U.S. patent application number 10/026203 was filed with the patent office on 2003-02-06 for absorbent material and production thereof.
Invention is credited to Andersson, Arne, Lindgren, Erik, Malmborg, Kerstin, Thebrin, Ingemar.
Application Number | 20030024670 10/026203 |
Document ID | / |
Family ID | 26700904 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030024670 |
Kind Code |
A1 |
Andersson, Arne ; et
al. |
February 6, 2003 |
Absorbent material and production thereof
Abstract
The invention relates to a method for production of paper,
wherein cellulosic fibres in an aqueous suspension are treated with
a carrier carrying an oil, wherein the carrier has a hydrophobic
and porous surface. The invention can impart improved sorptive
capacity to the produced paper. The invention also relates to paper
obtainable by the method. The invention further relates to a method
for producing an absorbent and an absorbent obtainable from the
method, and the use of a carrier and an oil carried by the carrier
for imparting an increased sorptive capacity to an absorbent
comprising cellulosic fibres.
Inventors: |
Andersson, Arne;
(Stenungsund, SE) ; Lindgren, Erik; (Bohus,
SE) ; Malmborg, Kerstin; (Stenungsund, SE) ;
Thebrin, Ingemar; (Stenungsund, SE) |
Correspondence
Address: |
Lainie E. Parker
Akzo Nobel Inc.
7 Livingstone Avenue
Dobbs Ferry
NY
10522-3408
US
|
Family ID: |
26700904 |
Appl. No.: |
10/026203 |
Filed: |
December 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60259142 |
Dec 28, 2000 |
|
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Current U.S.
Class: |
162/179 |
Current CPC
Class: |
D21H 21/16 20130101;
D21H 21/22 20130101 |
Class at
Publication: |
162/179 |
International
Class: |
D21H 013/00 |
Claims
1. Method for producing paper comprising adding to an aqueous
suspension of cellulosic fibers a carrier having a porous and
hydrophobic surface, wherein said carrier carries an oil.
2. Method according to claim 1, wherein the carrier is a
macroporous polymer.
3. Method according to claim 2, wherein the macroporous polymer has
an average pore diameter in the range from about 0.1 to about 50
.mu.m.
4. Method according to claim 2, wherein the macroporous polymer is
a thermoplastic polymer.
5. Method according to claim 1, wherein the oil is
triisooctylmellitate oil, soybean oil, or castor oil.
6. Method for producing paper comprising adding to an aqueous
suspension of cellulosic fibers a carrier carrying an oil, said
carrier having a hydrophobic surface and pores having an average
pore diameter in the range from about 0.1 to about 50 .mu.m.
7. Method according to claim 6, wherein said carrier carrying said
oil is added to the aqueous suspension of cellulosic fibers in an
amount of from about 0.1 to about 10 kg/metric tonne of cellulosic
fibers.
8. Paper obtained by a method comprising adding to an aqueous
suspension of cellulosic fibers a carrier having a porous and
hydrophobic surface, wherein said carrier carries an oil.
9. Paper according to claim 8, wherein the carrier is a macroporous
polymer.
10. Paper according to claim 8, wherein the carrier has pores
having an average pore diameter in the range from about 0.1 to
about 50 .mu.m.
11. Paper comprising a carrier having a porous and a hydrophobic
surface, wherein said carrier carries an oil.
12. Paper according to claim 11, wherein the carrier is a
macroporous polymer.
13. Paper according to claim 11, wherein the carrier has pores
having an average pore diameter in the range from about 0.1 to
about 50 .mu.m.
14. Paper according to claim 13, wherein at least 15 volume % of
the pores are filled with oil.
15. Paper according to claim 11, wherein the carrier has a specific
surface area from about 10 to about 40 m.sup.2/g.
16. Paper according to claim 11, wherein the oil is
triisooctylmellitate oil, soybean oil, or castor oil.
17. Process for treating cellulosic fibers comprising treating said
cellulosic fibers in an aqueous suspension with a carrier having a
porous and hydrophobic surface, wherein said carrier carries an
oil.
Description
[0001] The present invention relates to paper having improved
sorptive capacity and a method for producing such paper.
