U.S. patent application number 10/635062 was filed with the patent office on 2005-02-10 for attachment of superabsorbent materials to fibers using oil.
This patent application is currently assigned to Weyerhaeuser Company. Invention is credited to Halabisky, Donald D., Hamilton, Robert, Ma, Kiet, West, Hugh.
Application Number | 20050031841 10/635062 |
Document ID | / |
Family ID | 33552924 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050031841 |
Kind Code |
A1 |
Hamilton, Robert ; et
al. |
February 10, 2005 |
Attachment of superabsorbent materials to fibers using oil
Abstract
Oil is used in absorbent structures to promote the retention of
superabsorbent materials within the absorbent structures that are
formed from fibers and the superabsorbent material. The oil is
applied to either the fibers or the superabsorbent material or both
prior to or during the formation of the components into an
absorbent structure. Acquisition rates and fluid retention levels
of the absorbent structures are described.
Inventors: |
Hamilton, Robert; (Seattle,
WA) ; Ma, Kiet; (Federal Way, WA) ; West,
Hugh; (Seattle, WA) ; Halabisky, Donald D.;
(Tacoma, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY
INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
Weyerhaeuser Company
|
Family ID: |
33552924 |
Appl. No.: |
10/635062 |
Filed: |
August 5, 2003 |
Current U.S.
Class: |
428/292.1 |
Current CPC
Class: |
A61L 15/60 20130101;
Y10T 428/249924 20150401; A61L 15/34 20130101 |
Class at
Publication: |
428/292.1 |
International
Class: |
D04H 001/00 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. An article for absorbing an aqueous fluid, comprising: cellulose
fibers; superabsorbent material; and an oil applied to the
cellulose fibers or the superabsorbent material.
2. The article of claim 1, wherein the oil has a melting point
below about 25.degree. C.
3. The article of claim 1, wherein the oil comprises a
triglyceride.
4. The article of claim 1, wherein the oil is a fatty acid.
5. The article of claim 1, wherein the oil is olive oil, soybean
oil, safflower oil, cottonseed oil, linseed oil, tung oil, castor
oil, coconut oil, canola oil, corn oil, or jojoba oil.
6. The article of claim 1, wherein the oil is a saturated or
unsaturated alkane, alkene, alkyne, cycloalkane, cycloalkene,
cycloalkyne or combinations thereof.
7. The article of claim 1, wherein the oil is petroleum
derived.
8. The article of claim 7, wherein the oil is selected from the
group consisting of mineral oil, hexadecane, squalane, and
squalene.
9. The article of claim 1, wherein the oil is present on the fibers
in an amount ranging from about 0.5 to 20 wt. % based on the weight
of oven-dried fibers.
10. The article of claim 1, wherein the oil is present on the
superabsorbent material in an amount ranging from about 0.01 to
less than 10 wt. % based on the weight of the superabsorbent
material.
11. Treated fibers comprising: cellulose fibers; and an oil applied
to the fibers, the oil having a melting point below the temperature
at which the oil is applied to the fibers.
12. The treated fibers of claim 11, wherein the cellulose fibers
are wood pulp fibers.
13. The treated fibers of claim 11, wherein the oil is petroleum
derived.
14. The treated fibers of claim 11, wherein the oil comprises a
triglyceride.
15. Treated superabsorbent material comprising: superabsorbent
material; and an oil applied to the superabsorbent material, the
oil having a melting point below the temperature at which the oil
is applied to the superabsorbent material.
16. The treated superabsorbent material of claim 15, wherein the
oil is petroleum derived.
17. The treated superabsorbent material of claim 15, wherein the
oil comprises a triglyceride.
18. A method for retaining superabsorbent material within a web of
cellulose fibers comprising: providing cellulose fibers having an
oil applied thereto, the oil having a melting point below the
temperature at which the oil is applied to the fibers; and
contacting a superabsorbent material with the cellulose fibers
treated with an oil.
