U.S. patent application number 10/635098 was filed with the patent office on 2005-02-10 for method for making tissue product containing carboxylated cellulosic fibers.
This patent application is currently assigned to Weyerhaeuser Company. Invention is credited to Winslow, Alan R..
Application Number | 20050028956 10/635098 |
Document ID | / |
Family ID | 33552928 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028956 |
Kind Code |
A1 |
Winslow, Alan R. |
February 10, 2005 |
Method for making tissue product containing carboxylated cellulosic
fibers
Abstract
A tissue product having two or more layers, with at least one
layer including carboxylated cellulosic fibers. Methods for making
the tissue product.
Inventors: |
Winslow, Alan R.; (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: |
33552928 |
Appl. No.: |
10/635098 |
Filed: |
August 5, 2003 |
Current U.S.
Class: |
162/129 ;
162/146; 162/157.6; 162/9 |
Current CPC
Class: |
D21H 21/20 20130101;
D21H 27/38 20130101; D21H 11/20 20130101; D21F 11/145 20130101;
D21F 11/14 20130101 |
Class at
Publication: |
162/129 ;
162/009; 162/146; 162/157.6 |
International
Class: |
D21H 027/30 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for making a tissue product, comprising: (a) depositing
a first fibrous furnish onto a forming wire to provide a first
deposited furnish; (b) depositing a second fibrous furnish onto the
first deposited furnish to provide a wet web, wherein at least one
of the first fibrous furnish or the second fibrous furnish
comprises carboxylated cellulosic fibers; (c) withdrawing water
from the wet web to provide a sheet; and (d) drying the sheet to
provide the tissue product having at least two layers, wherein at
least one layer comprises carboxylated cellulosic fibers.
2. The method of claim 1, wherein the carboxylated cellulosic
fibers have a carboxyl content of from about 6 to about 60 meq/100
g cellulose.
3. The method of claim 1, wherein the carboxylated cellulosic
fibers have an aldehyde content of less than about 1 meq/100 g
cellulose.
4. The method of claim 1, wherein the first fibrous furnish or
second fibrous furnish comprises non-carboxylated fibers.
5. The method of claim 4, wherein the non-carboxylated fibers are
at least one of recycled fibers, bleached kraft hardwood pulp
fibers, bleached kraft softwood pulp fibers, bleached sulfite pulp
fibers, or bleached chemi-thermomechanical pulp fibers.
6. The method of claim 1, wherein the first fibrous furnish or
second fibrous furnish comprises a wet strength agent.
7. The method of claim 6, wherein the wet strength agent comprises
a polyacrylamide-epichlorohydrin resin.
8. The method of claim 6, wherein the strength agent comprises
cationic starch.
9. The method of claim 1, wherein the first fibrous furnish or
second fibrous furnish comprises carboxymethyl cellulose.
10. The method of claim 1 further comprising depositing a third
fibrous furnish onto the second deposited fibrous furnish, wherein
at least one of the first fibrous furnish, the second fibrous
furnish, or the third fibrous furnish comprises carboxylated
cellulosic fibers, to provide the tissue product having at least
three layers, wherein at least one layer comprises carboxylated
cellulosic fibers.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a tissue product containing
carboxylated cellulosic fibers and methods for making the tissue
product.
BACKGROUND OF THE INVENTION
[0002] Tissue paper or sheets, such as facial and toilet tissues
and paper toweling, are common commercially available consumer
products. Important physical attributes of these products include
strength, absorbency, and softness, among others.
[0003] An ideal tissue product has high wet and dry strength.
Strength is the ability of the tissue product, as well as tissue
product webs, to maintain physical integrity and to resist tearing,
bursting, and shredding under use conditions, including when wet.
An ideal tissue product, more specifically paper toweling, also has
high liquid absorbency. Absorbency is the measure of the ability of
the tissue product and tissue webs to absorb quantities to liquids,
including aqueous solutions and dispersions. Ideally, a tissue
product will have high absorbency with respect to the total
quantity of liquid absorbed given a mass of the tissue product as
well as a fast rate that the tissue product absorbs liquid.
[0004] Tissue products are paper sheets made by a process that
includes the steps of forming an aqueous papermaking furnish,
depositing the furnish on a forming wire, and removing the water
from the furnish to provide the sheet. The aqueous papermaking
furnish is an aqueous slurry of papermaking fibers and chemicals.
Although wood pulp is the major constituent of papermaking fibers,
other fibers can be included. Wood pulps include chemical pulps,
such as kraft and sulfite pulps; and mechanical pulps, such as
ground wood, thermomechanical pulps, and chemi-thermomechanical
pulps. Although blends of pulp fibers are often used in the furnish
for making tissue products, strengthening agents are commonly
included to increase tissue product wet and dry strength. In
addition to wood pulp, the furnish includes chemicals, for example,
strengthening agents and debonding agents, to enhance the strength
and softness of the tissue product.
[0005] Although suitable tissue products exist and significant
advances in tissue products have occurred, there exists a need for
further improvements in tissue products, particularly for tissue
products having increased strength and more particularly, increased
wet strength.
[0006] In the process of making tissue products, water from the
fibrous furnish deposit onto the foraminous support, must be
withdrawn and the wet sheet dried to provide the ultimate tissue
product. Again, although suitable processes exist and significant
advances in process development have occurred, there exists a need
for improved processes, particularly with regard to dewatering and
drying. The present invention seeks to fulfill these needs.
SUMMARY OF THE INVENTION
[0007] In one aspect, the invention provides a tissue product
having two or more layers, with at least one layer including
carboxylated cellulosic fibers. The carboxylated fiber-containing
layer can include from about 0.5 to about 100 percent by weight
carboxylated cellulosic fibers. The carboxylated fiber-containing
layer can also include a variety of other cellulosic and synthetic
fibers. In one embodiment, the carboxylated fiber-containing layer
includes about 75 percent by weight carboxylated fibers and about
25 percent by weight bleached spruce chemi-thermomechanical pulp
fibers. The carboxylated fiber-containing layer can also include a
wet strength agent and other additives, such as carboxymethyl
cellulose (CMC). The tissue product including carboxylated
cellulosic fibers, other fibers, wet strength agents, and other
additions has improved wet strength compared to tissues made with
conventional cellulosic fibers.
