U.S. patent application number 09/734097 was filed with the patent office on 2002-08-08 for opacity enhancement of tissue products with thermally expandable microspheres.
Invention is credited to Jimenez, Graciela, Negri, Alberto R..
Application Number | 20020104632 09/734097 |
Document ID | / |
Family ID | 26866666 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020104632 |
Kind Code |
A1 |
Jimenez, Graciela ; et
al. |
August 8, 2002 |
Opacity enhancement of tissue products with thermally expandable
microspheres
Abstract
The present invention is generally directed to an opaque tissue
product and a process for making the same. The tissue products of
the present invention comprise thermally expandable microspheres
which impart increased opacity to the tissues. The thermally
expandable microspheres are added to a fiber furnish during the wet
end of a manufacturing process for bath tissue, facial tissue,
towels, or the like.
Inventors: |
Jimenez, Graciela;
(Appleton, WI) ; Negri, Alberto R.; (Appleton,
WI) |
Correspondence
Address: |
Neil C. Jones
Nelson Mullins Riley & Scarborough, LLP.
Keenan Building, Third Floor
1330 Lady Street
Columbia
SC
29211
US
|
Family ID: |
26866666 |
Appl. No.: |
09/734097 |
Filed: |
December 11, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60171031 |
Dec 16, 1999 |
|
|
|
Current U.S.
Class: |
162/158 ;
162/163; 162/164.1 |
Current CPC
Class: |
D21H 21/285 20130101;
D21H 21/54 20130101 |
Class at
Publication: |
162/158 ;
162/163; 162/164.1 |
International
Class: |
D21H 021/00; D21H
013/36; D21H 021/10 |
Claims
What is claimed is:
1. A process for forming opaque tissue products wherein thermally
expandable microspheres are added to said tissue products in an
amount of about 1% or less based on the weight of the fiber furnish
and wherein the bulk value of said opaque tissue products is about
3 cm.sup.3/g or less.
2. A process according to claim 1 wherein said opaque tissue
products are sanitary bath tissue, facial tissue, towels, or the
like.
3. A process according to claim 1 wherein said thermally expandable
microspheres are added to said tissue products during the wet end
of a manufacturing process for said tissue products.
4. A process according to claim 3 wherein said thermally expandable
microspheres are added to said fiber furnish either just in front
of or at the headbox during said wet end of said manufacturing
process for said tissue products.
5. A process according to claim 3 wherein said tissue products
being formed have a low basis weight of up to about 30 gsm.
6. A process according to claim 3 wherein said tissue products
being have a basis weight of about 14 gsm to 18 gsm.
7. A process according to claim 3 wherein said fiber furnish is a
softwood fibers furnish.
8. A process according to claim 3 wherein said fiber furnish
comprises recycled fibers, Kraft fibers, fibers containing sulfite,
cellulosic fibers, or other such commercial fibers.
9. A process according to claim 3 wherein a cationic retention aid
is incorporated into said furnish in order to increase the
retention of said thermally expandable microspheres by said tissue
products.
10. A process according to claim 1 wherein said thermally
expandable microspheres are added in an amount of about 0.5%.
11. An opaque tissue product comprising a pulp and thermally
expandable microspheres in an amount of about 1% or less based on
the weight of the pulp and wherein the bulk of said opaque tissue
product is about 3 cm.sup.3/g or less.
12. The tissue product of claim 11 wherein said tissue product is a
sanitary bath tissue, facial tissue, towel, or the like.
13. The tissue product of claim 11 wherein said tissue product has
a basis weight of up to about 30 gsm.
14. The tissue product of claim 11 wherein said tissue product has
a basis weight of 14 gsm to about 18 gsm.
15. The tissue product of claim 11 wherein said tissue product
further comprises a cationic retention in order to increase the
retention of said thermally expandable microspheres by said tissue
product.
16. The tissue product of claim 11 wherein said tissue product is
more opaque than a tissue product of equal basis weight having no
thermally expandable microspheres incorporated therein.