19. A method for retaining superabsorbent material within a web of
cellulose fibers comprising: providing superabsorbent material
having an oil applied thereto, the oil having a melting point below
the temperature at which the oil is applied to the superabsorbent
material; and contacting cellulose fibers with the superabsorbent
material treated with an oil.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the attachment of
superabsorbent material to fibers using oil, methods of achieving
such attachment, and compositions for use in attaching
superabsorbent materials to fibers using oil.
BACKGROUND OF THE INVENTION
[0002] In the production of absorbent articles, such as diapers and
incontinent devices, it is known to combine superabsorbent
materials and cellulose fibers to form an absorbent core. The
absorbent core receives fluid to be absorbed and retains the fluid.
When superabsorbent materials are in the form of powder or small
particles, it is a challenge to retain the superabsorbent material
in the absorbent core which comprises a matrix of fibers, commonly
cellulose fibers. Various methods of retaining superabsorbent
material in an absorbent core have been described. For example, it
has been proposed that the cellulose fibers be embedded within the
surface of the superabsorbent material.
[0003] Another approach described in International Publication Nos.
WO 94/04352 and WO 94/04351 assigned to the assignee of the present
application provides polymeric or non-polymeric binders between the
superabsorbent material and the fiber. The binder is described as
binding the superabsorbent material to the fiber through hydrogen
or coordinate covalent bonds. The noted international publications
describe that the addition of small amounts of moisture to the
particles or fibers is desirable to promote binding between the
superabsorbent material and the fibers. The moisture is described
as being provided naturally by the ambient environment such as when
the relative humidity of the environment where the superabsorbent
material, binder and fibers are combined is approximately 60% to
75%, or higher. In instances where it is determined that the
moisture is necessary and the relative humidity is below a desired
level, capital equipment can be used in order to humidify the
manufacturing location where the superabsorbent material, binder
and fibers are contacted. While humidifying the manufacturing
location is effective, it requires a capital investment and
increases the costs of production.
[0004] Retaining the superabsorbent material in an absorbent core
over an extended period of time is another challenge that faces
manufacturers. The retention of superabsorbent materials in the
absorbent core may fail over time for a number of reasons such as
vigorous handling of the absorbent core which results in
dislodgment of the superabsorbent material or a reduction in the
moisture content of the absorbent core.
[0005] Diapers including an absorbent core of superabsorbent
material and cellulose fibers are typically manufactured by a
process that combines cellulose fibers and superabsorbent material.
In such a process, rolls or bales of cellulose fibers without
superabsorbent material are fiberized by a fiberizing apparatus
such as a hammermill. These fiberized cellulose fibers are
entrained in air and superabsorbent material is introduced to the
air entrained fibers. The air entrained combination of cellulose
fibers and superabsorbent material is delivered to an air lay
device such as a pad former, which draws the fibers and
superabsorbent material onto a screen and forms the fibers and
superabsorbent material into a particular shape. These formed pads
are then removed from the pad former for further processing. In
order to maximize the utilization of the superabsorbent material
and minimize the amount of superabsorbent material lost during
manufacturing, diaper manufacturers desire that superabsorbent
material be attached to the fiber during the time that the fiber
and superabsorbent material are air entrained together.
[0006] With this background, the present inventors have worked to
address the challenges above and have developed compositions and
methods that employ oil to assist in the retention of
superabsorbent materials in an absorbent article.
SUMMARY OF THE INVENTION
[0007] The present invention provides fibers and/or superabsorbent
materials treated with oil that are useful in absorbent cores
formed from the treated fibers and/or treated superabsorbent
materials and untreated fibers and/or untreated superabsorbent
materials. The compositions of the present invention can be formed
into absorbent articles for absorbing fluids such as aqueous fluids
like urine or blood. The compositions are useful in methods for
retaining superabsorbent materials in webs or masses of fibers
commonly used as absorbent structures in absorbent articles such as
diapers, incontinent devices and feminine hygiene products. The
methods provide absorbent structures that are able to retain
superabsorbent materials at a level that manufacturers of absorbent
articles should find desirable. Surprisingly, when oil is used in
accordance with the present invention, despite the hydrophobicity
of the oil, absorbent articles that include fibers or
superabsorbent material treated with the oil acquire and retain
fluids at a rate and in an amount that manufacturers and customers
of the absorbent articles should find desirable. Other advantages
of using oil as described below in more detail include the ability
to produce an absorbent article that retains superabsorbent
material irrespective of the humidity present when the absorbent
article is manufactured or the humidity that the manufactured
absorbent article is exposed to over time.