[0008] In another aspect of the invention, methods for making the
tissue product are provided. The product can be made on any type of
tissue machine, such as a through-air dried tissue machine or a
conventional tissue machine. In one embodiment of the method, the
tissue product is made by depositing a first fibrous furnish onto a
forming wire to provide a first deposited furnish; depositing a
second fibrous furnish onto the first deposited furnish to provide
a wet web; withdrawing water from the wet web to provide a sheet;
and drying the sheet to provide the tissue product having at least
two layers. At least one of the first fibrous furnish or the second
fibrous furnish includes carboxylated cellulosic fibers to provide
the tissue product in which at least one layer includes
carboxylated cellulosic fibers. In other embodiments, more than two
fibrous furnishes are deposited to provide a tissue product having
more than two layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] 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:
[0010] FIG. 1 is a schematic illustration of a through-air dried
tissue machine useful in making the tissue product of the
invention;
[0011] FIG. 2 is a table summarizing the composition and softwood
pulp refining conditions of representative tissue products of the
invention (sheets) compared to control sheets;
[0012] FIG. 3 is a table comparing the properties of sheets
prepared from control pulps;
[0013] FIG. 4 is a table summarizing the properties of sheets
prepared from a carboxylated fiber pulp and a control at 460-480
CSF, 25 lb/ton wet strength agent, and 4 lb/ton carboxymethyl
cellulose;
[0014] FIG. 5 is a table illustrating the effect of carboxymethyl
cellulose on the properties of sheets prepared from a carboxylated
fiber pulp and a control pulp at constant refining energy input and
25 lb/ton wet strength agent;
[0015] FIG. 6 is a table summarizing the composition and properties
of representative tissue products of the invention (handsheets)
prepared from pulps having three different carboxyl contents (4,
10, and 16 meq/100 g), three different refining conditions (7, 10,
and 13 sec.sup.2 PFR), three different wet strength agent addition
rates (20, 35, and 50 lb/ton), and three different carboxymethyl
cellulose addition rates (0, 2, and 4 lb/ton);
[0016] FIG. 7 is a graph illustrating pulp filtration resistance
(PFR) versus pulp PFI mill revolutions (PFI revs) for two
representative carboxylated fibers compared to control;
[0017] FIG. 8 is a graph illustrating wet burst versus pulp
filtration resistance for representative tissue (handsheets)
compared to control;
[0018] FIG. 9 is a graph illustrating tensile strength versus pulp
filtration resistance for representative tissue products of the
invention (handsheets) compared to control;
[0019] FIG. 10 is a graph comparing wet burst/dry tensile strength
ratio versus pulp filtration rate for representative tissue
products of the invention (handsheets) compared to control;
[0020] FIGS. 11A and 11B are a table summarizing the composition
and properties of representative tissue products of the invention
(handsheets) compared to control tissue products at three different
refining conditions (375, 475, and 575 CSF), three different wet
strength addition rates (0, 4, and 8 lb/ton), and three different
carboxymethyl cellulose addition rates (0, 4, and 8 lb/ton);
[0021] FIGS. 12A and 12B are graphs comparing actual and predicted
wet burst versus wet strength agent (KYMENE) amount added for
representative tissue products of the invention compared to tissue
products that do not include carboxylated cellulosic fibers; the
predicted curves are based on a combined regression model; FIG. 12A
illustrates wet burst versus wet strength agent addition for pulp
refined to CSF=475, and FIG. 12B illustrates wet burst versus wet
strength agent addition for pulp refined to CSF=375; the dashed
curve is the predicted curve for tissues containing carboxylated
pulp, the (+) points are actual points for tissues containing
carboxylated fiber pulp, the solid curve is the predicted curve for
control tissues including non-carboxylated fiber pulp, and the
(.diamond-solid.) points are actual points for control tissues
containing non-carboxylated fibers;
[0022] FIGS. 13A and 13B are graphs comparing actual and predicted
dry tensile versus wet strength agent (KYMENE) amount added for
representative tissue products of the invention compared to tissue
products that do not include carboxylated cellulosic fibers; the
predicted curves are based on a combined regression model; FIG. 13A
illustrates dry tensile versus wet strength agent addition for pulp
refined to CSF=475, and FIG. 13B illustrates dry tensile versus wet
strength agent addition for pulp refined to CSF=375; the dashed
curve is the predicted curve for tissues containing carboxylated
pulp, the (+) points are actual points for tissues containing
carboxylated fiber pulp, the solid curve is the predicted curve for
control tissues including non-carboxylated fiber pulp, and the
(.diamond-solid.) points are actual points for control tissues
containing non-carboxylated fibers;
[0023] FIGS. 14A and 14B are graphs comparing actual and predicted
wet burst/dry tensile ratio versus wet strength agent (KYMENE)
amount added for representative tissue products of the invention
compared to tissue products that do not include carboxylated
cellulosic fibers; the predicted curves are based on a combined
regression model; FIG. 14A illustrates wet burst/dry tensile versus
wet strength agent addition for pulp refined to CSF=475, and FIG.
14B illustrates wet burst/dry tensile versus wet strength agent
addition for pulp refined to CSF=375; the dashed curve is the
predicted curve for tissues containing carboxylated pulp, the (+)
points are actual points for tissues containing carboxylated fiber
pulp, the solid curve is the predicted curve for control tissues
including non-carboxylated fiber pulp, and the (.diamond-solid.)
points are actual points for control tissues containing
non-carboxylated fibers; and
[0024] FIGS. 15A and 15B illustrate representative tissue products
of the invention having two and three layers, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] In one aspect, the present invention provides a tissue
product that includes carboxylated cellulosic fibers. In another
aspect of the invention, methods for making the tissue product are
provided.
[0026] The tissue product of the invention includes carboxylated
cellulosic fibers that impart advantageous properties to these
tissue products superior to those for other tissue products that do
not include carboxylated cellulosic fibers. The tissue product of
the invention can be a facial tissue, toilet tissue, disposable
wipe, napkin, handkerchief, or paper towel.
[0027] The tissue product of the invention includes two or more
layers, and may include one or more plies. Layers can be made on a
tissue machine. A layer can include one or more types of fibers.
For example, a representative tissue of the invention is a three
layered paper towel sheet with two fiber types in each layer. A
representative toilet tissue may have three layers with the middle
layer having a different fiber type than the outer layers. Plies
refer to combining two or more tissues (sheets) during the
converting process. A finished product paper towel, toilet tissue,
facial tissue, or napkin may include one or more plies. The tissue
product of the invention includes at least two layers, with at
least one layer including carboxylated cellulosic fibers.
[0028] In one embodiment, the tissue product includes a layer that
includes carboxylated cellulosic fibers, other cellulosic fibers,
cationic additives such as wet strength agents, and, optionally,
other strength additives. The tissue product of the invention is
characterized as having comparable or improved wet strength,
cationic additive interaction, water retention value, bulk, dry
strength, absorbency, fiber refining energy requirement, and
on-machine dewatering compared to tissue products that do not
include carboxylated cellulosic fibers.