17. The tissue product of claim 11 wherein said tissue product
comprises thermally expandable microspheres in an amount of about
0.5%.
Description
[0001] The present invention is based on provisional patent
application Serial No. 60/171,031 filed Dec. 16, 1999, and priority
is hereby claimed therefrom.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a method of
incorporating thermally expandable microspheres into tissue
products so that the resulting products have increased opacity.
More particularly, the present invention is directed to the
incorporation of thermally expandable microspheres into the wet end
of a tissue manufacturing process so as to impart increased opacity
to tissue products such as bath tissue, facial tissue, and
towels.
BACKGROUND OF THE INVENTION
[0003] As lower basis weight tissue products evolve, new technical
challenges are created since many physical properties of tissue
products depend on the number and compactness of fibers present in
the structure after consolidation. The opacity or "see-through" of
tissue products is becoming a limiting factor in fiber assemblies
that utilize fewer fibers while maintaining the same or superior
strength as traditional fiber assemblies. Obviously, consumers
desire that such products have sufficient opacity to prevent
substantial see-through in the product.
[0004] Many different processes and compounds have been identified
which can affect the opacity of paper (as opposed to lighter weight
tissue) products. The measure of opacity in a finished sheet of
paper depends on the evaluation of diffuse reflectance (R), which
in turn is related through the Kubelka-Munk (K-M) theory to the
scattering (s) and absorption (k) coefficients of the elements in
the fibrous structure. These are basic properties that are
intrinsic to the medium.
[0005] In its simplest form, paper is an ensemble of fibers more or
less bonded to one another in zones of partial optical contact.
There are many interfaces between the solid particles and the air,
located all across the section and in many different angles. Light
coming into contact with paper will diffuse accordingly: a portion
will be reflected, some will be absorbed and the rest will be
transmitted. This diffusing effect depends on the difference
between refractive indexes of the adjoining faces and the number of
such interfaces.
[0006] Photoelectric instrumentation is used to evaluate spectral
reflectance. Several commercial models are available, and depending
on the type of backing used below the paper specimen during
measurement, different reflectance modes can be characterized. From
the standpoint of opacity, three of them are relevant: R.sub.0 when
the specimen is backed by a black-velvet lined cavity ("black
body"), R.sub.28 when the backing consist of a thick-enough opaque
pad of the same material, and R.sub.0.89 when measured against a
composite (sandwich) formed by a layer of pure magnesium oxide
covered by glass, having an effective reflectance of 89% of that of
a pure magnesium oxide surface.
[0007] In papermaking, opacity is defined as a contrast ratio
between reflectances of the sheet over white and black backgrounds.
For example, the ratio between R.sub.0 and R.sub.0.89 is known as
"Tappi Opacity". If the white body is an opaque pile of the paper
under examination, the ratio between R.sub.0 and R.sub..infin. is
called "Printing Opacity".
[0008] Assuming a homogeneous sheet, opacity (measured as
R.sub.0/R.sub.0.89 or R.sub.0/R.sub..infin.) can be unambiguously
characterized in terms of the K-M theory intrinsic parameters (s
and k), and in particular the elements sW and k/s. The first
represents the scattering power (W is the basis weight of the
sheet), and the latter determines the reflectivity R.sub..infin..
Some equations evolving from the K-M model are:
R.sub..infin.=1+k/s-{2k/s+(k/s).sup.2}.sup.0 5
and
R.sub.0=R.sub..infin.{e.sup.A-1}/{e.sub.A-R.sub..infin..sup.2}
[0009] where A=sW(1/R.sub..infin.-R.sub..infin.)