[0008] In one aspect, the present invention relates to articles for
absorbing aqueous fluids that include cellulose fibers and
superabsorbent material wherein the cellulose fibers or
superabsorbent material are treated with an oil. The invention also
relates to the cellulose fibers that have been treated with an oil
and superabsorbent materials that have been treated with an oil,
wherein the oil has a melting point below the temperature at which
the oil is applied to the fibers or superabsorbent material.
[0009] In another aspect, the present invention relates to methods
of retaining superabsorbent materials within a web of cellulose
fibers. In one embodiment, the method provides cellulose fibers
having an oil applied thereto, wherein the oil has a melting point
below the temperature at which the oil is applied to the fibers.
The oil treated cellulose fibers are then contacted with a
superabsorbent material. In another embodiment of this aspect of
the invention, the method provides superabsorbent materials having
an oil applied thereto, wherein the oil has a melting point below
the temperature at which the oil is applied to the superabsorbent
material. The oil treated superabsorbent material is then contacted
with cellulose fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0011] FIG. 1 is a graph illustrating the results of testing to
determine the levels of superabsorbent material retained within
various absorbent structures;
[0012] FIG. 2 is a graph illustrating the acquisition times for the
absorbent structures of FIG. 1;
[0013] FIG. 3 is a graph illustrating the amount of fluid acquired
by the absorbent structures of FIG. 1; and
[0014] FIG. 4 is an illustration of the device used in the saddle
wicking test.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] As used herein, the term "fiber" refers to natural or
synthetic fibers. Such fibers may be physically pretreated, e.g.,
by subjecting the fibers to steam, or chemically treated, e.g., by
crosslinking the fibers. The fibers may also be twisted or crimped
as desired.
[0016] A particular type of fiber are cellulose fibers. A
particular example of a cellulose fiber is wood pulp fiber. Wood
pulp fibers can be hardwood pulp fibers or softwood pulp fibers.
The pulp fibers may be chemical, thermomechanical,
chemithermomechanical or combinations thereof. Such wood pulp
fibers can be obtained from well known chemical processes such as
the kraft or sulfite processes. Other cellulose fibers include
lyocell, linen, chopped silk fibers, bagasse, hemp, jute, rice,
wheat, bamboo, corn, sisal, cotton, flax, kenaf, peat moss, and
mixtures thereof. When the fibers are cellulose fibers, they may be
pretreated with chemicals to result in lignin or cellulose-rich
fiber surfaces. In addition, the fibers may be bleached.
[0017] Examples of synthetic fibers include acrylic, polyester,
carboxylated polyolefin, and polyamine fibers.
[0018] As used herein, the term "superabsorbent material" refers to
polymers that swell on exposure to water and form a hydrated gel
(hydrogel) by absorbing large amounts of water. Superabsorbent
materials exhibit the ability to absorb large quantities of liquid,
i.e., in excess of 10 to 15 parts of liquid per part thereof. These
superabsorbent materials generally fall into three classes, namely
starch graft copolymers, crosslinked carboxymethylcellulose
derivatives and modified hydrophilic polyacrylates. Examples of
such absorbent polymers are hydrolyzed starch-acrylonitrile graft
copolymer, a neutralized starch-acrylic acid graft copolymer, a
saponified acrylic acid ester-vinyl acetate copolymer, a hydrolyzed
acrylonitrile copolymer or acrylamide copolymer, a modified
crosslinked polyvinyl alcohol, a neutralized self-crosslinking
polyacrylic acid, a crosslinked polyacrylate salt, carboxylated
cellulose, and a neutralized crosslinked isobutylene-maleic
anhydride copolymer.
