U.S. patent application number 10/741231 was filed with the patent office on 2005-06-23 for densification agent and oil treated cellulose fibers.
Invention is credited to Hamilton, Robert T., West, Hugh.
Application Number | 20050133180 10/741231 |
Document ID | / |
Family ID | 34523225 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050133180 |
Kind Code |
A1 |
West, Hugh ; et al. |
June 23, 2005 |
Densification agent and oil treated cellulose fibers
Abstract
Densification agent and oil treated cellulose fibers exhibit
densification properties that are superior to oil treated fibers
that have not been treated with a densification agent and cellulose
fibers that have not been treated with oil or a densification
agent. The densification agent and oil treated cellulose fibers are
useful in absorbent articles that may contain superabsorbent
materials.
Inventors: |
West, Hugh; (Seattle,
WA) ; Hamilton, Robert T.; (Seattle, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY
INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Family ID: |
34523225 |
Appl. No.: |
10/741231 |
Filed: |
December 19, 2003 |
Current U.S.
Class: |
162/158 ;
162/135; 162/175; 162/205 |
Current CPC
Class: |
A61L 15/28 20130101;
A61L 15/28 20130101; A61L 15/42 20130101; C08L 1/00 20130101; A61L
15/34 20130101 |
Class at
Publication: |
162/158 ;
162/175; 162/135; 162/205 |
International
Class: |
D21H 017/00; D21H
017/24; D21H 017/28 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A cellulose pulp sheet comprising: cellulose fibers; an oil
applied to the cellulose fibers; and a densification agent applied
to the cellulose fibers.
2. The cellulose pulp sheet of claim 1, wherein the cellulose
fibers are wood pulp fibers.
3. The cellulose pulp sheet of claim 1, wherein the oil has a
melting point below about 25.degree. C.
4. The cellulose pulp sheet of claim 1, wherein the oil comprises a
triglyceride.
5. The cellulose pulp sheet of claim 1, wherein the oil is a fatty
acid.
6. The cellulose pulp sheet 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.
7. The cellulose pulp sheet of claim 1, wherein the oil is
saturated or unsaturated alkane, alkene, alkyne, cycloalkane,
cycloalkene, cycloalkyne, or combinations thereof.
8. The cellulose pulp sheet of claim 1, wherein the oil is
petroleum derived.
9. The cellulose pulp sheet of claim 8, wherein the oil is selected
from the group consisting of mineral oil, hexadecane, squalane, and
squalene.
10. The cellulose pulp sheet 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 dry fibers.
11. The cellulose pulp sheet of claim 1, wherein the densification
agent comprises an agent having at least one hydrogen bonding
functionality.
12. The cellulose pulp sheet of claim 1, wherein the densification
agent comprises a saccharide.
13. The cellulose pulp sheet of claim 12, wherein the densification
agent further comprises at least one agent having hydrogen bonding
functionality.
14. The cellulose pulp sheet of claim 11 or 13, wherein the agent
having at least one hydrogen bonding functionality is selected from
the group consisting of alcohols, hydroxy acids, and polycarboxylic
acids.
15. The cellulose pulp sheet of claim 14, wherein the alcohols are
selected from the group consisting of polyols and glycols.
16. The cellulose pulp sheet of claim 13, wherein the weight ratio
of saccharide actives to actives in the at least one agent having a
hydrogen bonding functionality in the densification agent ranges
from about 70:30 to about 85:15.
17. The cellulose pulp sheet of claim 11 or 13, wherein the
densification agent is present in an amount ranging from about 0.5
to about 20 wt. % actives based on dry weight of the fibers.
18. The cellulose pulp sheet of claim 14, wherein hydroxy acid is
lactic acid.
19. The cellulose pulp sheet of claim 12, wherein the saccharide is
a high fructose corn syrup.
20. The cellulose pulp sheet of claim 19 having a densification
agent actives content ranging from about 3 to about 8 wt. %.
21. The cellulose pulp sheet of claim 11, wherein the agent having
at least one hydrogen bonding functionality is propylene
glycol.
22. A method for producing a cellulose pulp sheet comprising:
providing cellulose pulp; forming a cellulose pulp sheet from the
cellulose pulp; applying an oil to the cellulose pulp sheet; and
applying a densification agent to the cellulose pulp sheet.
23. The method of claim 22, wherein the oil and the densification
agent are applied to the cellulose pulp sheet simultaneously.