[0010] Opacity will increase with increasing sW values and with
decreasing k/s ratios as published elsewhere. Manipulation of the
equations from the K-M theory lead to:
Opacity=[100(B-1)]/(B-R.sub..infin..sup.2)
[0011] where
B=[R.sub..infin.(1-R.sub.0R.sub..infin.)/(R.sub..infin.-R.sub-
.0)]
[0012] Similarly for the scattering power, sW, a set of equations
follows:
sW=ln[(X+1)/(X-1)]/2b
[0013] where X=(1-aR.sub.0)/bR.sub.0,
a=0.5[(1/R.sub..infin.)+R.sub..infin- .] and b=0.5
[(1/R.sub..infin.]
[0014] These equations can be solved analytically or using known
graphical methods. But if the optical properties of different
grades of paper can be well characterized using K-M mathematical
model, changing those properties in a practical, cost-efficient way
is more complicated. For pulps that underwent a given pulping and
bleaching process, it is not easy to change reflectance properties
unless additives are used in the furnish, such as dyes to modify
the absorption coefficient and fillers or pigments to increase
light scattering. Increasing the basis weight is also a possibility
but this is against the current technological trend to lighter
tissue products.
[0015] An alternative that has been less exploited to increase
opacity in paper products is the manipulation of the apparent
density of the fibrous structure. Giertz showed a linear inverse
relationship between density and specific scattering coefficient,
since a higher density represents fewer voids in a structure (in
Formation and Structure of Paper, p.597, 1962). El-Hosseiny et al.
confirmed that over a broad range, the scattering coefficient (s)
relates to density (D) following the expression:
S=m-nD
[0016] where m and n are constants (Tappi 62(10):127).
[0017] Traditional approaches to increasing the opacity of
lightweight fibrous materials, such as tissues, include the use of
particulate fillers (such as Kaolin or calcium carbonate) and the
use of debonders. Also, microspheres that are not thermally
expandable have been used as compounds to aid in increasing the
opacity of tissue products. However, desired levels of opacity are
not always met by such more traditional methods of opacity
enhancement when lightweight tissue grades are involved. Properties
such as strength, softness, and low lint requirements become
limiting factors in tissue grade applications.
[0018] Thermally expandable microspheres have been available for
more than a decade; however, they have not been linked to opacity
enhancement. U.S. Pat. No. 5,155,138 to Lundquist is directed to
expandable thermoplastic microspheres themselves and a process for
the production and use thereof. This patent does not mention
opacity at all. Similarly, U.S. Pat. No. 4,477,518 to Cremona et
al. is directed to coated papers and cardboards that comprise a
coating layer containing hollow expandable microspheres. This
patent also does not mention increased opacity, and the papers
described therein are not tissue products.
[0019] Most of the art relating to the utilization of thermally
expandable microspheres involve applications of these microspheres
outside of the low basis weight tissue products field. For example,
U.S. Pat. No. 4,006,273 to Wolinski et al. is directed to raised
printing of fabrics, while U.S. Pat. No. 4,044,176, also to
Wolinski et al., is directed to a graphic arts media application
involving the use of thermally expandable microspheres. Japanese
Publication application No. 90/76,735 is directed to slightly
rough-textured sheets involving these microspheres, while EP 0 549
948 is directed to the use of thermally expandable microspheres in
smooth, anti-slip coatings.
[0020] A recent paper suggested the use of expandable microspheres
as a bulking/stiffening aid in heavy weight boxboard production.
See . Soderberg, "Expandable Microspheres in Board," World Pulp
& Paper Technology, 1995/96, at 143. Board machine trials
revealed that 1% of EXPANCEL.RTM. (a commercially available
thermally expandable microsphere) is equal to about 18-25% of
cellulosic fiber when comparing volume. This same technology can be
applied using appropriate microsphere grades to produce stiffer
printing, writing, or other fine papers. Such fine papers usually
have higher basis weights of about 60 grams per square meter
("gsm") to about 80 gsm which are well above the about 30 gsm upper
basis weight limit for the presently-described tissue products.
[0021] Other known applications of expandable microspheres include
the formation of sound-absorbing three-dimensional structures,
stiffer printable papers, printing substrates, non-slip coatings,
elastomeric fabrics, tapes, insulating materials, reinforcing
materials, high-grip surfaces, molded articles, and sealing
gaskets.