[0019] Superabsorbent particles are available commercially, for
example starch graft polyacrylate hydrogel fines (IM 1000F) from
Hoechst-Celanese of Portsmouth, Va., or larger particles such as
granules. Other superabsorbent particles are marketed under the
trademarks SANWET (supplied by Sanyo Kasei Kogyo Kabushiki Kaisha),
SUMIKA GEL (supplied by Sumitomo Kagaku Kabushiki Kaisha and which
is emulsion polymerized and spherical as opposed to solution
polymerized ground particles), FAVOR (supplied by Stockhausen of
Greensboro, N.C.), and NORSOCRYL (supplied by Atochem).
[0020] The term oil as used generally applies to a wide range of
substances. Oils may be derived from animals or from plant seeds or
nuts, and these types of oils tend to be chemically identical with
fats, with the only difference being one of consistency at room
temperature. Animal and plant oils are composed largely of
triglycerides of the fatty acids, oleic, palmitic, stearic, and
linolenic acid. Oils may also be derived from petroleum sources.
Petroleum-based oils generally include a mixture of hydrocarbons.
As used herein, the term "oil" refers to oils that have melting
points below the temperature at which the oil is applied to the
fibers or superabsorbent material as described below in more
detail. Such temperature will generally be below 25.degree. C., but
could be higher. If the melting point of the oil is greater than
the ambient temperature at which the oil is applied to the fibers
or superabsorbent material, the oil can be heated to liquefy it.
This ensures that the oils remain liquid during their application
to the fibers or superabsorbent material. Oils useful in the
present invention should also have a vapor pressure sufficiently
low to prevent evaporation either during their application or
during use.
[0021] The oil should not penetrate the walls of the fibers so
rapidly that it becomes unavailable to retain the superabsorbent
material when the superabsorbent material is contacted with the oil
treated fibers. The oil preferably resides on the surface of the
fibers during the useful life of the absorbent article made from
the fibers, oil and superabsorbent material. To that end, oils of
higher molecular weight penetrate the fiber wall more slowly than
oils of a lower molecular weight.
[0022] With certain oils, particularly those that include
unsaturated components such as soy bean oil, it has been observed
that while functioning like other oils to promote retention of
superabsorbent material within an absorbent structure comprising
fibers and a superabsorbent material, after extended exposure to
air it has been observed that soybean oil crosslinks and
solidifies. The solidified soybean oil increases the hydrophobicity
of the fibers to which it has been applied. For soybean oil and
other oils that might exhibit such crosslinking, crosslinking
inhibitors or stabilizers such as tert-butylhydroxyanisole (BHA, 2-
or 3-tert-butyl-4-methoxy-phenol); butylhydroxytoluene (BHT,
2,6-di-tert-butyl-4-methyl-phenol); ascorbic acid (vitamin C);
ascorbyl-palmitate; tocopherol (vitamin E); carnosic acid; and
sesamin can be used to inhibit such crosslinking.
[0023] Examples of "oils" as that term is used herein include fats
and their component fatty acids. As described above, fats are
naturally occurring esters of long chain carboxylic acids and the
triol glycerol. These esters are also referred to as triglycerides.
The hydrolysis of fats yields glycerol and three component
carboxylic acids. These straight chain carboxylic acids which may
be obtained from the hydrolysis of fats are called fatty acids and
include one carboxylic acid group. Fatty acids may be saturated or
unsaturated. The most common saturated fatty acids are lauric acid,
myristic acid, palmitic acid, and stearic acid. Other fatty acids
include oleic acid, linoleic acid, and linolenic acid. Generally,
the melting point of a fat depends on the amount of unsaturation in
the fatty acids. Fats with a preponderance of unsaturated fatty
acids generally have melting points below about 25.degree. C.