[0029] The tissue product includes at least one layer that includes
carboxylated cellulosic fibers. Carboxylated fibers can be prepared
by a variety of processes. Suitable carboxylated fibers have a
carboxyl content from about 5 to about 60 meq/100 g cellulose and a
degree of polymerization of at least about 600. Suitable
carboxylated fibers can be prepared by carboxylation processes
described in WO 01/29309 and U.S. Pat. No. 6,379,494, entitled
Method of Making Carboxylated Cellulose Fibers in Products of the
Method, each incorporated herein by reference in its entirety. In
these processes, the carboxylated fiber is produced by a two-stage
process: (1) catalytic cellulose oxidation (e.g., a catalytic
oxidizer and a secondary oxidizer, such as chlorine dioxide) and
(2) oxidized cellulose stabilization (e.g., reduction or
oxidation). The process can be integrated into a pulp mill bleach
plant to provide the carboxylated fiber pulp. In one embodiment,
suitable carboxylated fibers are prepared by chlorine dioxide
oxidation using triacetone amine ethylene glycol ketal catalyst
followed by oxidative stabilization with sodium chlorite and
hydrogen peroxide.
[0030] Suitable carboxylated fibers can be made from hardwood and
softwood chemical pulps. Suitable carboxylated fibers have a total
carboxyl content greater than about 6 meq/100 g cellulose and less
than about 60 meq/100 g cellulose. In one embodiment, the C6
carboxyl content is greater than about 2 meq/100 g cellulose. C6
carboxyl content refers to extent of carboxylation at C6 of the
anhydroglucose unit of cellulose to provide a glucuronic acid
derivative. Suitable carboxylated fibers have a low aldehyde
content, less than about 1 meq/100 g cellulose. Suitable
carboxylated fibers has a degree of polymerization greater than 700
in pre-acid form and greater than 850 in sodium salt form. In one
embodiment, the carboxylated fiber has an ISO brightness in the
range from about 75 to about 95 percent. In one embodiment, the
softwood carboxylated fiber viscosity is greater than about 18 mPa.
The carboxylated fiber can be provided to the tissue machine in
either dried or never-dried form.
[0031] The carboxylated fiber can be refined to drainage and
strength targets in a dilute aqueous suspension using commercially
available pulp refiners.
[0032] In addition to carboxylated fibers, the carboxylated
fiber-containing layer of the tissue product of the invention can
include one or more other pulp fibers. Suitable other pulp fibers
include, for example, recycled fibers, bleached kraft hardwood
fibers, bleached kraft softwood fibers (e.g., northern bleached
softwood kraft pulp, NBSK), bleached sulfite fibers, and bleached
chemi-thermomechanical pulp (BCTMP) fibers. In one embodiment, the
tissue product useful as a paper towel includes a layer that
includes a combination of carboxylated cellulosic fibers and BCTMP
fibers. Unbleached pulp fibers and non-pulp fibers can also be
used. The selection criteria of other fibers for inclusion in
addition to the carboxylated fiber will depend upon the end use
product being produced, and are well know to those familiar with
the art.
[0033] The carboxylated fiber content of a particular tissue
product will vary according to the end use of the product. For
example, a paper towel may include a layer that can contain from
about 0.5 to about 100 percent by weight carboxylated fiber based
on the total weight of fiber, and a facial or toilet tissue may
include a layer that can contain from about 10 to about 100 percent
carboxylated fiber based on the total weight of fiber.
[0034] In one embodiment, the carboxylated fiber-containing layer
of the tissue product of the invention includes a wet strength
agent. Suitable wet strength agents are cationic additives such as,
for example, cationic starch, urea-formaldehyde resins,
melamine-formaldehyde resins, polyethylenimine resins,
polyacrylamide resins, and polyacrylamide-epichlorohydrin resins.
In one embodiment, the wet strength agent is a
polyacrylamide-epichlorohydrin resin commercially available under
the designation KYMENE from Hercules Inc., Wilmington Del. The wet
strength agent can be present in the tissue product in an amount
from about 5 to about 50 lb/ton fiber. In one embodiment, the wet
strength agent is present in about 10 lb/ton fiber; in another
embodiment, about 25 lb/ton fiber; and in another embodiment, about
40 lb/ton fiber.
[0035] For paper towel products, the wet strength agent is a
permanent wet strength agent, such as a
polyacrylamide-epichlorohydrin resin. For toilet and facial tissue
products, the wet strength agent is a temporary wet strength agent,
such as cationic starch.
[0036] The carboxylated fiber-containing layer of the tissue
product can also include other strength additives. Other suitable
strength additives include, for example, carboxymethyl cellulose
(CMC). The carboxylated fiber-containing layer can include up to
about 10 lb/ton CMC based on the total weight of fibers. In one
embodiment, the carboxylated fiber-containing layer includes about
4 lb/ton CMC, and in another embodiment, the carboxylated
fiber-containing layer includes about 8 lb/ton CMC.
[0037] Other chemicals useful in making tissue products can
optionally be used during the tissue making process. Other useful
chemicals include retention aids, softeners, surfactants, Yankee
coating, and through-air dryer release spray.
[0038] As noted above, the tissue product of the invention is
characterized as having greater wet tensile and burst strength than
tissue made from commercial pulps (e.g., bleached northern softwood
kraft pulps); greater wet strength/dry strength ratio (wet
burst/dry tensile, WB/DT ratio, or wet tensile/dry tensile, WT/DT
ratio) than tissues made with commercial pulps; dry tensile
strength that is equal to or greater than that of tissue products
made from commercial pulps; and a greater Tensile Energy Absorption
(TEA) Index than tissue products made with commercial pulps.
[0039] In one embodiment, the tissue product of the invention
including carboxylated fibers has a wet burst/dry tensile ratio
from about 0.20 to about 0.40.
[0040] The other layers of the tissue product of the invention can
include one or more of the materials described above including, for
example, carboxylated cellulosic fibers.
[0041] In another aspect of the invention, a method for making a
tissue product that includes carboxylated cellulosic fibers is
provided. In one embodiment, the tissue product is made on a tissue
machine. In the method, the carboxylated fiber, which may be
refined, is combined with one or more other pulps, and strength
additives, as desired, and fed into the tissue machine headbox. The
carboxylated fiber can be a separate furnish or one of several
pulps mixed together to create one layer in the multi-layered
tissue sheet. The carboxylated fibers can make up from about 0.5
percent to 100 percent of the tissue furnish. The carboxylated
fiber can be present in one or more layers of a multi-layered
tissue sheet. The wet web or sheet produced by depositing the
headbox contents onto a foraminous support is processed through the
various unit operations of the tissue machine to produce a dry
tissue jumbo roll. The tissue jumbo roll can be further processed
through various converting equipment into the finished consumer
product, for example, toilet tissue, facial tissue, paper toweling.
The tissue product of the invention can be produced on a variety of
tissue machines including, for example, conventional machines,
creped through-air dried machines, or un-creped through-air dried
machines.