[0022] U.S. Pat. No. 4,619,734 to Andersson relates to the use of
expandable microspheres in low basis weight materials. However,
this patent is directed to the production of creped multilayered
sanitary paper with increased bulk softness, wherein the majority
of the microspheres are precisely located in the middle layer
(lower modulus structure, more flexible, less stiff). This patent
does not mention opacity at all, but instead focuses on higher
softness levels of the sanitary paper web. Also, Andersson requires
the use of relatively large amounts of the expandable microspheres,
specifically from 1% to 10%.
[0023] Thus, a need currently exists for a process wherein tissue
products are created that have enhanced opacity.
SUMMARY AND OBJECTS OF THE INVENTION
[0024] It is an object of the present invention to form opaque
tissue products through the incorporation of thermally expandable
microspheres into such tissue products while they are being
manufactured.
[0025] It is another object of the present invention to create
opaque tissue products of lower basis weights than higher basis
weight opaque tissue products currently available.
[0026] Some of the above-mentioned objects and, perhaps, other
objects are accomplished by incorporating thermally expandable
microspheres into low basis weight tissue products (i.e., less than
about 30 gsm). The thermally expandable microspheres may be added
in the wet end of a tissue manufacturing process prior to forming
the tissue web. In certain embodiments, the expandable microspheres
may be added just in front of or at the headbox during the wet end
of the paper making process.
[0027] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description, including the drawing, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWING
[0028] FIG. 1 is a schematic flow diagram of a wet-pressed tissue
making process.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] Reference now will be made in detail to the embodiments of
the invention, one or more examples of which are set forth below.
Each example is provided by way of explanation of the invention,
not limitation of the invention. In fact, it will be apparent to
those skilled in the art that various modifications and variations
can be made in the present invention without departing from the
scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment, can be used on
another embodiment to yield a still further embodiment.
[0030] Thus, it is intended that the present invention cover such
modifications and variations as come within the scope of the
appended claims and their equivalents. Other objects, features and
aspects of the present invention are disclosed in or are obvious
from the following detailed description. It is to be understood by
one of ordinary skill in the art that the present discussion is a
description of exemplary embodiments only, and is not intended as
limiting the broader aspects of the present invention, which
broader aspects are embodied in the exemplary constructions.
[0031] The present invention involves the use of thermally
expandable microspheres for restoring or enhancing the opacity
levels of tissue products. In addition, the present process is
applicable to the use in any wet-end chemistry application that is
pertinent to the production of strong, soft, low-lint, absorbent
tissue materials that may or may not exhibit other properties such
as odor control, anitmicrobial efficacy, etc. Such tissue products
may include bath tissue, facial tissue, and towels. The tissue
products of this invention can be single-ply products or multi-ply
products, such as two-ply, three-ply, four-ply or greater. One-ply
products are advantageous because of their lower cost of
manufacture, while multi-ply products are preferred by many
consumers. For multi-ply products it is not necessary that all
plies of the product be the same, provided at least one ply is in
accordance with this invention.
[0032] Papermaking fibers for making the tissue product webs of
this invention include any natural or synthetic fibers suitable for
the end use products listed above including, but not limited to:
nonwoody fibers, such as abaca, sabai grass, milkweed floss fibers,
pineapple leaf fibers; softwood fibers, such as northern and
southern softwood kraft fibers; hardwood fibers, such as
eucalyptus, maple, birch, aspen, or the like. In addition,
furnishes including recycled fibers may also be utilized. In making
the tissue products, the fibers are formed into a pulp furnish by
known pulp stock formation processes.