Specific examples of oils as that term is used herein include
soybean oil, cottonseed oil, linseed oil, tung oil, castor oil,
coconut oil, olive oil, canola oil, safflower oil, corn oil or
jojoba oil. Jojoba oil is a light yellow liquid at room temperature
that is not technically an oil or fat, but rather is a wax. A wax
is an ester of fatty acids with long chain monohydric alcohols. The
term oil as used herein is intended to include jojoba oil and other
waxes that are liquid at temperatures that they are applied to
fibers or superabsorbent materials in accordance with the present
invention. It should be understood that the foregoing is a list of
exemplary oils and the present invention is not necessarily limited
to the foregoing oils. It should be understood that use of the term
"oil" in this application refers not only to the oil itself
comprising a mixture of various fat and fatty acid components, but
also includes the individual isolated fats, and the isolated fatty
acids that result when the fats are hydrolyzed. For example, the
term "oil" as used herein also refers to the fatty acids oleic,
palmitic, stearic, and linolenic, that form the most common
triglycerides in many oils derived from animals and plants and
would be useful in accordance with the present invention to retain
superabsorbent material in an absorbent structure comprising fibers
and the superabsorbent material.
[0024] The term "oil" as used herein also refers to unsubstituted
alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes,
cycloalkynes, aromatics, and mixtures thereof derived from
petroleum or animal sources that have melting points below the
temperature at which the oil is applied to the fibers or as
described below in more detail, to the superabsorbent materail,
e.g., about 25.degree. C. Such oils are generally derived from
petroleum sources, but may also be derived from animal sources.
Oils of this type useful in the present invention should have vapor
pressure sufficiently low to prevent evaporation of the oil during
application or use. Specific examples of these types of oils
include mineral oil, paraffin oil, hexadecane, squalane, and
squalene.
[0025] As used herein, mineral oil is an example of a highly
refined liquid petroleum derivative. Mineral oil is light, clear,
colorless, and odorless and is also referred to as medicinal oil.
Mineral oil is used medicinally as an internal lubricant and for
the manufacture of salves and ointments.
[0026] Paraffin oil is an example of an oil that is either pressed
or dry distilled from paraffin distillate obtained from the
distillation of petroleum.
[0027] Squalane is an example of an alkane derived from animal
sources, such as the sebum. Squalene is an example of an alkene;
more specifically, a terpene derived from animal sources, such as
the human sebum or shark liver oil. Squalene may also be isolated
from oils derived from plants, such as olive oil, wheat germ oil,
rice bran oil, and yeast.
[0028] As described below in more detail, the present inventors
have observed that an absorbent structure formed from fibers or
superabsorbent material treated with an oil retains superabsorbent
material within the structure to a greater degree than the amount
of superabsorbent material retained within an absorbent structure
that includes superabsorbent material and fibers that have not been
treated with an oil in accordance with the present invention.
[0029] The retention of superabsorbent material within an air laid
absorbent structure that includes fibers and superabsorbent
material can be evaluating using a Rotap test as described
below.
[0030] A ten by ten centimeter pad cut from an absorbent structure
that includes fibers and superabsorbent material is placed on the
top screen of a stack of screens. The stack of screens from top to
bottom includes an 8-mesh screen, a 20-mesh screen, and a 200-mesh
screen. A collection pan is provided below the 200-mesh screen to
catch material that passes through the three screens. A lid is
placed atop the 8-mesh screen. The screen stack is placed in a
Rotap device which rotates the stack while at the same time,
hitting the lid with a hammer. Both the rotation and the hammering
occur at a frequency of about 2 Hz. Unless indicated otherwise, the
sample is processed for two minutes. At the end of two minutes, the
200-mesh screen has a mixture of superabsorbent material and fibers
collected on it. The fibers are easily lifted off with tongs and
the superabsorbent material is weighed. For longer testing times,
the superabsorbent material on the 200-mesh screen can be weighed
at intervals. Rotap machines are manufactured by W.S. Tyler,
Incorporated.
[0031] The present inventors have also observed that surprisingly,
the presence of the oil, which behaves as a hydrophobic material,
does not significantly alter the ability of the absorbent structure
to acquire and transport fluid. The ability of an absorbent
structure to acquire and transport fluid can be evaluated using the
saddle wick test described below.
[0032] The saddle wicking test is used to show liquid distribution
away from an initial dosing point into an absorbent structure. The
test also measures how fast the liquid is absorbed for three
separate doses into the absorbent structure. The test is carried
out in the saddle wicking device which comprises the device
illustrated in FIG. 4.
