Note: Descriptions are shown in the official language in which they were submitted.
CA 02208759 1997-06-25
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S P E C I F I C A T I 0 N
PROCESS FOR MANUFACTURING A WATER-DISINTEGRABLE SHEET
FIELD OF THE INVENTION
The present invention relates to a process for
manufacturing a water-disintegrable sheet adapted to be
dispersed or dissolved in water.
BACKGROUND ART
Wet wipes for cleaning use in household etc. are well
known. Water-dispersible or water-disintegrable sheet-like
articles typically as wet wipes are also well known, which
are rapidly dispersed or disintegrated in water so that they
can be directly thrown away into water, for example, in a
flush toilet, and flushed down a drain. It should be
understood that terms used herein "water-dispersible" and
"water-disintegrable" are synonymous with each other.
Generally, wet wipes having such characteristics are required
to have a high strength exhibited while they are used in a
wet condition and also a rapid integration when they are
thrown away into a large quantity of water. To assure that
these strength and integration should be compatible with each
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other, Japanese Laid-open Patent Application No. Heil-168999
discloses use of water-insoluble sodium/calcium salt of
carboxymethyl cellulose or sodium salt of carboxymethyl
cellulose. Japanese Patent Publication No. Sho48-27605
discloses a process for paper making wherein a wet paper
sheet obtained from water-insoluble carboxymethyl cellulose
is sprayed with aqueous solution of alkaline metal. Japanese
Laid-Open Patent Application No. Hei3-167400 discloses a
process for paper making including a step of mixing a water
dispersion of paper making stuff with water-insoluble
alkaline salt of carboxymethyl cellulose. Furthermore,
Japanese Laid-Open Patent Application No. HeiS-25792
discloses a process for paper making wherein a paper sheet
obtained from a mixture of water dispersion of paper making
stuff and alkaline salt of carboxymethyl cellulose is
impregnated with hydrated organic solvent containing
multivalent metal ion.
Carboxymethyl cellulose and/or salt thereof
conventionally used by the above-mentioned prior arts
generally lose their initial water-insolubility, then show a
tendency to swell and finally become water-soluble as degree
of substitution (D. S.) and pH thereof increase. When these
carboxymethyl cellulose and/or salt thereof are used as
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binders for paper making, the tendency to swell of the
binders will make it difficult to get a uniform mixture of
the binders with fibers dispersed in water. On the other
hand, the binders having become water-soluble will be
prohibited from being deposited on a sheet as an intermediate
product, strength of the sheet will be not so improved as
expected from an actual quantity of the binders mixed in a
water dispersion of paper making stuff. Although an aqueous
solution of the binders could be sprayed to a sheet obtained
from paper making stuff, swollen carboxymethyl cellulose
makes an aqueous solution thereof too viscous to be sprayed
in a uniform condition.
SUMMARY OF THE INVENTION
In view of problems as has have been described above,
it is a principal object of the invention to provide an
improved manufacturing process for making a disintegrable
sheet for wet wipes or the like to be used for cleaning sheet
materials in household etc. wherein a good quantity of
carboxymethyl cellulose and/or salt thereof can be
efficiently deposited on the sheet.
The object set forth above is achieved, according to
the invention, by a process for manufacturing a water-
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disintegrable sheet from carboxymethyl cellulose and/or salt
thereof and water-dispersible fibers, said process being
characterized in that a mixture of water-swelling or water-
insoluble carboxymethyl cellulose and/or salt thereof having
a degree of substitution (D.S.) - 0.30 - 0.60 and pH > 5.0
and water-dispersible fibers is subjected to a step of
foliating to obtain said water-disintegrable sheet and,
before or after said step of foliating of said process, said
mixture is added with a base.
Said base is preferably sodium carbonate. The process
according to the invention may further comprise a step of
impregnating said water-disintegrable sheet with aqueous
solution to obtain a wet wipe from said sheet.
DESCRIPTION OF PREFERRED EMBODIMENTS
Materials used in a manufacturing process of the
present invention include water-dispersible fibers which can
be foliated in the presence of carboxymethyl cellulose and/or
salt thereof. While it is preferred to use pulp fiber, it
is also possible to use natural fibers such as wool,
regenerated fiber such as rayon fiber, semi-synthetic fiber
such as acetate, or synthetic fiber such as nylon, polyester
etc. For such fibers, low water-swelling or water-insoluble
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carboxymethyl cellulose and/or salt thereof having D.S. -
0.30 - 0.60 and pH > 5.0 is used as binders. In order to
provide such binders with a high water-swelling property or
a high water-solubility, a base is added to the binders
before or after a foliating step of a sheet making process.
The base can be added during the foliating step if needed.
While any appropriate base and combination of bases can be
applied, it is preferred to use sodium carbonate for the
present invention. Preferably, well known paper making
techniques are used to foliate a mixture of fibers and
binders. It is also possible to use a so-called wet or dry
method for manufacturing nonwoven fabric or a method for
manufacturing nonwoven fabric using water jet streams. The
invention will be described more in detail.
Examples 1 - 5
Coniferous pulp for paper making (NBKP) and
carboxymethyl cellulose and/or salt thereof were mixed
together and dispersed in city water followed by adding a
necessary quantity of sodium carbonate to the water
dispersion for preparation of a paper making stuff. After
the stuff had been settled for a time, it was subjected to a
small-sized paper machine used exclusively for testing to
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obtain a wet paper sheet which was then dried at a
temperature of 110°C for 90 seconds using a dryer of rotary
drum type to obtain a dried sheet having a basis weight of
40g/mz. Then, the dried sheet was sprayed and impregnated
with aqueous solution of propylene glycol/calcium chloride/
deionized water mixed together at a ratio of 30/0.5/69.5(by
weight ) so as to obtain a quantity corresponding to 2 . 5 times
a weight of the dried sheets. The impregnated sheet was
settled for 24 hours at a temperature of 20°C to obtain a wet
wipe. Water-dispersibility and wet tensile strength of the
wet wipe were tested under measuring conditions which will be
described below. Test results for evaluating wet wipe
examples prepared in accordance with the present invention
( Example ) and wet wipes for control ( Control ) are summarized
in Table 1. Relationships between a series of Examples and
a series of Controls are as follows:
(1) Example 1 and Control 1
The test results of Example 1 and Control 1 show
effects of sodium carbonate (~ by weight) added to
carboxymethyl cellulose and/or salt thereof as measured in a
dried state during a paper making process.
(2) Example 2 and Control 2
The test results of Example 2 and Control 2 show
' CA 02208759 1997-06-25
effects of a degree of substitution (D.S.) as well as pH of
carboxymethyl cellulose and/or salt thereof.
(3) Example 3 and Control 3
The test results of Example 3 and Control 3 show
effects of a total quantity (~ by weight) of pulp and
carboxymethyl cellulose and/or salt thereof.
(4) Example 4 and Control 4
The test results of Example 4 and Control 4 show
effects of a period for which a water dispersion of pulp and
carboxymethyl cellulose and/or salt thereof should be settled
after an addition of sodium carbonate during a paper making
process.
(5) Example 5 and Control 5
The test results of Example 5 and Control 5 show
effects of a mixture ratio of pulp and carboxymethyl
cellulose and/or salt thereof.
Evaluation of water-dispersion
A lOcm X lOcm sample sheet of wet wipe was immersed in
300m1 of deionized water contained in a 300m1 glass beaker
followed by stirring by means of a magnetic stirrer(at
600rpm) and an extent of dispersion of the sample was
observed. Observation results were classified as follows:
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A: A sample sheet was disintegrated within 100 seconds.
B: A sample sheet was disintegrated within 200 seconds.
C: A sample sheet was not disintegrated within 200
seconds.
Evaluation of wet tensile strength
A sample sheet of wet wipe of 25mm wide and 150mm long
was elongated at a chucking distance of 100m and at an
elongation rate of 100mm/min to get tensile strength. It
was found that tensile strength of a wet wipe of at least
300g is sufficient for its practical use.
Results of the evaluations for Examples and Controls
are shown by TABLE 1. From the results it is concluded that:
(1) carboxymethyl cellulose and/or salt thereof should
present D.S. - 0.30 - 0.60 and pH > 5.0 (Example 2); (2) a
quantity of sodium carbonate should correspond to 10 - 400
by weight of carboxymethyl cellulose and/or salt thereof
(Example 1); (3) a weight ratio of pulp : carboxymethyl
cellulose and/or salt thereof should range from 98 . 2 to 55
. 45; (4) concentration of pulp and carboxymethyl cellulose
and/or salt thereof in a paper making stuff should range from
0.5 to 5~ by weight; and (5) a settling period after
addition of sodium carbonate should be 30 minutes or longer.
' CA 02208759 1997-06-25
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Examples 6 - 7
Coniferous pulp for paper making (NBKP) and
carboxymethyl cellulose and/or salt thereof were mixed
together and dispersed in city water to obtain a paper making
stuff which was foliated by a small-sized paper machine used
exclusively for testing. A wet sheet thus obtained was
sprayed and impregnated with a quantity of aqueous solution
of sodium carbonate corresponding to 2.4 - 8~ by weight of
carboxymethyl cellulose and/or salt thereof wherein said
quantity of aqueous solution corresponded to 2.5 times a
weight of the sheet as measured in its dry condition. Then,
the sheet was dried at a temperature of 110°C for 90 seconds
using a rotary drum type dryer and thereby a dried sheet
having a basis weight of 40g/m2 was obtained. The dried sheet
was sprayed and impregnated with aqueous liquid consisting of
propylene glycol/calcium chloride/deionized water mixed
together at a ratio of 30/0.5/69.5(by weight). The
impregnated sheet was settled for 24 hours at a temperature
of 20°C to obtain a wet wipe. Extent of water-dispersion as
well as wet tensile strength of the wet wipe were evaluated
under the same condition as Examples 1 - 5. Relationships
between Examples and Controls are as follows:
(1) Example 6 and Control 6
' CA 02208759 1997-06-25
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The test results of Example 6 and Control 6 show
effects of a quantity of sodium carbonate ( ~ by weight ) added
to carboxymethyl cellulose and/or salt thereof as measured in
a dried state during a paper making process.
(2) Example 7 and Control 7
The 'test results of Example 7 and Control 7 show
effects of degree of substitution (D.S.) as well as pH of
carboxymethyl cellulose and/or salt thereof.
Result of the evaluations for the respective Examples
and Controls are shown by TABLE 2.
~ ' . ' CA 02208759 1997-06-25
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' ~ ~ ' CA 02208759 1997-06-25
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Effect of the Invention
According to the process of the present invention,
water-dispersible fibers are mixed with. binders comprising
carboxymethyl cellulose and/or salt thereof having low
swelling tendency or water-insolubility so that a large
quantity of binders can be deposited on a sheet obtained from
the mixture of the fibers and the binders . Such binders are
denaturalized by addition of a base, to water-swelling or
water-soluble ones. These binders contribute to improvement
of tensile strength of the sheet. And the sheet is thrown
away into a large quantity of water after use, the binders
can be rapidly dissolved in the water, allowing the sheet to
be rapidly disintegrated and dispersed in the water.