Furthermore, the invention relates to a method for producing an
absorbent and an absorbent obtainable by the method. The invention
also relates to the use of a carrier and an oil for treating
cellulosic fibres to improve the sorptive capacity of an
absorbent.
BACKGROUND OF THE INVENTION
[0002] A wide variety of absorbents having sorptive capacity are
known today in the art of absorption. In the present context, the
term "sorptive capacity" includes both the rate by which an
absorbent takes up liquids, such as water or aqueous solutions,
including body fluids such as urine, blood and menstrual fluids,
and the liquid-retaining capacity of the absorbent. The sorptive
mechanism may be adsorption or absorption, or a combination
thereof. Absorbents may comprise e.g. fluff, impregnating paper, or
tissue paper.
[0003] As stated in Pulp and Paper Manufacture Vol. 2 pages
280-281, Joint Textbook Committee of the Paper Industry, 1987, the
term "fluff" applies to fibres which have been separated by
mechanical means from dry pulps for application in dry-formed
nonwoven webs or pads in the household or sanitary fields. As is
evident from this reference, both the rate of liquid uptake and the
liquid-holding capacity of a fluff-containing absorbent are
important when used in these fields. This is particularly valid
with regard to absorbent articles such as a catamenial products (e.
g. sanitary napkins, pantiliners, tampons etc.), diapers, bandages,
adult incontinence garments, and the like. Good liquid uptake and
liquid-holding capacity are important for the function of such
articles, constantly subjected to pressure imposed by the weight
and the movements of the bearer. Thus, it is important that the
liquid-holding capacity is high enough to retain the absorbed
liquid also under pressure. Furthermore, in order to give good
comfort to the bearer, the article should provide a feeling of
dryness, meaning that any rewetting from the article to the skin of
the bearer should be avoided, raising the requirements with regard
to liquid-holding capacity even higher. The same prerequisites also
apply to other types of absorbents, such as tissue paper, or
impregnating paper.
[0004] EP 889 993 relates to a method for production of
fluff-containing absorbents, wherein cellulosic fibres are treated
in presence of water with hydrophobic substances such as zeolites
and activated carbon.
[0005] However, problems have been associated with such hydrophobic
substances, e.g. the lack of aesthetic appearance of active
carbon-containing consumer's goods, such as a catamenial product,
being black as a consequence of the active carbon being present.
Drawbacks have also been associated in pulp treatment with
zeolites, as to the costs of such products, and the relatively low
affinity they have to the cellulosic fibres making up the formed
sorptive paper. Furthermore, zeolites may give rise to abrasive
wear of the paper machine and other equipment used when treating
the paper pulp, resulting from the relatively hard surface of
zeolites.
[0006] It has been desirable in this art to develop further
compositions capable of imparting improved sorptive capacity to
paper.
[0007] The main object of the present invention is to provide a
paper having improved sorptive capacity as well as the production
and use thereof in absorbents. A further object of the present
invention is to provide a method for producing paper having
improved sorptive capacity without the drawbacks referred to
above.
THE INVENTION
[0008] The present invention relates to a method for producing
paper comprising adding an oil and a carrier having a porous and
hydrophobic surface carrying said oil to an aqueous suspension of
cellulosic fibres.
[0009] It has been surprisingly found that the inventive method can
dramatically increase the sorptive capacity of the paper.
[0010] The carrier preferably is a macroporous carrier, preferably
a macroporous polymer. Any carrier suitable for carrying an oil,
especially a carrier having a fairly high affinity to the oil may
be used. Such carriers include both organic and inorganic porous
material which are wetted more readily by an oil than by the
aqueous pulp dispersion surrounding the carrier.
[0011] Preferably, the carrier is a thermoplastic, and more
preferably a dimensionally stable macroporous polymer. The average
diameter of the pores of the carrier suitably is in the range from
about 0.1 to about 50 .mu.m, preferably from about 0.2 to about 15
.mu.m.
[0012] For reasons of simplicity, a carrier in the form of a
preferred polymer will now be described herein more in detail.
However, the preferred properties of the polymer applies to any
suitable carrier in accordance with the present invention.