24. The method of claim 20, wherein the oil is applied to a first
side of the cellulose pulp sheet and the densification agent is
applied to a second side of the cellulose pulp sheet, the first
side being opposite the second side.
25. The method of claim 22, wherein the densification agent
comprises an agent having at least one hydrogen bonding
functionality.
26. The method of claim 22, wherein the densification agent
comprises a saccharide.
27. The method of claim 26, wherein the densification agent further
comprises an agent having at least one hydrogen bonding
functionality.
28. The method of claim 22, wherein the densification agent is
applied in an amount resulting in the application of about 0.5 to
about 20 wt. % actives based on dry weight of the fibers.
29. A method for producing a densified web of cellulose fibers
comprising: providing cellulose fibers treated with an oil and a
densification agent; fiberizing the cellulose fibers treated with
the oil and the densification agent; forming the fiberized
cellulose fibers treated with the oil and the densification agent
into a web; and compressing the web.
30. The method of claim 29, wherein the densification agent
comprises an agent having at least one hydrogen bonding
functionality.
31. The method of claim 29, wherein the densification agent
comprises a saccharide.
32. The method of claim 31, wherein the densification agent further
comprises an agent having at least one hydrogen bonding
functionality.
33. The method of claim 29, wherein the cellulose fibers treated
with an oil and a densification agent contain about 0.5 to about 20
wt. % actives based on dry weight of the cellulose fibers.
34. A method for modifying the densification properties of
cellulose fibers treated with an oil, the cellulose fibers before
treatment with the oil and after application and removal of a
compression load being densified to a first density, the cellulose
fibers after treatment with the oil and after application and
removal of the compression load being densified to a second
density, the first density being greater than the second density,
the method comprising: applying a densification agent to the oil
treated fibers, the densification agent applied to the oil treated
fibers in an amount that results in the fibers treated with the oil
and the densification agent densifying to a third density after
application and removal of the compression load, the third density
being greater than the first density.
35. The method of claim 34, wherein the third density is at least
2% greater than the first density when the compression load is 150
psi or less.
36. The method of claim 34, wherein the densification agent
comprises an agent having at least one hydrogen bonding
functionality.
37. The method of claim 34, wherein the densification agent
comprises a saccharide.
38. The method of claim 37, wherein the densification agent further
comprises an agent having at least one hydrogen bonding
functionality.
39. The method of claim 34, wherein the densification agent is
applied to the cellulose fibers in an amount resulting in the
application of about 0.5 to about 20 wt. % actives based on dry
weight of the cellulose fibers.
40. An article for absorbing an aqueous fluid, comprising:
cellulose fibers; superabsorbent materials; and an oil and a
densification agent applied to the cellulose fibers.
41. The article of claim 40, wherein the densification agent
comprises an agent having at least one hydrogen bonding
functionality.
42. The article of claim 40, wherein the densification agent
comprises a saccharide.
43. The article of claim 42, wherein the densification agent
further comprises an agent having at least one hydrogen bonding
functionality.
44. The article of claim 40, wherein the densification agent is
present in an amount such that about 0.5 to about 20 wt. % actives
based on dry weight of the cellulose fibers is present on the
cellulose fibers.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to cellulose fibers that have
been treated with an oil and a densification agent to modify the
properties of the cellulose fibers and to methods for producing
such modified cellulose fibers.
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,
including subjecting the formed pads to compression in order to
densify the pad by decreasing its thickness.
[0006] Reducing the thickness of the formed pads which are used in
diapers is important to diaper manufacturers so that they can
reduce the size of packaging which allows them to ship more diapers
per volume and to display a larger number of diapers in a limited
amount of shelf space. In addition, consumers find thinner diapers
more desirable.
[0007] The inventors of the subject application have described in
their prior application Ser. No. 10/635,062, filed on Aug. 5, 2003,
the use of oil applied to fibers or superabsorbent material to
achieve attachment of superabsorbent material to fibers. The
inventors' additional work in this area has led them to observe
that when oil is applied to fibers and pads are formed from such
oil treated fibers, the pads when compressed to increase their
density do not densify to as great a degree as pads that include
fibers that have not been treated with an oil.
[0008] 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 and which can be compressed to achieve
articles of desirable densities.
SUMMARY OF THE INVENTION
[0009] The present invention provides fibers treated with oil and a
densification agent that are useful in absorbent cores formed from
the treated fibers and 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. The compositions of the present invention
can be compressed to densities that manufacturers of absorbent
articles should find desirable.
