when immersed in
a large excess of water and agitated.
EXAMPLE 2
To the white water trays of the paper machine of Example 1 above,
is added 1.2 pounds per minute of a 50% by weight slurry in
ethylene glycol of a 60 mesh carboxy methyl cellulose powder.
Contact time prior to sheet formation is approximately 35 seconds.
The resulting dried sheet is similar in properties to that formed
in Example 1.
EXAMPLE 3
To the white water trays of the paper machine of Example 1 is added
2.4 pounds per minute of a slurry containing 25% by weight of an 80
mesh completely cold water soluble low molecular weight guar gum.
The resulting paper shows little or no dry abrasion resistance and
disintegrates when subjected to creping.
EXAMPLE 4
The procedure in Example 1 is repeated using a 40 mesh polyvinyl
alcohol otherwise identical to that of Example 1. The resulting
paper is grainy and cockled due to uneven drying and exhibits areas
of tight and loose bonding so that a harsh, weak product unsuitable
for use in flushable sanitary products results when the sheet is
creped.
EXAMPLE 5
To the wet pressed sheet formed on the paper machine of Example 1
without the binder slurry addition, is added 60 pounds per minute
of a 1% solution of polyvinyl alcohol in water by spraying the
sheet just after contact with the first drying can. The resulting
sheet is seen to be less evenly bonded than that of Example 1 and
exhibits streaks corresponding to light and heavy areas of the
spray application. Since one additional pound of water must also be
evaporated for each pound of paper produced, the drying section is
seen to be considerably less efficient than in Example 1.
EXAMPLE 6
Example 1 is repeated except that the polymer slurry is added to
the stock chest from which the stock slurry is fed to the machine.
The resulting paper exhibits practically no dry abrasion
resistance.
EXAMPLE 7
Example 1 is repeated except that the polymer solution is added to
the paper machine headbox where contact time is approximately 1.5
seconds. The resulting paper is very weakly and unevenly bonded,
showing areas which are very stiff and boardy and areas having
almost no abrasion resistance.
Various modifications and changes may be made in the
above-described procedure and chemicals for carrying out the
process of the present invention, the scope of which is defined in
the appended claims.
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