[0013] Generally, favourable results are attained when using a of
which at least 15 volume % of the polymer pores are filled with the
oil substantially immobilised therein, with optimum results being
obtained using a material of which at least 50 volume % and not
more than 95 volume % of the pores is filled with the oil.
Completely filled up pores may cause problems associated to
expansion of the oil, which may cause oil leakage from the pores.
If the polymer is totally filled up with oil, such difficulties can
be easily overcome by mixing the filled polymer with unfilled
(porous) polymer, so that the excess of oil can be taken up by
unfilled polymer material. The porous polymer is suitably used in
the form of grains having an average particle diameter from about
0.01 to about 5 mm, preferably from about 0.1 to about 1 mm.
Alternatively, the polymer, preferably being of organic origin, may
be employed in granulated form, as well as in the form of
membranes, or fibres which may be hollow or not. The specific
surface area of the macroporous polymer may be varied depending on
the oil used. However, as long as the oil remains in the pores of
the polymer, the polymer may have any specific surface area. A
skilled person can arrive at such appropriate surface area by
routine experimentation. However, the specific surface area
suitably ranges from about 10 to about 200 m.sup.2/g, preferably
from about 10 to about 40 m.sup.2/g, and most preferably from about
20 to about 30 m.sup.2/g.
[0014] Examples of suitable polymers include
polymethyl(meth)acrylate, styreneacrylonitrile copolymer, and
acrylonitrile-butadiene styrene copolymer, all of which may be
partially cross-linked or not. Further examples include low
pressure polyethylene, high pressure polyethylene, polypropylene,
polystyrene, acrylonitril-butadiene-styrene terpolymers,
styreneacrylonitrile copolymers, styrene-butadiene copolymers,
poly(4-methyl-pentene-1), and polybutene, or mixtures thereof.
[0015] The carrier suitably is selected from thermoplastic polymers
such as polyolefins or vinyl polymers, preferably from
polyethylene, polypropylene or mixtures thereof.
[0016] Suitably, the procedure used to prepare the oil-containing
carriers is as follows: firstly, 5-90 wt %, preferably 10-40 wt %,
of a polymer is dissolved by heating the polymer to a temperature
above its upper critical phase separation temperature T.sub.c in a
10-95 wt % mixture of one or more miscible oils, e.g. A and B, the
mixing ratio of A to B being so selected so as to phase separate
the polymer by cooling, resulting in a polymer-rich and a
polymer-poor (oily) phase. On further cooling, the formed structure
is fixed before the phase separation ends, due to vitrification or
crystallisation of the polymer, eventually resulting in a porous
polymer material filled with the mixture of compounds A and B which
may be used, either as such or after further addition of oil. The
size of the formed polymers may thereafter be reduced, e.g. by
grinding. Further details concerning the production of the
production procedure are disclosed in e.g. EP 653 950 and EP 662
344, the disclosures of which are hereby incorporated by
reference.
[0017] By the term "oil" is generally meant a liquid substantially
insoluble in water, but substantially soluble in organic solvents,
such oil being obtainable from plants, animals, mineral deposits,
as well as by synthesis. The oil suitably is a synthetic or a
natural oil, or mixtures thereof, in the form of a glycerol ester
of one or more, preferably unsaturated, fatty acids. The oil
suitably is selected from palmitic oil, olive oil, peanut oil,
paraffinic oil, fish oil, triisooctylmellitate oil, herring oil,
linseed oil, soybean oil, hydrogenated castor oil, strophanthus
seed oils, calendula officinalis seed oils, hydrogenated
strophanthus seed oils, hydrogenated calendula officinalis seed
oils, cardamine impatiens seed oils, ricinoleic fatty acid oil,
kamala oils, mallotus discolor oils, and mallotus claoxyloides oils
and/or castor oil or mixtures thereof, preferably from
triisooctylmellitate oil, soybean oil, castor oil, or mixtures
thereof.
[0018] According to one preferred embodiment of the invention, the
carrier is a polypropylene carrying an oil mixture of
triisooctylmellitate oil, soybean and castor oils.
[0019] By the term "paper" is meant herein particularly all types
of paper being used when absorption is required. Examples of such
paper include e.g. fluff, impregnating paper, or tissue paper, or
other paper having high absorption speed. It is to be noted in this
context that an absorbent may solely comprise paper. Thus, a paper
as such may also constitute an absorbent.
[0020] By the term "aqueous suspension" is meant herein any liquid
or solid particles, e.g. cellulosic fibres, in contact with water
or dispersed therein.
[0021] According to a preferred embodiment of the invention, the
cellulosic fibres are treated with the carrier and the oil carried
by the carrier in an aqueous suspension prior to being further
treated, e.g. before defibration of the fibres when producing
fluff. The carrier and the oil may be added before and after the
cellulosic fibres in the aqueous suspension have been formed to a
sheet.
[0022] In this context, the term "sheet" signifies a sheet or a
web. The formation of the sheet below referred to as "pulp sheet"
may follow either the wet method analogous to conventional paper
making, or the flash drying method. Both methods are described in
Pulp and Paper Manufacture, Vol. 1 page 753-757, Joint Executive
Committee of Vocational Education Committees of the Paper Industry,
1969.
[0023] The carrier and the oil are suitably added to the aqueous
suspension to treat the cellulosic fibres by contacting.
[0024] The amount added of carrier and oil suitably is from about
0.1 to about 10 kg/metric tonne of cellulosic fibres, preferably
from about 0.5 to about 5 kg/tonne. The treatment may be carried
out at any stage in the paper producing process, which process of
course comprises further conventional stages before and after the
method described herein. The oil and carrier, suitably being
applied in the form of an aqueous dispersion, suitably is added to
the stock, i.e. the aqueous suspension comprising the cellulosic
fibres, before forming pulp sheets, suitably at a dry cellulose
fibre content ranging from about 0.1 to about 7 wt %, more
preferably from about 0.2 to about 5 wt %, and most preferably from
about 0.3 to about 4 wt %. The oil and carrier may also be added to
the formed pulp sheet, suitably by spraying a pulp sheet suitably
having a dry fibre content from about 5 to about 50 wt %,
preferably from about 25 to about 45 wt %. Preferably, the oil and
carrier are contacted with the cellulosic fibres for at least one
minute, more preferably at least 30 seconds, and most preferably at
least about 5 seconds before drying.
[0025] The cellulosic fibres making up the pulp sheet are usually
obtained by disintegrating wood, conventionally in the form of
chips, fibres or bundles of fibres. In the present context, the
concept of "bundles of fibres" is regarded to be equivalent to the
concept of "fibres". The separated fibres may be obtained by means
of any pulp-making method known to a skilled person, e. g. by a
method for production of mechanical pulp (MP), stone groundwood
pulp (SGW), pressure groundwood pulp (PGW), refiner mechanical pulp
(RMP), thermomechanical pulp (TMP), chemi-mechanical pulp (CMP), or
chemi-thermomechanical pulp (CTMP), although the preferred pulps
are chemical pulps as, for instance, sulphate and sulphite pulps.
However, the cellulosic fibres may also advantageously be cotton
fibres. Another plausible source of fibres is recycled fibres from
wastepaper.
[0026] The present invention also relates to paper obtainable by
the method as above described. The paper produced suitably is
fluff, impregnating paper or tissue paper or other absorbing paper,
preferably fluff or tissue paper.
[0027] The invention also relates to paper, preferably fluff or
tissue paper, comprising cellulosic fibres, an oil and a carrier
having a porous and hydrophobic surface carrying said oil. The oil
and carrier suitably have characteristics as further described
herein. Preferably, the oil is selected from triisooctylmellitate
oil, soybean oil, castor oil or mixtures thereof. The oil-carrying
carrier is suitably homogeneously distributed in the paper.
[0028] The invention also relates to a method for producing an
absorbent comprising adding to an aqueous suspension of cellulosic
fibres a carrier having a hydrophobic and porous surface and an oil
carried by the carrier. Further characteristics are as described
herein.
[0029] The invention also relates to an absorbent comprising paper
obtainable from the method as described above, said absorbent
including e.g. sanitary napkins, pantiliners, tampons, diaper
bandages, adult incontinence garments and the like. Preferably, the
absorbent comprises fluff or tissue paper.