[0010] In one aspect, the present invention relates to a cellulose
pulp sheet that includes cellulose fibers, an oil applied to the
cellulose fibers, and a densification agent applied to the
cellulose fibers. The cellulose pulp sheet can be fiberized into
individualized fibers, laid into a pad, and then compressed. The
invention also relates to a method for producing a cellulose pulp
sheet which includes the steps of providing a cellulose pulp sheet,
applying an oil to the cellulose pulp sheet, and applying a
densification agent to the cellulose pulp sheet.
[0011] In another aspect, the present invention relates to a method
for producing a densified web of cellulose fibers that includes the
step of providing cellulose fibers. The cellulose fibers are
treated with an oil and a densification agent before being
fiberized. The fiberized cellulose fibers are compressed to form a
densified web.
[0012] In yet another aspect, the present invention relates to a
method for modifying the densification properties of cellulose
fibers treated with an oil. In this aspect, the fibers before
treatment with the oil, and after application and removal of a
compression load, can be densified to a first density. The oil
treated fibers when subjected to the same compression load and
release can be densified to a second density wherein the first
density is greater than the second density. The method of this
aspect of the present invention includes applying a densification
agent to the oil treated fibers. The densification agent is applied
to the oil treated fibers in an amount that results in the fibers
treated with the oil and the densification agent densifying to a
third density when subjected to and released from the compression
load. The third density being greater than the first density.
[0013] Manufacturers of absorbent articles will find the oil and
densification agent treated fibers of the present invention useful
in their absorbent products due to the densification properties of
cellulose pulp fibers treated in accordance with the present
invention. The methods of the present invention provide suitable
means for producing the cellulose pulp fibers that exhibit
superabsorbent retention properties and densification properties
that absorbent article manufacturers should find desirable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] 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:
[0015] FIG. 1 is a graph illustrating the results of compression
testing to determine the densification properties of absorbent
structures containing cellulose fibers treated in accordance with
the present invention;
[0016] FIG. 2 is a graph illustrating the results of compression
testing to determine the densification properties of structures
containing cellulose fibers treated in accordance with the present
invention and superabsorbent materials; and
[0017] FIG. 3 is a schematic illustration of a wet laid web
manufacturing line illustrating the application of a densification
agent to a wet laid web of cellulose fibers in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] 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.
[0019] 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.
[0020] Examples of synthetic fibers include acrylic, polyester,
carboxylated polyolefin, and polyamine fibers.
[0021] 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.
[0022] 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).
[0023] 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 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, the oil can be heated to
liquefy it. This ensures that the oils remain liquid during their
application to the fibers. Oils useful in the present invention
should also have a vapor pressure sufficiently low to prevent
evaporation either during their application or during use.
[0024] The oil should not penetrate the walls of the fibers so
rapidly that it becomes unavailable to retain the superabsorbent
material when 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. To that end, oils of higher molecular weight penetrate
the fiber wall more slowly than oils of a lower molecular
weight.
[0025] 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, paimitic 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. It should be understood that the foregoing is a list of
exemplary oils and that oils useful in the context of the present
invention are 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 to retain
superabsorbent material in an absorbent structure comprising
oil-treated fibers and superabsorbent material.
[0026] 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, 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.
[0027] 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.
[0028] Paraffin oil is an example of an oil that is either pressed
or dry distilled from paraffin distillate obtained from the
distillation of petroleum.
[0029] 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.
[0030] As used herein, the term saccharide refers to mono-, di-,
oligo-, and polysaccharides.
[0031] Monosaccharides are carbohydrates that cannot be hydrolyzed
into smaller, simpler carbohydrates. Examples of monosaccharides
include glucose, fructose, glyceraldehyde, dihydroxyacetone,
erythrose, threose, ribose, deoxyribose, galactose, and the
like.
[0032] Disaccharides are carbohydrates that on a molar basis
undergo hydrolysis to produce only two moles of a monosaccharide.
Examples of disaccharides include maltose, sucrose, cellobiose,
lactose, and the like.
[0033] Oligosaccharides are carbohydrates that on a molar basis
undergo hydrolysis to produce 3 to 10 moles of a monosaccharide.
Examples of oligosaccharides include those found in corn syrups and
other mixtures of breakdown products from polysaccharides, and the
like.
[0034] Polysaccharides are carbohydrates that on a molar basis
undergo hydrolysis to produce more than ten moles of a
monosaccharide. Examples of polysaccharides include starch, chitin,
hemicelluloses such as galactomannan, other polysaccharides found
in seaweed, and the like.
[0035] Active(s) as that term is used herein refers to the
non-water components of a composition. For instance, for high
fructose corn syrup the term "actives" refers to the solids content
of the high fructose corn syrup.
[0036] It should be understood that the term saccharide as used
herein not only refers to individual saccharides such as glucose,
fructose, or lactose, but also includes mixtures of
monosaccharides, disaccharides, oligosaccharides, and/or
polysaccharides.
[0037] Examples of saccharides that include a mixture of
monosaccharides, disaccharides, oligosaccharides, or
polysaccharides include corn syrup, high fructose corn syrup, and
honey. Corn syrup is generally a mixture of dextrose (glucose),
maltose, and maltodextrines and is available from numerous
commercial sources. High fructose corn syrup generally includes
fructose, dextrose, disaccharides, and other saccharides. Corn
syrup and high fructose corn syrup typically are available as
aqueous solutions and have a solids content that ranges from 70 to
85 wt. %. An exemplary high fructose corn syrup is available from
Archer-Daniels Midland Company under the trademark Corn Sweet.RTM.
42. It should be understood that other high fructose corn syrups
that are available from Archer-Daniels Midland Company and other
commercial sources are useful in the present invention.
[0038] Honey useful in accordance with the present invention
contains fructose and glucose as the predominate carbohydrates,
with maltose and sucrose present in small percentages. Honey is
available from numerous commercial sources.
[0039] In accordance with the present invention, the oil can be
applied to the fiber in a number of different ways. 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 retention of superabsorbent material, 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 oil-treated fibers desire that the fluid
absorption properties of such structures be similar to or superior
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.
[0040] 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. For example, 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.
[0041] 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 treated fibers.
[0042] In accordance with the present invention, a densification
agent is applied to the oil treated fibers in order to modify the
densification properties of the oil treated fibers. As discussed
above, and as illustrated in the examples in this application,
fibers treated with oils as described above, when subjected to and
released from a compression load, do not densify to as high a
density as fibers that have not been treated with an oil when they
are subjected to the same compression load.
[0043] When the oil treated fibers are treated with densification
agent in accordance with the present invention, the oil and
densification agent treated fibers when subjected to and released
from a compression load densify to a density that is higher than
the density that is achieved when fibers that have not been treated
with oil and a densification agent are subjected to the same
compression loading and releasing.
[0044] Densification agents useful in accordance with the present
invention include saccharides, agents having at least one hydrogen
bonding functionality and saccharides in combination with at least
one agent having hydrogen bonding functionality. Useful saccharides
have been described above. The solids content of the saccharide
applied to the cellulose pulp sheet as a densification agent is
preferably less than about 65 wt. %. When corn syrup, high fructose
corn syrup, honey, or sucrose is used as the source of saccharide,
they can be diluted with water in order to reduce the solids
content to below about 65 wt. %. The following description of the
application of the densification agent proceeds with reference to a
cellulose pulp sheet. It should be understood that the
densification agents can be applied to fibers that are in forms
other than a cellulose pulp sheet, for example, fibers that have
been separated from a pulp sheet.
[0045] In accordance with the present invention, the amount of
densification agent added to the cellulose pulp sheet can vary over
a wide range. Lower amounts of densification agent actives in the
treated cellulose sheets are within the present invention; for
example, amounts down to about 0.5 wt. % based on the dry fiber
content of the cellulose pulp sheet are within the scope of the
present invention. On the upper end, the amount of densification
agent added to the cellulose pulp sheet is generally limited to an
amount that maintains the water content of the cellulose pulp sheet
below about 20 wt. %. In preferred embodiments of the present
invention, the densification agent is added to the cellulose pulp
sheet in an amount that results in an actives content of less than
about 20 wt. % based on the weight of dry cellulose fiber in the
treated cellulose pulp sheet and more preferably less than about 10
wt. %. Useful results are achieved with actives loading ranging
from about 3 to about 8 wt. % based on dry fiber. Sufficient
amounts of densification agent actives should be added to the
cellulose pulp sheet so that when the cellulose pulp sheet is
fiberized the resulting fibers exhibit densification properties
that are superior to the densification properties of fibers that
have been treated with an oil, but not been treated with a
densification agent. As noted above, such actives content can be
achieved using a densification agent that has been diluted with
water. The extent of the dilution of the densification agent, and
therefore the ratio of water to densification agent actives, should
be selected so that the desired degree of densification agent
actives can be achieved without introducing so much water to the
pulp sheet that the pulp sheet becomes difficult to fiberize due to
the addition of excess water. It is well known that pulp which is
too wet is difficult to fiberize. The dilution should not be so
great that when the densification agent solution is added to the
cellulose pulp sheet to achieve the desired densification agent
active content, the densification agent and oil treated cellulose
pulp sheet does not exhibit the desired densification properties. A
water content of the cellulose pulp sheet after being treated with
densification agent of about 10 wt. % based on the weight of the
total product is exemplary. Lower water contents are contemplated
with an upper limit of about 15-20 wt. % based on the need to avoid
poor fiberization.