[0033] Softening agents, sometimes referred to as debonders, can be
added to the tissue making process to enhance the softness of the
tissue product. Such softening agents can be incorporated with the
fibers before, during or after dispersing the fibers in the
furnish. Such agents can also be sprayed or printed onto the web
after formation, while wet, or added to the wet end of the tissue
machine prior to formation. Suitable softening agents include,
without limitation, fatty acids, waxes, quaternary ammonium salts,
dimethyl dihydrogenated tallow ammonium chloride, quaternary
ammonium methyl sulfate, carboxylated polyethylene, cocamide
diethanol amine, coco betane, sodium lauryl sarcosinate, partly
ethoxylated quaternary ammonium salt, distearyl dimethyl ammonium
chloride, polysiloxanes, silicones, and the like. Examples of
suitable commercially available chemical softening agents include,
without limitation, Berocell 596 and 584 (quaternary ammonium
compounds) manufactured by Eka Nobel Inc., Adogen 442 (dimethyl
dihydrogenated tallow ammonium chloride) manufactured by Sherex
Chemical Company, Quasoft 203 (quaternary ammonium salt)
manufactured by Quaker Chemical Company, Arquad 2HT-75
(di(hydrogenated tallow) dimethyl ammonium chloride) manufactured
by Akzo Chemical Company, C-6027 (blend of cationic and non-ionic
surfactants) manufactured by Goldschmidt Incorporated, and Prosoft
TQ 1003 (quaternary ammonium salt) manufactured by Hercules, Inc.
Suitable amounts of softening agents will vary greatly with the
species of pulp selected and the desired characteristics of the
resulting tissue product. Such amounts can be, without limitation,
from about 0.05 to about 1 weight percent based on the weight of
fiber, more specifically from about 0.25 to about 0.75 weight
percent, and still more specifically about 0.5 weight percent.
[0034] The thermally expandable microspheres that are added to the
tissue products may be obtained from various manufacturers such as
Akzo-Nobel, Pierce & Stevens, Casco, and Dow Chemical. In
certain embodiments, EXPANCEL.RTM., a thermally expandable
microsphere-containing product, may be incorporated as a wet-end
opacity-enhancing additive as a tissue is being formed.
[0035] The use of such expandable microspheres allow the opening up
of the paper structure so as to create a bulkier (i.e., less dense)
web that will scatter light more efficiently. Accordingly, when
expandable microspheres are utilized in a paper product, the
resulting paper product will have a bulkier structure than the same
paper product at the same weight basis, that will have a higher
light scattering coefficient (or higher opacity at any given basis
weight).
[0036] While the present inventive process is applicable to any
form of papermaking machine configuration, any process of paper
formation and including single or multilayered web constructions
(either with or without pressing, with or without creping, etc.),
the microspheres are typically incorporated just in front of or at
the headbox during tissue product formation. However, they may be
added anywhere in the wet end prior to forming the web. The
incorporation of the microspheres results in a tissue product that
is better able to scatter light, which translates into a higher
opacity over the same basis weight material without the
microspheres.
[0037] In one particular embodiment of the present invention, 1% by
weight (based on the weight of pulp fibers) of EXPANCEL.RTM. is
added to a softwood fibers furnish, and opacity is increased by
almost six units in standard 60 gsm handsheets. (Although 60 gsm
handsheets were utilized in the testing set forth herein under
TAPPI method T205 sp-95, the light scattering data--which is
independent of basis weight --is applicable to the inventive
lighter weight products as well.) In other embodiments,
EXPANCEL.RTM. is added into a softwood fibers furnish at an amount
of about 15 lbs. of microspheres for every 2880 lbs. of paper
product produced. In other embodiments, 0.5% by weight of
EXPANCEL.RTM. microspheres were employed.
[0038] Currently, in commercial processes, only materials having a
basis weight of greater than or equal to 30 gsm have microspheres
incorporated into them. An important advantage of the process of
the present invention is the ability to impart increased opacity to
products of lower basis weights and, specifically, to products with
basis weights of 18 gsm of less and, more specifically, to products
with basis weights of 14 gsm to 18 gsm.
[0039] Other important advantages of tissue products formed
according to the process of the present invention include decreased
cost to manufacture, increased softness, retention of tensile
strength, and increased absorbency.