[0033] Referring to FIG. 4, the saddle wicking device 50 includes a
u-shaped receptacle 52 which is supported by spaced apart left
support plate 54 and right support plate 56. The support plates
include a u-shaped cutout portion that forms a cradle for receiving
and holding u-shaped receptacle in an upright position with its
open end facing upward. Located in the trough of the u-shaped
receptacle 52 are two spaced apart dams 58 and 60. Dams 58 and 60
include a lower edge 62 that mates with the bottom of the trough
defined by u-shaped receptacle 52. The upper edge 64 of dams 58 and
60 is spaced above the lower edge so dams 58 and 60 form upward
extending members that serve to block fluid which is dispensed
between the dams from flowing past the dams.
[0034] The opened top of the u-shaped receptacle is approximately
23.2 cm across. The u-shaped receptacle is about 17.1 cm deep. The
dams 58 and 60 are about 3.2 cm high at the bottom of the trough
and extend up along the u-shaped receptacle to a location where the
distance between one sidewall of the u-shaped receptacle to the
other sidewall is about 14.0 cm. Dams 58 and 60 are spaced
approximately 12.7 cm apart. The saddle wicking device can be
manufactured from any rigid material such as plastic. As described
below in more detail, sample 66 is positioned at the bottom of the
u-shaped receptacle between dams 58 and 60.
[0035] The absorbent articles comprising superabsorbent materials
and fibers having dimensions of about 30 cm long and 12.1 cm wide
were divided into 3.8 cm wide sections moving to the left and the
right of the center line of the sample. This results in the
definition of sections F1, F2, F3, F4 to the right of the center
line and B1, B2, B3, B4 to the left of the center line. These
patterns are marked on the absorbent structure. The sample is then
positioned and clamped in the saddle wicking device so that it
maintains the same curvature as the device. The absorbent structure
should not be bowed up in the center. Tape can be used if necessary
on the bottom of the saddle wicking device to keep the absorbent
structure from bowing up. An X is marked 2.5 cm to the right of the
center line. This defines the insult point. A funnel is positioned
5 cm above the X. The funnel provides a flow rate ranging between
5-7 ml per second. A first insult of 100 ml of synthetic urine is
dispensed from the funnel. The time is measured from the beginning
of the insult to the time when the synthetic urine is fully
absorbed into the absorbent structure. Full absorption is indicated
when no liquid is seen in the creases and folds of the absorbent
structure. The time is recorded for the first insult. The foregoing
is repeated twice more using 50 ml of synthetic urine in the second
and third insults. The times between starting of the insult and the
time when the applied synthetic urine is fully absorbed is recorded
for the second and third insult. The absorbent structure is then
cut into the sections F1-F4 and B1-B4, as described above. Cutting
of the absorbent structure should be completed within five minutes
after the timer was stopped for the third insult. Each section is
then weighed and the weight recorded. The cut sections are then
placed on Plexiglas sheets and dried in an oven at 92-100.degree.
C. for a minimum of 16 hours. The dried sections are then weighed
and the weight recorded. The weight of synthetic urine absorbed in
each respective zone is calculated by subtracting the dry weight
from the wet weight of the particular sections.
[0036] In accordance with the present invention, the oil can be
applied to the fiber or alternatively, the oil can be applied to
the superabsorbent material. The oil-treated fiber or oil-treated
superabsorbent material can then be combined with untreated
superabsorbent material or untreated fiber, respectively, to form
an absorbent article as described below in more detail. Oil-treated
fibers and oil-treated superabsorbent materials may also be
combined to form an absorbent article.