[0046] The densification agent is applied to the cellulose pulp
sheet in a number of different ways. The present invention is not
limited to any particular application technique. Examples of
suitable application techniques include spraying, rolling, dipping,
and the like. The densification agent can be applied to one or both
sides of the cellulose pulp sheet. Alternatively, the densification
agent can be applied to fibers that are not in sheet form, e.g.,
individualized fibers. The densification agent can be heated prior
to its application, although this is not required. For example,
when the densification agent includes only a saccharide as
described below in more detail, heating the densification agent
before application and/or applying it to fibers at a temperature
above about 20.degree. C. promotes the objectives of improving the
densification properties of the fibers in accordance with the
present invention.
[0047] As noted above, the densification agents of the present
invention can include a saccharide as described above, or they can
include a saccharide in combination with an agent that has at least
one hydrogen bonding functionality, or they can include an agent
that has at least one hydrogen bonding functionality. Useful
saccharides have been described above. Suitable agents having
hydrogen bonding functionality are described below in more
detail.
[0048] Useful agents having at least one hydrogen bonding
functionality can be either polymeric or nonpolymeric chemicals. A
plurality of suitable agents having at least one hydrogen bonding
functionality are described in U.S. Pat. No. 5,641,561; U.S. Pat.
No. 5,789,326; and U.S. Pat. No. 5,547,541 with reference to
various polymeric binders and nonpolymeric binders. These
discussions regarding the polymeric binders and nonpolymeric
binders and their ability to effect the densification properties of
cellulose are expressly incorporated herein by reference. Such
agents have a volatility less than water. The vapor pressure of the
agent may, for example, be less than 10 mm Hg at 25.degree. C., and
more preferably less than 1 mm Hg at 25.degree. C. The agents
include molecules that have at least one functional group capable
of forming a hydrogen bond. Suitable densification agents include
non-polymeric materials that have a functional group selected from
the group consisting of a carboxyl, a carboxylate, a carbonyl, a
sulfonic acid, a sulfonate, a phosphate, a phosphoric acid, a
hydroxyl, an amide, an amine, and combinations thereof. As used
herein, the term "non-polymeric" refers to a monomer, a dimer, a
trimer, tetramer, and oligomers. Examples of agents having at least
one hydrogen bonding functionality useful as a component of the
densification agents of the present invention that include the
functional groups set forth above include carboxylic acids,
alcohols, amino acids, amino alcohols, hydroxy acids, sulfonic
acids, sulfonates, amino-sulfonic acids, non-polymeric polyamides,
and non-polymeric polyamines.
[0049] Suitable carboxylic acids include non-polymeric
polycarboxylic acids that contain more than one carboxylic acid
functional group such as citric acid, propane tricarboxylic acid,
maleic acid, butane tetracarboxylic acid, cyclopentane
tetracarboxylic acid, benzene tetracarboxylic acid, tartaric acid,
and ascorbic acid.
[0050] Exemplary alcohols include polyols, primary alcohols,
secondary alcohols, or tertiary alcohols. A polyol is an alcohol
that contains a plurality of hydroxyl groups, and includes diols
such as the glycols (dihydric alcohols), ethylene glycol, propylene
glycol, butylene glycol, dipropylene glycol, trimethylene glycol;
and triols such as glycerin. Other useful polyols include
pentaerythritol and sorbitol. Esters of hydroxyl containing binders
also may be used with mono- and diesters of glycerin, such as
monoglycerides and diglycerides, being particular examples.
[0051] Useful amino acids include glycine, alanine, valine, serine,
threonine, cysteine, glutamic acid, lysine, or beta-alanine.
[0052] Exemplary amino alcohols are alcohols that contain an amino
group (--NR.sub.2), and include ethanolamine (2-aminoethanol) and
diglycolamine (2-(2-aminoethoxy) ethanol).
[0053] Useful hydroxy acids are acids that contain a hydroxyl
group, including hydroxy acetic acid, lactic acid, tartaric acid,
ascorbic acid, citric acid, and salicylic acid.
[0054] Useful sulfonic acids and sulfonates contain a sulfonic acid
group (--SO.sub.3H) or a sulfonate (--SO.sup.-.sub.3).
[0055] Useful amino sulfonic acids include taurine, which is
2-aminoethane sulfonic acid.
[0056] Useful non-polymeric polyamides have more than one amide
group, such as oxamide, urea, and biuret.
[0057] Useful non-polymeric polyamines include amines that have
more than one amine group, such as ethylenediamine,
ethylenldiaminetetraacetic acid, or the amino acids asparagine or
glutamine.
[0058] Other useful agents having at least one hydrogen bonding
functionality include glyoxal, phosphates and phosphoric acids.
[0059] Each of the agents described above is capable of forming
hydrogen bonds because it has a functional group that contains
electronegative atoms, particularly oxygens or nitrogens, or has
electronegative groups, particularly groups containing oxygens or
nitrogens and that also includes a hydrogen. The amino alcohols,
amino acids, carboxylic acids, alcohols and hydroxy acids all have
a hydroxyl group in which a hydrogen is bound to an electronegative
oxygen, creating a dipole that leaves the hydrogen partially
positively charged. The amino alcohols, amino acids, amides, and
amines all have an NR group in which a hydrogen may be bound to an
electronegative nitrogen that also leaves the hydrogen partially
positively charged. The partially positively charged hydrogen in
both cases can interact with an electronegative element, such as
oxygen or nitrogen, to form hydrogen bonds. The polycarboxylic
acids, hydroxy acids, amino acids, and amines also have a carboxyl
group with an electronegative oxygen that can interact with
hydrogen atoms. Similarly, hydrogen atoms that have positive
dipoles can interact with electronegative atoms such as oxygen or
nitrogen to form hydrogen bonds.
[0060] Particular families of agents having hydrogen bonding
functionality useful as a component in the densification agents of
the present invention include alcohols, hydroxy acids, and
polycarboxylic acids. These families of agents having hydrogen
bonding functionality are desirable due to their general acceptance
by customers of the products into which the fibers of the present
invention are incorporated.
[0061] The following discussion proceeds with reference to these
specific examples of agents having hydrogen bonding functionality,
however, it should be understood that the present invention is not
so limited. The following description also discusses the present
invention with reference to the specific saccharide high fructose
corn syrup; however, it should be understood that the present
invention is not so limited. The following description is equally
applicable to a densification agent that includes only a saccharide
or one that includes only an agent having at least one hydrogen
bonding functionality.
[0062] As noted above, a densification agent that includes a
saccharide and at least one material having hydrogen bonding
functionality can be applied to cellulose fibers that have been
treated with an oil to produce fibers that exhibit desirable
densification properties. The densification agents can be formed by
mixing saccharide(s) with the agent(s) having at least one hydrogen
bonding functionality. Water may be added to the mixture depending
on the water content of the various components.
[0063] In particular embodiments, the weight ratio of the
saccharide to the agent(s) having at least one hydrogen bonding
functionality in the densification agent ranges from 100:0, that
is, saccharide only to about 0:100, that is, no saccharide present,
only the non-saccharide densification agent. A narrower range for
the ratio of saccharide to non-saccharide actives component in the
densification agent ranges from about 70:30 to about 85:15. An
exemplary ratio is 80:20 saccharide: other agent. The foregoing
weight ratios are based on the weight of the actives in the
components making up the densification agent. It should be
understood that as the amount of the densification agent applied
varies, the amount of the various components in the densification
agent can change in order to achieve the desired levels of agent
loading described above.
[0064] FIG. 3 illustrates a wet laid sheet manufacturing line such
as a wood cellulose pulp sheet manufacturing line 10. In this
manufacturing line, a pulp slurry 12 is delivered from a headbox 14
through a slice 16 and onto a Fourdrinier wire 18. The pulp slurry
12 typically includes wood pulp fibers and may also include
synthetic or other non-cellulose fibers as part of the slurry.
Water is drawn from the pulp deposited on wire 18 by a conventional
vacuum system, not shown, leaving a deposited pulp sheet 20 which
is carried through a dewatering station 22, illustrated in this
case as two sets of calendar rolls 24, 26 each defining a
respective nip through which the pulp sheet or mat 20 passes. From
the dewatering station, the pulp sheet 20 enters a drying section
30. In a conventional pulp sheet manufacturing line, drying section
30 may include multiple canister dryers with the pulp mat 20
following a serpentine path around the respective canister dryers
and emerging as a dried sheet or mat 32 from the outlet of the
drying section 30. Other alternate drying mechanisms, alone or in
addition to canister dryers, may be included in the drying stage
30. The dried pulp sheet 32 has a maximum moisture content pursuant
to the manufacturer's specifications. Typically, the maximum
moisture content is no more than 10% by weight of the fibers and
most preferably no more than about 6% to 8% by weight. Unless
overly damp fibers are immediately used these fibers are subject to
degradation by, for example, mold or the like. The dried sheet 32
is taken up on a roll 40 for transportation to a remote location,
that is, one separate from the pulp sheet manufacturing line, such
as at a user's plant for use in manufacturing products. The dried
pulp sheets have a basis weight of about 200 g/m.sup.2 to about
1000 g/m.sup.2 or more and a density on the order of at least about
0.5 g/cm.sup.3 to about 1.2 g/cm.sup.3. Dried pulp sheets having
the foregoing basis weights are structurally distinct form lighter
basis weight sheets of wet laid or airlaid wood pulp fibers such as
tissue paper, paper towels, or other types of paper-like wet laid
or airlaid webs of cellulose fibers. Alternatively, the dried sheet
32 is collected in a baling apparatus 42 from which bales of the
pulp 44 are obtained for transport to a remote location.
[0065] The oil and densification agents of the present invention
can be applied to the pulp sheet from one or more applying devices,
one of which is indicated at 50 in FIG. 3. Any applying device may
be used, such as streamers, sprayers, roll coaters, curtain
coaters, immersion applicators, or the like. Sprayers are typically
easier to utilize and incorporate into a pulp-sheet manufacturing
line. As indicated by the arrows 52, 54, and 56, the oil and
densification agents may be applied at various locations or at
multiple locations on the pulp sheet manufacturing line, such as
ahead of the drying stage 30 (indicated by line 52), intermediate
the drying stage 30 (as indicated by line 54), or downstream from
the drying stage 30 (as indicated by the line 56). At location 52,
the water remaining in the sheet or mat 20 at this stage tends to
interfere with the penetration of the materials into the sheet.
Consequently, application of the oil and densification agent after
some drying has taken place, for example at location 54, is
preferable. If the oil and densification agent is applied at
location 56 in an amount which would cause the moisture content of
the sheet to exceed the desired maximum level, an additional drying
stage (not shown) may be included in the pulp manufacturing line to
bring the moisture content down to the desired level.
[0066] The rolls 40 or bales 44 of the treated wet laid web of
fibers may be transported to a remote location for use by a user.
These rolls or bales are then refiberized by a fiberizing device,
such as a hammermill which may be used alone or in conjunction with
other devices such as picker rolls or the like for breaking up the
sheet 32 or bales 42 into individual fibers. Depending on the end
use, the individualized fibers may be combined with particulate
material, such as superabsorbent particles, and/or airlaid into a
web and densified.
[0067] With this approach, the end user of the treated fibers may
readily select particles to be combined with the fibers. The user
has flexibility in air laying or otherwise processing the treated
fibers of the present invention into a finished product.
[0068] The oil and densification agent treated fibers and
superabsorbent material can be combined and then formed into an
absorbent structure in the following manner. Rolls or bales of
treated 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 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, including
subjecting the pad to a compression load to reduce the thickness of
the pad and increase its density. 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 100 to about
1000 grams per square meter (gsm), thicknesses ranging from about
1-6.66 millimeters and densities ranging from 0.15 to about 1
g/cm.sup.3.
[0069] It should be understood that in an alternative embodiment,
the oil and densification agent can be applied to the fibers while
they are air entrained.
[0070] As illustrated in the examples that follow, the addition of
densification agents to oil treated fibers in accordance with the
present invention does not significantly affect the superabsorbent
retention properties of the oil treated fibers. As illustrated in
the examples that follow, oil treated fibers treated with a
densification agent in accordance with the present invention
exhibit desirable densification properties.
[0071] 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
Preparation of Oil and High Fructose Corn Syrup Treated Cellulose
Pulp
[0072] Two 100-foot rolls of Southern Pine fluff in sheet form
available from Weyerhaeuser Company under the designation NB 416
from New Bern, N.C. 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 a solution of high fructose
corn syrup. The gravure coater results in the application of a
uniform coating of the high fructose corn syrup solution over one
entire surface of the pulp sheet from where it is rapidly soaked up
by the sheet. The high fructose corn syrup was obtained from
Archer-Daniels Midland Company of Decatur, Ill. under the trademark
CORN SWEET.RTM. 42. The high fructose corn syrup had an actives
content of 71% with the balance being water. The high fructose corn
syrup was diluted with water to an active content of 48.6 wt. %
based on total solution weight and applied to the wood pulp sheet
to achieve a loading of actives on a dry basis (i.e., corn syrup
solids) of 5 wt. % based on the dry fiber content of the pulp
sheet.
[0073] After application of the high fructose corn syrup, the
opposite side of the sheets were coated with an oil using a Black
Brothers gravure-type roll coater. The oil was a mineral oil
obtained from Chevron Texaco Corporation under the designation
Superla 35. The mineral oil was applied to a loading of 3 wt. % oil
based on the dry fiber content of the sheet.
[0074] The resulting sheets were fiberized and formed into pads
using a Fitz hammermill feeding an M&J continuous air lay pad
forming device. Pads were formed comprising treated fibers only,
having a basis weight of 300 grams per square meter, and pads
comprising 60 wt. % treated fibers and 40 wt. % superabsorbent
material for a total basis weight of 500 grams per square
meter.
[0075] Three 10 cm.times.10 cm pads were cut from the larger formed
pads and conditioned for at least two hours at 50% relative
humidity. Each pad was then subjected to a compression load
sequentially of 50 psi, 100 psi, and 150 psi, using a platen press.
The pressure applied by the platen press was relieved immediately
upon reaching the target pressure value. The density of each pad at
each pressure increment was measured within 5 seconds of relieving
the pressure. The density of the pad was determined by measuring
pad thickness by using a device that does not materially compress
the sample, weighing the pad, and calculating density as
Density=Weight/(10 cm.times.10 cm.times.Thickness), where the units
of thickness are cm, weight is grams, and density is grams/cubic
centimeter. The results are expressed as Sample 2 in Table 1 below
as a percentage of the density achieved when a control comprising
untreated wood pulp fiber was processed as described above.
[0076] The foregoing procedure was repeated with the exception that
the oil loading was 5 wt. % on dry fiber. The results for this
sample are summarized in Table 1 below under the designation Sample
3.
[0077] The above procedure for Sample 3 was repeated, substituting
an 80/20 wt. to weight percent blend of actives from the high
fructose corn syrup and propylene glycol. The propylene glycol was
obtained from Integra Chemical of Renton, Wash., and had a water
content of less than one percent. The resulting high fructose corn
syrup and propylene glycol solution was 52.7 wt. % actives, the
balance water. This composition was applied to the pulp sheets to a
loading of 6 wt. % actives based on the weight of dry fibers. The
results for this sample are summarized in Table 1 below under
Sample 4.
[0078] The procedure above for Sample 2 was repeated on a single
100-foot roll of pulp. For this sample, no high fructose corn syrup
or propylene glycol was applied and only mineral oil was applied to
a loading of 10.6 wt. % on dry fiber. When this pulp sample was
fiberized, it was fed to the hammermill device along with a roll of
untreated pulp. This combination of two sheets feeding the
hammermill, one coated and the other not, lead to a final oil
loading of 5.3 wt. % on dry fiber. The results for this sample are
summarized in Table 1 below under Sample 5 as a comparative
example.
[0079] The information set forth in Table 1 is graphically
illustrated in FIG. 1 (no sap) and FIG. 2 (40 wt. % superabsorbent
material). The reference numbers in FIGS. 1 and 2 correspond to the
Sample Nos. in Table 1.
[0080] The examples above illustrate that the application of high
fructose corn syrup alone or in combination with an agent having at
least one hydrogen bonding functionality to wood pulp cellulose
fibers treated with an oil improves the densification properties of
the oil-treated fibers.
1TABLE 1 Density of Sample/Density of Control Expressed as a
Percent Pressure Load FIBERS ONLY FIBER AND SAP (psi) 50 100 150 50
100 150 Sample 1 100 100 100 100 100 100 (control) Sample 2 113.1
108.4 102.8 116.8 109.3 107.0 Sample 3 112.3 110.6 103.9 114.3
110.6 109.7 Sample 4 119.9 112.9 109.2 118.8 112.4 112.3 Sample 5
94 86 79 93 89 84 (Comparative Example)
* * * * *