[0042] A schematic illustration of a through-air dried tissue
machine useful in making the representative tissue product of the
invention (i.e., a three-layered product) is shown in FIG. 1.
Referring to FIG. 1, tissue machine 100 includes layered head box
10 having top chamber 12, center chamber 16, and bottom chamber 14,
Fourdrinier wire 20 looped over and about breast roll 101, vacuum
suction boxes 30, and couch roll 102. In a representative operation
for making a three-layered tissue product, a first papermaking
furnish is pumped through top chamber 12, a second papermaking
furnish is pumped through center chamber 16, and a third furnish is
pumped through bottom chamber 14 onto wire 20 to form embryonic web
40 having layers 40a, 40b, and 40c. Dewatering occurs through wire
20 and vacuum boxes 30. As the wire makes its return in the
direction shown by the arrow, showers 50 clean the wire prior to
its beginning another pass over breast roll 101. At web transfer
zone 60, embryonic web 40 is transferred to foraminous carrier
fabric 62 by the action of vacuum transfer box 64. Carrier fabric
62 carries the web from transfer zone 60 past vacuum dewatering box
66 through predryers, or through-air dryers, 68 after which the web
is transferred to a Yankee dryer 70 by the action of pressure roll
103. The carrier fabric 62 is then cleaned and dewatered as it
completes its loop by passing showers 52 and vacuum dewatering box
54. The predried paper web is adhesively secured to the cylindrical
surface of Yankee dryer 70 by adhesive supplied by spray applicator
80. Drying is completed on steam-heated Yankee dryer 70 and by hot
air heated and circulated through drying hood 90. The web is then
dry creped from Yankee drier 70 by doctor blade 82 after which
sheet 42 including a Yankee-side layer 42a, a center layer 42b, and
an off-Yankee-side layer 42c. Sheet 42 then passes between calendar
rolls 104 and 105 and is reeled onto core 106 disposed on shaft 107
to provide roll 44.
[0043] In the method described above, a manufacture of a
three-layered tissue product is described. It will be appreciated
that two-layered tissue products and tissue products having more
than three layers can be prepared by the method and are within the
scope of this invention. With regard to the described method, the
carboxylated fiber-containing layer may be any one or more of the
layers. For example, the carboxylated fiber-containing layer of the
tissue product may be the middle layer of the tissue product, or
one or both of the outer layers of the tissue product.
[0044] In a representative trial, the NBSK (carboxylated fiber or
control) inclusion rate was 75 percent; the basis weight split
between layers (air/core/Yankee) was 33 percent/34 percent/33
percent; the reel basis weight was 20.5 gsm; the Yankee speed was
1100 mpm; and the twin-wire former/through-air drier wire speed
ratio was 1.15 which created a fabric crepe of 15 percent. The
machine was operated to control several machine variables: (1)
refining energy input to achieve target NBSK freeness or NBSK
refining energy input; and (2) through-air drier energy input was
adjusted to keep sheet solids exiting the through-air drier greater
than 85 percent. This trial was conducted on Metso Paper Karlstad
AB's pilot through-air dried paper machine located in Karlstad,
Sweden.
[0045] Representative tissue products in roll form were prepared on
the tissue machine described above. The tissue product produced by
the paper machine was typical of a premium consumer paper towel.
The tissue product included either commercial pulp (NBSK) or
carboxylated NBSK pulp fibers, bleached chemi-thermomechanical pulp
(BCTMP), a wet strength agent, and, optionally, carboxymethyl
cellulose. Experimental variables included NBSK or carboxylated
fiber refining energy input and strengthening agents' addition
rates.
[0046] The trial conditions are tabulated in FIG. 2. In the table,
PA control refers to a northern bleached softwood kraft pulp
(Prince Albert, Saskatchewan); TR962 refers to carboxylated pulp
fibers; TR963 refers to a fully bleached, Prince Albert northern
bleached softwood kraft pulp dried in the same manner as TR962;
inclusion rate refers to the percentage of the PA Control or TR962
or TR963 pulp included in the sheet, the remainder of the pulp
included in the sheet was a bleached chemi-thermomechanical pulp
(BCTMP) having a brightness of 80 and a Canadian Standard Freeness
(CSF) of 525, commercially available from Sodra Cell AB; the wet
strength agent was a polyamide-epichlorohydrin resin, KYMENE SLX
from Hercules; and the strength additive was carboxymethyl
cellulose, CMC 7-MT from Metsa Chemical.
[0047] The tissue products and their characteristics are summarized
in FIGS. 3-5. FIG. 3 is a table comparing the properties of sheets
prepared from control pulps. FIG. 4 is a table summarizing the
properties of sheets prepared from a carboxylated fiber pulp and a
control at 460-480 CSF, 25 lb/ton wet strength agent, and 4 lb/ton
carboxymethyl cellulose. FIG. 5 is a table illustrating the effect
of carboxymethyl cellulose on the properties of sheets prepared
from a carboxylated fiber pulp and a control pulp at 53 kWh/mt
refining energy input and 25 lb/ton wet strength agent.
[0048] The data shows that the tissue products including the
carboxylated cellulosic fibers have improved sheet properties at
equal inclusion rate, equal NBSK refining energy input, equal wet
strength agent addition rate, and equal CMC addition rate compared
to the tissue product made from commercial pulps. Improvements were
observed in dry tensile, wet tensile, and wet burst strength.
[0049] The tissue machine data shows that through-air drier
requires comparable total through-air drying power to dry the
tissues containing the carboxylated cellulosic fibers compared to
tissues made from commercial pulps at equal inclusion rate, equal
NBSK refining energy input, equal wet strength agent addition rate,
and equal carboxymethyl cellulose addition rate.
[0050] The data also shows that the carboxylated cellulosic fiber
pulp has a lower unrefined freeness than the control pulp and
refines to a lower freeness than the control pulp at equivalent
refining energy input or refines to an equal freeness with lower
refining energy.
[0051] Carboxylated fibers were used as single fiber furnishes to
produce tissue handsheets. In one series of experiments, tissue
handsheets were prepared from carboxylated cellulosic fibers
prepared from northern bleached softwood kraft pulp at three
carboxyl levels (3, 7, and 12 meq/100 g cellulose). These pulps
were refined to three different levels of refinement as measured by
pulp filtration resistance (PFR), 7, 10, and 13 sec.sup.2. Pulp
filtration resistance (PFR), like Canadian Standard Freeness (CSF),
is a measure of drainage of water from the pulp. In these
handsheets, the wet strength agent (KYMENE) was added at three
different levels (20, 35, and 50 lb/ton fiber). The tissue products
also included carboxymethyl cellulose (CMC) as a strength additive
at three different levels, 0, 2, and 4 lb/ton fiber. The results
are tabulated in FIG. 6.
[0052] The results show improvements in the tissue handsheet
properties of handsheets that include carboxylated fibers compared
to commercial NBSK pulp. Typical commercially available NBSK pulps
have a carboxyl level of about 3 to about 4 meq/100 g cellulose.
The data shows that handsheets including the carboxylated pulps
have higher wet burst strength and wet burst strength/dry tensile
strength ratio than handsheets made from commercial pulps.
[0053] Handsheets were also made including carboxylated pulp fibers
and compared to handsheets made using a northern bleached softwood
kraft pulp control (Prince Albert NBSK). The effect of refining, as
well as the amounts of strengthening agents, was determined. The
handsheets including the carboxylated pulps have a higher wet burst
strength and wet burst strength/dry tensile strength ratio compared
to the control handsheets made from commercial pulps. The
handsheets including carboxylated fibers had a dry tensile strength
that was slightly higher than control at lower refinement, and
slightly lower than the control at higher refinement. The results
are shown in FIGS. 7-10.
[0054] FIG. 7 is a graph illustrating pulp filtration resistance
(PFR) versus pulp PFI mill revolutions (PFI revs) for two
representative carboxylated fibers compared to control. Pulp
filtration resistance increases with pulp filtration instrument
revolutions for all handsheets.
[0055] FIG. 8 is a graph illustrating wet burst versus pulp
filtration resistance for representative tissue (handsheets)
compared to control with an equal wet strength agent addition rate
for all samples. Wet burst strength was measured on a Thwing Albert
Model 1300-177 Wet Burst Tester manufactured by Thwing Albert
Instrument Co., Philadelphia, Pa. Wet burst increases with
increasing pulp filtration resistance. Handsheets including
carboxylated fibers showed significantly greater wet burst as a
function of pulp filtration resistance compared to the control
handsheet.
[0056] FIG. 9 is a graph illustrating dry tensile strength versus
pulp filtration resistance for representative tissue products of
the invention (handsheets) compared to control. Dry tensile
increases with increasing pulp filtration resistance for all
handsheets. The greatest increase in dry tensile is seen from 5 to
about 10 sec.sup.2.
[0057] FIG. 10 is a graph comparing wet burst/dry tensile strength
ratio versus pulp filtration rate for representative tissue
products of the invention (handsheets) compared to control with an
equal wet strength agent addition rate for all samples. The wet
burst/dry tensile ratio increased slightly with increasing pulp
filtration resistance. The wet burst/dry tensile ratio for the
handsheets containing carboxylated fibers was significantly greater
than for the control handsheet.
[0058] The composition and properties of representative tissue
products of the invention (handsheets) and handsheets made from
commercial pulps (controls) are summarized in FIGS. 11A and 11B. In
the table, PA-pilot dried refers to a fully bleached, never-dried
northern bleached softwood kraft pulp that was dried at the Paper
and Pulp Research Institute of Canada (Point-Claire, Quebec);
Prince Albert refers to a northern bleached softwood pulp produced
commercially at Weyerhaeuser's Prince Albert, Saskatchewan pulp
mill; carboxylated refers to a carboxylated cellulosic fiber pulp
dried at the Paper and Pulp Research Institute of Canada
(Point-Claire, Quebec); CSF refers to Canadian Standard Freeness
(an alternative measure of drainage to PFR); BSWT refers to basis
weight (gsm); WB/DT refers to the wet burst/dry tensile ratio; and
WRV refers to water retention value.
[0059] The control handsheets included either a NBSK control pulp
(Prince Albert) or a second NBSK control pulp (PA-pilot dried) that
was dried in the same manner as the carboxylated fiber used in the
handsheets of the invention. For these handsheets, CSF was either
375, 475, or 575 ml, KYMENE was included at either 10, 25, or 40
lb/ton, CMC was included at either 0, 4, Or 8 lb/ton. The
handsheets including the carboxylated fibers had improved wet burst
strength, tensile strength, and wet burst/dry tensile ratio
compared to those handsheets made from either commercial NBSK pulps
at any given drainage (CSF).
[0060] Low density, low basis weight tissue handsheets were also
prepared from these pulps refined using an Esher-Wyss refiner and
including varying amounts of wet strength agent (KYMENE) and
carboxymethyl cellulose (CMC). FIGS. 12-14 compare the actual and
predicted performance of these handsheets based on regression
analysis of the handsheets data, and compare wet burst strength,
dry tensile strength, and wet burst/dry tensile strength versus wet
strength agent amount at various freeness.
[0061] Products of the invention more effectively utilize wet
strength agents (e.g., KYMENE) to create higher wet strength in
tissues. FIGS. 12A and 12B are graphs comparing the actual and
predicted wet burst strength of handsheets made with carboxylated
fibers with those of handsheets made with a control pulp at various
KYMENE addition rates. NBSK refining varies for each graph, and CMC
addition rate is 0 lbs./ton in both examples. The wet burst
strength of the handsheets containing carboxylated fibers is higher
than the control's at all KYMENE addition rates. FIG. 12A
illustrates wet burst versus wet strength agent addition for pulp
refined to CSF=475, and FIG. 12B illustrates wet burst versus wet
strength agent addition for pulp refined to CSF=375. The dashed
curve is the predicted curve for tissues containing carboxylated
pulp, the (+) points are actual points for tissues containing
carboxylated fiber pulp, the solid curve is the predicted curve for
control tissues including non-carboxylated fiber pulp, and the
(.diamond-solid.) points are actual points for control tissues
containing non-carboxylated fibers. Handsheets prepared from the
carboxylated fiber pulp have greater wet burst strength than the
control pulp in the commercially useful wet strength addition
ranges.
[0062] A preferred objective of this invention would be to produce
tissues with higher wet strength without increasing the tissues'
dry strength. FIGS. 13A and 13B are graphs comparing actual and
predicted dry tensile strength of handsheets made with carboxylated
fibers with those of handsheets made with control pulp at various
KYMENE addition rates. NBSK refining varies for each graph, and CMC
addition rate is 0 lbs./ton in both examples. The dry tensile
strength of the two handsheets are comparable up to approximately
25 lbs. KYMENE/ton. Therefore, one familiar with the art will
recognize that that the dry strength of the two handsheets are
comparable in the normally commercially viable range for KYMENE
inclusion. FIG. 13A illustrates dry tensile versus wet strength
agent addition for pulp refined to CSF=475, and FIG. 13B
illustrates dry tensile versus wet strength agent addition for pulp
refined to CSF=375. The dashed curve is the predicted curve for
tissues containing carboxylated pulp, the (+) points are actual
points for tissues containing carboxylated fiber pulp, the solid
curve is the predicted curve for control tissues including
non-carboxylated fiber pulp, and the (.diamond-solid.) points are
actual points for control tissues containing non-carboxylated
fibers. Handsheets prepared from the carboxylated fiber pulp have
comparable dry tensile strength to the control pulp in the
commercially useful wet strength addition ranges.