[0030] The invention further relates to the use of a carrier and an
oil carried by the carrier, in which the carrier has a porous and
hydrophobic surface, for treatment of cellulosic fibres to improve
the sorptive capacity of an absorbent comprising cellulosic
fibres.
[0031] The invention further relates to a process for treating
cellulosic fibres with a carrier having a porous and hydrophobic
surface and an oil carried by the carrier. The treatment is
intended to improve the sorptive capacity of an absorbent formed
from the treated cellulosic fibres, preferably fluff or tissue
paper or an absorbent comprising said fluff or tissue paper.
Further characteristics of the carrier and the oil are as described
hereabove.
[0032] The present invention is illustrated in more detail below by
means of an example. Unless otherwise stated the parts and
percentages below are given by weight. In the example below MPP-B
available from Akzo Nobel N. V., Arnhem, The Netherlands, was used.
MPP-B is a macroporous polymer containing an absorbed oil in the
pores thereof, as further described in EP 0 653 950 B1. The
particle size was 200-350 .mu.m and the extractive content 1 g
oil/g of polymer.
[0033] In the example below, produced fluff was tested with respect
to rewetting and wetting rate. The test method for the uptake rate
was SCAN-C 33:80, in which the fluff samples of 3 g, having a
diameter of 50 mm, were positioned vertically and loaded with a
weight of 500 g on top. Each sample was allowed to absorb water
from below, and the time taken until water penetrated through the
upper surface of the sample was determined by means of an
electronic detector. The shorter the time required to penetrate the
upper surface, the higher the uptake rate of the fluff. In the test
method for determination of rewetting or liquid holding capacity, a
fluff sample of 3 g having a diameter of 50 mm was positioned
vertically and loaded with a weight of 1 kg on top for 30 s, and
was then unloaded. 10 ml of water was applied to the sample under a
time period of 10 s and the liquid was allowed to drain the sample
for 30 s, after which the sample was loaded with a weight of 1 kg
for 4 minutes. 15 sheets, 8.times.8 cm, of filter paper were placed
on top of the sample and sheets are loaded with a weight of 5 kg
for one additional minute, after which the 15 sheets were weighed.
The increase of weight of the sheets was due to rewetting. Thus a
low increment indicates low rewetting, and consequently, a high
liquid retaining capacity, which is favourable.
Example 1
[0034] 10 g of bleached sulphate pulp was defiberised in 500 ml of
water together with the MPP-B product in addition rates from 1 to 4
kgltonne of dry pulp for 10 minutes. The composition of MPP-B
sample contained 50 wt % polypropylene, and 50 wt %
triisooctylmellitate oil (Emkarate 7930 ex ICI). Polymer beads
thereof were produced in an extrusion process using soybean oil and
castor oil as cell forming agents. The porosity of the polymer was
approximately 75% and the polymer had a cellular pore structure
with an average pore diameter of 15.+-.5 .mu.m (as determined from
SEM pictures). The polymer material was ground and subsequently
sieved in order to obtain a particle size fraction in the range
from 200-350 .mu.m. The thus produced particles were extracted with
acetone and subsequently filled with triisooctylmellitate oil. A
reference sample without MPP-B was also made. The thus obtained
stock was dewatered through the screen cloth of a wire mould,
producing pulp sheets having diameters of 210 mm. The sheets were
dried at 60.degree. C. for 120 minutes and then dry shredded into
fluff in a hammer mill. The fluff was formed into three samples
each sample weighing 3 g. The fluff samples thus obtained were
tested at ambient conditions of about 23.degree. C. and 50% RH
(relative humidity), with regard to rewetting as is set forth in
table 1 below.
1TABLE 1 Addition rate (kg/tonne Rewetting Examples Sample dry pulp
(gramme) 1 Reference (without 0 1.98 carrier and oil) 2 MPP-B 1
0.59 3 MPP-B 2 0.52 4 MPP-B 3 0.60 5 MPP-B 4 0.52
[0035] As can be seen, fluff comprising MPP-B imparted a
considerably increased liquid retaining capacity compared to the
reference, i.e. fluff not treated with MPP-B.
* * * * *