[0040] Various tissue-making processes are known to those in the
art. In particular, U.S. Pat. No. 5,129,988 to Farrington, Jr.;
U.S. Pat. No. 5,772,845 to Farrington, Jr. et al.; and U.S. Pat.
No. 5,494,554 to Edwards et al. disclose various tissue-making
methods and methods for forming multi-layered paper webs. Such
patents are incorporated herein in their entireties by reference
thereto.
[0041] FIG. 1 is a schematic flow diagram of a conventional
wet-pressed tissue making process useful in the practice of this
invention, although other tissue making processes can also benefit
from the method of this invention, such as thoroughdrying or other
non-compressive tissue making processes. The specific formation
mode illustrated in FIG. 1 is commonly referred to as a crescent
former, although many other formers well known in the papermaking
art can also be used. Shown is a headbox 21, a forming fabric 22, a
forming roll 23, a paper making felt 24, a press roll 25, a spray
boom 26, a Yankee dryer 27, and a creping blade 28. Also shown, but
not numbered, are various idler or tension rolls used for defining
the fabric runs in the schematic diagram, which may differ in
practice. As shown, the headbox 21 continuously deposits a stock
jet 30 between the forming fabric 22 and felt 24, which is
partially wrapped around the forming roll 23. Water is removed from
the aqueous stock suspension through the forming fabric by
centrifugal force as the newly-formed web traverses the arc of the
forming roll. As the forming fabric and felt separate, the set web
31 stays with the felt and is transported to the Yankee dryer
27.
[0042] At the Yankee dryer, creping chemicals may be continuously
applied in the form of an aqueous solution to the surface of the
Yankee dryer on top of the residual adhesive remaining after
creping. The creping chemicals can include one or more dry strength
agents. The solution is applied by any conventional means, such as
a spray boom 26 which evenly sprays the surface of the dryer with
the creping adhesive solution. The point of application on the
surface of the dryer is immediately following the creping doctor
blade 28, permitting sufficient time for the spreading and drying
of the film of fresh adhesive before contacting the web in the
press roll nip.
[0043] The wet web 31 is applied to the surface of the dryer by
means of the press roll or pressure roll 25 with an application
force typically of about 200 pounds per square inch (psi). The
incoming web is nominally at about 10% consistency (range from
about 8 to about 20%) at the time it reaches the press roll.
Following the pressing and dewatering step, the consistency of the
web is at or above about 30%. The side of the web in contact with
the surface of the Yankee dryer is referred to herein as the "dryer
side" of the web. The opposite side of the web is referred to as
the "air side" of the web. Sufficient Yankee dryer steam power and
hood drying capability are applied to the web to reach a final
moisture content of about 2.5% or less.
[0044] Also illustrated in FIG. 1 is the white water recycle
system. At the press roll nip, white water effluent 35 expressed
from the wet web is collected in catch pan 36. Because of the
presence of a substantial amount of water in the pressure roll nip,
some of the dry strength agent is transferred from the surface of
the Yankee into the white water, which also contains fines. The
collected white water 37 drains into wire pit 38. Thick stock 40
having a consistency of about 2 percent is diluted with white water
at the fan pump 39 to a consistency of about 0.1 percent. The
diluted stock 41 is subsequently injected into the headbox 21 to
form the wet web.
[0045] The microspheres may be added anywhere in the wet end of the
tissue making process. For example, the microspheres may be added
to the headbox 21, prior to headbox 21 in a separate apparatus that
then flows the microspheres into contact with the pulp furnish
(sometimes referred to as stock suspension) in the headbox 21, or
after the headbox 21 as a direct additive to the pulp furnish being
carried between forming fabric 22 and felt 24.
[0046] Although other brands of microspheres may be utilized, one
particular brand of microspheres is sold under the name
EXPANCEL.RTM. by Akzo Nobel. EXPANCEL.RTM. microspheres consist of
hollow, white, spherically-formed polymer particles encapsulating a
blowing agent (for example, liquid isobutane) under pressure. The
microspheres generally have a mean diameter of about 10-12 .mu.m.
The thermoplastic shell softens when heated so that the
gasification of the blowing agent expands the microspheres to a
final volume that is from 30 to more than 60 times larger than the
original volume at constant weight. Additional features of
EXPANCEL.RTM. are discussed in Technical Bulletin No. 13 for
EXPANCEL.RTM. Microspheres in Paper and in . Soderberg, "Expandable
Microspheres in Board," World Pulp & Paper Technology, 1995/96,
at 143, both of which are incorporated herein in their entireties
by reference thereto.
[0047] These microspheres start to expand upon heating above a
given temperature, depending on the chemistry of the copolymer. In
a particular embodiment of the present invention, EXPANCEL.RTM.
551-20 was employed, and it began expanding at a temperature of
from about 93.degree. C. to about 98.degree. C. However, other
grades of EXPANCEL.RTM. products (and other brands of expandable
microspheres) may expand at lower or higher temperatures and may,
thus, be suitable for particular engineered applications.
[0048] The surface of the microsphere shells, a copolymer of
acrylonitrile and vinylidene chloride, is very electronegative or
has a strong anionic character. In fact, the microspheres and the
fibers themselves are anionically charged. Thus, cationic polymeric
additives may be used in the process of the present invention to
achieve good retention. In particular embodiments of the present
invention, the cationic retention aid used is a cationic
polyacrylamide; however, any number of known cationic retention
aids may be used.
[0049] Suitable cationic polyamide resins include the water-soluble
polymeric reaction products of an epihalohydrin, preferably
epichlorohydrin, and a water-soluble polyamide having secondary
amine groups derived from polyalkylene polyamine and a saturated
aliphatic dibasic carboxylic acid containing from about 3 to 10
carbon atoms. The water soluble polyamide contains recurring groups
of the formula:
--NH(C.sub.nH.sub.2n,HN).sub.x--CORCO--
[0050] where n and x are each 2 or more and R is the divalent
hydrocarbon radical of the dibasic carboxylic acid. An important
characteristic of these resins is that they are phase compatible
with polyvinyl alcohol. Suitable materials of this type are
commercially available under the trademarks KYMENE.RTM. (Hercules,
Inc.) and CASCAMID.RTM. (Borden) and are more fully described in
U.S. Pat. No. 2,926,116 issued to Keim, U.S. Pat. No. 3,058,873
issued to Keim et al., and U.S. Pat. No. 4,528,316 issued to
Soerens, all of which are herein incorporated by reference. The
creping adhesive also preferably includes polyvinyl alcohol. The
amount of the thermosetting cationic polyamide resin in the creping
composition, on a solids weight percent basis, can be from about 10
to about 80 percent, more specifically from about 20 to about 60
percent.
EXAMPLES
[0051] The present invention may be understood by reference to the
following Examples, without being limited thereto. The Examples
were performed in order to demonstrate the opacity enhancement in
fibrous structures.
Examples 1-5
[0052] These five Examples demonstrate the increased opacity and
decreased density of softwood kraft pulp sheets after the addition
of thermally expandable microspheres. Specifically, in these
Examples, EXPANCEL.RTM. 551-20 was used as the source of the
thermally expandable microspheres. Also, the retention of the
EXPANCEL.RTM. onto the sheets was facilitated by the addition of a
cationic polyacrylamide retention aid (Nalco 7520), and the
handsheets were produced according to a TAPPI Standard Procedure
T205 sp-95 (with the only deviation from the standard being the use
of a Valley Steam hot plate at a temperature of 213.+-.2.degree. F.
instead of the typical pressing procedure).
[0053] The handsheet mold used in this standard procedure was a
square wire mesh of plain weave bronze. Sufficient amounts of a
thoroughly mixed pulp stock were used to produce handsheets having
a basis weight of 60 gsm. As the handsheets were being formed, two
different amounts of the EXPANCEL.RTM. product were used as
indicated in the tables below. In addition, a control handsheet
without microspheres was also formed. The test handsheets were not
pressed.
[0054] A Valley Steam hot plate was used as the dryer for these
test handsheets. This hot plate has a convex surface and is covered
with a standard canvas held down by a lead filled brass tube. The
pulp sheets were placed, wire side up, on the polished surface of
the sheet dryer, wherein the canvas was carefully lowered over the
sheet. A weight was fastened to the lead filled brass tube. Most
tested handsheets were dried for 2 minutes; however, two of the
five Examples herein were dried for five minutes to verify that the
microspheres had expanded to their full expansion capacity. The
dried sheets were then removed from the dryer and trimmed to the
desired size.
[0055] The handsheets described above were tested for various
physical characteristics including bulk, scattering coefficient,
and opacity levels. The data collected appears in Table I
below:
1TABLE I Scattering Example Minutes EXPANCEL Bulk Coefficient No.
Dried % (cm.sup.3/g) (m.sup.2/kg) Opacity 1 2.0 0.0% 1.729 34.95
76.1 2 2.0 0.5% 1.907 36.41 79.6 3 5.0 0.5% 2.117 41.45 81.4 4 2.0
1.0% 2.053 40.69 81.1 5 5.0 1.0% 2.072 41.20 81.8
[0056] The bulk of the handsheets is the inverse of the apparent
density of those handsheets as evidenced by the units of
cm.sup.3/g.
[0057] The scattering coefficient of each handsheet was determined
after performing an industry standard test (TAPPI Test Method T-220
sp-96) for measuring light-scattering coefficients. In this
procedure, an opacimeter (Technibrite Micro TB-1C available from
Technidyne Corporation of New Albany, Ind.) is used, and the
working standard of reflectance is calibrated to absolute scale.
The working standard is then placed over the opening of the
opacimeter, and the instrument is adjusted to read the value of the
absolute reflectance of the working standard. Readings are obtained
by placing each sheet in the opacimeter with its smooth side
against the black body and reading the reflectivity without
adjustment of the instrument. Light scattering and opacity readings
are taken and performed according to TAPPI Test Method T519
om-96.
[0058] The opacity measurements of each handsheet were taken and
recorded above. Opacity is weight dependent and thus is measured
somewhat differently than bulk and scattering coefficient as
explained above.
[0059] The measurement of opacity is determined by a ratio of
reflectance measurements. The opacity of the sheet is influenced by
thickness. The method used for the opacity measurements was TAPPI
Test Method T-425 om-96. The essential principle of this method of
opacity determination is as follows: the reflectance of paper when
combined with a white backing is higher than that of paper when
combined with a black backing because, in the former case, light
transmitted through the imperfectly opaque sheet is largely
reflected by the white backing, and a portion of the light is
transmitted through the paper a second time thus increasing the
total reflection. The opacity tests were performed with an opacity
meter equipped with an accurate linear or a corrected photometric
system according to the aforementioned TAPPI Test Method T519
om-96.
[0060] The data collected in Table I reflects the increased opacity
and improved scattering coefficient with the addition of the
EXPANCEL.RTM. 551-20 thermally expandable microspheres. Example 1,
the control Example, had the lowest bulk, scattering coefficient,
and opacity rating of all five Examples. Furthermore, Example 5,
wherein 1.0% of the EXPANCEL.RTM. was added and wherein the
handsheet was dried for five minutes instead of two, exhibited the
highest opacity rating of the five Examples. Also, the tissue
product of Example 5 was not as bulky as the product of Example 3
wherein 0.5% of the EXPANCEL.RTM. was added and wherein the product
was dried for five minutes. Thus, with the addition of
EXPANCEL.RTM. to the handsheets, both opacity and scattering
coefficient significantly increased, while the sheets did not
experience a large increase in bulk.
[0061] These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims. Therefore, the spirit and scope of the appended
claims should not be limited to the description of the preferred
versions contained therein.
* * * * *