[0063] FIGS. 14A and 14B are graphs comparing actual and predicted
wet burst/dry tensile strength ratio of handsheets made with
carboxylated fibers with those of handsheets made with control pulp
versus KYMENE addition rate. NBSK refining varies for each graph,
and CMC addition rate is 0 lbs./ton in both examples. This wet
burst strength/dry tensile strength ratio combines the data from
FIGS. 12A-13B. Products of the invention show substantial
improvement in this ratio at all KYMENE addition rates. FIG. 14A
illustrates wet burst/dry tensile versus wet strength agent
addition for pulp refined to CSF=475, and FIG. 14B illustrates wet
burst/dry tensile versus wet strength agent addition for pulp
refined to CSF=375. The dashed curve is the predicted curve for
tissues containing carboxylated pulp, the (+) points are actual
points for tissues containing carboxylated fiber pulp, the solid
curve is the predicted curve for control tissues including
non-carboxylated fiber pulp, and the (.diamond-solid.) points are
actual points for control tissues containing non-carboxylated
fibers. Handsheets prepared from the carboxylated fiber pulp have
greater wet burst/dry tensile ratio than the control pulp in the
commercially useful wet strength addition ranges.
[0064] Representative tissue products of the invention are
illustrated in FIGS. 15A and 15B. FIG. 15A illustrates a
representative two-layer tissue product (200) having first layer
202 and second layer 204. FIG. 15B illustrates a representative
three-layer tissue product (210) having first layer 212, second
layer 214, and third layer 216.
[0065] The methods used for determining the parameters noted herein
are described below.
Basis Weight Determination Method
[0066] The area of several sheets of paper is determined from
lineal measurements and the mass is determined by weighing. The
ratio of the mass to the area is the basis weight (i.e.,
g/m.sup.2). The values of many physical properties of paper such as
burst, tear, tensile, bulk, and caliper are interpreted and
specified with regard to the particular basis weight involved. Ten
sheets of sample paper are selected and cut to obtain a total
sample target area of 5,000 cm.sup.2. From each sample, randomly
select two sheets. Measure each side of the selected sheet. If the
lengths of any two opposite edges differ by more than 1 mm, the
sample must be recut, as the sides are not sufficiently parallel.
Average the measurements of the opposing sides and record to the
nearest 0.25 mm. Weigh each specimen on the balance and record the
weight. The basis weight (or grammage), g/m.sup.2, for each
specimen is calculated as follows:
BW(g/m.sup.2)=10.sup.6.times.M/(L.times.W)
[0067] where M=mass of the specimen (g); L=mean length of sample
specimens (mm); and W=mean width of sample specimens (mm).
[0068] Related methods for determining basis weight include ISO
536: 1995 (E), Paper and Board, Determination of Grammage; and
TAPPI T 410 om-98, Grammage of Paper and Paperboard (Weight per
Unit Area).
Tensile Strength Determination Method
[0069] This method is used to determine three breaking properties
of paper: the force required to cause tensile failure in a specimen
of specified width (breaking load or tensile strength); the
elongation of the specimen at failure (the difference between the
strained length and the original length expressed as a ratio); and
the energy absorbed per unit area by the specimen for failure
(tensile energy absorption or TEA). The tests are performed on an
Instron 4422 Universal Testing System. The crosshead moves at a
uniform predetermined rate of speed. The modulus of elasticity
(Young's modulus) can also be determined with this method. For
measuring tensile index and/or breaking length, basis weight of the
sample is required.
[0070] The tensile properties of paper in paper products generally
indicate resistance to potential breaking during printing and other
converting operations where a variety of in-plane stresses act upon
the sheet. The elongation is indicative of the ability of the paper
to conform to a desired contour, and this occurs repeatedly in
printing presses and other processes. The tensile energy absorption
(TEA) is an indicator of how the paper will stand up to repetitive
stresses, and is, therefore, a measure of durability. Tensile
properties are dependent upon characteristics of the original pulp
(wood species, pulping type and conditions, degree of bleaching)
and subsequent treatment during papermaking (degree of refining,
type and amount of additives, amount of recycled material). Tensile
strength is important in pulp manufacture because its strength
properties influence those of the paper from which it is made.
[0071] All samples should be conditioned and tested at
23+/-1.degree. C. and 50+/-2% relative humidity. Cut specimens 25
mm (about 1 inch) wide and about 250 mm long, with the test
direction (machine direction or cross machine direction) parallel
with the long dimension. Handsheet specimens should be cut 15 mm
wide by 125-145 mm long. The specimen length must be sufficient for
the test span plus clamping regions of about 25 mm for each clamp.
Select the load cell appropriate for the materials being tested.
For most tests, a 50 kg type load cell having a test range from
1-50 kg is used. For testing very strong grades (linerboard and
containerboard), use a "CT" type load cell having the capacity to
test from 5-250 lb (100 kg). For handsheets, a 25 kg load cell
having a test range from 0.5-25 kg is appropriate. Prepare the
Instron instrument by identifying the test method needed, which is
instrument frame specific and load cell specific. Alternatively,
the method can be created or modified using the technician's
guidebook and Instron manuals. Set the grip span at 180 mm with the
jog remote and a steel ruler in the bottom clamp. Rezero the span
by activating GL reset on the control panel. Label the specimen and
test direction (i.e., MD or CD). For determination of modulus of
the elasticity, measure each test strip for thickness at three
positions along the strip length. Record the average strip
thickness in mm.
[0072] For calibration, connect the appropriate load cell and its
connector cable to the correct Instron frame. The electronic
calibration method then calibrates the Instron device.
[0073] To obtain sample measurements, select the appropriate test
method and follow the program prompts for specific instructions and
inputs. The standard speed used is 25.4 mm per minute (about 1 inch
per minute) and clamping pressure should remain constant at 65 psi.
Insert specimens, up to 10 at a time for thin papers, into the
upper jaw to ensure vertical alignment with the lower jaw when both
jaws are clamped. The clamps must be perpendicular to the length of
the specimen (and to the direction of pull) for accurate testing.
Once the specimen is clamped into the lower jaw, follow the method
prompts and allow the computer to start testing. To verify the
software calculations, print out the REP file and a graph of the
first sample. Use the elongation and maximum load values from the
graph to calculate tensile, elongation, and breaking length.
Modulus of elasticity can be calculated by drawing a line tangent
to the elastic region of the curve and calculating the slope. Ten
specimens per sample are tested.
[0074] To calculate breaking load (B) in units of kN/m, the
following formula is used:
B(kN/m)=9.80665f/w
[0075] where f=load at failure (kg) and w=specimen width (mm).