[0037] The particular way that oil is applied to the fibers is not
critical. Examples of techniques for applying oil to the fibers
include the use of a gravure-type roll coater to coat a web of the
fibers. Alternatively, oil can be sprayed onto a web of the fibers
or the fibers can be immersed in a bath of oil. The oil may also be
added to the fibers as a web of the fibers is being broken up, such
as in a hammermill. The amount of oil applied to the fibers should
be sufficient to achieve the retention of superabsorbent material
in accordance with the present invention, but not so much as to
have a significant adverse affect on the fluid absorption
properties of the fibers, such as the fluid acquisition rate or the
amount of fluid absorbed by a web of the fibers. Manufacturers of
absorbent articles that include absorbent structures containing the
oil-treated fibers or oil-treated superabsorbent materials of the
present invention desire that the fluid absorption properties of
such structures be similar to the fluid absorption properties of
the absorbent structures that the manufacturer is considering
replacing. Ideally, the absorbent structures would exhibit fluid
acquisition properties that are at least as desirable as the fluid
acquisition properties of similar absorbent structures manufactured
from untreated fibers. The amount of oil applied to the fibers
should also not be so great that it adversely impacts the
fiberization of the web of oil-treated fibers. Suitable amounts of
oil applied to the fibers include about 0.5 wt. % to about 20 wt. %
oil based on the weight of oven dried fibers. A narrower range is
1.0 wt. % to about 15 wt. % oil based on the weight of oven dried
fibers and an even narrower range is 1.0 wt. % to about 10 wt. %
oil based on the weight of oven dried fibers.
[0038] The form of the fibers to which the oil is applied can vary.
If a roll coater is used, the fibers can be in the form of a sheet
of fibers. The oil can be applied to a wet laid sheet of fibers
having a basis weight of at least 350 grams per meter.sup.2 and a
density of at least about 400 kg/meter.sup.3.
[0039] The oil may be added neat, or it may be diluted with solvent
that evaporates after application of the oil to the fibers. The
solvent should not adversely affect the attachment of
superabsorbent material to the fibers or the fluid acquisition and
fluid retention properties of an absorbent article that contains
the oil-treated fibers.
[0040] In the embodiment wherein the oil is applied to the
superabsorbent material, again the method of application is not
critical. The oil may be applied by spraying onto the
superabsorbent material, or immersing the superabsorbent material
in a bath of the oil.
[0041] The amount of oil applied to the superabsorbent material
should be enough to result in attachment of the oil-treated
superabsorbent material to fibers when combined with fibers, but
should not be so great that it has a significant adverse affect on
the fluid acquisition and fluid retention properties of a web of
the fibers once the oil-treated SAP is combined therewith. In
addition, the amount of oil employed should not be so great that it
has a significant adverse affect on the absorbent properties of the
superabsorbent material itself. Suitable amounts of oil applied to
the superabsorbent material ranges from about 0.01 wt % to less
than 10 wt. % oil based on the weight of superabsorbent
material.
[0042] The oil-treated fibers and untreated superabsorbent
material, the oil-treated superabsorbent material and untreated
fibers, or the oil treated fibers and oil treated superabsorbent
material can be combined and then formed into an absorbent
structure in the following manner. The following description makes
reference to fibers and superabsorbent material. It should be
understood that the following description is applicable to the
situation where oil-treated fibers are combined with untreated
superabsorbent material, untreated fibers are combined with
oil-treated superabsorbent material, or oil-treated fibers are
combined with oil-treated superabsorbent material. Rolls or bales
of fibers, without particles, are fiberized by a fiberizing device
such as a hammermill. The individualized fibers are air entrained
during which time the superabsorbent material can be added thereto.
The air entrained fiberized fibers and superabsorbent material are
then delivered to an air laying device, such as a pocket former,
and formed into a desired shape. The formed pad is removed from the
air laying device for further processing. The formed pads are in
the form of a web or mass of fibers used as absorbent structures in
absorbent articles such as the ones discussed above. The webs or
masses of fibers have basis weights ranging from about 0.01 to
about 0.05 g/cm.sup.2, thicknesses ranging from about 0.3-2
millimeters and densities ranging from 0.15 to about
1/cm.sup.3.
[0043] It should be understood that in an alternative embodiment,
the oil can be applied to the combination of the fibers and
superabsorbent material while they are air entrained together.
[0044] Combining the fibers and superabsorbent material can be
carried out under a wide range of humidity conditions. In order to
achieve retention of superabsorbent material within the absorbent
article comprising the fibers and superabsorbent material, it is
not required that any particular level of humidity be maintained
when the two components are combined. Satisfactory retention can be
achieved at relative humidity levels below about 70%, below about
60% and even below about 50%.