[0076] To calculate tensile index (T) in units of Nm/g, the
following formula is used:
T(Nm/g)=9810f/wg
[0077] where g=condition to basis weight (g/m.sup.2).
[0078] To calculate breaking length (L) in units of km, the
following formula is used:
L=1000f/wg.
[0079] To calculate elongation (.epsilon.) in units of %, the
following formula is used:
.epsilon.(%)=100(sf-s)/s
[0080] where s=initial (unstrained) span (mm); and sf=span at
failure (mm).
[0081] Tensile energy absorption (TEA), J/m.sup.2, is the work done
in stressing the specimen to failure and is measured by the
integral of the tensile stress over the range of the tensile
strain, from zero to maximum strain. The TEA is expressed as energy
per unit area (test span.times.width) of the test specimen. The TEA
computation is performed by the acquisition software. The TEA
index, J/g, is obtained by dividing the TEA by the specimen basis
weight (g/m.sup.2). The modulus of elasticity (E), GPa, is
calculated from the slope of the elastic region of the
stress/strain curve using the following formula:
E(GPa)=0.00981[(L2-L1(s)]/[(w)(t)(E2-E1)]
[0082] where L1=the lower of two loads located in the elastic
region of the curve (kg); L2=the higher of the two loads (kg);
E1=the specimen elongation at L1 (mm); E2=the specimen elongation
at L2 (mm); and T=average specimen thickness (mm).
[0083] Related methods for determining tensile properties include
ISO 1924-2: 1994-(E) Paper and Board, Determination of Tensile
Properties, Part 2: Constant Rate of Elongation Method; and TAPPI T
494 om-96, Tensile Breaking Properties of Paper and Paperboard
(Using Constant Rate of Elongation Apparatus).
Thickness Determination Method
[0084] This method is used to determine the single sheet thickness
of paper and paperboard by use of a motor driven micrometer using a
specified load applied for a specified time. The method is suitable
for using the IPC Soft Platen technique for measuring apparent
thickness. This technique employs a micrometer with pressure faces
covered with soft neoprene, rubber. This has the effect of reducing
thickness readings due to the ability of the latex to conform to
surface irregularities. This is useful when measuring materials
with rough or irregular surfaces, such as linerboard and corrugated
medium.
[0085] Thickness is an important property for paper as it
influences properties such as structure (bulk), stiffness, opacity,
and fold. Variations in thickness are also very useful in order to
monitor important machine variables.
[0086] Samples are conditioned and tested at 23+/-1.degree. C. and
at 50+/-2% relative humidity.
[0087] The samples should be sufficient to obtain a minimal of 20
and up to 50 readings. Clean the surfaces of the platens with
lint-free paper and adjust the micrometer reading to zero. Insert a
single specimen into the caliper opening, allowing the pressure
faces to close and the reading to stabilize. Perform 50 tests per
sample (e.g., 5 readings per sheet on each of 10 sheets). After
each sample, check that the instrument zero has not drifted. If it
has, clean the platens and readjust as necessary.
[0088] Single sheet thickness is reported in mm (to the nearest
0.001 mm) or in mils (thousandths of inch).
[0089] To calculate air-dry bulk (cm.sup.3/g), the following
formula is used:
Bulk(cm.sup.3/g)=1000A/B
[0090] where A=thickness (mm), and B=air-dry basis weight
(g/m.sup.2).
[0091] To calculate air-dry ("apparent") density (kg/m.sup.3), the
following formula is used:
Density(kg/m.sup.3)=B/A
[0092] where A=thickness (mm), and B=air-dry basis weight
(g/m.sup.2).
[0093] Related methods for determining thickness include TAPPI T
411 om-97, Thickness (Caliper) of Paper, Paperboard, and Combined
Board; TAPPI T 551 pm-92, Thickness of Paper and Paperboard (Soft
Platen Method); and ISO 534: 1988(E) Paper and Board, Determination
of Thickness and Apparent Bulk Density or Apparent Sheet
Density.
Canadian Standard Freeness Determination Method
[0094] The Canadian Standard Freeness (CSF) test method is used to
evaluate the changes in the drainage characteristics of pulp during
refining. In addition, the method is used to monitor head box stock
as a precursor of how the dilute pulp suspension will behave on the
wet end of the paper machine in releasing water. The freeness is
highly dependent on degree of refining and therefore is a fairly
good indicator of pulp bulk and strength properties. The method is
suitable for all types of pulps that can be used by itself or in
connection with other test methods (laboratory refining using the
PFI, Escher-Wyss, Valley Beater). The method is based on a
modification of ISO 5267-2. In the method, the volume of water
drained from 3 oven-dried (OD) g of pulp at 0.3% consistency in a
standard tester is captured and measured. The amount drained
depends mainly on the quantity of debris (i.e., fines) present and
to a lesser extent on the degree of fibrillation, flexibility, and
compressibility of the fibers.
[0095] Pulps with a dry matter content equal to or greater than 20%
are soaked in deionized water for at least four hours and for no
longer than 48 hours. The pulp is then disintegrated as described
in method WM 1-5263 Disintegration of Pulp. For pulps not being
refined, disintegrate the equivalent of 24-30 OD g in 2450-2900 mL
deionized water for 5 minutes (15,000 revolutions) in the standard
disintegrator. All samples are tested immediately after preparation
(e.g., disintegration, refining). The CSF of refined pulps can
change with time. The oven-dry consistency of the sample being
tested should be 0.3%+/-0.02%. Using the testing device, which
includes a chamber and a funnel having a traditional bottom orifice
and a second side orifice, place a graduated cylinder under the
side orifice of the funnel to collect discharge. Place a 1000 mL
beaker under the bottom orifice to collect all discharge.
Thoroughly mix the diluted sample and withdraw the equivalent of
3.00 OD g in a 1000-mL graduated cylinder. This amount is
calculated from a consistency measurement of the sample:
[0096] Amount of sample withdrawn (g)=3.00 g (100)/% consistency.
Adjust the sample to 0.30% consistency by diluting the graduated
cylinder contents to the 1000 mL mark. Pour the contents into the
upper chamber of freeness tester. Close and clamp the top lid of
the chamber and close the air-cock on the top lid of the chamber.
Open the bottom lid and open the air-cock on the top. When the
discharge has completely stopped from the side orifice, collect the
volume in the appropriate graduated cylinder. Read the volume of
this discharge to the nearest 1 mL for values below 100 mL, to the
nearest 2 mL for values between 100 mL and 250 mL, and to the
nearest 500 mL for values exceeding 250 mL. Freeness (CSF) is
reported to the nearest whole mL.
[0097] Related methods for determining pulp freeness are described
in TAPPI T 227 om-94, Freeness of Pulp; and ISO 5267-2: 1980 Pulps,
Determination of Drainability, Part 2: "Canadian Standard" Freeness
Method.
Water Retention Value Determination Method
[0098] Water retention value (WRV) can be a useful tool in
evaluating the performance of pulps relative to dewatering behavior
on the paper machine. The usefulness of the method on a particular
application may vary depending upon the type of stock, additives,
machine configuration, and other factors. The method provides
standard values of centrifugal force, time of centrifuging, and
simple preparation so that results can be compared at standard
values. WRV, as measured by this method, is the amount of water
retained by a pulp sample after being subjected to a centrifugal
force equal to 900 times the force of gravity for 30 minutes (2
minutes to reach maximum speed). The basis weight of the pulp is
1400 g/m.sup.2 (OD). The method is a modification of TAPPI UM-256.
To perform the tests, a laboratory centrifuge with free-swinging
head (IEC model HN-SII or equivalent) with digital rpm meter is
required.
[0099] The consistency of the pulp, if in dilute form, must be
accurately known to the nearest 0.1%. Dried pulps should be soaked.
Weigh the equivalent of 0.709 OD g of pulp, if dry soak in small
container with deionized water for a minimum of four hours. Tear
the soaked pulp into "pea"-sized pieces (3-7 mm) if previously
dried and place into a container and fill with deionized water.
Blend the pulp and water mixture for about 30 seconds, carefully
pour the slurry into a centrifuge tube making sure a uniform pad is
formed and remove supernatant water. Centrifuge at 2600+/-20 rpm
for 30 minutes. After centrifuging, remove the pads from the tubes
and weigh the pads to the nearest 0.001 g. Dry the pads by placing
in an oven and drying at 105+/-3.degree. C. for at least 12 hours,
but not more than 72 hours. Weigh the dry pads to the nearest 0.001
g.
[0100] The water retention value (WRV), in units of g water/g
fiber, is calculated using the following formula:
WRV(g/g)=(W-D)/D
[0101] where W=mass of pad after centrifuging (g), and D=dry mass
of pad (g).
Pulp Filtration Resistance Determination Method
[0102] Pulp filtration resistance (PFR) is a measure of a pulp's
resistance to drainage. PFR is an important tool for judging a
pulp's ability to dewater at various levels of refining. This has a
direct impact on paper machine predrier temperatures and machine
speed. The test consists of three timed filtrations of 100 mL of
the slurry through a screen in the PFR nozzle. This screen is made
of the same monofilament material used as handsheet wires. The
method for carrying out the PFR measurement is described in U.S.
Pat. No. 5,228,954.
[0103] The PFR is, like the Canadian Standard Freeness (CSF), a
method for measuring the drainage rate of pulp slurries. It is
believed that the PFR is a superior method for characterizing
fibers with respect to their drainage characteristics. For purposes
of estimation, the CSF may be related to the PFR by the following
formula:
PFR=11270/CSF-10.77,
[0104] where the PFR is in units of seconds and the CSF is in units
of milliliters. Because this relationship is subject to error it
should be used for estimation purposes only. A more accurate method
of measuring the PFR is as follows.
[0105] The PFR is measured by discharging three successive aliquots
of a 0.1% consistency slurry from a proportioner and filtering
through a screen connected to the proportioner discharge. The time
required to collect each aliquot is recorded and the screen is not
removed or cleaned between filtrations.
[0106] The proportioner (obtained from Special Machinery
Corporation, 546 Este Avenue, Cincinnati, Ohio 45232, Drawing
#C-PP-318) is equipped with a PFR attachment (also obtained from
Special Machinery Corporation, Drawing #4A-PP-103, part #8). The
PFR attachment is loaded with a clean screen (a 11/8" die cut
circle of the same type of screen used for handsheeting, Appleton
Wire 84.times.76M, is used and it is loaded with the sheet side
"up" in the tester).
[0107] A 0.10% consistency slurry of disintegrated pulp is prepared
in the proportioner at a volume of 19 liters, with the PFR
attachment in position. A 100 ml volumetric flask is positioned
under the outlet of the PFR attachment. The proportioner outlet
valve is opened and a timer started, the valve is closed and timer
stopped the instant 100 ml is collected in the volumetric flask
(additional liquid will probably drain into the flask after the
valve is closed). The time is recorded to the nearest 0.10 seconds,
noted as "A".
[0108] The filtrate is discarded, the flask repositioned, and
another 100 ml aliquot is collected by the same procedure without
removing or cleaning the screen between filtrations. This time
interval is recorded as "B".
[0109] Again, the filtrate is discarded, the flask repositioned,
and another 100 ml aliquot is collected by the same procedure
without removing or cleaning the screen between filtrations. This
time interval is recorded as "C".
[0110] PFR is then calculated using the following equation: 1 PFR =
( E ) .times. ( B + C - ( 2 .times. A ) ) 1.5
[0111] where A, B, and C are the recorded time intervals, and E is
a function of temperature used to correct the PFR to the value that
would be observed at 75.degree. F.:
E=1+(0.013.times.(T-75)),
[0112] where T is the slurry temperature measured to the nearest
.degree. F. in the proportioner after taking the last aliquot.
Handsheet Preparation and Wet Burst Test Method
[0113] Handsheet Preparation. About 30-31 g of pulp was refined in
a PFI Refiner to 570.+-.5 mL Canadian Standard Freeness. Nineteen
grams (dry basis) of the refined pulp in a total of 2000 mL of
water was placed in a British disintegrator, 2.28 g of 12.5% KYMENE
557H solution was added, and the slurry was disintegrated for 10
minutes. The resulting disintegrated pulp slurry was diluted to 19
L to form a 0.1% consistency slurry. The drainage rate of this
slurry was measured by the amount of time taken to pass 300 mL of
filtrate water, using a liquid slurry head height of 36 inches,
through a 1.0 inch diameter circular handsheet forming wire
containing 84.times.76 wires per inch. The forming wire was
obtained from Albany International, 435 Sixth St., Menasha, Wis.,
54952.
[0114] Wet Burst Test Method. A 12 inch.times.12 inch deckle box
was used to form handsheets of approximately 26 g/m.sup.2 basis
weight and approximately 240 kg/r.sup.3 density on the forming wire
described above. Five sheets were formed for each pulp. The sheets
were not wet pressed. Dewatering of the handsheets was accomplished
by passing the sheets still on the forming wire over a vacuum slit.
The sheets were dried on a steam-heated drum dryer and cured in an
oven for one hour at 105.degree. C. Wet burst strength of the
sheets was measured on a Thwing Albert Model 1300-177 Wet Burst
Tester manufactured by Thwing Albert Instrument Co., Philadelphia,
Pa., 19154. Eight measurements were made for each pulp and the
average calculated and taken as the wet burst strength.
[0115] 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.
* * * * *