[0045] As illustrated in the examples that follow, the addition of
oil to fibers or superabsorbent material in accordance with the
present invention does not significantly affect the fluid
acquisition and fluid retention properties of absorbent structures
formed therefrom. Absorbent structures of the present invention
acquire and retain fluids despite the presence of the hydrophobic
oil. Absorbent structures produced in accordance with the present
invention are soft and flexible.
[0046] The following examples are intended to illustrate certain
embodiments of the present invention and are not intended to limit
the scope of the present invention.
EXAMPLE 1
Oil Treatment of Fibers
[0047] Pulp sheets of southern pine fluff available from
Weyerhaeuser Company under the designation NB416 with a starting
moisture content of 6% by weight based on total sheet weight were
coated in a Black Brothers gravure-type roll coater with mineral
oil. The mineral oil was USP mineral oil purchased at a Rite Aid
pharmacy carrying the label "Rite Aid Mineral Oil USP" and a CAS
number 8020-83-5 and 8012-95-1, with alternative CAS numbers
39355-35-6, 79956-36-8 and 83046-05.3. The gravure coater applied a
uniform coating of the mineral oil over one entire surface of the
pulp sheet from where it was rapidly soaked up by the sheet. The
mineral oil was applied to the pulp sheet at a rate of 10.5 parts
by weight mineral oil to 100 parts of oven dried pulp. The treated
sheet was stored in a plastic zippered bag for 24 hours at room
temperature to allow the added oil to migrate within the sheet. The
pulp sheets were then fiberized in a hammermill and combined with a
superabsorbent material (available from Stockhausen under the
designation SXM77) prior to delivery to a pocket former similar to
pocket formers conventionally used in the manufacture of diapers
and feminine hygiene products which was operated to produce a pad
having a target fiber basis weight of 300 grams per square meter
and a superabsorbent material basis weight of 200 grams per square
meter. The pocket former was run at 18 pads per minute formation
rate. The humidity ranged between 39% relative humidity at the
beginning of the runs and 31% relative humidity at the end of the
runs. The temperature started out at about 16.5.degree. C. and by
the end of the runs had risen to about 22.5.degree. C.
[0048] Some of the resulting pads were collected and subjected to
Rotap testing. Other pads were densified to 0.25 cc/gm and
subjected to saddle wick testing according to the techniques
described above. In the Rotap testing, the pads were vibrated for
two minutes. In the saddle wick testing, synthetic urine was
employed using three insults of 100 ml, 50 ml, and 50 ml. The
results are depicted in FIGS. 1, 2, and 3 as RP-SO.
CONTROL EXAMPLE 1
[0049] For this control example, pads were prepared from the same
type of fibers and superabsorbent material as Example 1 without
mineral oil applied to the fibers. The same conditions as Example 1
were employed in preparing the pads of this control example. The
collected pads were subjected to Rotap testing and saddle wick
testing under the same conditions described in Example 1. The
results are depicted in FIGS. 1, 2, and 3 as NB416.
CONTROL EXAMPLE 2
[0050] In this control example, a commercial modified pulp
available from Weyerhaeuser Company under the designation RP-S4 was
used to form pads of such fibers and the same superabsorbent
material described in Example 1. RP-S4 contains wood pulp fibers
treated with a number of agents comprising molecules having at
least two hydrogen bond or coordinate covalent bond forming
functional groups or combinations of such functional groups which
are contained on the fibers for the purpose of attaching
superabsorbent material to the fibers. The pads were formed using
the same conditions as Example 1. The collected pads were subjected
to the Rotap testing and saddle wick testing under the same
conditions described in Example 1. The results are illustrated in
FIGS. 1, 2, and 3 as RP-S4.
[0051] The results illustrate that absorbent articles prepared from
fibers treated with oil in accordance with the present invention
and combined with superabsorbent material retain the superabsorbent
material to the same level or greater than the pads prepared
according to the control examples. Additionally, the results
illustrate that absorbent articles formed in accordance with the
present invention with oil present exhibit fluid acquisition rates
and fluid retention levels similar to the pads prepared in
accordance with the control example.
[0052] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *